Mod 2.3 Training Notes PDF

THAKUR INSTITUTE OF AVIATION TECHNOLOGY TRAINING NOTES FORWORD UNCONTROLLED COPY  ITISIMPORTANTTONOTE THAT THE INFORMATION IN THIS BOOK IS OF STUDY/ TRAINING PURPOSES ONLY AND NO REVISION SERVICE WILL BE PROVIDED TO THE HOLDER.  WHEN CARRYING OUT APROCEDURE/ WORK ONAIRCRAFT/ AIRCRAFT...

THAKUR INSTITUTE OF AVIATION TECHNOLOGY TRAINING NOTES FORWORD UNCONTROLLED COPY  ITISIMPORTANTTONOTE THAT THE INFORMATION IN THIS BOOK IS OF STUDY/ TRAINING PURPOSES ONLY AND NO REVISION SERVICE WILL BE PROVIDED TO THE HOLDER.  WHEN CARRYING OUT APROCEDURE/ WORK ONAIRCRAFT/ AIRCRAFT EQUIPMENT YOU MUSTALWAYS REFER TO THE RELEVANT AIRCRAFT MAINTENANCE MANUAL OREQUIPMENT MANUFACTURER'S HANDBOOK.  FOR HEALTH ANDSAFETY IN THE WORKPLACE YOU SHOULD FOLLOW THE REGULATIONS/ GUIDELINES AS SPECIFIED BYTHE EQUIPMENT MANUFACTURER, YOUR COMPANY, NATIONAL SAFETY AUTHORITIES AND NATIONAL GOVERNMENTS. JULY 2024 Copyright Notice © Copyright. All worldwide rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form by any other means whatsoever : i.e. photocopy, electronic, mechanical recording or otherwise without the prior written permission of Thakur Institute of Aviation Technology. TIAT 2.3 3- 1 THAKUR INSTITUTE OF AVIATION TECHNOLOGY Knowledge Levels – Category A, B1, B2, B3 and C Aircraft Maintenance Licence Basic knowledge for categories A, B1, B2 and B3 are indicated by the allocation of knowledge levels indicators (1, 2 or 3) against each application subject. Category C applicants must meet either the category B1 or the category B2 basic knowledge levels. The knowledge level indicators are defined as follows : LEVEL 1  A familiarization with the principal elements of the subject. Objectives : The applicant should be familiar with the basic elements of the subject.  The applicant should be able to give a simple description of the whole subject, using common words and examples.  The applicant should be able to use typical terms. LEVEL 2  A general knowledge of the theoretical and practical aspects of the subject.  An ability to apply that knowledge. Objectives : The applicant should be able to understand the theoretical fundamentals of the subject.  The applicant should be able to give a general description of the subject using, as appropriate, typical examples.  The applicant should be able to use mathematical formulae in conjunction with physical laws describing the subject.  The applicant should be able to read and understand sketches, drawings and schematics describing the subject.  The applicant should be able to apply his knowledge in a practical manner using detailed procedures. LEVEL 3  A detailed knowledge of the theoretical and practical aspects of the subject.  A capacity to combine and apply the separate elements of knowledge in a logical and comprehensive manner. Objectives : The applicant should know the theory of the subject and interrelationships with other subjects.  The applicant should be able to give a detailed description of the subject using theoretical fundamentals and specific examples.  The applicant should understand and be able to use mathematical formulae related to the subject.  The applicant should be able to read, understand and prepare sketches, simple drawings and schematics describing the subject.  The applicant should be able to apply his knowledge in a practical manner using manufacturer’s instructions.  The applicant should be able to interpret results from various sources and measurements and apply corrective action where appropriate. TIAT 2.3 3- 2 THAKUR INSTITUTE OF AVIATION TECHNOLOGY Module 2.3: Thermodynamics Certification Statement These Study Notes comply with the syllabus of EASA Regulation (EC) No.1321/2014 Annex III (Part-66) Appendix I, as amended by Regulation (EC) No.989/2023, and the associated Knowledge Levels as specified below: EASA 66 Level Objective Reference B1 B2 Thermodynamics 2.3 a. Temperature: thermometers and temperature scales: Celsius, Fahrenheit and Kelvin; 2 2 Heat definition; b. Heat capacity, specific heat; 2 2 Heat transfer: convection, radiation and conduction; Volumetric expansion; First and second law of thermodynamics; Gases: ideal gases laws; specific heat at constant volume and constant pressure, work done by expanding gas; Isothermal, adiabatic expansion and compression, engine cycles, constant volume and constant pressure, refrigerators and heat pumps; Latent heats of fusion and evaporation, thermal energy, heat of combustion TIAT 2.3 3- 3 THAKUR INSTITUTE OF AVIATION TECHNOLOGY 2.3 THERMODYNAMICS motion would cease, and no additional heat could be extracted from the substance. 2.3 (a) When temperatures are measured with respect to the absolute TEMPERATURE zero reference, they are expressed as zero in the absolute or Temperature of body means a measure of hotness or coldness of a.Kelvin scale. Thus, absolute zero may be expressed as 0° substance or an object with reference to some standard value. K., as - 2730 C., or as -459.40 F, (used as -4600F) for the most Temperature is a dominant factor affecting the physical properties calculations. of fluids. It is of particular concern when calculating changes in When working with temperatures, always make sure which the state of gases. The three temperature scales used extensively system of measurement is being used and know how to convert arc the centigrade, the Fahrenheit, and the absolute or Kelvin from one to another. The conversion formulas are shown in B of scales. The centigrade scale is constructed by using the freezing figure 7-5. For purposes of calculations, the Rankin scale and boiling points of water, under standard conditions, as fixed illustrated in A of figure 7-5 is commonly used to convert pointsofzeroand100, respectively, with 100 equal divisions Fahrenheit to absolute. For Fahrenheit readings above zero, between. The Fahrenheit scale uses 320 as the freezing point of 4600 is added. Thus 720 F equals 4600 plus 720, or 5320 absolute. water and 2120 as the boiling point, and has 180 equal divisions If the Fahrenheit reading is below zero, it is subtracted from 460°. between. The absolute or Kelvin scale is constructed with its Thus -400 F equals 4600minus 400 or4200 absolute or – 40 0 C. It zero point established as - 273°C. or- 459.4°F, below the freezing should be stressed that the Rankin scale does not indicate point of water. The relationships of the other fixed points of the absolute temperature readings in accordance with the Kelvin scales are shown in B. scale, but these conversions may be used for the calculations of Absolute zero, one of the fundamental constants of physics, is changes in the state of gases. For 10 C rise in temperature equals commonly used in the study of gases. It is usually expressed in 1.80 F rise in Fahrenheit scale. So if in centigrade temperature terms of the centigrade scale. If the heat energy of a given gas rises 1000 C, which is equivalent to 1800 F. sample could he progressively reduced, some temperature would The Kelvin and centigrade scales are used more extensively in be reached at which the motion of the molecules would cease scientific work; therefore, some technical manuals may use these entirely. If accurately determined, this temperature could then be scales in giving directions and operating instructions. The taken as a natural reference, or as a true "absolute zero" value. Fahrenheit scale is commonly used in the United States, and most Experiments with hydrogen indicated that if a gaswerecooledto- people are familiar with it. Therefore, the Fahrenheit scale is used 273.16°C.(used as -273° for most calculations),all molecular in most areas of this text. Alcohol thermometers are used with colored alcohol rather than mercury thermometers in very cold regions because alcohol has a TIAT 2.3 3- 4 THAKUR INSTITUTE OF AVIATION TECHNOLOGY lower freezing point than mercury. Pure ethanol (alcohol) freezes Temperature is the measure of the thermal energy or average heat at -1140 C where mercury freezes at -38.80 C. of the molecules in a substance. Some forms of energy which can be converted Theometers & Temperature Scales Into heat energy are as follows: 1. Mechanical Energy: This includes all methods of producing increased motion of molecules such as friction, impact of bodies, or compression of gases. 2. Electrical Energy: Electrical energy is converted to heat energy when an electric current flows through any form of resistance. This might be an electric iron, electric light, or an electric blanket. 3. Chemical Energy: Most forms of chemical reaction convert stored potential energy into heat. Some examples are the explo- sive effects of gun powder, the burning of oil or wood, and the combining of oxygen and grease. 4. Radiant Energy: Electromagnetic waves of certain frequencies produce heat when they are absorbed by the bodies they strike. Included are X-rays, light r a y s , and infrared rays. 5. Nuclear Energy: Nuclear energy stored in the nucleus of atoms is released during the process of nuclear fission in a nuclear Fig 3.1 reactor or atomic explosion. The Sun: AU(atomic unit) heat energy, can be directly or indirectly traced to the nuclear reactions occurring in the sun. HEAT Heat is a form of energy. It is produced only by the conversion of one of the other forms of energy. Heat may also be defined as the total kinetic energy of the molecules of any substance. TIAT 2.3 3- 5 THAKUR INSTITUTE OF AVIATION TECHNOLOGY 2.3 (b) Solved Examples HEAT CAPACITY Example Heat capacity, also known as thermal capacity is the amount of Determine the heat capacity of copper of mass 70 g and the heat required to change the temperature of a given amount of matter by 1°C. temperature difference is 20oC if 300 J of heat is lost. The SI unit for heat capacity of an object is joule per kelvin (J/K Solution: or J⋅K−1). Since an increment of temperature of one degree Given parameters are, Celsius is the same as an increment of one kelvin, that is the same Mass m = 70 g, unit as J/°C. Temperature difference T = 20oC, Heat lost Δ Q = 300 J FORMULA FOR HEAT CAPACITY the Heat capacity formula is given by The heat Capacity formula is expressed as the product of mass, Q = mc ΔT specific heat, and change in the temperature which is c= 300 / 20 mathematically given as: c= 15 J/oC Example Q = mcΔT Determine the heat capacity of 3000 J of heat is used to heat the Where, iron rod of mass 10 Kg from 20oC to 40oC.  Q is the heat capacity in Joules Solution:  m is the mass in grams  c is the specific heat of an object in J/g °C Given parameters are Mass m = 10 Kg,  ΔT is the change in the temperature in °C Temperature difference Δ T = 20oC, Heat lost ΔQ = 3000 J The Heat capacity formula is given by Q = mc ΔT c= 3000 / 20 c= 150 J/oC TIAT 2.3 3- 6 THAKUR INSTITUTE OF AVIATION TECHNOLOGY Specific Heat Q = m × c × ΔT Or Specific heat refers to the ratio of the quantity of heat that we require to raise the temperature of a body by one degree that we need to increase the temperature of an equivalent mass of liquid Q = mcΔT (water) by one degree. Also, we use the term in a narrower sense to mean the amount of heat, in calories that we require to raise the temperature of one gram of a substance by one Celsius Derivation of Specific Heat Formula degree. Q = refers to the heat energy in Joules (J) m = refers to the mass of the substance in kilogram (kg) In simple words, it is the ratio of the amount of heat required to c = refers to the specific heat in joules per kilogram (J/kg⋅k) increase the temperature of an object by one degree to the Δ = refers to the symbol of change amount of heat required to increase the temperature of the same Δt = refers to the change in temperature in kelvins (K) amount of water by one degree. Solved Examples on Specific Heat Formula SPECIFIC HEAT CAPACITY Example 1 The heat capacity of 1 gram of a substance is called its specific If the specific heat of gold is 129 J/kg⋅k. Then what quantity of heat capacity (or specific heat), while the heat capacity of 1 mole heat energy is required to raise the temperature of 100 g of gold of a substance is called its molar heat capacity. by 50.0 K? Specific Heat Formula Solution: As we discussed above the specific heat is the relation of First of all, write down the things given in the question temperature change of an object with water. Mass of the gold = 100 g converting it into kg, we get 0.100 kg. Specific heat = 129 J/kg⋅k. Also, the formula is like this: Temperature = 50.0 K Heat energy = (mass of the object or substance) × (specific heat) × (Change in temperature) TIAT 2.3 3- 7 THAKUR INSTITUTE OF AVIATION TECHNOLOGY Now put all the values in the formula. But, before that, we have Calculations: to reorganize the formula to find specific heat. Q = mcΔT Q = (0.100 kg) (129 J/kg⋅k) (50.0 K) 𝑄 Q = mcΔT → c = mΔT So, the energy required to raise the temperature of 100 g gold is 645 J. Now putting values in the rearranged formula Example 2 C = 1676000/(5.00kg)(80.0) Suppose a pot is heated by transferring 1676 KJ of heat energy C = 4190 J/kg⋅k to the water. Moreover, if there is 5.000 kg of water in the pot and the temperature is raised by 80.0 K then find the specific heat Hence, the specific heat of water is 4190 J/kg⋅k. of water? 1. CONDUCTION - A PARTICLE VIEW Solution: Let's begin our discussion by returning to our thought experiment in which a metal can containing hot water was placed within a Styrofoam cup containing cold water. Heat is transferred from Let’s write down the things given in the question the hot water to the cold water until both samples have the same Mass (m) = 5.00 kg temperature. In this instance, the transfer of heat from the hot Temperature (T) = 80.0 K water through the metal can to the cold water is sometimes Specific heat (c) = 1676 KJ referred to as conduction. Conductive heat flow involves the transfer of heat from one location to another in the absence of Now we have to convert the specific heat into Joules because it is any material flow. There is nothing physical or material moving in Kilojoules. from the hot water to the cold water. Only energy is transferred from the hot water to the cold water. Other than the loss of energy, there is nothing else escaping from the hot water. And So, the conversion is like this other than the gain of energy, there is nothing else entering the 1 KJ = 1,000 J cold water. How does this happen? What is the mechanism that So, 1676 KJ = 1,000 × 1676 = 16,76,000 J makes conductive heat flow possible? A question like this is a practical-level question. To understand the answer, we have to think about matter as consisting of tiny TIAT 2.3 3- 8 THAKUR INSTITUTE OF AVIATION TECHNOLOGY particles atoms, molecules and ions. These particles are in particles of the container or even the surrounding air. Even the constant motion; this gives them kinetic energy. As mentioned wigglers that are fixed in a position along the perimeter are doing previously in this lesson, these particles move throughout the some banging. Being at the perimeter, their wiggling results in space of a container, colliding with each other and with the walls collisions with the particles that are next to them; these are the of their container. This is known as translational kinetic energy particles of the container or of the surrounding air. and is the main form of kinetic energy for gases and liquids. But these particles can also vibrate about a fixed position. This gives At this perimeter or boundary, the collisions of the little the particles vibrational kinetic energy and is the main form of bangers and wigglers are elastic collisions in which the total kinetic energy for solids. To put it more simply, matter consists amount of kinetic energy of all colliding particles is conserved. of little wigglers and little bangers. The wigglers are those The net effect of these elastic collisions is that there is a transfer particles vibrating about a fixed position. They possess of kinetic energy across the boundary to the particles on the vibrational kinetic energy. The bangers are those particles that opposite side. The more energetic particles will lose a little move through the container with translational kinetic energy and kinetic energy and the less energetic particles will gain a little collide with the container walls. kinetic energy. Temperature is a measure of the average amount of kinetic energy possessed by the particles in a sample of matter. So on average, there are more particles in the higher temperature object with greater kinetic energy than there are in the lower temperature object. So when we average all the collisions together and apply the principles associated with elastic collisions to the particles within a sample of matter, it is logical to conclude that the higher temperature object will lose some kinetic energy and the lower temperature object will gain some kinetic energy. The collisions of our little bangers and wigglers will continue to transfer energy until the temperatures of the two objects are identical. When this state of thermal equilibrium has Fig. 3.2 been reached, the average kinetic energy of both objects' particles is equal. At thermal equilibrium, there are an equal number of collisions resulting in an energy gain as there are collisions The container walls represent the perimeters of a sample of resulting in an energy loss. On average, there is no net energy matter. Just as the perimeter of your property (as in real estate transfer resulting from the collisions of particles at the perimeter. property) is the furthest extension of the property, so the perimeter of an object is the furthest extension of the particles within a sample of matter. At the perimeter, the little bangers are colliding with particles of another substance - the TIAT 2.3 3- 9 THAKUR INSTITUTE OF AVIATION TECHNOLOGY of energy outward from the hot water to the cold water. The average kinetic energy of the hot water particles gradually decreases; the average kinetic energy of the cold-water particles gradually increases; and eventually, thermal equilibrium would be reached at the point that the particles of the hot water and the cold water have the same average kinetic energy. At the macroscopic level, one would observe a decrease in temperature of the hot Fig. 3.3 water and an increase in temperature of the cold water. At the macroscopic level, heat is the transfer of energy from the high temperature object to the low temperature object. At the particle level, heat flow can be explained in terms of the net effect of the collisions of a whole bunch of little bangers. Warming and cooling is the macroscopic result of this particle-level phenomenon. Now let's apply this particle view to the scenario of the metal can with the hot water positioned inside of a Styrofoam Fig.3.4 cup containing cold water. On average, the particles with the greatest kinetic energy are the particles of the hot water. Being a fluid, those particles move about with translational kinetic energy and bang upon the particles of the metal can. As the hot water particles bang upon the particles of the metal can, they transfer energy to the metal can. This warms the metal can up. Most metals are good thermal conductors so they warm up quite quickly throughout the bulk of the can. The can assumes nearly the same temperature as the hot water. Being a solid, the metal can consists of little wigglers. The wigglers at the outer perimeter of the metal can bang upon particles in the cold water. The collisions between the particles of the metal can and the particles of the cold water result in the transfer of energy to the cold water. This slowly Fig. 3.5 warms the cold water up. The interaction between the particles of the hot water, the metal can and the cold water results in a transfer TIAT 2.3 3- 10 THAKUR INSTITUTE OF AVIATION TECHNOLOGY The mechanism in which heat is transferred from one object to their neighbors. As they wiggle more vigorously, they bang another object through particle collisions is known as conduction. into their neighbors and increase their vibrational kinetic energy. In conduction, there is no net transfer of physical stuff between These particles in turn begin to wiggle more vigorously and their the objects. No material moves across the boundary. The changes collisions with their neighbors increase their vibrational kinetic in temperature are wholly explained as the result of the gains and energy. The process of energy transfer by means of the losses of kinetic energy during collisions. little bangers continues from the particles at the inside of the mug (in contact with the coffee particles) to the outside of the CONDUCTION THROUGH THE BULK OF AN OBJECT mug (in contact with the surrounding air). Soon the entire coffee mug is warm and your hand feels it. We have discussed how heat transfers from one object to another through conduction. But how does it transfer through the bulk of an object? For instance, suppose we pull a ceramic coffee mug out of the cupboard and place it on the countertop. The mug is at room temperature - maybe at 26°C. Then suppose we fill the ceramic coffee mug with hot coffee at a temperature of 80°C. The mug quickly warms up. Energy first flows into the particles at the boundary between the hot coffee and the ceramic mug. But then it flows through the bulk of the ceramic to all parts of the ceramic mug. How does heat conduction occur in the ceramic itself? The mechanism of heat transfer through the bulk of the ceramic mug is described in a similar manner as it before. The ceramic mug consists of a collection of orderly arranged wigglers. These are particles that wiggle about a fixed position. As the ceramic particles at the boundary between the hot coffee and the mug warm up, they attain a kinetic energy that is much higher than Fig.3.6 TIAT 2.3 3- 11 THAKUR INSTITUTE OF AVIATION TECHNOLOGY This mechanism of conduction by particle-to-particle interaction is very common in ceramic materials such as a coffee mug. Does it work the same in metal objects? For instance, you likely have noticed the high HEAT TRANSFER BY CONVECTION temperatures attained by the metal handle of a skillet when placed upon a stovetop. The burners on the stove transfer heat to the metal skillet. If Is conduction the only means of heat transfer? Can heat be the handle of the skillet is metallic, it too attains a high temperature, transferred through the bulk of an object in methods other than certainly high enough to cause a bad burn. The transfer of heat from the conduction? The answer is yes. The model of heat transfer skillet to the skillet handle occurs by conduction. But in metals, the through the ceramic coffee mug and the metal skillet involved conduction mechanism is slightly more complicated. In a manner conduction. The ceramic of the coffee mug and the metal of the similar to electrical conductivity, thermal conductivity in metals occurs skillet are both solids. Heat transfer through solids occurs by by the movement of free electrons. Outer shell electrons of metal atoms conduction. This is primarily due to the fact that solids have are shared among atoms and are free to move throughout the bulk of the orderly arrangements of particles that are fixed in place. Liquids metal. These electrons carry the energy from the skillet to the skillet and gases are not very good conductors of heat. In fact, they are handle. The details of this mechanism of thermal conduction in metals considered good thermal insulators. Heat typically does not flow are considerably more complex than the discussion given here. The through liquids and gases by means of conduction. Liquids and main point to grasp is that heat transfer through metals occurs without gases are fluids; their particles are not fixed in place; they move any movement of atoms from the skillet to the skillet handle. This about the bulk of the sample of matter. The model used for qualifies the heat transfer as being categorized as thermal conduction. explaining heat transfer through the bulk of liquids and gases involves convection. Convection is the process of heat transfer from one location to the next by the movement of fluids. The moving fluid carries energy with it. The fluid flows from a high temperature location to a low temperature location. Fig. 3.7 TIAT 2.3 3- 12 THAKUR INSTITUTE OF AVIATION TECHNOLOGY To understand convection in fluids, let's consider the heat Convection also explains how an electric heater placed on the floor of a transfer through the water that is being heated in a pot on a stove. cold room warms up the air in the room. Air present nears the coils of Of course the source of the heat is the stove burner. The metal the heater warm up. As the air warms up, it expands, becomes less dense pot that holds the water is heated by the stove burner. As the and begins to rise. As the hot air rises, it pushes some of the cold air metal becomes hot, it begins to conduct heat to the water. The near the top of the room out of the way. The cold air moves towards the water at the boundary with the metal pan becomes hot. Fluids bottom of the room to replace the hot air that has risen. As the colder air expand when heated and become less dense. So as the water at approaches the heater at the bottom of the room, it becomes warmed by the bottom of the pot becomes hot, its density decreases. The the heater and begins to rise. Once more, convection currents are slowly difference in water density between the bottom of the pot and the formed. Air travels along these pathways, carrying energy with it from top of the pot results in the gradual formation of circulation the heater throughout the room currents. Hot water begins to rise to the top of the pot displacing the colder water that was originally there. And the colder water that was present at the top of the pot moves towards the bottom of the pot where it is heated and begins to rise. These circulation currents slowly develop over time, providing the pathway for heated water to transfer energy from the bottom of the pot to the surface. Fig. 3.9 Convection is the main method of heat transfer in fluids such as water and air. It is often said that heat rises in these situations. Fig. 3.8 The more appropriate explanation is to say that heated fluid rises. For instance, as the heated air rises from the heater on a floor, it carries more energetic particles with it. As the more energetic particles of the heated air mix with the cooler air near the ceiling, TIAT 2.3 3- 13 THAKUR INSTITUTE OF AVIATION TECHNOLOGY the average kinetic energy of the air near the top of the room unit into the adjacent room. This is another example of forced increases. This increase in the average kinetic energy convection. corresponds to an increase in temperature. The net result of the rising hot fluid is the transfer of heat from one location to another HEAT TRANSFER BY RADIATION location. The convection method of heat transfer always involves the transfer of heat by the movement of matter. This is not to be A final method of heat transfer involves radiation. Radiation is confused with the caloric theory discussed earlier in this lesson. the transfer of heat by means of electromagnetic waves. In caloric theory, heat was the fluid and the fluid that moved was To radiate means to send out or spread from a central location. the heat. Our model of convection considers heat to be energy Whether it is light, sound, waves, rays, flower petals, wheel transfer that is simply the result of the movement of more spokes or pain, if something radiates then it protrudes or spreads energetic particles. outward from an origin. The transfer of heat by radiation involves the carrying of energy from an origin to the space The two examples of convection discussed here - heating water surrounding it. The energy is carried by electromagnetic waves in a pot and heating air in a room - are examples of natural and does not involve the movement or the interaction of matter. convection. The driving force of the circulation of fluid is Thermal radiation can occur through matter or through a region natural - differences in density between two locations as the of space that is void of matter (i.e., a vacuum). In fact, the heat result of fluid being heated at some source. (Some sources received on Earth from the sun is the result of electromagnetic introduce the concept of buoyant forces to explain why the waves traveling through the void of space between the Earth and heated fluids rise. We will not pursue such explanations here.) the sun. Natural convection is common in nature. The earth's oceans and atmosphere are heated by natural convection. In contrast to All objects radiate energy in the form of electromagnetic waves. natural convection, forced convection involves fluid being The rate at which this energy is released is proportional to the forced from one location to another by fans, pumps and other Kelvin temperature (T) raised to the fourth power. devices. Many home heating systems involve force air heating. Air is heated at a furnace and blown by fans through ductwork Radiation rate = k T4 and released into rooms at vent locations. This is an example of forced convection. The movement of the fluid from the hot The hotter the object, the more it radiates. The sun obviously location (near the furnace) to the cool location (the rooms radiates off more energy than a hot mug of coffee. The throughout the house) is driven or forced by a fan. Some ovens temperature also affects the wavelength and frequency of the are forced convection ovens; they have fans that blow heated air radiated waves. Objects at typical room temperatures radiate from a heat source into the oven. Some fireplaces enhance the energy as infrared waves. Being invisible to the human eye, we heating ability of the fire by blowing heated air from the fireplace do not see this form of radiation. An infrared camera is capable of detecting such radiation. Perhaps you have seen thermal TIAT 2.3 3- 14 THAKUR INSTITUTE OF AVIATION TECHNOLOGY photographs or videos of the radiation surrounding a person or animal or a hot mug of coffee or the Earth. The energy radiated from an object is usually a collection or range of wavelengths. This is usually referred to as an emission spectrum. As the temperature of an object increases, the wavelengths within the spectra of the emitted radiation also decrease. Hotter objects tend to emit shorter wavelength, higher frequency radiation. The coils of an electric toaster are considerably hotter than room temperature and emit electromagnetic radiation in the visible spectrum. Fortunately, this provides a convenient warning to its users that the coils are hot. The tungsten filament of an incandescent light bulb emits electromagnetic radiation in the visible (and beyond) range. This radiation not only allows us to see, it also warms the glass bulb that contains the filament. Put Fig. 3.10 your hand near the bulb (without touching it) and you will feel Our discussion on this page has pertained to the various the radiation from the bulb as well. methods of heat transfer. Conduction, convection and radiation have been described and illustrated. The macroscopic has been Thermal radiation is a form of heat transfer because the explained in terms of the particulate-an ongoing goal of this electromagnetic radiation emitted from the source carries energy chapter of The Physics Classroom Tutorial. The last topic to be away from the source to surrounding (or distant) objects. This discussed in Lesson 1 is more quantitative in nature. On the next energy is absorbed by those objects, causing the average kinetic page, we will investigate the mathematics associated with the energy of their particles to increase and causing the temperatures rate of heat transfer. to rise. In this sense, energy is transferred from one location to another by means of electromagnetic radiation. The image at the Thermal expansions right was taken by a thermal imaging camera. The camera detects It is common observation that most substances (solids, liquids and the radiation emitted by objects and represents it by means of a gases) expand on being heated and contract and being cooled. color photograph. The hotter colors represent areas of objects that If the three states of matter is heated equally, it will be found that are emitting thermal radiation at a more intense rate. Black dull gas will expand maximum, liquid will expand more than solid but surface is the best absorber of thermal radiation. less than gaseous matter. Illustrative examples: You may have observed that sometimes sealed bottles with metallic lids are so tightly screwed that one has to put the lid in TIAT 2.3 3- 15 THAKUR INSTITUTE OF AVIATION TECHNOLOGY hot water for some time to open the lid this would allow the Superficial expansion (change in area) metallic cover to expand their by making it loose to unscrew it Cubical expansion (change in volume) easily. To give a quantitative meaning to the expansion of solid we The expansion joints being provided on railway tracks and on introduce a concept of coefficient of linear expansion of the concrete highways. material, superficial expansion of the material, coefficient of In metal pipes carrying an oil or another liquid over long volume expansion of the material distances, loops are generally provided at regular intervals this is Coefficient of linear expansion of the material: to avoid strain that could otherwise develop in the pipe due to It is the ratio between the increases in length to the initial length changes in the temperature. of a material of solid when its temperature is increased by 10C. In the case of gases, a balloon partially inflated in a cool room OR may expand to full size when placed in warm water. On the other It is the fractional change in the length per degree rise in hand a fully inflated balloon when immersed in cold water would temperature. starts shrinking due to contraction of the air inside. L2=L 1 [1 + α (T2 –T1)] Activity : Where, α is a constant for a given material and is called the Blacksmiths make use of the effect of expansion on heating when coefficient of the linear expansion of the material. they are required to fix a metallic ring on the rim of wooden wheel of a bullock cart for these they make the metallic ring a little VOLUMETRIC EXPANSION smaller in diameter than that of the wheel. The ring expands on The volume of a gas, solid or liquid changes if the temperature, heating and fits on the wheel. the pressure or the forces acting on that gas/solid/liquid change. Then it is allowed to contract by pouring water over it which can thus fit over the wheel tightly. Unit of length is meter in MKS When a solid is in bulk form that is in the form of a cube, cuboid, system and foot in FPS system. 1 meter equals to 1.094 yards or or sphere, etc. then on heating, its volume increases, this is called 39.37 inches and 1 inch equals to 2.54 centimeter. volume expansion. THERMAL EXPANSIONS IN SOLIDS We know that solids have definite shape so there are three types of thermal expansions in solids Linear expansion (change in length) TIAT 2.3 3- 16 THAKUR INSTITUTE OF AVIATION TECHNOLOGY Coefficient Of Volume Expansion A THERMODYNAMIC SYSTEM The coefficient of volume expansion of the material of bulk solid In a diagram of a generic thermodynamic system, thermodynamics is defined as the increase in its volume per unit of original volume makes no distinction between kinetic and potential energy and it per degree rise in temperature. Its SI unit is K-1 but it is commonly does not assume the existence of atoms and molecules. In the expressed in 0C-1 (per degree Celsius). context of chemistry, the internal energy is the sum of the kinetic energy of the molecules, and the potential energy represented by the chemical bonds between the atoms and any other It is observed that if the change in volume of the solid is ∆V then intermolecular forces that may be operative. ∆V proportional to the product of the original volume(V) and the change in temperature(∆T). THE FIRST LAW OF THERMODYNAMICS Thus, it can be written as; ∆V∝V×∆T The first law of thermodynamics, also known as Law of ∆V=γV×∆T Conservation of Energy, states that energy can be neither be Here, γ is the co-efficient of volumetric expansion of the given created nor destroyed; it can only be transferred or changed from solid material one form to another. For example: The dissolution of ammonium nitrate in water in a single-use cold pack may appear to destroy Therefore, γ = ∆v/(v×∆T) energy as the temperature of the cold pack decreases. However, From the above relation, the heat energy is only converted to a different form, chemical energy that is invested in chemical bonds. 1. The coefficient of volume expansion of the material of bulk solid is defined as the increase in its volume per unit of A way of expressing the first law of thermodynamics is that any original volume per degree rise in temperature. change in the internal energy (∆U) of a system is equal to the heat (q) added to the system minus the work done (w) by the system. 2. Its SI unit is K-1 but it is commonly expressed in 0C-1 (per ΔU=q-w. degree Celsius). This law says that there are two kinds of processes, heat and work, that can lead to a change in the internal energy of a system. Since For example, a steel block with a volume of 1 cubic meter might both heat and work can be measured and quantified, this is the expand to 1.002 cubic meters when the temperature is raised by same as saying that any change in the energy of a system must 50 K. This is an expansion of 0.2%. result in a corresponding change in the energy of the world outside the system. In other words, energy cannot be created or destroyed. If heat flows into a system or the surroundings to do TIAT 2.3 3- 17 THAKUR INSTITUTE OF AVIATION TECHNOLOGY work on it, the internal energy increases and the sign of q or w is positive. Conversely, heat flow out of the system or work done by Definition of Work the system will be at the expense of the internal energy, and will Work can be defined as the product of the force used to move an therefore be negative. object times the distance the object is moved. w=Fxd 2. THE SECOND LAW OF THERMODYNAMICS Imagine a system that consists of a sample of ammonia trapped in Entropy: Entropy is the measure of disorder of molecules of the a piston and cylinder, as shown in the figure below. Assume that system, due to loss or gain of heat by a body. the pressure of the gas pushing up on the piston just balances the weight of the piston, so that the volume of the gas is constant. The second law of thermodynamics says that the entropy of any Now assume that the gas decomposes to form nitrogen and isolated system not in thermal equilibrium almost always hydrogen, increasing the number of gas particles in the container. increases. Isolated systems spontaneously evolve towards thermal If the temperature and pressure of the gas are held constant, this equilibrium—the state of maximum entropy of the system—in a means that the volume of the gas must increase. process known as "thermalization". Equivalently, perpetual motion machines of the second kind are impossible. More simply put: the entropy of the world only increases and never decreases. A simple application of the second law of thermodynamics is that 2 NH3(g) N2(g) + 3 H2(g) a room, if not cleaned and tidied, will invariably become more messy and disorderly with time - regardless of how careful one is to keep it clean. When the room is cleaned, its entropy decreases, but the effort to clean it has resulted in an increase in entropy outside the room that exceeds the entropy lost. 3. THE THIRD LAW OF THERMODYNAMICS The third law of thermodynamics states that the entropy of a system approaches a constant value as the temperature approaches Fig. 3.11 zero. The entropy of a system at absolute is typically zero, and in all cases is determined only by the number of different ground The volume of the gas can increase by pushing the piston partway states it has. Specifically, the entropy of a pure crystalline substance out of the cylinder. The amount of work done is equal to the at absolute zero temperature is zero. This statement holds true if product of the force exerted on the piston times the distance the the perfect crystal has only one state with minimum energy. piston is moved. TIAT 2.3 3- 18 THAKUR INSTITUTE OF AVIATION TECHNOLOGY w=Fxd is a seething mass of high speed molecules traveling at hundreds of meters per second. If the water were tossed across the room, The pressure (P) the gas exerts on the piston is equal to the this microscopic energy would not necessarily be changed when force (F) with which it pushes up on the piston divided by the we superimpose an ordered large scale motion on the water as a surface area (A) of the piston. whole. U is the most common symbol used for internal energy. Related energy quantities which are particularly useful in Area of cross section = 𝜋𝑟2 chemical thermodynamics are enthalpy, Helmholtz free energy, Thus, the force exerted by the gas is equal to the product of its and Gibbs free energy pressure times the surface area of the piston. F = P×A Enthalpy, H is the thermodynamic function that accounts for heat Substituting this expression into the equation defining work gives flow in processes occurring at constant pressure when no forms of the following result. work are performed other than P-V work. w = (P ×A) × d H = E + PV The product of the area of the piston times the distance the piston At constant pressure, a change in enthalpy equals the change in moves is equal to the change that occurs in the volume of the internal energy plus the product of the constant pressure times the system when the gas expands. By convention, the change in the change in volume. volume is represented by the symbol V. ΔH = ΔE + P ΔV V=A×d When ΔH is positive, the system has gained heat from the surroundings-endothermic. The magnitude of the work done when a gas expands is therefore equal to the product of the pressure of the gas times the change in When ΔH is negative, the system has lost heat to the surroundings the volume of the gas. - exothermic. |w| = P V Enthalpy of reaction, the enthalpy change for a chemical reaction is expressed by the equation: INTERNAL ENERGY: Internal energy is defined as ΔH = H products – H reactants the energy associated with the random, disordered motion of Here is an example of a thermochemical equation: molecules. It is separated in scale from the macroscopic ordered 2 H2 (g) + O2 (g) → 2 H2O (g) ΔH = − 483.6 energy associated with moving objects; it refers to the invisible This equation indicates two moles of hydrogen gas burn to form microscopic on the atomic and molecular scale. For example, a two moles of water at a constant pressure, releasing 483.6 kJ of room temperature glass of water sitting on a table has no apparent heat. energy, either potential or kinetic. But on the microscopic scale it TIAT 2.3 3- 19 THAKUR INSTITUTE OF AVIATION TECHNOLOGY striking against each other and against the walls of the container, an increase in temperature with the resulting increase in molecular motion causes a corresponding increase in the number of collisions between the molecules. The increased number of collisions results in an increase in pressure because a greater number of molecules strike against the walls of the container in a given unit of time. Fig. 3.12 If the container were an open vessel, the gas would expand and over flow from the container. However, if the container is sealed and possesses elasticity (such as a rubber balloon), the increased Enthalpy change during a chemical reaction can also be represented in an enthalpy diagram, showing the reactants at the pressure causes the container to expand. top and the products at the bottom. For instance, when making a long drive on a hot day, the Guidelines for using thermochemical equations and enthalpy pressure in the tires of an automobile increases, and a tire which diagrams: The magnitude of ΔH is directly proportional to the appeared to be some- what "soft" in cool morning temperature amount of reactant consumed in the process. may appear normal at a higher midday temperature. The enthalpy change for a reaction is equal in magnitude, but Such phenomena as these have been explained and set forth in opposite in sign, to ΔH for the reverse reaction. the form of laws pertaining to gases and tend to support the The enthalpy change for a reaction depends on the state of the kinetic theory. reactants and products. At any given instant, some molecules of a gas are moving in one direction, some in another di-rection; some are traveling fast KINETICTHEORYOF GASES while some are traveling slowly; some may even be in a State of The simple structure of gases makes them readily adaptable to rest. The combined effect of these varying ve-locities mathematical analysis from which has evolved a detailed theory corresponds to the temperature of the gas. In any considerable of the’ he ha viol' of gases. This is called the kinetic theory of amount of gas, there are so many molecules present that in gases. The theory assumes that a body of gas is composed of accordance with the "laws of probability" some average velocity identical molecules which behave like minute elastic spheres, can be found. If this average velocity were pos-sessed by spaced relatively far apart and continuously in motion and the every molecule in the gas, it would produce the same effect collisions between the molecules are perfectly elastic. at a given temperature as the total of the many varying The degree of molecular motion is dependent upon the velocities gas was kept constant and the pressure doubled, the temperature of the gas. Since the mole-cules are continuously volume was reduced to half the former value. TIAT 2.3 3- 20 THAKUR INSTITUTE OF AVIATION TECHNOLOGY P2 = 66.6 psig. BOYLE'S LAW A gas which conforms to Boyle’s law is termed an ideal gas. When pressure is increased upon such a gas, its volume As previously stated, compressibility is an out-standing decreases proportionally and its density is increased. Thus, the characteristic of gases. The English scientist Robert Boyle was density of a gas varies directly with the pressure, if the among the first to study this characteristic which he called the temperature remains constant as in the case of an ideal gas. "springiness of air. "By direct measurement he discovered that Density also varies with temperature, since gases expand when when the temperature of a combined sample of as the applied heated and contract when cooled. pressure was decreased, the result in volume increased. From The useful applications of Boyle's law are many and varied. these observations, he concluded that for a constant temperature Some applications more common to aviation are: (1)The carbon the product of the volume and pressure of an enclosed gas remains dioxide(Co2) bottle used to inflate life rafts and life-vests (2) the constant but liquid and solid are not compressible. Boyle's law is compressed oxygen and the acetylene tanks used in welding; normally stated: "The volume of an enclosed dry gas varies (3) the compressed air brakes and shock absorbers and (4) the inversely with its pressure, provided the temperature remains use of oxygen tanks for high-altitude flying and emergency use. constant." This law can be demonstrated by confining a quantity of gas in a CHARLES’LAW cylinder which has a tightly fitted piston. A force is then applied to the piston so as to compress the gas in the cylinder to some The French scientist Jacques Charles provided much of the specific volume. When the force applied to the piston is doubled, foundation for the modern kinetic theory of gases. He found that the gas is compressed to one half its original volumes. all gases expand and contract indirect proportion to the change in In equation form, this relationship may be expressed either or the absolute temperature, provided the pressure is held constant. where V1.and P1 is the original volume and pressure, and V2 and In equation form, this part of the law may be expressed. P2 are the revised volume and pressure. V1T2 = V2T1 Example of Boyle'slaw:4cu.ft.of nitrogen is under a pressure of It is observed that if the temperature of gas is increased or 100 psig. The nitrogen is allowed to expand to a volume of 6 decreased by one degree Kelvin then the volume of gas also will cu.ft. What is the new gage pressure? increase or decrease by 1/273 ratio. Formula or equation: P1V1 =P2V2 or, Substituting value, This equation means that with constant volume, the absolute 4 × (100) = 6 × P2 pressure of a gas varies directly with the absolute temperature. P2 = 4 × 100/6 P1T2 = P2T1 TIAT 2.3 3- 21 THAKUR INSTITUTE OF AVIATION TECHNOLOGY Examples of Charles' law: A cylinder of gas under a pressure of General Gas Law 1,800 psig at 700F is left out in the sun in the tropics and heats up The facts concerning gases discussed in the preceding sections to a temperature of 1300F.Whatis the new pressure within the are summed up. Boyle's law is expressed and the effects of cylinder? temperature changes on pressure and volume (Charles' law) is illustrated respectively. The pressure and temperature must be converted to absolute By combining Boyle's and Charles' laws, a single expression can pressure and temperature. be derived which states all the information contained in both. Formula & Equation: This expression is called the general gas law, a very useful form P1 T1 of which is given in the following equation. = P2 T2 (NOTE: The capital P and T signify absolute pressure and 0 0 T1 = 70 F = 530 absolute temperature, respectively.) T2= 1300F = 5900absolute P1V1 P2V2 1800+14.7 530 = Substituting: = T1 T2 P2 590 Then, 590 × 1814.7 P2= = 2,020psia. GAY-LUSSAC’S LAW 530 Converting absolute pressure to gage pressure: This law discovered by Joseph Louis Gay-Lussac in the early Absolute pressure = gauge pressure + atmospheric pressure. 1800's. However, the Chem Team's knowledge of this is much Therefore, 2,020.0psia - 14.7psi = 2005.3 psig. less sure than concerning Boyle's or Charles' Law. He gives the relationship between pressure and temperature when Free balloon flights into the stratosphere, the expanding gases of volume and amount are held constant. jet-propelled aircraft, and the effects of clouds and weather on If the temperature of a container is increased, the pressure instrument recordings may be explained by the use of Charles' increases. law. Here are practical applications of a law of physics that aid the If the temperature of a container is decreased, the pressure pilot, air controller, and aerographer in their work. Flying is decreases. Why? made safer when humans are able to apply this law to handle Suppose the temperature is increased. This means gas molecules weather data so vital to aviation. will move faster and they will impact the container walls more often. This means the gas pressure inside the container will TIAT 2.3 3- 22 THAKUR INSTITUTE OF AVIATION TECHNOLOGY increase, since the container has rigid walls (volume stays Make sure to convert any Celsius temperature to Kelvin before constant). using it in your calculation. Gay-Lussac's Law is a direct mathematical relationship. This means there are two connected values and when one goes up, the Example #1: 10.0 L of a gas is found to exert 97.0 kPa at 25.0°C. other also increases. What would be the required temperature (in Celsius) to change the The mathematical form of Gay-Lussac's Law is: P ÷ T = k pressure to standard pressure? This means that the pressure-temperature fraction will always be the same value if the volume and amount remain constant. Solution: change 25.0°C to 298.0 K and remember that standard Let P1 and T1 be a pressure-temperature pair of data at the start of pressure in kPa is 101.325. Insert values into the equation (the an experiment. If the temperature is changed to a new value called Chem Team will use the left-hand one in the graphic above) and T2, then the pressure will change to P2. Keep in mind that when get: volume is not discussed (as in this law), it is constant. That means a container with rigid walls. As with the other laws, the exact value of k is unimportant in our The answer is 311.3 K, but the question asks for Celsius, so you context. It is important to know the P-T data pairs obey a constant subtract 273 to get the final answer of 38.3°C. Notice that the relationship, but it is not important for us what the exact value of volume never enters the problem. This is because the problem is the constant is. Besides which, the value of K would shift based asking about the relationship between pressure and temperature; on what pressure units (atm, mmHg, or kPa) you were using. the volume (as well as the moles) remains constant. We know this: P1 ÷ T1 = k Example #2: 5.00 L of a gas is collected at 22.0°C and 745.0 And we know this: P2 ÷ T2 = k mmHg. When the temperature is changed to standard, what is the Since k = k, we can conclude that P1 ÷ T1 = P2 ÷ T2. new pressure? Solution: convert to Kelvin and insert: This equation of P1 ÷ T1 = P2 ÷ T2 will be very helpful in solving Gay-Lussac's Law problems. This graphic simply restates the above in a way. Cross multiply and divide for the new pressure. Sometimes a problem will give you one pressure in one unit and ask for the new pressure in a different unit. In that case, simply do Notice the similarities to the Charles' Law graphic. This is the problem and then convert the pressure to the different unit. because both laws are direct relationships. TIAT 2.3 3- 23  THAKUR INSTITUTE OF AVIATION TECHNOLOGY Thermal Expansion of Gases Types of cycles Examples The most common cycles are: the diesel cycle (for diesel engines),  Thermal expansion of nitrogen gas in car tires occurs due to the the Otto cycle (for gasoline engines). rise in temperature caused by friction.... CONSTANT VOLUME CYCLE:  Expansion of a partially filled balloon to its full size when immersed in warm water. During the constant volume process heat addition and heat  Air bubbles trapped inside cake batter expand when baked. rejection take place and no work transfer, because of this it is also ADIABATIC EXPANSION known as a constant volume cycle. During the adiabatic processes [compressions/expansion] only work transfer taken place but no Adiabatic expansion is defined as the expansion (increase in heat transfer occurs. volume) in which there is no heat transfer occurs between a system and its surroundings. Work is done by the system at the expense of its internal energy. Example: Expansion of air-fuel mixture in IC engine. ISOTHERMAL EXPANSION Isothermal expansion is the type of thermodynamic process in which the temperature of the system remains constant, and the system expands, or the pressure decreases. The melting of a substance at its melting point (constant temperature) is an example of an isothermal expansion process. ENGINE CYCLES This cycle has four stages: intake, compression, combustion expansion, and exhaust. These four stages are repeated over and Fig. 3.13 over again to create power and convert chemical energy into mechanical energy. TIAT 2.3 3- 24 THAKUR INSTITUTE OF AVIATION TECHNOLOGY The area enclosed by the cycle on a P-V diagram is proportional HEAT PUMPS to the work produced by the cycle. On this page we have shown an ideal Otto cycle in which there is no heat entering (or leaving) the gas during the compression and power strokes, no friction A working fluid such as a non-CFC refrigerant is used in a basic losses, and instantaneous burning occurring at constant volume. heat pump. The basic components of a heat pump in are a condenser, an expansion valve, an evaporator and a compressor. CONSTANT PRESSURE CYCLE : In the outdoor coils (the evaporator), heat transfer QC occurs to Diesel cycle is called constant pressure cycle because the heat the working fluid from the cold outdoor air, turning it into a gas. addition process in diesel cycle is done at constant pressure The electrically driven compressor (work input W) raises the whereas petrol cycle is called constant volume cycle as here the temperature and pressure of the gas and forces it into the condenser heat addition is done at constant volume. (Heat rejection in both coils that are inside the heated space. the cycles is done at constant volume). Because the temperature of the gas is higher than the temperature inside the room, heat transfer to the room occurs and the gas condenses to a liquid. The liquid then flows back through a pressure-reducing valve to the outdoor evaporator coils, being cooled through expansion. (In a cooling cycle, the evaporator and condenser coils exchange roles and the flow direction of the fluid is reversed).So the heat exchanger does not transfer fluid like convection process to warm the cold zone or to cool the hot zone. Fig. 3.14 TIAT 2.3 3- 25 THAKUR INSTITUTE OF AVIATION TECHNOLOGY Since the efficiency of a heat engine is Eeff = W/Qh, we see that COPhp=1/Eeff. Since the efficiency of any heat engine is less than 1, it means that COPhp is always greater than 1—that is, a heat pump always has more heat transfer Qh than work put into it. Another interesting point is that heat pumps work best when temperature differences are small. The efficiency of a perfect engine (or Carnot engine) is Eeff C = 1 (Tc:Th, Ratio of temperature difference i.e between absolute temperature of hot and cold reservoir) thus, the smaller the temperature difference, the smaller the efficiency and the greater the COPhp. AIR CONDITIONERS AND REFRIGERATORS Air conditioners and refrigerators are designed to cool something down in a warm environment. As with heat pumps, work input is required for heat transfer from cold to hot. The quality of air Fig. 3.15 conditioners and refrigerators is judged by how much heat transfer Qc occurs from a cold environment compared with how much work input W is required. A good refrigerant has low condensing Simple Heat Pump pressure and low evaporating temperature. What is considered the benefit in a heat pump is considered waste heat in a refrigerator. A simple heat pump has four basic components: (1) condenser, (2) We thus define the coefficient of performance (COPref) of an air expansion valve, (3) evaporator, and (4) compressor. conditioner or refrigerator to be COPref = Qc/W. Since, Qh= QC+W and COPhp= Qh/W, COEFFICIENT OF PERFORMANCE we derive that, COPref= COPhp−1. Also, from Qh>QC, we see that an air conditioner will have a lower coefficient of performance The quality of a heat pump is judged by how much heat transfer than a heat pump. Qh occurs into the warm space compared with how much work input W is required. We define a heat pump's coefficient of performance (COPhp) = Qh/W. TIAT 2.3 3- 26 THAKUR INSTITUTE OF AVIATION TECHNOLOGY Thermodynamics defines macroscopic variables (such as temperature compared to surroundings, there will be transfer of temperature, internal energy, entropy, and pressure) that describe heat from system to the surroundings. average properties of material bodies and radiation, explains how they are related and by what laws they change with time. Heat transfer is given by Q=m×c×ΔT Everything that is not a part of the system constitutes Where m is the mass c is the specific heat and the surroundings. The system and surroundings are separated by a Δ T is the temperature difference in K. boundary. If our system is one mole of a gas in a container, then the boundary is simply the inner wall of the container itself. The Question 2: Calculate the Heat lost by the block when iron block single property that the boundary must have is that it be clearly decreases its temperature from 60oC to 40oC if the mass of the defined, so we can clearly say whether a given part of the world is in our system or in the surroundings. If matter is not able to pass body is 2 kg. across the boundary, then the system is said to be closed; Specific heat of iron C = 0.45 kJ/kgK. otherwise, it is open. A closed system may still exchange energy Solution: with the surroundings unless the system is an isolated one, in which case neither matter nor energy can pass across the Given: Initial temperature Ti = 60oC = 333 K boundary. Final temperature Tf = 40oC = 313 K Mass of the body m = 2 kg HEAT EXCHANGER ∆ T = 333 K - 313 K = 20 K The Heat lost is given by Q = m c ∆ T A heat exchanger is a device that allows heat from a fluid (a liquid = 2 Kg × 0.45 kJ/kg K × 20 K or a gas) to pass to a second fluid (another liquid or gas) without = 18 K J. the two fluids having to mix together or come into direct contact. COOLING CURVE If that's not completely clear, consider this. In theory, we could get the heat from the gas jets just by throwing cold water onto A cooling curve is a line graph that represents the change them, but then the flames would go out! The essential principle of of phase of matter, typically from a gas to a solid or a liquid to a a heat exchanger is that it transfers the heat without transferring solid. The independent variable (X-axis) is time and the dependent the fluid that carries the heat. variable (Y-axis) is temperature. Below is an example of a cooling curve used in castings. HEAT TRANSFER FORMULA Heat transfer is all about the transfer of heat from one point to another. If we consider any system which will be at higher TIAT 2.3 3- 27 THAKUR INSTITUTE OF AVIATION TECHNOLOGY kinetic energy stays the same while the potential energy decreases due to releasing of latent heat. HEATING CURVE FOR WATER Like many substances, water can take numerous forms that are broadly categorized by the phase of matter including liquid, solid, and gas. A way to graph boiling points and freezing points of substances are heating and cooling curves. Heating curves show how the temperature changes as the substance is heated up; a heating curve for water is shown in the following figure. The plateaus on the curve mark the phase changes. Fig. 3.16 The initial point of the graph is the starting temperature of the matter, here noted as the "pouring temperature". When the phase change occurs there is a "thermal arrest", that is the temperature stays constant. This is because the matter has more internal energy as a liquid or gas than in the state that it is cooling to. The amount of energy required for a phase change is known as latent heat. The "cooling rate" is the slope of the cooling curve at any point. In the part of the curve where the temperature decreases, the kinetic energy also decreases while the potential energy stays the same. However, at the phase transition, where the curve is flat, the Fig. 3.16 Heating Curve of Water TIAT 2.3 3- 28 THAKUR INSTITUTE OF AVIATION TECHNOLOGY water molecules. When impurities are added in water boiling The phase transitions of water point increases and melting point decreases. When heat is applied to a solid substance, the first change is melting; as a substance melts, the temperature then stays the same. LATENT HEAT For water, this occurs at 0o C. Water solidifies into ice, its solid phase, under very cold conditions or high pressure. Ice commonly Latent heat is the energy released or absorbed by a body or takes the structure of hard, amalgamated crystals, like ice cubes, a thermodynamic system during a constant-temperature process. or loosely accumulated granular crystals, like snow. A typical example is a change of state of matter, meaning a phase transition such as the melting of ice or the boiling of After all of the solid substance has melted into liquid, the water. The term was introduced around1762 temperature of the liquid begins to increase as heat is absorbed. by Scottish chemist Joseph Black. It is derived from the The liquid phase is the most common form of water within Latin latere (to lie hidden). Black used the term in the context Earth's atmosphere and surface. The term water generally refers to of calorimetry when referring to the heat transferred that caused a the liquid phase of water. change of volume while the thermodynamic system was held at The liquid will begin to boil when enough heat has been absorbed constant temperature. by the solution that the temperature reaches the boiling point, In contrast to latent heat, energy is called a sensible energy or where again, the temperature remains constant until all of the heat when it causes processes that do result in a change of the substance has become gaseous. For water, this phase transition temperature of the system. occurs at 1000C. Liquid water becomes water vapor or steam The latent heat energy required is given by the formula when it enters the gaseous phase, it contains more energy than water. Water vapor is distinguishable because it assumed the Q= m L configuration of a transparent cloud, such as when steam rises off a hot pot of water. Where m is the mass of the substance and L is specific latent heat of fusion or vaporization which measures the heat energy to Water has a high boiling point because of its hydrogen bonding change 1 kg of solid in to liquid. characteristics; water is both a strong hydrogen bond donor and acceptor. When heat is first applied to water, it must first break TABLE OF LATENT HEATS the intermolecular hydrogen bonds that water has formed with itself. After breaking the bonds, heat can then start to vaporize The following table shows the latent heats and change of phase temperatures of some common fluids and gases. TIAT 2.3 3- 29 THAKUR INSTITUTE OF AVIATION TECHNOLOGY Latent Melting Latent Heat Boiling USAGE Heat Substance Point Vaporization Point Fusion °C kJ/kg °C kJ/kg Two of the more common forms of latent heat (or enthalpies or energies) encountered are latent heat of fusion (melting) Alcohol, ethyl 108 −114 855 78.3 and latent heat of vaporization (boiling). These names describe the direction of energy flow when changing from one phase to the Ammonia 332.17 −77.74 1369 −33.34 next: from solid to liquid, and liquid to gas. −78 −57 Carbon dioxide 184 574 In both cases the change is endothermic, meaning that the system absorbs energy on going from solid to liquid to gas. The change Helium 21 −268.93 is exothermic (the process releases energy) for the opposite direction. For example, in the Earth's atmosphere, when a Hg -380 C molecule of water evaporates from the surface of any body of water, energy is transported by the water molecule into a lower −259 −253 Hydrogen(2) 58 455 temperature air parcel that contains less water vapor than its surroundings. Because energy is needed to overcome the Lead 23.0 327.5 871 1750 molecular forces of attraction between water particles, the process of transition from a parcel of water to a parcel of vapor requires Nitrogen 25.7 −210 200 −196 the input of energy causing a drop in temperature in its Oxygen 13.9 −219 213 −183 surroundings. If the water vapor condenses back to a liquid or solid phase onto a surface, the latent energy absorbed during Refrigerant R134a −101 215.9 −26.6 evaporation is released as sensible heat onto the surface. The large value of the enthalpy of condensation of water vapor is the Refrigerant R152a −116 326.5 -25 reason that steam is a far more effective heating medium than boiling