Thermodynamics - Chapter 1 - Zagazig University - 2020-2021 - PDF

‫السالم عليكم ورحمة الله وبركاته‬ ‫وحفظ مصر من كل سوء ومكروه‬ Zagazig University College of Engineering.Mechanical power Engineering Dept Thermodynamics  First Year  General Intorduction  Prof. Mohammed Mansour ...

‫السالم عليكم ورحمة الله وبركاته‬ ‫وحفظ مصر من كل سوء ومكروه‬ Zagazig University College of Engineering.Mechanical power Engineering Dept Thermodynamics  First Year  General Intorduction  Prof. Mohammed Mansour  2020-2021   Chapter 1 General Introduction Thermodynamics can be defined as the study of energy, energy transformations and its relation.to matter Some examples of Application Areas of Thermodynamics: 1-The human body. 2-Power plants. 3-Refrigeration and air conditioning systems. 4-Car radiators. 5-Internal combustion engine. 6-Heat pipes..7-Airplanes Heat pipe configuration 1.1Definitions State, Property.The condition of a system at any instant of time is called its state A property is any quantity whose numerical value depends.on the state Intensive property (of a system): Does not depend on system size; eg. pressure, density, temperature Extensive property (of a system): Extensive property depends on system size; eg. volume, energy Process, Cycle When any property of a system changes in value there is a change in state, and the system is said to undergo a process. When a system in a given initial state goes through a sequence of processes and finally returns to its.initial state, it is said to have undergone a cycle 1.2System and Control Volume System: A quantity of matter or a region in space chosen for study. Surroundings: The mass or region outside the system Boundary: The real or imaginary surface that separates the system from its surroundings. The boundary of a system can be fixed or movable. 1.3 Types of thermodynamic system On the basis of mass and energy transfer the thermodynamic system is divided into three types. 1.Closed system 2.Open system 3.Isolated system Closed system: A system in which the transfer of energy but not mass can takes place across the boundary is called closed system. The mass inside the closed system remains constant. For example: Boiling of water in a closed vessel. Since the water is boiled in closed vessel so the mass of water cannot escapes out of the boundary of the system but heat energy continuously entering and leaving the boundary of the vessel. It is an example of closed system. Open system: A system in which the transfer of both mass and energy takes place is called an open system. This system is also known as control volume. For example: Boiling of water in an open vessel is an example of open system because the water and heat energy both enters and leaves the boundary of the vessel. Isolated system: A system in which the transfer of mass and energy cannot takes place is called an isolated system. For example: Tea present in a thermos flask. In this the heat and the mass of the tea cannot cross the boundary of the thermos flask. Hence the thermos flak is an isolated system. Here we have studied about what is thermodynamic system and different types of thermodynamic system. whatever we have discussed above keeps an important role in the study of subject thermodynamic. If anyone does not know about these topics then it becomes very difficult to understand the thermodynamic subject. if you find anything missing in that then don't forget to comment. 1.4 Equilibrium: A state of balance. Thermal equilibrium: If the temperature is the same throughout the entire system 1.5 Zeroth law of thermodynamics The zeroth law of thermodynamics states that if two thermodynamic systems are each in thermal equilibrium with a third, then they are in thermal equilibrium with each other. 1.6Dimensions and Units :Fundamental Dimensions are.1 mass, M; length, L; time, t; temperature, T Derived Dimensions.2 Can be calculated or derived multiplying or dividing fundamental dimensions. Examples: area, velocity, density and volume SI base units The seven SI base units and the interdependency of their definitions: for example, to extract the definition of the meter from the speed of light, the definition of the second must be known while the ampere and candela are both dependent on the definition of energy.time which in turn is defined in terms of length, mass and The System International d ’Unties (SI), or International System of Units, defines seven units of measure as a basic set from which all other SI units are :derived. The SI base units and their physical quantities are  meter for length  kilogram for mass  second for time  ampere for electric current  Kelvin for temperature  candela for luminous intensity  mole for the amount of substance.  Name Symbol Measur Dimension e symbol metre m length L kilogram kg mass M second s time T ampere electric A I current thermod kelvin K t ynamic t emperat ure moleamountmol N of subst ance Candela luminou cd J s intensi ty Units and dimensions of some properties Property or Unit Dimension quantity Area m2 L2 Volume m3 L3 speed, velocity m s-1 LT-1 Density kg m-3 ML-3 specific m3kg-1 L3M-1 volume Force N MLT-2 pressure N/m2 ML-1 T-2 (Pa) energy, work, J ML2T-2 Temperature 1.7 It may be defined as the degree of hotness or coldness of a body. Measurement of.temperature is made by some form of thermometer 1.7.1Temperature Scales Two temperatures scales are in common Fahrenheit and Celsius (centigrade) scales based on the fact that the melting point of ice and boiling point of water occur at certain fixed temperature at standard atmospheric pressure (14.7psi, 760mmHg). Celsius (centigrade) Scale The melting point of ice or is 0˚C, the boiling point water is 100˚C. There are.100 spaces or degrees on scale between freezing and boiling temperatures Fahrenheit scale The melting point of ice or freezing temperature of water is 32˚F.The boiling point water is 212˚F. This provides 180 spaces or degrees between the freezing and boiling temperature 1.7.2Absolute temperature scales Two absolute temperature scales are used with very low.temperature work or in solving thermodynamic Both Metric system and international system (SI) use the Kelvin.scale and British system uses the Rankine Celsius temperature can be converted to Kelvin temperature by.adding 273˚ to the Celsius reading K = ˚C + 273 Fahrenheit scale can be converted to Rankine scale by adding.460 to the Fahrenheit reading R = ˚F+ 460 Temperature conversion We can easily convert temperature from one scale to another by using of the four equations given below:  Example (1.1) Converts 392 ˚F to C° and K Solution C = 5/9(F°-32)˚ )392-32(5/9 = )360(5/9 = C˚ 200 = K = C °+ 273 273 + 200 = K 473 = Example (1.2) Converts 105 ˚C to °F, and R Solution F = 9/5 х ˚C + 32˚ х 105 + 32 9/5 = F˚ 221 = 32 + 189 = R = ˚F + 460 221+460 = 1-7-3Temperature Measurements :the most common devices for measuring temperature as shown in the figures below are 1. Glass thermometer 2. Digital thermometers 3. Thermocouples 4. Dial gauge thermometers 5. Thermistors Figure1.1 A thermometer Figure 1.2 J-Type Thermocouple Figure 1.3 Dial gauge thermometers 1.8Weight Weight is a term for the localized gravitational force acting upon a body. The unit of weight is therefore the Newton ,N Pressure 1.9 Pressure is defined as force per unit area. Thus, if a uniformly distributed force(F) is applied over an area (A), then the pressure P exerted is given :by the equation then the unit of pressure becomes N/m2, which is the basic unit of pressure in the SI system of units. This unit of pressure is sometimes.called the Pascal (pa) Atmospheric pressure 1-9-1 Atmospheric pressure is due to the weight of the column of air above the earth’s surface. The atmospheric pressure varies slightly from day to :day and is recorded by a barometer, but usual values are.kN/m2 = 10.4 m of water = 760 mm of mercury = 1.013 bar 101.325 Gauge pressure and absolute pressure 1-9-2 Pressure in a pipe line or a vessel is normally measured above the atmospheric pressure by some sort of pressure gauge. The manometer gauge shown in Fig. (1-6) is being used to measure the pressure in a pipe line. Suppose the gauge to give a reading of hmm difference between the water levels in the two limbs of the U tube. The pressure of the gas P is being balanced by the atmospheric pressure Pat plus the pressure due to the column of water h, hence Pab = Pat + ρgh Where: ρ is density g is acceleration of gravity h is height Pat is atmospheric pressure Pab is absolute pressure Example (1.3) What pressure will support a column of mercury (density = 13,600 kg m−3) 80 ?cm high Solution P = 13, 600 × 9.81 × 0.80 Pa and therefore P = 1.0673 × 105 Pa 1-9-2Pressure Measurements the most common devices for measuring pressure shown below are.Pressure gauges-1.Manometers-2.Dead weight gauge (tester)-3  Figure1.5 Pressure gauge Figure1.6 A simple manometers to measure pressure gauge Hand pump – 1 2 - Testing Pump 3 - Pressure Gauge to be calibrated 4 - Calibration Weight 5 - Weight Support 6 - Piston 7 - Cylinder Figure1.7Dead weight tester  Pressure units conversion  V Pascal Bar Technical atmos Standard atmos Torr Pounds per square i  T phere phere nch  E )Pa( )bar( )at( )atm( )Torr( )psi( Pa 1 m 2/ N 1 ≡ 10−5 10−5×1.0197 10−6×9.8692 10−3×7.5006 10−4×1.450377 bar 1 105 cm2/dyn 106 ≡ 1.0197 0.98692 750.06 14.50377 1×0.980665 at 1 0.980665 cm2/kp 1 ≡ 0.9678411 735.5592 14.22334 05 atm 1 105×1.01325 1.01325 1.0332 p0 ≡ 760 ≡ 14.69595 Torr 1 133.3224 10−3×1.333224 10−3×1.359551 10−3×1.315789 mmHg 1 ≈ 10−2×1.933678 psi 1 103×6.8948 10−2×6.8948 10−2×7.03069 10−2×6.8046 51.71493 in2/ lbF 1 ≡ 2 PdV 1 Work 1.10 If a system exists in which a force at the boundary of the system is moved through a distance, then work is done by or on the.system For example, if a force F acts on a body so as to produce a displacement L in the direction of the force, work done by the force w=FxL unit of work If F = force in Newton’s (N) L= distance in (m) then the unit of the work becomes N.m this unit of work called.Joule (J) Work and the pressure-volume diagram 1-10-1 when an expansion takes place in a thermal engine. For the whole 2 PdV 1 Example (1.4) A fluid in a cylinder is at a pressure of 700 kN/m2. It is expanded at constant pressure from a volume of 0.28 m3 to a.volume of 1.68 m3. Determine the work done Solution work done = P ( V2 - V1) = 700 x 103 (1.68 - 0.28) = 9.8 x 105 J Power 1-11 Energy 1.12  Example (1.5) A mass of 250 kg is to be raised by 5 m against gravity. What energy input ?is required to achieve this ?If the mass is lifted in 5 s. What power is required to do this Solution F = 250 × 9.81 N Or F = 2452.5 N The work done (or energy required) W in raising the mass against this force is W = F × distance and therefore W= 2452.5 × 5 J or W= 1.23 × 10 4 J power = 1.23 × 104 / 5 W W 204.4 = Density 1-13 It’s a mass per unit volume, unit of density is kg/m3 Specific volume 1.14 It’s volume per unit mass, unit of specific volume is m3/kg Specific heat 1.15 It defined as the amount of heat required to raise the temperature of a unit mass of any substance one degree centigrade. unit of specific heat is kJ/kg.K Sensible heat 1.16 Sensible heat is the energy required to change the temperature of a.substance with no phase change latent heat 1.17 The heat, which causes a change in of state of a substance without any ,change in its temperature Enthalpy and Entropy 1.18 Enthalpy (h or i).a thermodynamic measure of the thermal energy change in a reaction Unit of enthalpy is J Entropy (s) A thermodynamic quantity that changes in a reversible process by an amount equal to the heat absorbed or emitted divided by the.thermodynamic temperature.Unit of entropy is J/K S = Q / T.Where S is a change of entropy.Q is heat. T is absolute temperature Solved examples on chapter 1 1-Unit of specific entropy is a-kJ/K. b-W. c-kJ/K.kg. d-kJ. 2- Which one of the following expressions can be converted into the unit a Joule? a-Pa m2 b- Pa m3 c- Pa/ m2 d-N/kg Any quantity whose numerical value depends on the state is -3 .property.- a.b-state.c-cycle d-process.Solved examples on chapter 1 cont Dimension of power is-4 a-ML2 T-2. b-ML2 T-3. c-ML T-2. d-ML2 T-1. 5-Dial gauge thermometer is used to measure a-temperature b-Pressure. c-Power. d-work. 6-The heat which causes a change the temperature without changing its state is a-Sensible heat b-Latent heat. c-Specific heat.  Thermodynamics ___________________________________________________ :Choose the best answer-1 i- Dimension of work is a. ML2 T-2. b. ML2 T-3. c. ML T-2. d. ML2 T-1. ii- The heat which causes a change the temperature without changing its state is e. Sensible heat. f. Latent heat. g. Specific heat. h. Enthalpy. iii- The absolute temperature scales are a-oC and oF b-oCand K. c- oF and R. d-K and R.. iv-Dead gauge tester is used to measure a-Temperature. b-Work. c-Pressure. d-Power. v- Unit of entropy a. kJ/K. b. W. c. kJ/K.kg. d. kJ. vi-Which one of the following expressions can be converted into the unit a Joule? a-Pa m2 b- Pa m2 c- Pa/ m3 d-N/kg  2-A manometer is used to measure the pressure in a tank.The fluid used has a specific gravity of 0.85 and the manometer column height is 55 cm , if the local atmospheric pressure is 96 kPa ,determine the absolute pressure within the tank in kPa and bar. 3-The tempeature of the lubricating oil in an automobile engine is measured as 150 oF, what is the temperature 0f this oil in o C ,K, and R. 4-At what absolute temperature do the Celsius and Fahrenheit temperature scales give the same numerical value? 5-Pressures up to 3000 bar are measured with a dead weight gauge.The piston diameter is 4 mm. What is the approximate mass in kg of the weight required? 6-The reading on a mercury manometer is 56.38 cm. atmospheric pressure is 101.78 kPa. What is the absolute pressure in kPa, if mercury is 13.534 gm cm-3? 7-Verify that the S.I Unit of kinematic and potential energy is J.  8- 1 kg of steel, specific heat capacity 450 J/kg.K, is heated from 15 oC 100 oC.Determine the heat transfer. 9-At a speed of 50 km/hr, the resistance of a car is 900 N, neglecting losses, determine the power output of the engine of the car at this speed. 10-The mass of unknown gas mixture in the room that is 4m×3m×5m is known to be 600kg.What is the density and specific volume of the gas? 11-What is the pressure of 500 kN/m2 in head of water of density 1000 kg/m3 (also for a mercury of density 13.6×103 kg/m3 , and a fluid with specific gravity 0.87?). 12-A 1 m3 container is filled with 0.12 m3 of granite ( =2750 kg/ m3), 0.15 m3 of sand ( =1500 kg/ m3) and 0.20 m3 of liquid 25 oC water ( =979 kg/ m3),the rest of the volume 0.53 m3 is air with density of 1.15 kg/m3,find the overall (average specific volume and density.