Lecture 1 Introductory Concepts and Definitions (Revision 1) PDF

FUNDAMENTALS OF ENGINEERING THERMODYNAMICS Prepared by: ENGR. CINDY MAY C. BELIVESTRE MS in Mechanical Engineering Faculty, Department of Agricultural and Biosystems Engineering  COURSE SYLLABUS I. Introductory Concepts and Definitions II. Energy and the First Law of Thermodynamics...

FUNDAMENTALS OF ENGINEERING THERMODYNAMICS Prepared by: ENGR. CINDY MAY C. BELIVESTRE MS in Mechanical Engineering Faculty, Department of Agricultural and Biosystems Engineering  COURSE SYLLABUS I. Introductory Concepts and Definitions II. Energy and the First Law of Thermodynamics III. Evaluating Properties (Midterm Exam) I. Control Volume Analysis Using Energy II. The Second Law of Thermodynamics III. Using Entropy (Final Exam) Prepared by: Engr. Cindy May C. Belivestre  CRITERIA FOR GRADING Midterm Examination – 30% Final Examination – 30% Quizzes/Problem Set – 35% Assignments – 5% Total: 100% Prepared by: Engr. Cindy May C. Belivestre  GRADING PRACTICES AND POLICIES 1. All graded course requirements have corresponding submission or compliance deadlines. Students shall ensure that these deadlines are strictly followed. 2. Only submissions/compliance within the deadline will be graded. Opportunity for submission/compliance beyond the deadline will be given to students with valid reasons. Please inform your instructor if this is the case. Prepared by: Engr. Cindy May C. Belivestre  3. Short quizzes that are given after each topic/sub- topic can be attempted by the student only once. In some instances, the Instructor may allow the student to have multiple attempts. A score of 60% or higher must be obtained in order to pass the short quiz. For multiple attempts, only the highest score will be recorded. 4. Students may request to take make-up exams or quizzes by sending a formal request (please indicate date in the request) via e-mail to the Instructor. Proof or evidence (e.g., scanned or photo of medical certificate) indicating the reason of missing the exam or quiz should be included in the request. Prepared by: Engr. Cindy May C. Belivestre  6. Students can view their progress and their scores on each graded course requirement through the course’ LMS page. A separate official class record indicating the General Weighted Average or the Mean Percent Score (MPS) will also be provided to the students. 7. An “INC” is given only to a student whose class standing throughout the semester is passing but: i. fails to take major examination due to a valid reason; or ii. fails to complete all requirements for the course due to a valid reason; or iii. fails to conduct any of the laboratory exercises and submit the corresponding outputs/reports/worksheets. 8. A student whose final MPS falls at 55.00 to below 60.00 shall be subject to instructor’s evaluation. A removal examination may or may not be given. Passing the removal examination will give the student a final grade of 3.00. Failing it will mean a final grade of 5.0. The result shall not be used to improve the final MPS of the student. Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics LECTURE 1 Introductory Concepts and Definitions Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics After the end of this lesson, you should be able to:  Identify the unique vocabulary associated with thermodynamics through the precise definition of basic concepts to form a sound foundation for the development of the principles of thermodynamics.  Review the metric SI and the English unit systems that will be used throughout the text.  Explain the basic concepts of thermodynamics such as system, state, state postulate, equilibrium, process, and cycle.  Discuss and define the properties of a system. Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics  Review concepts of temperature, temperature scales, pressure, and absolute and gage pressure.  Discuss an intuitive systematic problem-solving technique. Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics I. What is thermodynamics? Thermodynamics is the science that deals with heat and work and those properties of substances that bear a relation to heat and work. One excellent definition of thermodynamics is that it is the science of energy and entropy. The basis of thermodynamics is experimental observation. Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics The principles drawn from thermodynamics pave the way for significant improvements in surface transportation, air travel, space flight, electricity generation and transmission, building heating and cooling, and improved medical practices. Thermodynamics will continue to advance human well-being by addressing looming societal challenges owing to declining supplies of energy resources: oil, natural gas, coal, and fissionable material; effects of global climate change and burgeoning population. Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics II. Selected Areas of Application of Engineering Thermodynamics Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics Aircraft and rocket propulsion Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics Alternative energy systems Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics Fuel cells Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics Geothermal systems Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics Biomedical applications Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics Ocean thermal, wave, and tidal power generation Solar-activated heating, cooling, and power generation Thermoelectric and thermionic devices Wind turbines Automobile engines Bioengineering applications Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics Combustion systems Compressors, pumps Cooling of electronic equipment Cryogenic systems, gas separation, and liquefaction Fossil and nuclear-fueled power stations HVAC Absorption refrigeration and heat pumps Vapor-compression refrigeration and heat pumps Steam and gas turbines Power production Propulsion Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics Propulsion System of roller coaster rides Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics III. Defining Systems In mechanics, if the motion of a body is to be determined, i. define a free body ii. identify all the forces exerted on it by other bodies. iii. Newton’s second law of motion is then applied. In thermodynamics the term system is used to identify the subject of the analysis. i. define the system ii. Identify relevant interactions with other systems iii. one or more physical laws or relations are applied. Prepared by: Engr. Cindy May C. Belivestre  Thermodynamic System ME 100 Thermodynamics  Thermodynamic System  a device or combination of devices containing a quantity of matter that is being studied.  Boundary  real or imaginary layer that separates the system from its surroundings  Surroundings  physical space outside the system boundary  Types of Systems  Closed System (Control / Fixed Mass)  Open (Control Volume) Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics Closed System (control / fixed mass) Energy, not mass, crosses closed-system boundaries Figure 1. Piston cylinder assembly containing gas Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics Closed System with Moving Boundary What have you observed for the mass and volume? Figure 2. Piston cylinder assembly containing gas (moving Prepared by: Engr. Cindy May C. Belivestre boundary)  ME 100 Thermodynamics Figure 3. Piston found in engines Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics Figure 4. Piston-cylinder assembly in engines Prepared by: Engr. Cindy May C. Belivestre  Open System (Control Volume) ME 100 Thermodynamics Mass and energy cross control volume boundaries Prepared by: Engr. Cindy May C. Belivestre Isolated System Closed system where no heat or work (energy) may cross the system boundary Typically a collection of the main system (or several systems) and its surroundings is considered an isolated system Isolated system boundary Give a real life example work system of an mass isolated Surr 1 heat system. Surr 2 Surr 3 Figure 6  IV. Macroscopic versus Microscopic Points of View  The behavior of a system may be investigated from either a microscopic or macroscopic point of view.  Macroscopic (Classical thermodynamics) i. study large number of particles (molecules) that make up the substance in question ii. does not require knowledge of the behavior of individual molecules  Microscopic (Statistical thermodynamics) i. concerned within behavior of individual particles (molecules) ii. study average behavior of large groups of individual particles Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics  From the macroscopic point of view, we are always concerned with volumes that are very large compared to molecular dimensions and, therefore, with systems that contain many molecules.  Because we are not concerned with the behavior of individual molecules, we can treat the substance as being continuous, disregarding the action of individual molecules.  This continuum concept, of course, is only a convenient assumption that loses validity when the mean free path of the molecules approaches the order of magnitude of the dimensions of the vessel, as, for example, in high-vacuum technology.  In much engineering work the assumption of a continuum is valid and convenient, going hand in hand with the macroscopic point of view. Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics V. Selecting the System Boundary Figure 7. Example of a control volume (open system) in biology. Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics In general, the choice of system boundary is governed by two considerations: (1) what is known about a possible system, particularly at its boundaries, and (2) The objective of the analysis. Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics Figure 8. Air compressor and storage tank. Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics What is the purpose of an air compressor? Figure 9. Air compressor Prepared by: Engr. Cindy May C. Belivestre  VI. Properties and State of a Substance  If we consider a given mass of water, we recognize that this water can exist in various forms. If it is a liquid initially, it may become a vapor when it is heated or a solid when it is cooled. Thus, we speak of the different phases of a substance.  Phase - defined as a quantity of matter that is homogeneous throughout. When more than one phase is present, the phases are separated from each other by the phase boundaries. In each phase the substance may exist at various pressures and temperatures or, to use the thermodynamic term, in various states.  State - condition of a system as described by its properties.  ME 100 Thermodynamics  The state may be identified or described by certain observable, macroscopic properties.  Property - a macroscopic characteristic of a system such as mass, volume, energy, pressure, and temperature Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics VII. Processes and Cycles  Whenever one or more of the properties of a system change, we say that a change in state has occurred.  The path of the succession of states through which the system passes is called the process.  Process - transformation from one state to another  A system is said to be at steady state if none of its properties changes with time.  Thermodynamics also deals with quantities that are not properties, such as mass flow rates and energy transfers by work and heat. Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics  Examples of processes: 1. Quasi-equilibrium process - one in which the deviation from thermodynamic equilibrium is infinitesimal, and all the states the system passes through during a quasiequilibrium process may be considered equilibrium states. Many actual processes closely approach a quasi-equilibrium process and may be so treated with essentially no error. If the weights on a piston are small and are taken off one by one, the process could be considered quasi-equilibrium. However, if all the weights are removed at once, the piston will rise rapidly until it hits the stops. Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics 2. Non-equilibrium processes - limited to a description of the system before the process occurs and after the process is completed and equilibrium is restored. We are unable to specify each state through which the system passes or the rate at which the process occurs. Several processes are described by the fact that one property remains constant. The prefix iso- is used to describe such a process. 3. Isothermal process – constant temperature process 4. Isobaric (isopiestic) process - constant pressure process 5. Isochoric process – constant volume process. Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics  When a system in a given initial state goes through a number of different changes of state or processes and finally returns to its initial state, the system has undergone a cycle.  In a cycle, all the properties have the same value they had at the beginning. Example: Steam (water) that circulates through a steam power plant undergoes a cycle. What is a four- stroke-cycle internal- combustion engine? Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics VIII. Types of properties  Extensive properties - vary directly with the size of the system Examples: volume, mass, total energy  Intensive properties - are independent of the size of the system Examples: temperature, pressure, color  Extensive properties per unit mass are intensive properties.” Example: specific volume v = Volume/Mass = V/m (reciprocal of density) Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics IX. STATE AND EQUILIBRIUM Thermodynamics deals with equilibrium states. The word equilibrium implies a state of balance. In an equilibrium state there are no unbalanced potentials (or driving forces) within the system. A system in equilibrium experiences no changes when it is isolated from its surroundings. There are many types of equilibrium, and a system is not in thermodynamic equilibrium unless the conditions of all the relevant types of equilibrium are satisfied. Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics Thermal equilibrium - if the temperature is the same throughout the entire system Mechanical equilibrium - is related to pressure, and a system is in mechanical equilibrium if there is no change in pressure at any point of the system with time. Phase equilibrium - if a system involves two phases and the mass of each phase reaches an equilibrium level and stays there. Chemical equilibrium - if its chemical composition does not change with time, that is, no chemical reactions occur. A system will not be in equilibrium unless all the relevant equilibrium criteria are satisfied. Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics X. Measuring Mass, Length, Time, and Force Unit - any specified amount of a quantity by comparison with which any other quantity of the same kind is measured. Example: Units of length - meters, centimeters, kilometers, feet, inches, and miles Units of time – seconds, minutes, and hours Primary Dimensions – mass, length, time What are some examples of secondary dimensions? Secondary Dimensions – measured in terms of primary dimensions Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics SI Units  Système International d'Unités (International System of Units)  legally accepted system in most countries  published and controlled by an international treaty organization. Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics  Since it is frequently necessary to work with extremely large or small values when using the SI unit system, a set of standard prefixes is provided to simplify matters. Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics Example When you buy a box of breakfast cereal, the printing may say “Net weight: One pound (454 grams).” Technically, this means that the cereal inside the box weighs 1.00 lbf on earth and has a mass of 453.6 g (0.4536 kg). Using Newton’s second law, the actual weight of the cereal on earth is Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics Analysis: 𝟏𝑵 𝟏 𝒌𝒈 W = mg = (453.6 g)(9.81 m/s2) = 𝟒. 𝟒𝟗 𝑵 𝟏 𝒌𝒈.𝒎/𝒔𝟐 𝟏𝟎𝟎𝟎 𝒈 Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics English Engineering Units  Although SI units are the worldwide standard, at the present time many segments of the engineering community regularly use other units.  For many years to come, engineers will have to be conversant with a variety of units.  English Engineering System Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics EXAMPLE. Using unity conversion ratios, show that 1.00 lbm weighs 1.00 lbf on earth. Known: A mass of 1.00 lbm is subjected to standard earth gravity. Its weight in lbf is to be determined. Assumptions: Standard sea-level conditions are assumed. Properties: The gravitational constant is g = 32.174 ft/s2. Analysis: 𝟏 𝒍𝒃𝒇 W = mg = (1.00 lbm)(32.174 ft/s2 )( 𝟐) = 𝟏.00 𝒍𝒃𝒇 𝟑𝟐.𝟏𝟕𝟒 𝒍𝒃𝒎·𝒇𝒕 /𝒔 Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics XI. Three measurable intensive properties that are particularly important in engineering thermodynamics are:  Specific volume  Pressure  Temperature Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics Macroscopic perspective,  Matter is distributed continuously throughout a region.  At any instant, the density ρ at a point is defined as  Mass associated with a particular volume V is determined in principle by integration Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics XII. SPECIFIC VOLUME  Specific volume - reciprocal of the density - volume per unit mass - intensive property - may vary from point to point 𝟏 𝑽 𝒗= = 𝝆 𝒎 Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics Specific Volume on a Molar Basis  Mole - amount of a given substance numerically equal to its molecular weight. kilomole (kmol) or amount of substance pound mole (lbmol) Where: n = number of kilomoles of a substance m = mass M = molecular weight Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics  To signal that a property is on a molar basis, a bar is used over its symbol. Can you still remember Avogadro’s number? What is its value? Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics Specific Volume on a Molar Basis Where: 𝒗 - volume per kmol or lbmol M - the molecular weight (kg/kmol or lb/lbmol)  Units: 𝑚3 /kmol or 𝑓𝑡 3 /lbmol Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics XIII. PRESSURE Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics PRESSURE  Pressure is defined as a normal force exerted by a fluid per unit area.  The counterpart of pressure in solids is normal stress. however, pressure is a scalar quantity while stress is a tensor. What do we mean by these last two statements?  Pressure at a point IS THE SAME in all directions as long as the fluid is at rest.  Pressure can vary from point to point within a fluid at rest. Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics Pressure, unless stated otherwise, refers to absolute pressure (P). Absolute pressure - pressure with respect to the zero pressure of a complete vacuum. The lowest possible value of absolute pressure is zero. Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics Pressure Measurement  Manometers and barometers - measure pressure in terms of the length of a column of liquid such as mercury, water, and oil. Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics Manometer  one end open to the atmosphere  other end attached to a tank containing a gas at a uniform pressure.  pressures at equal elevations in a continuous mass of a liquid or gas at rest are equal Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics Gas pressure Where: 𝑷𝒂𝒕𝒎 = local atmospheric pressure ρ = density of the manometer liquid g = acceleration of gravity, L = difference in the liquid levels. Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics Example of Manometer Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics Barometer  closed tube filled with liquid mercury  mercury vapor inverted in an open container of liquid mercury.  measures air pressure Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics  Force balance gives the atmospheric pressure as  Because the pressure of the mercury vapor is much less than that of the atmosphere Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics  Pressures measured with manometers and barometers are frequently expressed in terms of the length L - millimeters of mercury (mmHg), - inches of mercury (inHg), - inches of water (inH2O), etc. Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics Example. Determine the atmospheric pressure at a location where the barometric reading is 740 mmHg and the gravitational acceleration is g = 9.805 m/s2. Assume the temperature of mercury to be 10°C, at which its density is 13,570 kg/m3. Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics Analysis: 𝑃𝑎𝑡𝑚 = ρ𝑔𝐿 𝑘𝑔 𝑚 1𝑁 1 𝑘𝑃𝑎 𝑃𝑎𝑡𝑚 = 13,570 3 9.805 2 (0.740𝑚)( )( ) 𝑚 𝑠 1 𝑘𝑔 𝑚/𝑠 2 1000 𝑁/𝑚2 𝑷𝒂𝒕𝒎 = 𝟗𝟖. 𝟓 𝒌𝑷𝒂 Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics Other Pressure Measurement Devices  Bourdon tube – elliptical cross-section tube coil that straightens under the influence of gas pressure  Pressure transducer – converts pressure to electrical signal; i.) flexible diaphragm w/strain gage ii) piezo-electric quartz crystal Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics Bourdon tube gage Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics BUOYANCY Buoyant Force – the resultant pressure force acting on a completely or partially submerged body in a liquid Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics Archimedes’ principle “The buoyant force has a magnitude equal to the weight of the displaced liquid.” Figure. Evaluation of buoyant force for a submerged body Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics 𝑭𝑩 = 𝝆 𝒈 𝑽 Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics PRESSURE UNITS Fluid Pressure (N/m2)  Fnormal  P  lim   Asmall  A  SI Units: 1 Pascal (Pa) = 1 N/m2 Other Units 1 kPa = 103 N/m2 1 bar = 105 N/m2 = 0.1MPa 1 MPa = 106 N/m2 1 atm = 101.325 kPa = 29.92 inHg Prepared by: Engr. Cindy May C. Belivestre = 14.696 lbf/in2 (psi)  ME 100 Thermodynamics English units: lbf/ft 2 , lbf/in2  Pressure measuring devices often indicate the DIFFERENCE between: - absolute pressure of a system - absolute pressure of the atmosphere existing outside the measuring device. Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics Gage Pressure / Vacuum Pressure - the magnitude of the difference of absolute pressures (system & surroundings) Gage Pressure - the pressure of the system is greater than the local atmospheric pressure Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics Vacuum Pressure - when the local atmospheric pressure is greater than the pressure of the system Note: absolute and gage pressures in pounds force per square inch are written as psia and psig Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics Figure. Relationships among the absolute, atmospheric, gage, and vacuum pressures. Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics PRACTICE PROBLEMS: 1. A gas enters a compressor that provides a pressure ratio (exit pressure to inlet pressure) equal to 8. If a gage indicates the gas pressure at the inlet is 5.5 psig, what is the absolute pressure, in psia, of the gas at the exit? Atmospheric pressure is 14.5 lbf/in.2. Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics 2. AIR IS CONTAINED IN A VERTICAL PISTON–CYLINDER ASSEMBLY SUCH THAT THE PISTON IS IN STATIC EQUILIBRIUM. THE ATMOSPHERE EXERTS A PRESSURE OF 101 KPA ON TOP OF THE 0.5-M-DIAMETER PISTON. THE GAGE PRESSURE OF THE AIR INSIDE THE CYLINDER IS 1.2 KPA. THE LOCAL ACCELERATION OF GRAVITY IS G = 9.81 M/S2. SUBSEQUENTLY, A WEIGHT IS PLACED ON TOP OF THE PISTON CAUSING THE PISTON TO FALL UNTIL REACHING A NEW STATIC EQUILIBRIUM POSITION. AT THIS POSITION, THE GAGE PRESSURE OF THE AIR INSIDE THE CYLINDER IS 2.8 KPA. DETERMINE (A) THE MASS OF THE PISTON, IN KG, AND (D) THE MASS OF THE ADDED WEIGHT, IN KG. Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics 3. AN OBJECT IS SUBJECTED TO AN APPLIED UPWARD FORCE OF 10 LBF. THE ONLY OTHER FORCE ACTING ON THE OBJECT IS THE FORCE OF GRAVITY. THE ACCELERATION OF GRAVITY IS 32.2 FT/S2. IF THE OBJECT HAS A MASS OF 50 LB, DETERMINE THE NET ACCELERATION OF THE OBJECT, IN FT/S2. IS THE NET ACCELERATION UPWARD OR DOWNWARD? 4. The specific volume of 5 kg of water vapor at 1.5 MPa, 440°C is 0.2160 m3/kg. Determine (a) the volume, in m3, occupied by the water vapor, (b) the amount of water vapor present, in moles, and (c) the number of molecules. Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics XIV. TEMPERATURE  intensive property  indicative of a body’s internal energy  Measure of “hotness” or “coldness” of objects.  when the temperature of an object changes, other properties also change  used to determine when a system is in thermal equilibrium, i.e., when all points have the same temperature Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics  Unit conversions: K = ºC + 273.15 ºR = ºF + 459.67 ºF = 1.8 ºC + 32 K = 1.8 ºR Can you give a real life scenario where the equality of temperature is applied?  Equality of temperature: when two bodies are in thermal communication, no change in any observable property occurs. Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics  Thermal (heat) interaction  Thermal equilibrium – when temperatures are equal  In thermodynamics definition, TEMPERATURE is a physical property that determines whether systems will be in thermal equilibrium. Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics The Zeroth Law Of Thermodynamics “When two objects are in thermal equilibrium with a third object, they are in thermal equilibrium with one another.”  Basis of temperature measurement.  The third object is usually a thermometer. Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics THERMOMETERS  Any object with at least one measurable property that changes as its temperature changes can be used as a thermometer.  Thermometric property - any physical property that changes measurably with temperature. Examples of thermometric properties: Length of a column of liquid, e.g. mercury and alcohol thermometers. Electrical resistance  Thermometric substance – a substance that exhibits changes in the thermometric property Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics TYPES OF THERMOMETERS  Liquid-in-glass thermometer - consists of a glass capillary tube connected to a bulb filled with a liquid such as alcohol and sealed at the other end - not well suited for applications where extreme accuracy is required. Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics PROBE THERMOMETERS one of the most common types of thermometer. deliver instant temperature readings of foods, liquids and semi-solid samples. often equipped with a pointed tip making them ideal for penetration and immersion. ideal for use in the catering trade for hygiene testing, retail outlets, and laboratories. Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics INFRARED THERMOMETERS  go-to types of thermometer for non- contact measurement.  The non-contact feature makes them the best tool for measuring extremely high or low surface temperatures. Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics K-TYPE THERMOCOUPLES (K-TYPETHERMOMETERS) more specialized and niche types of thermometer. deal with extreme temperatures and are most common in laboratories and industry. caters for applications that need high precision. Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics TEMPERATURE DATA LOGGERS  allow the recording of continuous temperature measurements.  Once activated, they record the temperature at predetermined intervals and save it to memory.  It is typical to download the data and view it on a graph but some devices display the data in real-time.  Most devices are compatible with any pc, laptop or tablet. Prepared by: Engr. Cindy May C. Belivestre  COMPARISON OF TEMPERATURE SCALES ME 100 Thermodynamics Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics ENGINEERING DESIGN AND ANALYSIS  Engineering has existed since ancient times, when humans devised inventions such as the wedge, lever, wheel and pulley.  Latin for engineer is “ingenium”, meaning "cleverness" and ingeniare, meaning "to contrive, devise"  Engineers are called upon to design and analyze devices intended to meet human needs. Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics  ENGINEERS frequently do ANALYSIS, whether explicitly as part of a design process or for some other purpose.  Analyses involving systems of the kind considered use, directly or indirectly, one or more of three basic laws.  These laws, which are independent of the particular substance or substances under consideration, are 1. the conservation of mass principle 2. the conservation of energy principle 3. the second law of thermodynamics Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics METHODOLOGY FOR SOLVING THERMODYNAMICS PROBLEMS I. Known: State briefly in your own words what is known. This requires that you read the problem carefully and think about it. Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics METHODOLOGY FOR SOLVING THERMODYNAMICS PROBLEMS II. Find: State concisely in your own words what is to be determined. III. Schematic and Given Data:  Draw a sketch of the system to be considered.  Decide whether a closed system or control volume is appropriate for the analysis, and then carefully identify the boundary.  Label the diagram with relevant information from the problem statement. Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics Methodology for Solving Thermodynamics Problems III. Schematic and Given Data:  Record all property values you are given or anticipate may be required for subsequent calculations.  Sketch appropriate property diagrams locating key state points and indicating, if possible, the processes executed by the system.  The importance of good sketches of the system and property diagrams cannot be overemphasized. They are often instrumental in enabling you to think clearly about the problem. Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics IV. Engineering Model:  List all simplifying assumptions and idealizations made to reduce it to one that is manageable.  The development of an appropriate model is a key aspect of successful problem solving. Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics V. Analysis:  Using your assumptions and idealizations, reduce the appropriate governing equations and relationships to forms that will produce the desired results.  It is advisable to work with equations as long as possible before substituting numerical data. Prepared by: Engr. Cindy May C. Belivestre  ME 100 Thermodynamics THANK YOU! Prepared by: Engr. Cindy May C. Belivestre