ME 2322 Thermodynamics I PRE-LECTURE Lesson 10 Complete the items below Name:

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1 Lesson (5 pt) If P > P sat (T), the phase is a subcooled liquid. 2. (5 pt) if P < P sat (T), the phase is superheated vapor. 3. (5 pt) if T > T sat (P), the phase is superheated vapor. 4. (5 pt) If T < T sat (P), the phase is subcooled liquid. 5. (5 pt) If u f <= u <= u g, the phase is a 2-phase mixture. 6. (5 pt)if u < u f, the phase is a subcooled liquid. 7. (5 pt) If u > u g, the phase is a superheated vapor. 8. (5 pt) The phase of water at 2.00 bars and 0.7 m 3 /kg is a 2-phase mixture. 9. (5 pt) The phase of water at 2.00 bars and m 3 /kg is a subcooled liquid. 10. (5 pt) The phase of water at 2.00 bars and 0.95 m 3 /kg is a superheated vapor. 11. (5 pt) The u of water at 5.00 bars and 200 o C is kj/kg. 12. (10 pt) A compressed (subcooled) liquid can be approximated as a saturated liquid at the same temperature with good accuracy. 13. (5 pt) The h of water at 150 o C and 10 bars is about kj/kg. 14. (10 pt) Write the definition of c P below. c P h T P 15. (10 pt) Write the definition of c v below. c v u T v 16. (10 pt) Write the definition of the specific heat ratio, k, below. k = c P / c v

2 Lesson (10 pt) The specific volume, internal energy and enthalpy of an incompressible substance only depend upon temperature, not pressure. 2. (10 pt) The equation for calculating the change in the specific internal energy of an incompressible whose specific heat do not change with temperature is: 3. (10 pt) The equation for calculating the change in the specific internal energy of an incompressible whose specific heat do not change with temperature is: +v P 4. (10 pt) Write the equation of state of an ideal gas below. Pv = RT 5. (10 pt) Write the definition of the compressibility factor below. z = Pv / RT 6. (15 pt) Gasses can be treated as ideal gases when the pressure is low or the temperature is high relative to the critical pressure and temperature. 7. (5 pt) When an ideal gas undergoes an isochoric process of increasing pressure, the temperature increases/decreases. 8. (5 pt) When an ideal gas undergoes an isothermal process of increasing pressure, the volume increases/decreases. 9. (5 pt) When an ideal gas undergoes an isobaric process of increasing temperature, the volume increases/decreases. 10. (10 pt) When using the ideal gas equation of state, you must use absolute pressures and absolute temperatures. 11. (10 pt) Write the relationship between the universal gas constant and the gas constant of a specific gas below. R = R u / M

3 Lesson (10pt) In general, there are 2 specific heats, specific heat at constant volume and specific heat at constant pressure. 2. (15pt) The equation defining the specific heat at constant pressure: 3. (10 pt) The specific enthalpy and internal energy of ideal gases only depends upon temperature, not pressure. 4. (15 pt) The equation for calculating the change in the specific enthalpy of an ideal gas whose specific heats do not change with temperature is: 5. (10 pt) The equation that relates the two specific heats of ideal gases is: c P c v = R 6. (10 pt) A special case of the polytropic process is when n = k where k is the specific heat ratio. 7. (10 pt) The first law for a closed system consisting of an ideal gas whose specific heats do not vary with temperature reduces to: q w = c v (T 2 - T 1 ) 8. (10 pt) When the specific heats of an ideal gas change significantly with temperature, one must use ideal gas tables to determine changes in specific enthalpy and internal energy. 9. (10pt) The independent variable in an ideal gas table is the temperature.

4 Lesson2 1) (5 pt) A CLOSED SYSTEM is also known as a control mass. 2) (5 pt) A CONTROL VOLUME is also known as a open system. 3) (5 pt) A CONTROL SURFACE forms the boundary of a system. 4) (5pt) Properties that depend upon the size of a system are also extensive Properties. 5) (5 pt) PROPERTIES PER UNIT MASS are also INTENSIVE Properties. 6) (5 pt) INTENSIVE PROPERTIES do/do not change as the size of the system changes? 7) (10 pt)describe how EQUILIBRIUM differs between mechanics courses and thermal science courses below: Mechanics all forces are in balance Thermal Science Other factors including mechanical, thermal, phase, and chemical equilibrium must be considered 8) (10 pt) Describe an EQUILIBRIUM STATE below: When a system is isolated and it condition does not change, it is said to be in an equilibrium state. 9) (10 pt) List the base units of the SI system below: mass-kg, length-m, time-s 10) (10 pt) List the base units of the EES system below: mass-lb, length-ft, time-s, force- lbf 11) (10 pt) What is the lb-lbf unit conversion constant in the EES unit system? 1 lbf = ft-lbm/s 2 12) (10 pt) What is the kg-n unit conversion constant in the SI system? 1 N = 1 kg-m/s 2 13) (10 pt) What is the weight (in lbf) of a person on the moon where g = 5 ft/ s2 whose earth mass is 100 lb? lbf

5 Lesson 3 1) (5 pt) A Pascel (Pa) is defined as 1 N/m 2. 2) (10 pt) Write the relationship between absolute and gage pressures below using the textbook symbols: P gage = P abs + P atm 3) (10 pt) Write the change of pressure with depth for a fluid of constant density below in terms of the density and specific weight below: P = ρg z = g z 4) (5 pt) When one remains at the same level in a fluid, the fluid pressure increases/decreases/remains the same. 5) (10 pt) At standard conditions, an absolute pressure of 24 in of H 2 O equals psia. 6) (10pt) At standard conditions, a barometer reads 730 mm Hg. What is this pressure in kpa units? 97.2 kpa 7) (10 pt) Specific gravity is defined as the ratio of a substance s density to that of water. Write the definition of specific gravity in terms of the substances specific volume and that o f water below. SG = v h2o / v 8) (10 pt) Specific weight is defined as the weight per unit volume. Write the equation for specific weight in terms of specific volume and gravitational acceleration below. SW = g/v 9) (10 pt) Write the equation for density below. Use the symbols of your textbook. ρ = m / V 10) (10 pt) Write the equation for specific volume below. Use the symbols of your textbook. v = V / m 11) (10 pt) How are density and specific volume related? Use an equation below to state this relationship. v = 1 / ρ

6 Lesson 4 1. (10 pt) The equation for specific kinetic energy (KE/m) is: ke = V 2 /2. 2. (10pt) The equation for specific potential energy (PE/m) is: pe = gz. 3. (5 pt) The integral of a point function (exact differential) such as volume results in the change in the volume. 4. (5 pt) The integral of a path function (inexact differential) such as work results in the total amount done. 5. (10 pt) The general equation for work transfer in vector form is: W = int P dot ds. 6. (10 pt) Write the thermodynamic definition of work below. Work is any interaction between a system and surroundings that can be reduced to the lifting of a weight. 7. (5 pt) Work produced by a system is positive or negative? 8. (5 pt) Work is not a property. 9. (5 pt) Write the definition of power below. Power is the rate at which work is transferred. 10. (10 pt) Write the equation for expansion/compression work below. W = int PdV 11. (5 pt) Write the definition of a quasi-equilibrium process below. A process during which the system is always infinitesimally close to equilibrium. 12. (5 pt) Areas below a quasi-equilibrium process line on a P-V or P-v diagram represent work. 13. (5 pt) Write the equation for a polytropic process below. Pv n = constant. 14. (10 pt) Write the equation for the expansion/compression work of a polytropic process below. W = (1/1-n)(P 2 V 2 -P 1 V 1 )

7 Lesson 5 1. (10 pt) Internal energy is the sum of all the forms of energy except kinetic and potential energy. 2. (15 pt) The equation for specific kinetic energy is: ke = V 2 /2. 3. (15pt) The equation for specific potential energy is; pe = gz. 4. (15 pt) The equation for quasi-equilibrium expansion/compression work is: W = intpdv 5. (10 pt) The only two forms of energy transfer associated with a closed system are heat transfer and work. 6. (5 pt) Heat transfer is due to a temperature difference between the system and surroundings. 7. (5 pt) Heat transfer into a system is considered positive/negative. 8. (5 pt) Heat is not a property. 9. (5 pt)the sign convention for Q is the same as/opposite to that of W. 10. (5 pt) An adiabatic process is one with no heat transfer. 11. (10 pt) The equation for electrical power (rate at which electrical work is transferred) is: Wdot = VI.

8 Lesson 6 1) (10 pt) The general equation for work transfer in vector form is: 2) (5 pt) The equation for shaft power is: 3) (5 pt) The equation for stress work is: 4) (5 pt) The first law of thermodynamics is a statement of the conservation of energy principle. 5) (15 pt) The rate at which energy enters a system minus the rate at which it leaves must equal the rate at which the energy of a system changes 6) (15 pt) For this course, the only energy forms considered are kinetic, potential, and internal energies. 7) (10 pt) Energy is transferred to and from a system by work and heat transfers. 8) (15) Write the first law for a closed system below: 9) (10 pt) Write the first law for a transient system below: 10) (10 pt) Write the first law for a cyclic device below:

9 Lesson 7 1. (10 pt) A thermal energy reservoir exchanges heat with a cyclic system 2. (20 pt) In order to be considered a power cycle, a system must: Receive heat from a high-temperature reservoir Convert part of the heat to work Reject waste heat to a low-temperature reservoir Operate in a cycle 3. (10 pt) Write the first law as applied to a heat engine below: 4. (10 pt) Write the equation for the thermal efficiency of a heat engine in terms of the heat transfers below: 5. (10 pt) Write the equation for the thermal efficiency of a heat engine in terms of the work and heat in below. 6. (5 pt) Write the equation for the refrigerator coefficient of performance in terms of the heat addition and work input below: COP r = Q in / W in 7. (5 pt) Write the equation for the heat pump coefficient of performance in terms of the heat rejection and work input below: COP hp = Q out / W in 8. (20 pt) In order to be considered a heat pump cycle, a system must: Receive heat from a low-temperature reservoir Convert the added work into heat Reject heat to a high-temperature reservoir Operate in a cycle 9. (10 pt) The change in the working fluid properties of a cyclic device each time a cycle is completed is zero.

10 Lesson 8 1) (5 pt) A PURE SUBSTANCE is Chemically homogeneous throughout. 2) (10 pt) Write the general state principle (postulate) in terms of the work modes below: A state is completely determined when number of relevant work modes + 1 independent properties are know. 3) (10 pt) Describe how one distinguishes a simple compressible substance. The only relevant work mode is volume expansion/compression. 4) (5 pt) How many independent intensive properties does a simple compressible substance have? 2 5) (5 pt) Pressure is/is not independent of temperature for a 2-phase mixture. 6) (10 pt) Define a saturation state. A state where the substance is 2-phase or ready to change phase 7) (10 pt) What are the critical pressure and temperature of water? bar, K 8) (10 pt) The lines on a P-v state diagram that mark the vapor dome of a phase-changing system represent saturation states. 9) (5 pt) The triple-point on a phase diagram becomes a line on a P-v state diagram. 10) (5 pt) The peak of the liquid-vapor saturation dome is known as the Critical point. 11) (10 pt) Sketch the phase diagram for water below 12) (10 pt) Sketch the P-v state diagram for the liquid and vapor phases of water below.

11 13) (5 pt) Add isothermal process lines to the sketch of Problem 12.

12 Lesson 9 1) (5 pt) A SATURATED LIQUID is a liquid about to change into a Vapor. 2) (5 pt) A SATURATED VAPOR is a vapor about to change into a liquid. 3) (5 pt) A COMPRESSED LIQUID is a liquid whose pressure is Higher than the saturation pressure at the same temperature. 4) (5 pt) A SUPERHEATED VAPOR is a vapor whose temperature is greter than the saturation temperature at the same pressure. 5) (10 pt) When a system is at the saturation pressure and temperature which of the phases below can be present? Clearly mark your answers. a. Subcooled liquid b. Saturated liquid c. Saturated vapor d. Superheated vapor 6) (10 pt) SI Saturated liquid-vapor pressure-temperature pairs for water are listed in Tables A- 2 or 2E and 3 or 3E 7) (10 pt) In the liquid-vapor saturation tables the saturated liquid states are noted by the f subscript and saturated vapor states by the g_ subscript. 8) (10 pt) Define the quality in words below: The mass fraction of vapor in a saturated mixture 9) (10 pt) Use an equation to define the quality below: z = z f +x(z g -z f ) 10) (5 pt) Does quality have any meaning for a subcooled liquid of superheated vapor? NO 11) (10 pt) The specific volume of a liquid-vapor mixture of water at 160 o C with a quality of 50% is: m^3/kg 12) (10 pt) The quality of an ammonia mixture whose specific volume is 0.1 m 3 /kg and pressure is 3.25 bars is: 26% 13) (5 pt) Sublimination is the direct conversion of a solid to a vapor.

CONCEPTS AND DEFINITIONS. Prepared by Engr. John Paul Timola

CONCEPTS AND DEFINITIONS. Prepared by Engr. John Paul Timola CONCEPTS AND DEFINITIONS Prepared by Engr. John Paul Timola ENGINEERING THERMODYNAMICS Science that involves design and analysis of devices and systems for energy conversion Deals with heat and work and