Thermal Energy Storage Systems and Applications. Ibrahim Dincer
What is the weight of a 10 kg substance in N, kN, kgf, and lbf?
15 1.15 The vacuum pressure of a tank is given to be 40 kPa. If the atmospheric pressure is 95 kPa, what is the gauge pressure and absolute pressure in kPa, kN/m2, lbf/in2, psi, and mmHg.
16 1.16 Express the temperature −40°C in units of Fahrenheit (°F), Kelvin (K), and Rankine (R).
17 1.17 The temperature of air changes by 10°C during a process. Express this temperature change in Kelvin (K), Fahrenheit (°F), and Rankine (R) units.
18 1.18 The specific heat of water at 25°C is given to be 4.18 kJ/kg°C. Express this value in kJ/kg K, J/g°C, kcal/kg°C, and Btu/lbm°F.
19 1.19 A 0.2 kg mass of R134a at 700 kPa pressure and at 4°C is heated until 50% of mass is vaporized. Determine the temperature at which the refrigerant is vaporized, and the sensible heat and the latent heat are transferred to the refrigerant.
20 1.20 A 0.5 lbm mass of R134a at 100 psa pressure and 40°F is heated until 50% of mass is vaporized. Determine the temperature at which the refrigerant is vaporized, and the sensible heat and the latent heat are transferred to the refrigerant.
21 1.21 A 2 kg mass of ice initially at −18°C is heated until 75% of the mass is melted. Determine the sensible heat and the latent heat transferred to the water. The specific heat of ice at 0°C is 2.11 kJ/kg°C, and the latent heat of fusion of water at 0°C is 334.9 kJ/kg.
22 1.22 A 2 kg mass of ice initially at −18°C is heated until it becomes liquid water at 20°C. Determine the sensible heat and the latent heat transferred to the water. The specific heat of ice at 0°C is 2.11 kJ/kg°C, and the latent heat of fusion of water at 0°C is 334.9 kJ/kg.
23 1.23 Refrigerant 134a enters the evaporator of a refrigeration system at −24°C with a quality of 25% at a rate of 0.22 kg/s. If the refrigerant leaves the evaporator as a saturated vapor, determine the rate of heat transfer to the refrigerant. If the refrigerant is heated by water in the evaporator, which experiences a temperature rise of 16°C, determine the mass flow rate of water.
Ideal Gases and the First Law of Thermodynamics
1 1.24 What is the compressibility factor?
2 1.25 When can we invoke the ideal gas assumption for real gases?
3 1.26 Define isothermal, isobaric, and isochoric processes.
4 1.27 What is an isentropic process? Is a constant‐entropy process necessarily reversible and adiabatic?
5 1.28 What is the difference between heat and work?
6 1.29 An elastic tank contains 0.8 kmol of air at 23°C and 600 kPa. Determine the volume of the tank. If the volume is doubled at the same pressure, what is the temperature at the new state?
7 1.30 A 50 l piston–cylinder device contains oxygen at 52°C and 170 kPa. If the oxygen is heated until its temperature reaches 77°C, what is the amount of heat transfer during the process?
8 1.31 A 50 l rigid tank contains oxygen at 52°C and 170 kPa. If the oxygen is heated until its temperature reaches 77°C, what is the amount of heat transfer during the process?
9 1.32 A 50 l rigid tank contains oxygen at 52°C and 170 kPa. If the oxygen is heated until the temperature reaches 77°C, what is the entropy change during the process?
10 1.33 A rigid tank contains 2.5 kg of oxygen at 52°C and 170 kPa. If the oxygen is heated in an isentropic process until it reaches 77°C, what is the pressure at the final state? What is the work interaction during this process?
11 1.34 A piston–cylinder device contains 2.5 kg oxygen at 52°C and 170 kPa. If the oxygen is heated until it reaches 77°C, what is the work done and the amount of heat transfer during the process?
Exergy
1 1.35 What is the Kelvin–Planck statement of the second law of thermodynamics?
2 1.36 What is the Clausius statement of the second law of thermodynamics?
3 1.37 Define the terms energy, exergy, entropy, and enthalpy.
4 1.38 What is the second‐law efficiency? How does it differ from the first‐law efficiency?
5 1.39 What is the relationship between entropy generation and irreversibility?
6 1.40 What are the two common causes of irreversibility?
7 1.41 During an irreversible process, do the parameters mass, energy, entropy, and exergy decrease or increase or remain conserved?
8 1.42 How does an exergy analysis help the goal of more efficient energy‐resource use? What are the advantages of using exergy analysis?
General Aspects of Fluid Flow
1 1.43 What is the physical meaning of the Reynolds number? What makes the flow laminar and what makes it turbulent?
2 1.44 What is viscosity? How does viscosity change with temperature for gases and for liquids?
General Aspects of Heat Transfer
1 1.45 What is the difference between heat conduction and heat convection?
2 1.46 Define the terms forced convection and natural convection, and explain the difference between them.
3 1.47 Define the term heat generation. Give some examples.
4 1.48 What are the modes of heat transfer? Explain the physical mechanism of each mode.
5 1.49 How much energy does it take to convert 10.0 kg of ice at 0°C to water at 25°C?
6 1.50 A 20 cm thick wall of a house made of brick (k = 0.72 W/m°C) is subjected to inside air at 22°C with a convection heat transfer coefficient of 15 W/m2 °C. The temperature of the inner surface of the wall is 18°C and the outside air temperature is −1°C. Determine the temperature of the outer surface of the wall and the heat transfer coefficient at the outer surface.
7 1.51 A satellite is subjected to solar energy at a rate of 300 W/m2. The absorptivity of the satellite surface is 0.75 and its emissivity is 0.60. Determine the equilibrium temperature of the satellite.
8 1.52 An 80‐cm‐diameter spherical tank made of steel contains liquefied natural gas (LNG) at −160°C. The tank is insulated with a 4 cm thickness of insulation (k = 0.015 W/m°C). The tank is subjected to ambient air at 18°C with a convection heat transfer coefficient of 20 W/m2 °C. How long will it take for the temperature of the LNG to decrease to −150°C. Neglect the thermal resistance of the steel tank. The density and the specific heat of LNG are 425 kg/m3 and 3.475 kJ/kg°C, respectively.
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