Questions and Answers of Fundamentals Of Thermodynamics

A handheld pump for a bicycle (Fig. P6.91) has a volume of 25 cm3 when fully extended. You now press the plunger (piston) in while holding your thumb over the exit hole so that an air pressure of 300
Extend the previous problem to solve using Table B.3.Data from previous problem An insulated piston/cylinder setup contains carbon dioxide gas at 800 kPa, 300 K that is then compressed to 6 MPa
An insulated piston/cylinder setup contains carbon dioxide gas at 800 kPa, 300 K that is then compressed to 6 MPa in a reversible adiabatic process. Calculate the final temperature and the specific
Air in a rigid tank is at 100 kPa, 300 K with a volume of 0.75m3. The tank is heated to 400 K, state 2. Now one side of the tank acts as a piston, letting the air expand slowly at constant
Consider a small air pistol (Fig. P6.86) with a cylinder volume of 1 cm3 at 250 kPa, 27◦C. The bullet acts as a piston initially held by a trigger. The bullet is released, so the air expands in an
R-410a at 300 kPa, 20◦C is brought to 200◦C in a constant-volume process. Evaluate the change in specific entropy using Table B.4 and using ideal gas with Cv = 0.695 kJ/kgK.
R-410a at 400 kPa is brought from 20◦C to 120◦C in a constant-pressure process. Evaluate the change in specific entropy using Table B.4 and using ideal gas with Cp = 0.81 kJ/kgK.
Water at 150◦C, 400 kPa is brought to 1200◦C in a constant-pressure process. Find the change in specific entropy using (a) The steam tables, (b) The ideal gas water Table A.8,
A closed rigid container is filled with 1.5 kg water at 100 kPa, 55◦C, 1 kg of stainless steel and 0.5 kg of polyvinyl chloride, both at 20◦Cand 0.1 kg of hot air at 400 K, 100 kPa. It is now
Prove that the two relations for changes in s, Eqs. 6.16 and 6.17, are equivalent once we assume constant specific heat. P2 R In P1 T2 $2 - S1 = Cpo I (6.16) T2 V2 + R In T S2 - S1 = Cyo In
Three kilograms of air is in a piston/cylinder keeping constant pressure at 27◦C, 300 kPa. It is now heated to 500 K. Plot the process path in a T–s diagram and find the heat transfer in the
A rigid tank contains 1 kg methane at 500 K, 1500 kPa. It is now cooled down to 300 K. Find the heat transfer and the change in entropy using ideal gas.
Air inside a rigid tank is heated from 300 to 350 K. Find the entropy increase s2 − s1. What is the entropy increase if the tank is heated from 1300 to 1350 K?
Find the total work the heat engine can give out as it receives energy from the rock bed as, described in Problem 5.60 (see Fig. P6.74). Write the entropy balance equation for the control volume that
A computer CPU chip consists of 50 g silicon, 20 g copper, and 50 g polyvinyl chloride (plastic). It heats from 15◦C to 75◦C as the computer is turned on. How much did the entropy increase?
A constant pressure container of 1.2 kg steel contains 1.5 kg of R-134a at 40C, 500 kPa. The container is placed in a refrigerator that brings it to −20◦C. Find the process heat transfer and the
In a sink, 5 L of water at 70◦C is combined with 1 kg of aluminum pots, 1 kg of flatware (steel), and 1 kg of glass, all put in at 20◦C. What is the final uniform temperature and change in stored
Heat transfer to a block of 1.5-kg ice at−10◦Cmelts it to liquid at 10◦C in a kitchen. Find the entropy change of the water.
Water at 1000 kPa, 200◦C is brought to saturated vapor in a piston/cylinder with an isobaric process. Find the specific work and heat transfer. Estimate the specific heat transfer from the area in
Water at 100 kPa, 25◦C is brought to the boiling point in a piston/cylinder with an isobaric process. The heat is supplied by a heat pump with the cold side at the ambient temperature of 25◦C.
A rigid, insulated vessel contains superheated vapor steam at 3 MPa, 400◦C. A valve on the vessel is opened, allowing steam to escape, as shown in Fig. P6.57. The overall process is irreversible,
A heavily insulated cylinder/piston contains ammonia at 1200 kPa, 60◦C. The piston is moved, expanding the ammonia in a reversible process until the temperature is −20◦C. During the process,
Water at 1000 kPa, 250◦C is brought to saturated vapor in a rigid container, shown in Fig. P6.51. Find the final T and the specific heat transfer in this isometric process. H2O FIGURE P6.51
A piston/cylinder has 2 kg water at 1000 kPa, 200◦C that is now cooled with a constant loading on the piston. This isobaric process ends when the water reaches a state of saturated liquid. Find the
Water in a piston/cylinder at 400◦C, 2000 kPa is expanded in a reversible adiabatic process. The specific work is measured to be 415.72 kJ/kg out. Find the final P and T and show the P–v and
A piston/cylinder contains 0.5 kg of water at 200 kPa, 300◦C, and it now cools to 150◦C in an isobaric process. The heat goes into a heat engine that rejects heat to the ambient at 25◦C (shown
A piston/cylinder contains 0.25 kg of R-134a at 100 kPa. It will be compressed in an adiabatic reversible process to 400 kPa and should be at 70◦C. What should the initial temperature be?
A piston/cylinder maintaining constant pressure contains 0.1 kg saturated liquid water at 100◦C. It is now boiled to become saturated vapor in a reversible process. Find the work term and then the
A piston/cylinder receives R-410a at 500 kPa and compresses it in a reversible adiabatic process to 1800 kPa, 60◦C. Find the initial temperature.
A piston/cylinder compressor takes R-410a as saturated vapor 500 kPa and compresses it in a reversible adiabatic process to 3000 kPa. Find the final temperature and the specific compression work.
R-410a at 1 MPa and 60◦C is expanded in a piston/ cylinder to 500 kPa, 40◦C in a reversible process. Find the sign for both the work and the heat transfer for this process.
Water at 1 MPa, 250◦C is expanded in a piston/ cylinder to 200 kPa, x = 1.0 in a reversible process. Find the sign for the work and the sign for the heat transfer.
Water is used as the working fluid in a Carnot-cycle heat engine, where it changes from saturated liquid to saturated vapor at 200◦C as heat is added. Heat is rejected in a constant-pressure
Do Problem 6.36 using refrigerant R-134a instead of R-410a.Data from Problem 6.36Consider a Carnot-cycle heat pump with R-410a as the working fluid. Heat is rejected from the R-410a at 35◦C, during
Consider a Carnot-cycle heat pump with R-410a as the working fluid. Heat is rejected from the R-410a at 35◦C, during which process the R-410a changes from saturated vapor to saturated liquid. The
Two kilograms of water at 400 kPa with a quality of 25% has its temperature raised 20◦C in a constant pressure process. What is the change in entropy?
Two kilograms of water at 120◦C with a quality of 25% has its temperature raised 20◦C in a constant volume process. What are the new quality and specific entropy?
Determine the missing properties among (T, P, v, s)a. H2O 20◦ C, v = 0.001000 m3/kgb. R-410a 400 kPa, s = 1.17 kJ/kg-Kc. NH3 10◦C, v = 0.1 m3/kgd. N2 101.3 kPa, s = 3.5 kJ/kg-K
Find the missing properties of P, v, s, and x for CO2 and indicate each state on a T–s diagram relative to the two-phase region.a. −20◦C, 2000 kPab. 20◦C, s = 1.49 kJ/kg-Kc. −10◦C, s
Find the entropy for the following water states and indicate each state on a T–s diagram relative to the two-phase region.a. 250◦C, v = 0.02 m3/kgb. 250◦C, 2000 kPac. −2◦C, 100 kPa
Find the missing properties of P, v, s, and x for ammonia (NH3) ata. T = 65◦C, P = 600 kPab. T = 20◦C, u = 800 kJ/kgc. T = 50◦C, v = 0.1185 m3/kg
Determine the missing property among P, T, s, and x for R-410a ata. T =−20◦C, v = 0.1377 m3/kgb. T = 20◦C, v = 0.01377 m3/kgc. P = 200 kPa, s = 1.409 kJ/kgK
Determine the entropy for these states.a. Nitrogen, P = 2000 kPa, 120 Kb. Nitrogen, 120 K, v = 0.0050 m3/kgc. R-410a, T = 25◦C, v = 0.01 m3/kg
Use the inequality of Clausius to show that heat transfer from a cold space toward a warmer space without work is an impossible process, i.e., a heat pump with no work input.
Use the inequality of Clausius to show that heat transfer from a warm space toward a colder space without work is a possible process, i.e., a heat engine with no work output.
A 500 W electric space heater with a small fan inside heats air by blowing it over a hot electrical wire. For each control volume, (a) Wire at Twire only, (b) All the room air at Troom,
An electric baseboard heater receives 1500 W of electrical power that heats room air, which loses the same amount through the walls and windows. Specify exactly where entropy is generated in that
A reversible heat pump has a flux of s entering as ˙QL/TL. What can you say about the exit flux of s at TH?
Process A: Air at 300 K, 100 kPa is heated to 310 K at constant pressure. Process B: Air at 1300 K is heated to 1310 K at constant 100 kPa. Use the table below to compare the property changes.
Air at 20◦C, 100 kPa is compressed in a piston/ cylinder without any heat transfer to a pressure of 200 kPa. How do the properties (T, v, u, and s) change (increase, stay about the same, or
Air at 290 K, 100 kPa in a rigid box is heated to 325 K. How do the properties (P, v, u, and s) change (increase, stay about the same, or decrease)?
A reversible process in a piston/cylinder is shown in Fig. P6.8. Indicate the storage change u2 − u1 and transfers 1w2 and 1q2 as positive, zero, or negative. P 1 FIGURE P6.8 2. 2.
A reversible process in a piston/cylinder is shown in Fig. P6.7. Indicate the storage change u2 − u1 and transfers 1w2 and 1q2 as positive, zero, or negative. 2. FIGURE P6.7
Liquid water at 20◦C, 100 kPa is compressed in a piston/cylinder without any heat transfer to a pressure of 200 kPa. How do the properties (T, v, u, and s) change (increase, stay about the same, or
Water at 100◦C, quality 50% in a rigid box is heated to 110◦C. How do the properties (P, v, x, u, and s) change (increase, stay about the same, or decrease)?
Consider the previous setup with the mass mA and the piston/cylinder of mass mp starting out at two different temperatures (Fig. P6.3). After a while, the temperature becomes uniform without any
CV A is the mass inside a piston/cylinder; CV B is that plus part of the wall out to a source of 1Q2 at Ts. Write the entropy equation for the two control volumes, assuming no change of state of
A window air conditioner cools a room at TL = 68 F with a maximum of 1.2 kW power input. The room gains 0.33 Btu/s per degree temperature difference from the ambient, and the refrigeration COP is β
The air conditioner in the previous problem is turned off. How quickly does the house heat up in degrees per second (F/s)?Data from previous problem An air conditioner on a hot summer day
An air conditioner on a hot summer day removes 8 Btu/s of energy from a house at 70 F and pushes energy to the outside, which is at 88 F. The house has 30 000 lbm mass with an average specific heat
Carbon dioxide is used in an ideal gas refrigeration cycle, the reverse of Fig. 5.24. Heat absorption is at 450 R and heat rejection is at 585 R where the pressure changes from 180 psia to 360 psia.
A power plant with a thermal efficiency of 40% is located on a river similar to the setup in Fig. P5.61. With a total river mass flow rate of 2 × 105 lbm/s at 60 F, find the maximum power production
Using the given heat pump in the previous problem, how warm could it make the shelter in the arctic night?Data from previous problemArctic explorers are unsure if they can use a 5-kW motor-driven
Arctic explorers are unsure if they can use a 5-kW motor-driven heat pump to stay warm. It should keep their shelter at 60 F; the shelter loses energy at a rate of 0.3 Btu/s per degree difference
A small house kept at 77 F inside loses 12 Btu/s to the outside ambient at 32 F.A heat pump is used to help heat the house together with possible electric heat. The heat pump is driven by a 2.5-kW
In a remote location, you run a heat engine to provide the power to run a refrigerator. The input to the heat engine is 1450 R and the low T is 700 R; it has an actual efficiency equal to half that
A nuclear reactor provides a flow of liquid sodium at 1500 F, which is used as the energy source in a steam power plant. The condenser cooling water comes from a cooling tower at 60 F. Determine the
Consider the setup with two stacked (temperature-wise) heat engines, as in Fig. P5.4. Let TH = 1500 R, TM = 1000 R, and TL = 650 R. Find the two heat engine efficiencies and the combined overall
Consider the combination of a heat engine and a heat pump, as given in Problem 5.41, with a low temperature of 720 R. What should the high temperature be so that the heat engine is reversible? For
A large heat pump should upgrade 4000 Btu/s of heat at 175 F to be delivered as heat at 280 F. What is the minimum amount of work (power) input that will drive this?
A steam power plant has 1200 F in the boiler, 630 Btu/s work out of the turbine, 900 Btu/s is taken out at 100 F in the condenser, and the pump work is 30 Btu/s. Find the plant’s thermal
R-410a enters the evaporator (the cold heat exchanger) in an air-conditioner unit at 0 F, x = 28% and leaves at 0 F, x = 1. The COP of the refrigerator is 1.5 and the mass flow rate is 0.006 lbm/s.
A window air-conditioner unit is place on a laboratory bench and tested in cooling mode using 0.75 Btu/s of electric power with a COP of 1.75. What is the cooling power capacity, and what is the net
A water cooler for drinking water should cool 10 gal/h water from 65 F to 50 F using a small refrigeration unit with a COP of 2.5. Find the rate of cooling required and the power input to the unit.
An industrial machine is being cooled by 0.8 lbm/s water at 60 F that is chilled from 95 F by a refrigeration unit with a COP of 3. Find the rate of cooling required and the power input to the unit.
A large coal-fired power plant has an efficiency of 45% and produces net 1500MW of electricity. Coal releases 12 500 Btu/lbm as it burns, so how much coal is used per hour?
A lawnmower tractor engine produces 18 hp using 40 Btu/s of heat transfer from burning fuel. Find the thermal efficiency and the rate of heat transfer rejected to the ambient.
A window-mounted air conditioner removes 3.5 Btu from the inside of a home using 1.75 Btu work input. How much energy is released outside, and what is its COP?
Ona cold (−10◦C) winter day, a heat pump provides 20kWto heat a house maintained at 20◦C and it has a COPHP of 4 using the maximum power available. The next day a storm brings the outside
A Carnot heat engine operating between a high TH and low TL energy reservoirs has an efficiency given by the temperatures. Compare this to two combined heat engines, one operating between TH and an
A furnace, shown in Fig.P5.115, can deliver heat, QH1, at TH1, and it is proposed to use this to drive a heat engine with a rejection at Tatm instead of direct room heating. The heat engine drives a
A combination of a heat engine driving a heat pump (see Fig. P5.114) takes waste energy at 50◦C as a source Qw1 to the heat engine, rejecting heat at 30◦C. The remainder, Qw2, goes into the heat
A Carnot heat engine, shown in Fig. P5.113, receives energy from a reservoir at Tres through a heat exchanger where the heat transferred is proportional to the temperature difference as ˙Q H =
Air in a rigid 1-m3 box is at 300 K, 200 kPa. It is heated to 600 K by heat transfer from a reversible heat pump that receives energy from the ambient at 300 K besides the work input. Use constant
An air conditioner on a hot summer day removes 8 kW of energy from a house at 21◦C and pushes energy to the outside, which is at 31◦C. The house has a mass of 15 000 kg with an average specific
Give an estimate for the COP in the previous problem and the power needed to drive the heat pump when the outside temperature drops to −15◦C.Data from previous problemA house should be heated by
Redo the previous problem, assuming the actual devices both have a performance that is 60% of the theoretical maximum.Data from previous problemWe wish to produce refrigeration
We wish to produce refrigeration at−30◦C.Areservoir, shown in Fig. P5.104, is available at 200◦Cand the ambient temperature is 30◦C.Thus, work can be done by a cyclic heat engine operating
Consider a combination of a gas turbine power plant and a steam power plant, as shown in Fig. P5.4. The gas turbine operates at higher temperatures (thus called a topping cycle) than the steam power
Consider the combination of the two heat engines, as in Fig. P5.4. How should the intermediate temperature be selected so that the two heat engines have the same efficiency, assuming Carnot cycle
The air conditioner in the previous problem is turned off. How quickly does the house heat up in degrees per second (◦C/s)?Data from previous problemAn air conditioner on a hot summer day removes 8
In the previous problem, it was assumed that the COP will be the same when the outside temperature drops. Given the temperatures and the actual COP at the −10°C winter day, give an estimate for a
On a cold (−10°C) winter day, a heat pump provides 20 kW to heat a house maintained at 20°C, and it has a COPHP of 4. How much power does the heat pump require? The next day, a storm brings the
A window air conditioner cools a room at TL = 22°C, with a maximum of 1.2 kW power input possible. The room gains 0.6 kW per degree temperature difference to the ambient, and the refrigeration COP
The room in Problem 5.90 has a combined thermal mass of 2000 kg wood, 250 kg steel, and 500 kg plaster board, Cp = 1kJ/kg-K. Estimate how quickly the room heats up if the air conditioner is turned
A window air conditioner cools a room at TL =20◦C with a maximum of 1.2kWpower input. The room gains 0.6 kW per degree temperature difference to the ambient, and the refrigeration COP is β =0.6
Arctic explorers are unsure if they can use a 5-kW motor-driven heat pump to stay warm. It should keep their shelter at 15◦C. The shelter loses energy at a rate of 0.5 kW per degree difference to
Consider a room at 20◦C that is cooled by an air conditioner with a COP of 3.2 using a power input of 2 kW, and the outside temperature is 35◦C. What is the constant in the heat transfer Eq. 5.14
A small house that is kept at 20◦C inside loses 12 kW to the outside ambient at 0◦C. A heat pump is used to help heat the house together with possible electric heat. The heat pump is driven by a
A house is cooled by a heat pump driven by an electric motor using the inside as the low temperature reservoir. The house gains energy in direct proportion to the temperature difference as ˙Q gain =

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