Questions and Answers of Fundamentals Of Thermodynamics

The products of combustion of a jet engine leave the engine with a velocity relative to the plane of 500 m/s, a temperature of 525◦C, and a pressure of 75 kPa. Assuming that k = 1.32, Cp = 1.15
A stagnation pressure of 110 kPa is measured for an air flow where the pressure is 100 kPa and the temperature is 20◦C in the approach flow. What is the incoming velocity?
A 4-cm inner-diameter pipe has an inlet flow of 10 kg/s water at 20◦C, 200 kPa. After a 90 degree bend, as shown in Fig. P15.24, the exit flow is at 20◦C, 190 kPa. Neglect gravitational effects
A jet engine receives a flow of 150 m/s air at 75 kPa, 5◦C, across an area of 0.6 m2 with an exit flow at 450 m/s, 75 kPa, 800 K. Find the mass flow rate and thrust.
An irrigation pump takes water from a lake and discharges it through a nozzle, as shown in Fig. P15.30. At the pump exit the pressure is 900 kPa, and the temperature is 20◦C. The nozzle is located
If the sound of thunder is heard 5 s after the lightning is seen and the temperature is 20◦C, how far away is the lightning?
A jet flies at an altitude of 12 km where the air is at −40◦C, 45 kPa, with a velocity of 1000 km/h. Find the Mach number and the stagnation temperature on the nose.
Steam flowing at 15 m/s, 1800 kPa, 300◦C, expands to 1600 kPa in a converging nozzle. Find the exit velocity and area ratio Ae/Ai.
An air flow at 600 kPa, 600 K, M = 0.3 flows into a convergent-divergent nozzle with M = 1 at the throat. Assume a reversible flow with an exit area twice the throat area and find the exit pressure
Helium flows at 500 kPa, 500 K, with 100 m/s into a convergent-divergent nozzle. Find the throat pressure and temperature for reversible flow and M = 1 at the throat.
The products of combustion, use air, enter a convergent nozzle of a jet engine at a total pressure of 125 kPa and a total temperature of 650◦C. The atmospheric pressure is 45 kPa, and the flow is
A normal shock in air has an upstream total pressure of 500 kPa, a stagnation temperature of 500 K, and Mx = 1.4. Find the downstream stagnation pressure.
Consider the diffuser of a supersonic aircraft flying at M = 1.4 at such an altitude that the temperature is−20◦C and the atmospheric pressure is 50 kPa. Consider two possible ways in which the
A flow into a normal shock in air has a total pressure of 400 kPa, a stagnation temperature of 600 K, and Mx = 1.2. Find the upstream temperature Tx, the specific entropy generation in the shock, and
Find the speed of sound in air at 15 lbf/in.2 at the two temperatures of 32 F and 90 F. Find the answer for carbon dioxide and argon gases.
A jet plane flies at an altitude of 40 000 ft where the air is at −40 F, 6.5 psia, with a velocity of 625 mi/h. Find the Mach number and the stagnation temperature on the nose.
Steam flowing at 50 ft/s, 200 psia, 600 F, expands to 150 psia in a converging nozzle. Find the exit velocity and area ratio Ae/Ai.
An air flow at 90 psia, 1100 R,M = 0.3 flows into a convergent-divergent nozzle with M = 1 at the throat. Assume a reversible flow with an exit area twice the throat area and find the exit pressure
A normal shock in air has an upstream total pressure of 75 psia, a stagnation temperature of 900 R, and Mx = 1.4. Find the downstream stagnation pressure.
Develop a program that calculates the stagnation pressure and temperature from a static pressure, temperature, and velocity. Assume the fluid is air with constant specific heats. If the inverse
A pump can deliver liquid water at an exit pressure of 400 kPa using 0.5 kW of power. Assume that the inlet is water at 100 kPa, 15◦C, and that the pipe size is the same for the inlet and exit.
The throttle plate in a carburetor severely restricts the air flow where at idle it is critical flow. For normal atmospheric conditions, estimate the inlet temperature and pressure to the cylinder of
For an experiment in the laboratory, the air flow rate should be measured. The range should be 0.05 to 0.10 kg/s, and the flow should be delivered to the experiment at 110 kPa. Size one (or two in
An afterburner in a jet engine adds fuel that is burned after the turbine but before the exit nozzle that accelerates the gases. Examine the effect on nozzle exit velocity of having a higher inlet
In all the problems in the text, the efficiency of a pump or compressor has been given as a constant. In reality, it is a function of the mass flow rate and the fluid state through the device.
A large heat pump should upgrade 4MWof heat at 65◦C to be delivered as heat at 145◦C. What is the minimum amount of work (power) input that will drive this?
An ideal (Carnot) heat engine has an efficiency of 40%. If the high temperature is raised 15%, what is the new efficiency keeping the same low temperature?
The simple refrigeration cycle is shown in Problem 5.23 and in Fig. 5.6. Mention a few of the processes that are expected to be irreversible.Data from Problem 5.23A window air conditioner (Fig.
Consider the four cases of a heat engine in Problem 5.34 and determine if any of those are perpetual machines of the first or second kind.Data from Problem 5.34For each of the cases below, determine
Consider a heat engine and heat pump connected as shown in Fig. P5.41. Assume that TH1 = TH2 > Tamb and determine for each of the three cases if the setup satisfies the first law and/or violates
A water cooler for drinking water should cool 25 L/h water from 18◦C to 10◦C while the water reservoirs also gains 60 W from heat transfer. Assume that a small refrigeration unit with a COP of
An experimental power plant outputs 130 MW of electrical power. It uses a supply of 1200 MW from a geothermal source and rejects energy to the atmosphere. Find the power to the air and how much air
In a Rankine cycle 0.9MWis taken out in the condenser, 0.63MWis taken out from the turbine, and the pump work is 0.03MW. Find the plant’s thermal efficiency. If everything could be reversed, find
A window-mounted air conditioner removes 3.5 kJ from the inside of a home using 1.75 kJ work input. How much energy is released outside and what is its coefficient of performance?
A lawnmower tractor engine produces 18 hp using 40 kW of heat transfer from burning fuel. Find the thermal efficiency and the rate of heat transfer rejected to the ambient.
Does a reversible heat engine burning coal (which in practice cannot be done reversibly) have impacts on our world other than depletion of the coal reserve?
A tank contains 1 m3 air at 100 kPa, 300 K. A pipe of flowing air at 1000 kPa, 300 K is connected to the tank and is filled slowly to 1000 kPa. Find the heat transfer needed to reach a final
A somewhat simplified flow diagram for a nuclear power plant is given in Fig. P4.121. Mass flow rates and the various states in the cycle are shown in the accompanying table.The cycle includes a
An air flow is brought from 20◦C, 100 kPa to 1000 kPa, 330◦C by an adiabatic compressor driven by a 50-kW motor. What are the mass flow rate and the exit volume flow rate of air?
A compressor receives R-410a as saturated vapor at 400 kPa and brings it to 2000 kPa, 60◦C. Then a cooler brings it to a state of saturated liquid at 2000 kPa (see Fig. P4.54). Find the specific
Hoover Dam across the Colorado River dams up Lake Mead 200mhigher than the river downstream (see Fig. P6.47). The electric generators driven by water-powered turbines deliver 1300MWof power. If the
R-410a enters the evaporator (the cold heat exchanger) in an air-conditioner unit at −20◦C, x = 28% and leaves at −20◦C, x = 1. The COP of the refrigerator is 1.5 and the mass flow rate is
A sports car engine delivers 100 hp to the driveshaft with a thermal efficiency of 25%. The fuel has a heating value of 40 000 kJ/kg. Find the rate of fuel consumption and the combined power rejected
An industrial machine is being cooled by 0.4 kg/s water at 15◦C that is chilled from 35◦C by a refrigeration unit with a COP of 3. Find the rate of cooling required and the power input to the
A window air conditioner (Fig. P5.23) discards 1.7 kW to the ambient with a power input of 500 W. Find the rate of cooling and the COP. W = 0.5 kW Cool side inside Hot side outside Compressor 1.7 kW
A large coal fired power plant has an efficiency of 45% and produces net 1,500 MW of electricity. Coal releases 25 000 kJ/kg as it burns so how much coal is used per hour?
After you have driven a car on a trip and it is back home, the car’s engine has cooled down and thus is back to the state in which it started. What happened to all the energy released in the
A combination of two refrigerator cycles is shown in Fig. P5.7. Find the overall COP as a function of COP1 and COP2. TL TH REF1 (REF2 IN @TM W, W2 1 FIGURE P5.7
Compare two heat engines receiving the same Q, one at 1200 K and the other at 1800 K, both of which reject heat at 500 K. Which one is better?
A combination of two heat engines is shown in Fig. P5.4. Find the overall thermal efficiency as a function of the two individual efficiencies. TH TL Он (HE1) (HE2) @ TM FIGURE P5.4
Suppose we forget the model for heat transfer, ˙Q = CA ΔT ; can we draw some information about the direction of Q from the second law?
Compare two domestic heat pumps (A and B) running with the same work input. If A is better than B, which one provides more heat?
Two heat engines operate between the same two energy reservoirs, and both receive the same QH. One engine is reversible and the other is not. What can you say about the two QL’s?
A coflowing heat exchanger receives air at 800 K, 1 MPa and liquid water at 15◦C, 100 kPa, as shown in Fig. P4.215. The air line heats the water so that at the exit the air temperature is 20◦C
The air–water counterflowing heat exchanger given in Problem 4.95 has an air exit temperature of 360 K. Suppose the air exit temperature is listed as 300 K; then a ratio of the mass flow rates is
A 2-m3 insulated tank contains saturated vapor steam at 4MPa.Avalve on top of the tank is opened, and saturated vapor escapes. During the process any liquid formed collects at the bottom of the tank,
An insulated tank of volume V contains a specified ideal gas (with constant specific heat) as P1, T1. A valve is opened, allowing the gas to flow out until the pressure inside drops to P2. Determine
A mass-loaded piston/cylinder containing air is at 45 lbf/in.2, 60 F with a volume of 9 ft3, while at the stops V = 36 ft3. An air line, 75 lbf./in.2, 1100 R is connected by a valve, as shown in Fig.
A tank contains 10 ft3 of air at 15 psia, 540 R. A pipe of flowing air at 150 psia, 540 R is connected to the tank and it is filled slowly to 150 psia. Find the heat transfer needed to reach a final
A 1-gal tank initially is empty, and we want to fill it with 0.03 lbm R-410a. The R-410a comes from a line with saturated vapor at 20 F. To achieve the desired amount, we cool the tank while we fill
An R-410a heat pump cycle shown in Fig. P4.123 has an R-410a flow rate of 0.1 lbm/s with 4 Btu/s into the compressor. The following data are given:Calculate the heat transfer from the compressor, the
The intercooler in the previous problem uses cold liquid water to cool the nitrogen. The nitrogen flow is 0.1 lbm/s, and the liquid water inlet is 77 F and is set up to flow in the opposite direction
A two-stage compressor takes nitrogen in at 80 F, 20 psia and compresses it to 80 psia, 800 R. Then it flows through an intercooler, where it cools to 580 R, and the second stage compresses it to 400
A de-super heater has a flow of ammonia of 3 lbm/s at 150 psia, 200 F that is mixed with another flow of ammonia at 80 F and quality 25% in an adiabatic mixing chamber, Find the flow rate of the
Two flows of air are both at 30 psia; one has 1 lbm/s at 720 R and the other has 2 lbm/s at 520 R. The two flows are mixed together in an insulted box to produce a single exit flow at 30 psia. Find
A copper wire has been heat treated to 1800 R and is now pulled into a cooling chamber that has 3 lbm/s air coming in at 70 F; the air leaves the other end at 120 F. If the wire moves 0.5 lbm/s
Steam at 80 psia, 600 F is used to heat cold water at 60 F to 170 F for a domestic hot water supply. How much steam per lbm liquid water is needed if the steam should not condense?
A dual-fluid heat exchanger has 10 lbm/s water entering at 100 F, 20 psia and leaving at 50 F, 20 psia. The other fluid is glycol entering at 10 F, 22 psia and leaving at 50 F, 22 psia. Find the
An evaporator has R-410a at 0 F and quality 20% flowing in, with the exit flow being saturated vapor at 0 F. Knowing that there is no work, find the specific heat transfer.
An oven has five radiant heaters, each one is rated at 15 Btu/s. It should heat some 4 lbm steel plates from 77 F to 1400 R. How many of these plates per minute can it heat?
A condenser (cooler) receives 0.1 lbm/s of R-410a at 300 psia, 140 F and cools it to 70 F. Assume the exit properties are as for saturated liquid, with the same T. What cooling capacity (Btu/h) must
An air flow is brought from 77 F, 14.7 psia to 150 psia, 620 F by an adiabatic compressor driven by a 50 kW motor. What are the mass flow rate and the exit volume flow rate of air?
A compressor in an industrial air conditioner compresses ammonia from a state of saturated vapor at 20 psia to a pressure of 125 psia. At the exit, the temperature is measured to be 200 F and the
Asmall expander (a turbine with heat transfer) has 0.1 lbm/s of helium entering at 160 psia, 1000 R and leaving at 40 psia, 540 R. The power output on the shaft is measured as 55 Btu/s. Find the rate
Saturated vapor R-410a at 75 psia is throttled to 15 psia. What is the exit temperature? Repeat the question if you assumed it behaves like an ideal gass.
Saturated liquid R-410a at 30 F is throttled to 40 psia in a refrigerator. What is the exit temperature? Find the percent increase in the volume flow rate.
R-410a at 90 F, 300 psia is throttled so that it becomes cold at 10 F. What is the exit P?
Refrigerant R-410a flows out of a cooler at 70 F, 220 psia, after which it is throttled to 77 psia. Find the state (T, x) for the exit flow.
A meteorite hits the upper atmosphere at 10 000 ft/s where the pressure is 0.1 atm and temperature −40 F. How hot does the air become right in front of the meteorite assuming no heat transfer in
A sluice gate dams water up 15 ft. A 0.5-in.- diameter hole at the bottom of the gate allows liquid water at 70 F to come out. Neglect any changes in internal energy and find the exit velocity and
A diffuser receives 0.2 lbm/s steam at 80 psia, 600 F. The exit is at 150 psia, 700 F with negligible kinetic energy, and the flow is adiabatic. Find the diffuser inlet velocity and the inlet area.
A pool is to be filled with 2500 ft3 water from a garden hose of 1 in. diameter flowing water at 6 ft/s. Find the mass flow rate of water and the time it takes to fill the pool.
Refrigerant R-410a at 100 psia, 60 F flows at 0.1 lbm/s in a 2.5-ft2 cross-sectional area pipe. Find the velocity and the volume flow rate.
A 2-m3 storage tank contains 95% liquid and 5% vapor by volume of liquified natural gas (LNG) at 160 K, as shown in Fig. P4.155. It may be assumed that LNG has the same properties as pure methane.
A mass-loaded piston/cylinder shown in Fig. P4.154, containing air, is at 300 kPa, 17◦C with a volume of 0.25 m3, while at the stops V = 1 m3. An air line, 500 kPa, 600 K, is connected by a valve
An insulated spring-loaded piston/cylinder device, shown in Fig. P4.153, is connected to an air line flowing air at 600 kPa and 700 K by a valve. Initially, the cylinder is empty and the spring force
A steam engine based on a turbine is shown in Fig. P4.152. The boiler tank has a volume of 100 L and initially contains saturated liquid with a very small amount of vapor at 100 kPa. Heat is now
Three air flows, all at 200 kPa, are connected to the same exit duct and mix without external heat transfer. Flow 1 has 1 kg/s at 400 K, flow 2 has 3 kg/s at 290 K, and flow 3 has 2 kg/s at 700 K.
A flow of 2 kg/s of water at 500 kPa, 20◦C is heated in a constant-pressure process to 1700◦C. Find the best estimate for the rate of heat transfer needed.
A pipe of radius R has a fully developed laminar flow of air at P0, T0 with a velocity profile of V = Vc[1 − (r/R)2], where Vc is the velocity on the center-line and r is the radius, as shown in
A 2-m-tall cylinder has a small hole in the bottom as in Fig. P4.141. It is filled with liquid water 1 m high, on top of which is a 1-m-high air column at atmospheric pressure of 100 kPa. As the
A 1-L can of R-134a is at room temperature, 20◦C, with a quality of 50%. A leak in the top valve allows vapor to escape and heat transfer from the room takes place, so we reach a final state of
A 200-L tank (see Fig. P4.139) initially contains water at 100 kPa and a quality of 1%. Heat is transferred to the water, thereby raising its pressure and temperature. At a pressure of 2 MPa, a
A nitrogen line at 300 K, 0.5 MPa, shown in Fig. P4.137, is connected to a turbine that exhausts to a closed, initially empty tank of 50 m3. The turbine operates to a tank pressure of 0.5 MPa, at
A 25-L tank, shown in Fig. P4.136, that is initially evacuated is connected by a valve to an air supply line flowing air at 20◦C, 800 kPa. The valve is opened, and air flows into the tank until the
Find the final state for the previous problem if the valve is closed when the tank reaches 2 MPa.
A 2.5-L tank initially is empty, and we want to fill it with 10 g of ammonia. The ammonia comes from a line with saturated vapor at 25◦C. To achieve the desired amount, we cool the tank while we
A proposal is made to use a geothermal supply of hot water to operate a steam turbine, as shown in Fig. P4.125. The high-pressure water at 1.5MPa,180◦C is throttled into a flash evaporator chamber,
A modern jet engine has a temperature after combustion of about 1500 K at 3200 kPa as it enters the turbine section (see state 3, Fig. P4.124). The compressor inlet is at 80 kPa, 260 K (state 1) and
An R-410a heat pump cycle shown in Fig. P4.123 has an R-410a flow rate of 0.05 kg/s with 5 kW into the compressor. The following data are given:Calculate the heat transfer from the compressor, the

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