Questions and Answers of Fundamentals Of Thermodynamics

For the steam power plant shown in Problem 4.118, determine the rate of heat transfer in the economizer, which is a low-temperature heat exchanger. Also find the rate of heat transfer needed in the
For the steam power plant shown in Problem 4.118, assume that the cooling water comes from a lake at 15◦C and is returned at 25◦C. Determine the rate of heat transfer in the condenser and the
The following data are for a simple steam power plant as shown in Fig. P4.118. State 6 has x6 =0.92 and velocity of 200 m/s. The rate of steam flow is 25 kg/s, with 300 kW of power input to the pump.
The intercooler in the previous problem uses cold liquid water to cool the nitrogen. The nitrogen flow is 0.1 kg/s, and the liquid water inlet is 20◦C and is set up to flow in the opposite
A two-stage compressor takes nitrogen in at 20◦C, 150 kPa and compresses it to 600 kPa, 450 K. Then it flows through an inter cooler, where it cools to 320 K, and the second stage compresses it to
A flow of 5 kg/s water at 100 kPa, 20◦C should be delivered as steam at 1000 kPa, 350◦C to some application. Consider compressing it to 1000 kPa, 20◦C and then heat it at a constant rate of
To keep a jet engine cool, some intake air bypasses the combustion chamber. Assume that 2 kg/s of hot air at 2000 K and 500 kPa is mixed with 1.5 kg/s air at 500 K, 500 kPa without any external heat
A geo thermal supply of hot water at 500 kPa, 150◦C is fed to an insulated flash evaporator at the rate of 1.5 kg/s. A stream of saturated liquid at 200 kPa is drained from the bottom of the
A de-super heater has a flow of ammonia of 1.5 kg/s at 1000 kPa, 100◦C that is mixed with another flow of ammonia at 25◦C and quality 50% in an adiabatic mixing chamber. Find the flow rate of the
An open feedwater heater in a power plant heats 4 kg/s water at 45◦C, 100 kPa by mixing it with steam from the turbine at 100 kPa, 250◦C, as in Fig. P4.107. Assume the exit flow is saturated
A flow of water at 2000 kPa, 20◦C is mixed with a flow of 2 kg/s water at 2000 kPa, 180◦C. What should the flow rate of the first flow be to produce an exit state of 200 kPa and 100◦C?
An automotive radiator has glycerine at 95◦C enter and return at 55◦C as shown in Fig. P4.100. Air flows in at 20◦C and leaves at 25◦C. If the radiator should transfer 25 kW, what is the mass
In a co-flowing (same-direction) heat exchanger, 1 kg/s air at 500Kflows into one channel and 2 kg/s air flows into the neighboring channel at 300 K. If it is infinitely long, what is the exit
A heat exchanger, shown in Fig. P4.95, is used to cool an air flow from 800 to 360 K, with both states at 1 MPa. The coolant is a water flow at 15◦C, 0.1 MPa. If the water leaves as saturated
A dual-fluid heat exchanger has 5 kg/s water entering at 40◦C, 150 kPa and leaving at 10◦C, 150 kPa. The other fluid is glycol, entering at −10◦C, 160 kPa and leaving at 10◦C, 160 kPa. Find
A condenser (heat exchanger) brings 1 kg/s water flow at 10 kPa quality 95% to saturated liquid at 10 kPa, as shown in Fig. P4.91. The cooling is done by lake water at 20◦C that returns to the lake
Two steady flows of air enter a control volume, as shown in Fig. P4.89. One is a 0.025 kg/s flow at 350 kPa, 150◦C, state 1, and the other enters at 450 kPa, 15◦C, state 2.Asingle flow exits at
A compressor receives 0.1 kg/s of R-134a at 150 kPa, −10◦C and delivers it at 1000 kPa, 40◦C. The power input is measured to be 3 kW. The compressor has heat transfer to air at 100 kPa coming
A steam turbine receives steam from two boilers (see Fig. P4.87). One flow is 5 kg/s at 3MPa, 700◦C and the other flow is 10 kg/s at 800 kPa, 500◦C. The exit state is 10 kPa, with a quality of
Cogeneration is often used where a steam supply is needed for industrial process energy. Assume that a supply of 5 kg/s steam at 0.5 MPa is needed. Rather than generating this from a pump and boiler,
A compressor receives 0.05 kg/s R-410a at 200 kPa, −20◦C and 0.1 kg/s R-410a at 400 kPa, 0◦C. The exit flow is at 1000 kPa, 60◦C, as shown in Fig. P4.85. Assume it is adiabatic, neglect
An adiabatic steam turbine in a power plant receives 5 kg/s steam at 3000 kPa, 500◦C. Twenty percent of the flow is extracted at 1000 kPa, 350◦C to a feedwater heater, and the remainder flows out
A river flowing at 0.5 m/s across a 1-m-high and 10-m-wide area has a dam that creates an elevation difference of 2 m. How much energy could a turbine deliver per day if 80% of the potential energy
An irrigation pump takes water from a river at 10◦C, 100 kPa and pumps it up to an open canal, where it flows out 100 m higher at 10◦C. The pipe diameter in and out of the pump is 0.1 m, and the
An evaporator has R-410a at −20◦C and quality 20% flowing in, with the exit flow being saturated vapor at −20◦C. Knowing that there is no work, find the specific heat transfer.
An oven has five radiant heaters; each one is rated at 15 kW. It should heat some 2-kg steel plates from 20◦Cto 800 K. How many of these plates per minute can it heat?
Carbon dioxide used as a natural refrigerant flows through a cooler at 10 MPa, which is supercritical, so no condensation occurs. The inlet is at 220◦Cand the exit is at 50◦C. Find the specific
A compressor in an industrial air conditioner compresses ammonia from a state of saturated vapor at 200 kPa to a pressure of 1000 kPa. At the exit, the temperature is measured to be 100◦C and the
A factory generates compressed air from 100 kPa, 17◦C by compression to 1000 kPa, 600 K, after which it cools in a constant pressure cooler to 300 K, (see Fig. P4.54). Find the specific compressor
A refrigerator uses the natural refrigerant carbon dioxide where the compressor brings 0.02 kg/s from 1MPa,−20◦C to 6 MPa using 2 kW of power. Find the compressor exit temperature.
A compressor brings nitrogen from 100 kPa, 290 K to 2000 kPa. The process has a specific work input of 450 kJ/kg and the exit temperature is 450 K. Find the specific heat transfer using constant
A small turbine, shown in Fig. P4.48, is operated at part load by throttling a 0.25-kg/s steam supply at 1.4 MPa and 250◦C down to 1.1 MPa before it enters the turbine, and the exhaust is at 10
A wind turbine with a rotor diameter of 20 m takes 40% of the kinetic energy out as shaft work on a day with a temperature of 20◦C and a wind speed of 35 km/h. What power is produced?
Air at 20 m/s, 1500 K, 875 kPa with 5 kg/s flows into a turbine and it flows out at 25 m/s, 850 K, 105 kPa. Find the power output using constant specific heats.
Carbon dioxide used as a natural refrigerant flows out of a cooler at 10 MPa, 40◦C, after which it is throttled to 1.4 MPa. Find the state (T, x) for the exit flow.
Saturated liquid R-134a at 25◦C is throttled to 300 kPa in a refrigerator. What is the exit temperature? Find the percent increase in the volume flow rate.
Carbon dioxide is throttled from 20◦C, 2000 kPa to 800 kPa. Find the exit temperature, assuming ideal gas, and repeat for real gas behavior.
The front of a jet engine acts similarly to a diffuser, receiving air at 900 km/h, −5◦C, and 50 kPa, bringing it to 80 m/s relative to the engine before entering the compressor (see Fig. P4.30).
A meteorite hits the upper atmosphere at 3000 m/s, where the pressure is 0.1 atm and the temperature is −40◦C. How hot does the air become right in front of the meteorite assuming no heat
A diffuser, shown in Fig. P4.28, has air entering at 100 kPa and 300 K with a velocity of 200 m/s. The inlet cross-sectional area of the diffuser is 100 mm2. At the exit the area is 860 mm2, and the
The wind is blowing horizontally at 30 m/s in a storm at Po, 20◦ C toward a wall, where it comes to a stop (stagnation) and leaves with negligible velocity similar to a diffuser with a very large
Air at 35◦C, 105 kPa flows in a 100-mm×150-mm rectangular duct in a heating system. The mass flow rate is 0.015 kg/s. What are the velocity of the air flowing in the duct and the volume flow rate?
Track the process described in Problem 3.115 so that you can sketch the amount of heat transfer added and the work given out as a function of the volume.Data from Problem 3.115Two kilograms of
Using states with given (P, v) and properties from the supplied software, track the process in Problem 3.105. Select five pressures away from the initial toward the final pressure so that you can
Examine the sensitivity of the final pressure to the containment room volume in Problem 3.101. Solve for the volume for a range of final pressures, 100–250 kPa, and sketch the pressure versus
Ammonia is contained in a sealed, rigid tank at 30 F, x = 50% and is then heated to 200 F. Find the final state P2, u2 and the specific work and heat transfer.
A 20-lb mass of water in a piston/cylinder with constant pressure is at 1100 F and a volume of 22.6 ft3. It is now cooled to 100 F. Show the P–v diagram and find the work and heat transfer for the
Find the rate of conduction heat transfer through a 1.5-cm-thick hardwood board, k = 0.09 Btu/ h-ft-R, with a temperature difference between the two sides of 40 F.
A crane uses 7000 Btu/h to raise a 200-lbm box 60 ft. How much time does it take?
A computer CPU chip consists of 0.1 lbm silicon, 0.05 lbm copper, and 0.1 lbm polyvinyl chloride (plastic). It now heats from 60 F to 160 F as the computer is turned on. How much energy did the
A constant-pressure piston/cylinder has 2 lbm of water at 1100 F and 2.26 ft3. It is now cooled to occupy 1/10th of the original volume. Find the heat transfer in the process.
Superheated vapor ammonia enters an insulated nozzle at 30◦C, 1000 kPa, as shown in Fig. P4.25,with a low velocity and at a rate of 0.01 kg/s. The ammonia exits at 300 kPa with a velocity of 450
In a jet engine a flow of air at 1000 K, 200 kPa, and 30 m/s enters a nozzle, as shown in Fig. P4.23, where the air exits at 850 K, 90 kPa. What is the exit velocity, assuming no heat loss? Fuel in
A diffuser receives 0.1 kg/s steam at 500 kPa, 350◦C. The exit is at 1 MPa, 400◦C with negligible kinetic energy and the flow is adiabatic. Find the diffuser inlet velocity and the inlet area.
An airport ventilation system takes 2.5 m3/s air at 100 kPa, 17◦C into a furnace, heats it to 52◦C, and delivers the flow to a duct with cross-sectional area 0.4 m2 at 110 kPa. Find the mass flow
A 0.6-m-diameter household fan takes air in at 98 kPa, 20◦C and delivers it at 105 kPa, 21◦C with a velocity of 1.5 m/s (see Fig. P4.18). What are the mass flow rate (kg/s), the inlet velocity,
A flat channel of depth 1 m has a fully developed laminar flow of air at P0, T0 with a velocity profile of V = 4Vcx(H − x)/H2, where Vc is the velocity on the centerline and x is the distance
A pool is to be filled with 60 m3 water from a garden hose of 2.5 cm diameter flowing water at 2 m/s. Find the mass flowrate of water and the time it takes to fill the pool.
A large brewery has a pipe of cross-sectional area 0.2 m2 flowing carbon dioxide at 400 kPa, 10◦C with a volume flow rate of 0.3 m3/s. Find the velocity and the mass flow rate.
A storage tank for natural gas has a top dome that can move up or down as gas is added to or subtracted from the tank, maintaining 110 kPa, 290 K inside. A pipeline at 110 kPa, 290 K now supplies
You blow a balloon up with air. What kinds of work terms, including flow work, do you see in that case? Where is energy stored?
An underwater turbine extracts a fraction of the kinetic energy from the ocean current. How do the temperature and water velocity influence the power? Hint: write the power term as mass flow rate
Pipes that carry a hot fluid like steam in a power plant, exhaust pipe for a diesel engine in a ship, etc., are often insulated. Is that done to reduce heat loss or is there another purpose?
Air at 500 kPa is expanded to 100 kPa in two steady flow cases. Case one is a nozzle and case two is a turbine; the exit state is the same for both cases. What can you say about the specific turbine
Which of the properties (P, v, T ) can be controlled in a flow? How?
What effect can be felt upstream in a flow?
A cylindrical tank of height 2 m with a cross sectional area of 0.5 m2 contains hot water at 80◦C, 125 kPa. It is in a room with temperature T0 = 20◦C, so it slowly loses energy to the room air
Write a program to solve Problem 3.123 for a range of initial velocities. Let the car mass and final velocity be input variables.Data from Problem 3.123A car with mass 1275 kg is driven at 60 km/h
Use the supplied software to track the process in Problem 3.96 in steps of 10◦C until the two-phase region is reached, after that step with jumps of 5% in the quality. At each step write out T, x,
Ammonia vapor is compressed inside a cylinder by an external force acting on the piston. The ammonia is initially at 30◦C, 500 kPa, and the final pressure is 1400 kPa. The following data have been
A piston/cylinder arrangement of initial volume 0.025 m3 contains saturated water vapor at 200◦C. The steam now expands in a quasi-equilibrium isothermal process to a final pressure of 200 kPa
A mass of 6 lbm nitrogen gas at 3600 R, V = C, cools with 1 Btu/s. What is dT/dt?
The water in tank A is at 270 F with quality of 10% and mass 1 lbm. It is connected to a piston/cylinder holding constant pressure of 40 psia initially with 1 lbm water at 700 F. The valve is opened,
Oxygen at 50 lbf/in.2, 200 F is in a piston/cylinder arrangement with a volume of 4 ft3. It is now compressed in a polytropic process with exponent, n = 1.2, to a final temperature of 400 F.
A closed rigid container is filled with 3 lbm water at 1 atm, 130 F, 2 lbm of stainless steel and 1 lbm of polyvinyl chloride, both at 70 F, and 0.2 lbm of air at 700 R, 1 atm. It is now left alone
Ammonia (1 lbm) in a piston/cylinder at 30 psia, 20 F is heated in a process in which the pressure varies linearly with the volume to a state of 240 F, 40 psia. Find the work and the heat transfer in
A rigid tank holds 1.5 lbm R-410a at 100 F as saturated vapor. The tank is now cooled to 60 F by heat transfer to the ambient. Which two properties determine the final state? Determine the amount of
Saturated vapor R-410a at 200 psia in a constant pressure piston/cylinder is heated to 140 F. Find the specific heat transfer.
Saturated vapor R-410a at 60 F in a rigid tank is cooled to 0 F. Find the specific heat transfer.
A piston of 4 lbm is accelerated to 60 ft/s from rest. What constant gas pressure is required if the area is 4 in.2, the travel distance is 4 in., and the outside pressure is 15 psia?
The air drag force on a car is 0.225 A ρ V2. Verify that the unit becomes lbf.
An ideal gas in a piston/cylinder is heated with 2 Btu in an isothermal process. How much work is involved?
Look at the R-410a value for uf at −60 F. Can the energy really be negative? Explain.
Consider the system shown in Fig. P3.241. Tank A has a volume of 100 L and contains saturated vapor R-134a at 30◦C. When the valve is cracked open, R-134a flows slowly into cylinder B. The piston
A system is now heated to the final temperature of 20◦C. Find the work and heat transfer in the process and draw the P–v diagram. Po mp R-410a FIGURE P3.237
A constant pressure container is filled with 1 kg of stainless steel and 0.5 kg of PVC (polyvinyl chloride) both at 20C and 0.25 kg of hot air at 500 K, 100 kPa. The container is now left alone with
Water at 20◦C and 100 kPa is brought to 100 kPa and 1500◦C. Find the change in the specific internal energy, using the water tables and ideal-gas tables.
Repeat Problem 3.130 for oxygen gas.Data from Problem 3.130We want to find the change in u for carbon dioxide between 600 K and 1200 K.a. Find it from a constant Cv0 from Table A.5.b. Find it from a
A piston/cylinder arrangement B is connected to a 1-m3 tank A by a line and valve, shown in Fig. P3.240. Initially both contain water, with A at 100 kPa, saturated vapor and B at 400◦C, 300 kPa, 1
A piston/cylinder setup, shown in Fig. P3.238, contains R-410a at −20◦C, x = 20%. The volume is 0.2 m3. It is known that Vstop = 0.4 m3, and if the piston sits at the bottom, the spring force
Ammonia (2 kg) in a piston/cylinder is at 100 kPa, −20◦C and is now heated in a poly tropic process with n = 1.3 to a pressure of 200 kPa. Do not use the ideal gas approximation and find T2, the
A 1-m3 tank containing air at 25◦C and 500 kPa is connected through a valve to another tank containing 4 kg of air at 60◦C and 200 kPa (Fig. P3.232). Now the valve is opened and the entire system
A piston/cylinder arrangement has a linear spring and the outside atmosphere acting on the piston shown in Fig. P3.231. It contains water at 3 MPa and 400◦C with a volume of 0.1 m3. If the piston
A piston/cylinder system contains 50 L of air at 300◦C, 100 kPa, with the piston initially on a set of stops. A total external constant force acts on the piston, so the balancing pressure inside
Two springs with the same spring constant are installed in a massless piston/cylinder arrangement with the outside air at 100 kPa. If the piston is at the bottom, both springs are relaxed, and the
A piston/cylinder setup (Fig. P3.171) contains 1 kg of water at 20◦C with a volume of 0.1 m3. Initially, the piston rests on some stops with the top surface open to the atmosphere, P0, and a mass
A tank has a volume of 1 m3 with oxygen at 15◦C, 300 kPa. Another tank contains 4 kg oxygen at 60◦C, 500 kPa. The two tanks are connected by a pipe and valve that is opened, allowing the whole
Two rigid tanks are filled with water (Fig. P3.214). Tank A is 0.2 m3 at 100 kPa, 150◦C and tank B is 0.3 m3 at saturated vapor of 300 kPa. The tanks are connected by a pipe with a closed valve. We
Water in tank A is at 250 kPa with quality 10% and mass 0.5 kg. It is connected to a piston/cylinder holding constant pressure of 200 kPa initially with 0.5 kg water at 400◦C. The valve is opened,
The cylinder volume below the constant loaded piston has two compartments, A and B, filled with water, as shown in Fig. P3.212. A has 0.5 kg at 200 kPa and 150◦C and B has 400 kPa with a quality of

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