FUNDAMENTALS OF THERMODYNAMICS
10th Edition
ISBN: 9781119634928
Author: Borgnakke
Publisher: WILEY
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Chapter 4, Problem 4.64P
In a co-flowing (same-direction) heat exchanger,
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4. The following heat exchanger uses 10 kg/s of hot air to heat and boil liquid water into
saturated steam at 500 kPa.
(a) Find the steam flow (kg/s)
(b) Determine whether the process is allowed by the second law (Answer: It is not!)
(c) On the surface, the process looks OK as Tair>Twater at both the inlet and outlet. You
should be able to see the problem if you sketch the air and the water temperature
profiles as you move left to right through the exchanger. (Hints: The air will be essentially
a straight line, while the water will not. For the water, think about what happens when it
is changing phase.) This is called a pinch point violation, and it is a very important design
consideration in advanced combined cycle systems and in nuclear power plants.
Air
100 kPa
160°C
10 kg/s
Saturated Vapor
500 kPa
Air: 160°C
Steam: 151.8°C
Q
Air
100 kPa
30°C
Liquid Water
500 kPa, 20°C
Air: 30°C
Water: 20°C
Air enters a cooler at 1450C and at a pressure of 3 bar and is cooled to 450C by passing through tubes of 10 mm inside diameter surrounded by water which enters the cooler at 150C and exits at 300C. Assuming the heat exchanger is counter flow, find:
I) The mean temperature difference.
ii) If the air velocity is limited to 6.5 m/s, what is the required length of tube?
Neglect the resistance of the tube and assume water side heat transfer coefficient is 232 W/m2K.
3.13 Air at 2 kg/s and 27°C and a stream of water at 1.5 kg/s and 60°C
each enter a heat exchanger. Evaluate the exit temperatures if A =
12 m², U = 185 W/m²K, and:
a. The exchanger is parallel flow;
b. The exchanger is counterflow [Tħout = 54.0°C];
c. The exchanger is cross flow, one stream mixed;
d. The exchanger is cross flow, neither stream mixed.
[Thout = 53.62°C]
Chapter 4 Solutions
FUNDAMENTALS OF THERMODYNAMICS
Ch. 4 - A temperature difference drives a heat transfer...Ch. 4 - What is the effect can be felt upstream in a flow?Ch. 4 - Prob. 4.3PCh. 4 - Air at 500 kPa is expanded to l00 kPa in two...Ch. 4 - A windmill takes out a fraction of the wind...Ch. 4 - An underwater turbine extracts a fraction of the...Ch. 4 - A liquid water turbine at the bottom of a dam...Ch. 4 - You blow a balloon up with air. What kinds of work...Ch. 4 - Storage tanks of cryogenic liquids (O2,N2,CH4) are...Ch. 4 - A large brewery has a pipe of cross-sectional area...
Ch. 4 - A pool is to be filled with 60m3 water from a...Ch. 4 - Natural gas, CH4 , flowing in a 5cm -diameter pipe...Ch. 4 - A boiler receives a constant flow of 5000kg/h...Ch. 4 - A 0.6m -diameter household fan takes air in at...Ch. 4 - Liquid water at 15°C flows out of nozzle straight...Ch. 4 - A nozzle receives an ideal gas flow with a...Ch. 4 - In a jet engine a flow afar at 1000K,200kPa, and...Ch. 4 - The wind is blowing horizontally at 30m/s in a...Ch. 4 - A meteorite hits the upper atmosphere at 3000m/s ,...Ch. 4 - Carbon dioxide is throttled from 20C,2000kPa to...Ch. 4 - Saturated liquid R-410A at 25°C is throttled to...Ch. 4 - Carbon dioxide used as a natural refrigerant flows...Ch. 4 - Liquid water at 180C,2000kPa is throttled into a...Ch. 4 - Methane at 1MPa,250K is throttled through a valve...Ch. 4 - A steam turbine has an n1et of 3kg/s water at 1200...Ch. 4 - Air at 20m/s,1500K,875kPa with 5kg/s flows into a...Ch. 4 - Solve the previous problem using Table A.7.Ch. 4 - A wind turbine can extract at most a fraction...Ch. 4 - A liquid water turbine receives 2kg/s water at...Ch. 4 - A small high-speed turbine operating on compressed...Ch. 4 - Hoover Dam across the Colorado River dams up Lake...Ch. 4 - What is the specific work one can get from Hoover...Ch. 4 - R-410A in a commercial refrigerator flows into the...Ch. 4 - A compressor brings nitrogen from 100kPa,290K to...Ch. 4 - A refrigerator uses the natural refrigerant carbon...Ch. 4 - A factory generates compressed air from l00kPa,17C...Ch. 4 - A compressor brings R-134a from...Ch. 4 - An exhaust fan in a building should be able to...Ch. 4 - Prob. 4.39PCh. 4 - The air conditioner in a house or a car has a...Ch. 4 - A boiler section boils 3kg/s saturated liquid...Ch. 4 - A superheater takes 3kg/s saturated water vapor in...Ch. 4 - Carbon dioxide enters a steady-state, steady-flow...Ch. 4 - Find the heat transfer in Problem 4.13.Ch. 4 - A chiller cools liquid water for air-conditioning...Ch. 4 - Saturated liquid nitrogen at 600 kPa enters a...Ch. 4 - Prob. 4.47PCh. 4 - Liquid nitrogen at 90K,400kPa flows into a probe...Ch. 4 - Liquid glycol flows around an engine, cooling it...Ch. 4 - An irrigation pump takes water from a river at...Ch. 4 - A pipe from one building to another flows water at...Ch. 4 - A river flowing at 0.5m/s across a 1-m-high and...Ch. 4 - A cutting tool uses a nozzle that generates a...Ch. 4 - An adiabatic steam turbine in a power plant...Ch. 4 - Prob. 4.55PCh. 4 - A steam turbine receives steam from two boilers...Ch. 4 - Prob. 4.57PCh. 4 - Prob. 4.58PCh. 4 - A condenser (heat exchanger) brings 1kg/s water...Ch. 4 - Steam at 500kPa,300C is used to heat cold water at...Ch. 4 - A dual-fluid heat exchanger has 5kg/s water...Ch. 4 - An energy recovery heat exchanger, shown in Fig....Ch. 4 - Do the previous problem if the water is heated to...Ch. 4 - In a co-flowing (same-direction) heat exchanger,...Ch. 4 - An a water counter flowing heat exchanger has one...Ch. 4 - An automotive radiator has glycol at 95°C enter...Ch. 4 - Prob. 4.67PCh. 4 - Two air flows are combined to a single flow. One...Ch. 4 - An open feedwater heater in a power plant heats...Ch. 4 - A de-superheater has a flow of ammonia of 1.5kg/s...Ch. 4 - A mixing chamber with heat transfer receives 2kg/s...Ch. 4 - A geothermal supply of hot water at 500kPa,150C is...Ch. 4 - A flow of 5kg/s water at l00kPa,20C should be...Ch. 4 - A two-stage compressor takes nitrogen ri at...Ch. 4 - The intercooler in the previous problem uses cold...Ch. 4 - Prob. 4.76PCh. 4 - A modern jet engine has a temperature after...Ch. 4 - A proposal is made to use a geothermal supply of...Ch. 4 - Prob. 4.79PCh. 4 - An initially empty canister of volume 0.2m3 is...Ch. 4 - Repeat the previous problem but use the line...Ch. 4 - A tank contains 1m3 air at 100kPa,300K . A pipe...Ch. 4 - A 2.5L tank initially is empty, and we want to...Ch. 4 - An insulated 2m3 tank is to be charged with R-134a...Ch. 4 - Repeat the previous problem if the valve is closed...Ch. 4 - A 3m3 ? cryogenic storage tank contains nitrogen...Ch. 4 - A nitrogen line at 300K,0.5MPa , shown in Fig....Ch. 4 - Prob. 4.88PCh. 4 - A 200L tank (see Fig. P4.89) initially contains...Ch. 4 - A 1-L can of R-410A is at room temperature, 20°C,...Ch. 4 - Steam at 3MPa,400C enters a turbine with a...Ch. 4 - In a glass factory a 2m -wide sheet of glass at...Ch. 4 - Assume a setup similar to that of the previous...Ch. 4 - Three a flows, all at 200 kPa, e connected to the...Ch. 4 - A 1m3,40kg rigid steel tank contains air at 500...Ch. 4 - An insulated spring-loaded piston/cylinder device,...Ch. 4 - A piston/cyl. setup like Fig. 4.96 is such that at...Ch. 4 - A mass-loaded piston/cylinder shown in Fig. P4.98,...Ch. 4 - A flow of 2kg/s of water at 500kPa,20C is heated...Ch. 4 - Refrigerant R-410A at l00psia,60F flows at...Ch. 4 - A pool is to be filled with 2500ft3 water from a...Ch. 4 - Liquid water at 60 F flows out of a nozzle...Ch. 4 - Prob. 4.103EPCh. 4 - Prob. 4.104EPCh. 4 - Nitrogen gas flows into a convergent nozzle at...Ch. 4 - A meteorite hits the upper atmosphere at 10000ft/s...Ch. 4 - Refrigerant R-410A flows out of a cooler at...Ch. 4 - Saturated vapor R-410A at 75 psia is throttled to...Ch. 4 - A wind turbine can exact at most a fraction 16/27...Ch. 4 - A liquid water turbine receives 4Ibm/s water at...Ch. 4 - Prob. 4.111EPCh. 4 - What is the specific work one can get from Hoover...Ch. 4 - A small-speed turbine operating on compressed air...Ch. 4 - R.410A in a commercial refigerator flows into the...Ch. 4 - An exhaust fan in a building should be able to...Ch. 4 - Carbon dioxide gas enters a steady-state,...Ch. 4 - Prob. 4.117EPCh. 4 - Liquid glycol flows around an engine, cooling t as...Ch. 4 - Prob. 4.119EPCh. 4 - Prob. 4.120EPCh. 4 - Do the previous problem if the water is just...Ch. 4 - A dual-fluid heat exchanger has l0Ibm/s water...Ch. 4 - Steam at 80psia,600F is used to heat cold water at...Ch. 4 - Prob. 4.124EPCh. 4 - Two flows of air are both at 30 psia one has...Ch. 4 - A de-superheater has a flow of ammonia of 3Ibm/s...Ch. 4 - A two-stage compressor takes nitrogen n at...Ch. 4 - The intercooler in the previous problem uses cold...Ch. 4 - Prob. 4.129EPCh. 4 - Prob. 4.130EPCh. 4 - A tank contains l0ft3 of air at 15psia,540R . A...Ch. 4 - Prob. 4.132EPCh. 4 - In a glass factory a 6 ft-wide sheet of glass at...Ch. 4 - A mass-loaded piston/cylinder containing air is at...
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