Questions and Answers of Fundamentals Thermal Fluid

Steam is to be condensed on the shell side of a 1-shell-pass and 8-tube-passes condenser, with 50 tubes in each pass, at 30°C (hfg= 2431 kJ/kg). Cooling water (cp= 4180 J/kg·K) enters the
Saturated water vapor at 100°C condenses in a 1-shell and 2-tube heat exchanger with a surface area of 0.5 m2and an overall heat transfer coefficient of 2000 W/m2·K. Cold water (cpc= 4179
Ethanol is vaporized at 78°C (hfg= 846 kJ/kg) in a double-pipe parallel-flow heat exchanger at a rate of 0.03 kg/s by hot oil (cp= 2200 J/kg·K) that enters at 120°C. If the heat
Water (cp = 4180 J/kg·K) enters the 2.5-cminternal-diameter tube of a double-pipe counter-flow heat exchanger at 17°C at a rate of 1.8 kg/s. Water is heated by steam condensing at 120°C (hfg =
Consider a cross-flow engine oil heater that uses ethylene glycol flowing at a temperature of 110°C to heat the oil initially at 10°C. The ethylene glycol enters a tube bank consisting of
Consider operation of a single pass cross-flow heat exchanger with water (cp = 4193 J/kg·K) (mixed) and methanol (cp = 2577 J/kg·K) (unmixed). Water entering and exiting the heat exchanger at 90°C
Consider a recuperative cross-flow heat exchanger (both fluids unmixed) used in a gas turbine system that carries the exhaust gases at a flow rate of 7.5 kg/s and a temperature of 500°C. The air
Oil in an engine is being cooled by air in a crossflow heat exchanger, where both fluids are unmixed. Oil (cph= 2047 J/kg·K) flowing with a flow rate of 0.026 kg/s enters the heat exchanger at
A cross-flow air-to-water heat exchanger with an effectiveness of 0.65 is used to heat water (cp = 4180 J/kg·K) with hot air (cp = 1010 J/kg·K). Water enters the heat exchanger at 20°C at a rate
A cross-flow heat exchanger with both fluids unmixed has an overall heat transfer coefficient of 200 W/m2·K, and a heat transfer surface area of 400 m2. The hot fluid has a heat capacity of 40,000
Air (cp = 1005 J/kg·K) enters a cross-flow heat exchanger at 20°C at a rate of 3 kg/s, where it is heated by a hot water stream (cp = 4190 J/kg·K) that enters the heat exchanger at 70°C at a rate
In a one-shell and eight-tube pass heat exchanger, the temperature of water flowing at rate of 50,000 lbm/h is raised from 70°F to 150°F. Hot air (cp = 0.25 Btu/lbm·°F) that flows on the tube
A shell-and-tube heat exchanger with 2-shell passes and 8-tube passes is used to heat ethyl alcohol (cp = 2670 J/kg·K) in the tubes from 25°C to 70°C at a rate of 2.1 kg/s. The heating is to be
Oil is being cooled from 180°F to 120°F in a 1-shell and 2-tube heat exchanger with an overall heat transfer coefficient of 40 Btu/h·ft2·°F. Water (cpc= 1.0
A shell-and-tube heat exchanger with 2-shell passes and 12-tube passes is used to heat water (cp = 4180 J/kg·K) with ethylene glycol (cp = 2680 J/kg·K). Water enters the tubes at 22°C at a rate of
Ethylene glycol is heated from 25°C to 40°C at a rate of 2.5 kg/s in a horizontal copper tube (k = 386 W/m·K) with an inner diameter of 2.0 cm and an outer diameter of 2.5 cm. A saturated vapor
A double-pipe parallel-flow heat exchanger is to heat water (cp = 4180 J/kg·K) from 25°C to 60°C at a rate of 0.2 kg/s. The heating is to be accomplished by geothermal water (cp = 4310 J/kg·K)
How is the thermal resistance due to fouling in a heat exchanger accounted for? How do the fluid velocity and temperature affect fouling?
In a one-shell and two-tube heat exchanger, cold water with inlet temperature of 20°C is heated by hot water supplied at the inlet at 80°C. The cold and hot water flow rates are 5000 kg/h and
A one-shell and two-tube type heat exchanger has an overall heat transfer coefficient of 300 Btu/h·ft2·°F. The shell side fluid has a heat capacity rate of 20,000 Btu/h·°F, while the tube side
A thin-walled double-pipe, counter-flow heat exchanger is to be used to cool oil (cp = 0.525 Btu/lbm·°F) from 300°F to 105°F at a rate of 5 lbm/s by water (cp = 1.0 Btu/lbm·°F) that enters at
Reconsider Prob. 22€“87. Using an appropriate software, investigate the effects of the inlet temperature of hot water and the heat transfer coefficient on the rate of heat transfer and the
Cold water (cp= 4180 J/kg·K) leading to a shower enters a thin-walled double-pipe counter-flow heat exchanger at 15°C at a rate of 0.25 kg/s and is heated to 45°C by hot water (cp=
Reconsider Prob. 22–85. Using an appropriate software, investigate the effects of the mass flow rate of water and the tube length on the outlet temperatures of water and air. Let the mass flow rate
Water (cp = 4180 J/kg·K) is to be heated by solarheated hot air (cp = 1010 J/kg·K) in a double-pipe counter-flow heat exchanger. Air enters the heat exchanger at 90°C at a rate of 0.3 kg/s, while
Hot water (cph = 4188 J/kg·K) with mass flow rate of 2.5 kg/s at 100°C enters a thin-walled concentric tube counter-flow heat exchanger with a surface area of 23 m2 and an overall heat transfer
Hot water enters a double-pipe counter-flow waterto-oil heat exchanger at 190°F and leaves at 100°F. Oil enters at 70°F and leaves at 130°F. Determine which fluid has the smaller heat capacity
Consider an oil-to-oil double-pipe heat exchanger whose flow arrangement is not known. The temperature measurements indicate that the cold oil enters at 20°C and leaves at 55°C, while the hot oil
The radiator in an automobile is a cross-flow heat exchanger (UAs = 10 kW/K) that uses air (cp = 1.00 kJ/kg·K) to cool the engine-coolant fluid (cp = 4.00 kJ/kg·K). The engine fan draws 30°C air
Consider a heat exchanger that has an NTU of 0.1. Someone proposes to triple the size of the heat exchanger and thus triple the NTU to 0.3 in order to increase the effectiveness of the heat exchanger
Consider a heat exchanger that has an NTU of 4. Someone proposes to double the size of the heat exchanger and thus double the NTU to 8 in order to increase the effectiveness of the heat exchanger and
How is the NTU of a heat exchanger defined? What does it represent? Is a heat exchanger with a very large NTU (say, 10) necessarily a good one to buy?
Consider two double-pipe counter-flow heat exchangers that are identical except that one is twice as long as the other one. Which heat exchanger is more likely to have a higher effectiveness?
Consider a shell-and-tube water-to-water heat exchanger with identical mass flow rates for both the hot- and cold-water streams. Now the mass flow rate of the cold water is reduced by half. Will the
Consider a double-pipe counter-flow heat exchanger. In order to enhance heat transfer, the length of the heat exchanger is now doubled. Do you think its effectiveness will also double?
Under what conditions can a counter-flow heat exchanger have an effectiveness of one? What would your answer be for a parallel-flow heat exchanger?
Explain how the maximum possible heat transfer rate Qmax in a heat exchanger can be determined when the mass flow rates, specific heats, and the inlet temperatures of the two fluids are specified.
Consider a heat exchanger in which both fluids have the same specific heats but different mass flow rates. Which fluid will experience a larger temperature change: the one with the lower or higher
Can the temperature of the cold fluid rise above the inlet temperature of the hot fluid at any location in a heat exchanger? Explain.
Explain how you can evaluate the outlet temperatures of the cold and hot fluids in a heat exchanger after its effectiveness is determined.
For a specified fluid pair, inlet temperatures, and mass flow rates, what kind of heat exchanger will have the highest effectiveness: double-pipe parallel-flow, double-pipe counterflow, cross-flow,
What does the effectiveness of a heat exchanger represent? Can effectiveness be greater than one? On what factors does the effectiveness of a heat exchanger depend?
A single-pass cross-flow heat exchanger is used to cool jacket water (cp= 1.0 Btu/lbm·°F) of a diesel engine from 190°F to 140°F, using air (cp= 0.245 Btu/lbm·°F) with
A shell-and-tube heat exchanger with 2-shell passes and 8-tube passes is used to heat ethyl alcohol (cp= 2670 J/kg·K) in the tubes from 25°C to 70°C at a rate of 2.1 kg/s. The heating
Repeat Prob. 22–64 for a mass flow rate of 3 kg/s for water.Repeat Prob.A shell-and-tube heat exchanger with 2-shell passes and 12-tube passes is used to heat water (cp = 4180 J/kg·K) in the tubes
A shell-and-tube heat exchanger with 2-shell passes and 12-tube passes is used to heat water (cp = 4180 J/kg·K) in the tubes from 20°C to 70°C at a rate of 4.5 kg/s. Heat is supplied by hot oil
Reconsider Prob. 22–62. Using an appropriate software, investigate the effect of the mass flow rate of water on the rate of heat transfer and the tubeside surface area. Let the mass flow rate vary
A shell-and-tube heat exchanger is used for heating 10 kg/s of oil (cp = 2.0 kJ/kg·K) from 25°C to 46°C. The heat exchanger has 1-shell pass and 6-tube passes. Water enters the shell side at 80°C
A test is conducted to determine the overall heat transfer coefficient in a shell-and-tube oil-to-water heat exchanger that has 24 tubes of internal diameter 1.2 cm and length 2 m in a single shell.
In an industrial facility a counter-flow double-pipe heat exchanger uses superheated steam at a temperature of 250°C to heat feed water at 30°C. The superheated steam experiences a
A performance test is being conducted on a doublepipe counter-flow heat exchanger that carries engine oil and water at a flow rate of 2.5 kg/s and 1.75 kg/s, respectively. Since the heat exchanger
In a textile manufacturing plant, the waste dyeing water (cp= 4295 J/kg·K) at 75°C is to be used to preheat fresh water (cp= 4180 J/kg·K) at 15°C at the same flow rate in a
Reconsider Prob. 22–54. Using an appropriate software, investigate the effect of the exhaust gas inlet temperature on the rate of heat transfer, the exit temperature of exhaust gases, and the rate
Hot exhaust gases of a stationary diesel engine are to be used to generate steam in an evaporator. Exhaust gases (cp = 1051 J/kg·K) enter the heat exchanger at 550°C at a rate of 0.25 kg/s while
Reconsider Prob. 22€“52E. Using an appropriate software, investigate the effect of the condensing steam temperature on the rate of heat transfer, the rate of condensation of steam, and the
Steam is to be condensed on the shell side of a 1-shell-pass and 8-tube-passes condenser, with 50 tubes in each pass at 90°F (hfg= 1043 Btu/lbm). Cooling water (cp= 1.0 Btu/lbm·°F)
Cold water (cp = 4180 J/kg·K) leading to a shower enters a thin-walled double-pipe counter-flow heat exchanger at 15°C at a rate of 1.25 kg/s and is heated to 45°C by hot water (cp = 4190 J/kg·K)
Reconsider Prob. 22–49. Using an appropriate software, investigate the effects of oil exit temperature and water inlet temperature on the overall heat transfer coefficient of the heat exchanger.
A thin-walled double-pipe counter-flow heat exchanger is to be used to cool oil (cp = 2200 J/kg·K) from 150°C to 40°C at a rate of 2 kg/s by water (cp = 4180 J/kg·K) that enters at 22°C at a
A counter-flow heat exchanger is stated to have an overall heat transfer coefficient of 284 W/m2·K when operating at design and clean conditions. Hot fluid enters the tube side at 93°C and
In a parallel flow heat exchanger, hot fluid enters the heat exchanger at a temperature of 150°C and a mass flow rate of 3 kg/s. The cooling medium enters the heat exchanger at a temperature of
Consider the flow of engine oil (cp= 2048 J/kg·K) through a thin-walled copper tube at a rate of 0.3 kg/s. The engine oil that enters the copper tube at an inlet temperature of 80°C is to
A single pass heat exchanger is to be designed to heat 100,000 lbm of water in an hour from 60°F to 100°F by condensation of water vapor at 230°F on the shell side. Each tube has an inner diameter
A heat exchanger contains 400 tubes with inner diameter of 23 mm and outer diameter of 25 mm. The length of each tube is 3.7 m. The corrected log mean temperature difference is 23°C, while the inner
Glycerin (cp = 2400 J/kg·K) at 20°C and 0.5 kg/s is to be heated by ethylene glycol (cp = 2500 J/kg·K) at 60°C in a thin-walled double-pipe parallel-flow heat exchanger. The temperature
Reconsider Prob. 22–40. Using an appropriate software, investigate the effects of temperature and mass flow rate of geothermal water on the length of the tube. Let the temperature vary from 100°C
A stream of hydrocarbon (cp = 2.2 kJ/kg·K) is cooled at a rate of 720 kg/h from 150°C to 40°C in the tube side of a double-pipe counter-flow heat exchanger. Water (cp = 4.18 kJ/ kg·K) enters the
A double-pipe parallel-flow heat exchanger is used to heat cold tap water with hot water. Hot water (cp= 4.25 kJ/kg·K) enters the tube at 85°C at a rate of 1.4 kg/s and leaves at 50°C.
For specified inlet and outlet temperatures, for what kind of heat exchanger will the ΔTlm be greatest: double-pipe parallel-flow, double-pipe counter-flow, cross-flow, or multipass shell-and-tube
When the outlet temperatures of the fluids in a heat exchanger are not known, is it still practical to use the LMTD method? Explain.
In the heat transfer relation Q = UAsFΔTlm for a heat exchanger, what is the quantity F called? What does it represent? Can F be greater than one?
Explain how the LMTD method can be used to determine the heat transfer surface area of a multipass shelland-tube heat exchanger when all the necessary information, including the outlet temperatures,
Can the outlet temperature of the cold fluid in a heat exchanger be higher than the outlet temperature of the hot fluid in a parallel-flow heat exchanger? How about in a counter-flow heat exchanger?
The temperature difference between the hot and cold fluids in a heat exchanger is given to be ΔT1 at one end and ΔT2 at the other end. Can the logarithmic temperature difference ΔTlm of this heat
How does the log mean temperature difference for a heat exchanger differ from the arithmetic mean temperature difference? For specified inlet and outlet temperatures, which one of these two
In the heat transfer relation Q = UAs ΔTlm for a heat exchanger, what is ΔTlm called? How is it calculated for a parallel-flow and counter-flow heat exchanger?
Show that the temperature profile of two fluid streams (hot and cold) that have the same heat capacity rates is parallel to each other at every section of the counter flow heat exchanger.
Under what conditions will the temperature rise of the cold fluid in a heat exchanger be equal to the temperature drop of the hot fluid?
What is the heat capacity rate? What can you say about the temperature changes of the hot and cold fluids in a heat exchanger if both fluids have the same capacity rate? What does a heat capacity of
Consider a condenser in which steam at a specified temperature is condensed by rejecting heat to the cooling water. If the heat transfer rate in the condenser and the temperature rise of the cooling
Under what conditions is the heat transfer relation valid for a heat exchanger? Q = mc„(T_ out - Tin) = m,C4 (T, in – T, cu pe C, out ph h.
What are the common approximations made in the analysis of heat exchangers?
Hot engine oil with heat capacity rate of 4440 W/K (product of mass flow rate and specific heat) and an inlet temperature of 150°C flows through a double pipe heat exchanger. The double pipe heat
Reconsider Prob. 22–21. Using an appropriate software, plot the overall heat transfer coefficient based on the inner surface as a function of fouling factor as it varies from 0.0001 m2·K/W to
Repeat Prob. 22–20, assuming a fouling factor Rf, i = 0.0005 m2·K/W on the inner surface of the tube.Repeat Prob.Water at an average temperature of 110°C and an average velocity of 3.5 m/s flows
Water at an average temperature of 110°C and an average velocity of 3.5 m/s flows through a 5-m-long stainless steel tube (k = 14.2 W/m·K) in a boiler. The inner and outer diameters of the tube are
A counter-flow heat exchanger is stated to have an overall heat transfer coefficient, based on outside tube area of 50 Btu/h·ft2·°F when operating at design and clean conditions. After a period of
A jacketted-agitated vessel, fitted with a turbine agitator, is used for heating a water stream from 10°C to 54°C. The average heat transfer coefficient for water at the vessel’s inner-wall can
Water at an average temperature of 180°F and an average velocity of 4 ft/s flows through a thin-walled 3/4-indiameter tube. The water is cooled by air that flows across the tube with a velocity of
Reconsider Prob. 22–15. Using an appropriate software, plot the overall heat transfer coefficient as a function of the limestone thickness as it varies from 1 mm to 3 mm and discuss the
Repeat Prob. 22–14 by assuming a 2-mm-thick layer of limestone (k = 1.3 W/m·K) forms on the outer surface of the inner tube.Repeat Prob.A long thin-walled double-pipe heat exchanger with tube and
A long thin-walled double-pipe heat exchanger with tube and shell diameters of 1.0 cm and 2.5 cm, respectively, is used to condense refrigerant-134a by water at 20°C. The refrigerant flows through
The tube in a heat exchanger has a 2-in inner diameter and a 3-in outer diameter. The thermal conductivity of the tube material is 0.5 Btu/h·ft·°F, while the inner surface heat transfer
Under what conditions can the overall heat transfer coefficient of a heat exchanger be determined from U = (1/hi + 1/ho)-1?
What are the common causes of fouling in a heat exchanger? How does fouling affect heat transfer and pressure drop?
In a thin-walled double-pipe heat exchanger, when is the approximation U = hi a reasonable one? Here U is the overall heat transfer coefficient and hi is the convection heat transfer coefficient
Consider a double-pipe parallel-flow heat exchanger of length L. The inner and outer diameters of the inner tube are D1 and D2, respectively, and the inner diameter of the outer tube is D3. Explain
Under what conditions is the thermal resistance of the tube in a heat exchanger negligible?
What are the heat transfer mechanisms involved during heat transfer in a liquid-to-liquid heat exchanger from the hot to the cold fluid?
How does a cross-flow heat exchanger differ from a counter-flow one? What is the difference between mixed and unmixed fluids in cross-flow?

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