Question: Reconsider Prob. 21–88. Using appropriate software,

> Under what conditions is the thermal resistance of the tube in a heat exchanger negligible?

> Can the temperature of the hot fluid drop below the inlet temperature of the cold 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, crossflow, or multipass shell-and-tube heat exchanger?

> What does the effectiveness of a heat exchanger represent? Can effectiveness be greater than 1? On what factors does the effectiveness of a heat exchanger depend?

> A single-pass crossflow 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 an in

> A shell-and-tube heat exchanger with two shell passes and eight 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 done by water

> Repeat Prob. 22–62 for a mass flow rate of 3 kg/s for water. Data from Prob. 22-62: A shell-and-tube heat exchanger with two 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. H

> Complete this table for refrigerant-134a:

> A shell-and-tube heat exchanger with two 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 (cp = 2300 J/kg⋅K) that enters the shell side at 170°C at

> Reconsider Prob. 22–60. Using appropriate software, investigate the effect of the mass flow rate of water on the rate of heat transfer and the tube-side surface area. Let the mass flow rate vary from 0.4 kg/s to 2.2 kg/s. Plot the rate of heat transfer a

> A shell-and-tube heat exchanger with two 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 0.8 kg/s and leaves at 70°C. Ethylene glycol enters the

> What are the heat transfer mechanisms involved during heat transfer in a liquid-to-liquid heat exchanger from the hot to the cold fluid?

> A one-shell-pass and eight-tube-passes heat exchanger is used to heat glycerin (cp = 0.60 Btu/lbm⋅°F) from 80°F to 140°F by hot water (cp = 1.0 Btu/lbm⋅°F) that enters the thin-walled 0.5-in-diameter tubes at 175°F and leaves at 120°F. The total length o

> A shell-and-tube heat exchanger is used for heating 14 kg/s of oil (cp = 2.0 kJ/kg⋅K) from 20°C to 46°C. The heat exchanger has one shell pass and six tube passes. Water enters the shell side at 80°C and leaves at 60°C. The overall heat transfer coeffici

> 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. Cold water (cp = 4180 J/kg⋅K) enters the tubes at 20°C

> In an industrial facility, a counterflow double-pipe heat exchanger uses superheated steam at a temperature of 250°C to heat feedwater at 30°C. The superheated steam experiences a temperature drop of 70°C as it exits the

> A performance test is being conducted on a double-pipe counterflow 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 has been in service for a long time, it is suspected that

> In a textile manufacturing plant, the waste dyeing water (cp = 4295 J/kg⋅K) at 80°C is to be used to preheat fresh water (cp = 4180 J/kg⋅K) at 10°C at the same flow rate in a double-pipe counterfl

> Complete this table for H2O:

> Reconsider Prob. 22–52. Using 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 of evaporation of water. Let the temperature of exhaust gase

> 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 water enters as saturated liquid and evaporates at 200°C (h

> Reconsider Prob. 22–50E. Using appropriate software, investigate the effect of the condensing steam temperature on the rate of heat transfer, the rate of condensation of steam, and the mass flow rate of the cold water. Let the steam tem

> Steam is to be condensed on the shell side of a one-shell pass and eight-tube-passes condenser, with 60 tubes in each pass at 90°F(hfg = 1043 Btu/lbm). Cooling water (cp = 1.0 Btu/lbm⋅°F) enters the tubes at 55&Aci

> How does a crossflow heat exchanger differ from a counterflow one? What is the difference between mixed and unmixed fluids in crossflow?

> Reconsider Prob. 21–97. Using appropriate software, investigate the effects of the side length and the emissivity of the cubic enclosure, and the emissivity of the spherical tank on the net rate of radiation heat transfer. Let the side

> Repeat Prob. 21–97 by replacing the cubic enclosure with a spherical enclosure whose diameter is 3 m. Data from Prob. 21-97: A spherical tank of diameter D = 2 m that is filled with liquid nitrogen at 100 K is kept in an evacuated cubi

> Cold water (cp = 4180 J/kg⋅K) leading to a shower enters a thin-walled double-pipe counterflow heat exchanger at 15°C at a rate of 1.25 kg/s and is heated to 60°C by hot water (cp = 4190J/kg⋅K) that enters at 100°C at a rate of 4 kg/s. If the overall hea

> A spherical tank of diameter D = 2 m that is filled with liquid nitrogen at 100 K is kept in an evacuated cubic enclosure whose sides are 3 m long. The emissivities of the spherical tank and the enclosure are ε1 = 0.1 and ε2 = 0

> Reconsider Prob. 22–47. Using appropriate software, investigate the effects of oil exit temperature and water inlet temperature on the overall heat transfer coefficient of the heat exchanger. Let the oil exit temperature vary from 30°C to 70°C and the wa

> Reconsider Prob. 4–22E. Using appropriate software, determine the missing properties of water. Repeat the solution for refrigerant-22, and ammonia. Data from Prob. 4-22E: Complete this table for H2O:

> Two concentric spheres of diameters D1 = 0.3 m and D2 = 0.6 m are maintained at uniform temperatures T1 = 800 K and T2 = 500 K and have emissivities ε1 = 0.5 and ε2 = 0.7, respectively. Determine the net rate of radiation heat transfer between the two sp

> A thin-walled double-pipe counterflow heat exchanger is to be used to cool oil (cp = 2200 J/kg⋅K) from 150°C to 50°C at a rate of 2.5 kg/s with water (cp = 4180 J/kg⋅K) that enters at 22°C at a rate of 1.5 kg/s. The diameter of the tube is 2.5 cm, and it

> Liquid nitrogen is stored in a spherical tank of 1 m diameter where the tank surface is maintained uniformly at 80 K. The spherical tank is enclosed by a 1.6-m-diameter concentric sphere with uniform surface temperature of 273 K. Both spherical surfaces

> A counterflow 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 exits at 71°C, while cold

> This experiment is conducted to determine the emissivity of a certain material. A long cylindrical rod of diameter D1 = 0.01 m is coated with this new material and is placed in an evacuated long cylindrical enclosure of diameter D2 = 0.1 m and emissivity

> 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 (Tg = 110°C) condenses on the outside-tube surface with the

> Two very long concentric cylinders of diameters D1 = 0.35 m and D2 = 0.5 m are maintained at uniform temperatures of T1 = 950 K and T2 = 500 K and have emissivities ε1 = 1 and ε2 = 0.55, respectively. Determine the net rate of radiation heat transfer bet

> 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 30°C with a mass flow rate of 0.5 kg/s and leaves at a tempe

> Air is flowing between two infinitely large parallel plates. The upper plate is at 500 K and has an emissivity of 0.7, while the lower plate is a black surface with temperature at 330 K. If the air temperature is 290 K, determine the convection heat tran

> 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 be cooled by cold water (cp = 4180 J

> Determine a positive real root of this equation using appropriate software: 2x3 − 10x0.5 − 3x = −3

> A furnace is shaped like a long semicylindrical duct of diameter D = 15 ft. The base and the dome of the furnace have emissivities of 0.5 and 0.9 and are maintained at uniform temperatures of 550 and 1800 R, respectively. Determine the net rate of radiat

> 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 of 1.2 in and a wall thickness of 0.12 in. The inner surf

> Consider a 30-cm-diameter hemispherical enclosure. The dome is maintained at 600 K, and heat is supplied from the dome at a rate of 65 W while the base surface with an emissivity of 0.55 is maintained at 400 K. Determine the emissivity of the dome.

> 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 surface convection heat transfer coefficient is 3410 W/

> Electricity is generated and transmitted in power lines at a frequency of 50 Hz (1 Hz = 1 cycle per second). Determine the wavelength of the electromagnetic waves generated by the passage of electricity in power lines.

> 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 70°C in a thin walled double-pipe parallel flow heat exchanger. The temperature difference between the two fluids is 15°C at the outlet of the heat

> What is the role of the baffles in a shell-and-tube heat exchanger? How does the presence of baffles affect the heat transfer and the pumping power requirements? Explain.

> A furnace is shaped like a long equilateral-triangular duct where the width of each side is 2 m. Heat is supplied from the base surface, whose emissivity is ε1 = 0.8, at a rate of 800 W/m2 while the side surfaces, whose emissivities are 0.4, are maintain

> Reconsider Prob. 22–38. Using 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 to 200°C, and the mass flow rate from 0.1 kg/s to 0.5 kg/s. P

> Complete this table for H2O:

> Consider two rectangular surfaces perpendicular to each other with a common edge that is 1.6 m long. The horizontal surface is 0.8 m wide, and the vertical surface is 1.2 m high. The horizontal surface has an emissivity of 0.75 and is maintained at 450 K

> 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) available at 140°C at a mass flow rate of 0.3 kg/s. The inner

> Two long, parallel 20-cm-diameter cylinders are located 30 cm apart from each other. Both cylinders are black and are maintained at temperatures 425 K and 275 K. The surroundings can be treated as a blackbody at 300 K. For a 1-m-long section of the cylin

> 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 counterflow heat exchanger. Water (cp = 4.18 kJ/kg⋅K) enters the heat exchanger at 10°C at a rate of 540 kg/h. The outside dia

> Two infinitely long parallel plates of width w are located at w distance apart, as shown in Fig. The two plates behave as black surfaces, where surface A1 has a temperature of 700 K and surface A2 has a temperature of 300 K. Determine the radiation heat

> 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. The heat exchanger is not we

> Two parallel disks of diameter D = 3 ft separated by L = 2 ft are located directly on top of each other. The disks are separated by a radiation shield whose emissivity is 0.15. Both disks are black and are maintained at temperatures of 1350 R and 650 R,

> For specified inlet and outlet temperatures, for what kind of heat exchanger will the ΔTlm be greatest: double-pipe parallel-flow, double-pipe counterflow, crossflow, or multipass shell-and tube heat exchanger?

> Two parallel black disks are positioned coaxially at a distance of 0.25 m apart in surroundings with a constant temperature of 300 K. The lower disk is 0.2 m in diameter and the upper disk is 0.4 m in diameter. If the lower disk is heated electrically at

> 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 1?

> A perfectly fitting pot and its lid often stick after cooking, and it becomes very difficult to open the lid when the pot cools down. Explain why this happens and what you would do to open the lid.

> Consider a hemispherical furnace of diameter D = 5 m with a flat base, as shown in Fig. The dome of the furnace is black, and the base has an emissivity of 0.7. The base and the dome of the furnace are maintained at uniform temperatures of 400 and 1000 K

> Explain how the LMTD method can be used to determine the heat transfer surface area of a multipass shell-and-tube heat exchanger when all the necessary information, including the outlet temperatures, is given.

> Two parallel disks of diameter D = 0.6 m separated by L = 0.4 m are located directly on top of each other. Both disks are black and are maintained at a temperature of 450 K. The back sides of the disks are insulated, and the environment that the disks ar

> 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 counterflow heat exchanger? Explain.

> A furnace is of cylindrical shape with R = H = 3 m. The base, top, and side surfaces of the furnace are all black and are maintained at uniform temperatures of 500, 700, and 1400 K, respectively. Determine the net rate of radiation heat transfer to or fr

> 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 exchanger be greater than both ΔT1 and ΔT2? Explain.

> How do ultraviolet and infrared radiation differ? Do you think your body emits any radiation in the ultraviolet range? Explain.

> 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 quantities is larger?

> A dryer is shaped like a long semicylindrical duct of diameter 1.5 m. The base of the dryer is occupied with water soaked materials to be dried. The base is maintained at a temperature of 370 K, while the dome of the dryer is maintained at 1000 K. If bot

> What is a regenerative heat exchanger? How does a static type of regenerative heat exchanger differ from a dynamic type?

> Is iced water a pure substance? Why?

> The room shown in Fig. P21–78E is 20 ft by 20 ft wide and 9 ft high. The floor is at 100°F, the walls are at 60°F, and the ceiling is at 40°F. All surfaces are assumed to be black. Calculate the net radi

> 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 a counterflow heat exchanger?

> Two black parallel rectangles with dimensions 3 ft × 5 ft are spaced apart by a distance of 1 ft. The two parallel rectangles are experiencing radiation heat transfer as black surfaces, where the top rectangle receives a total of 180,000 Btu

> 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?

> Reconsider Prob. 21–75. Using appropriate software, evaluate the effect of the distance L between the black coaxial parallel disks (D = 1 m) on the radiation heat transfer coefficient. By varying the distance L between the disks from 0.

> 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 infinity for a fluid in a heat exchanger mean?

> Consider two black coaxial parallel circular disks of equal diameter D that are spaced apart by a distance L. The top and bottom disks have uniform temperatures of 500°C and 520°C, respectively. Determine the radiation heat transfer

> 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 water are known, explain how the rate of condensation o

> Consider a person whose exposed surface area is 1.9 m2, emissivity is 0.85, and surface temperature is 30°C. Determine the rate of heat loss from that person by radiation in a large room whose walls are at a temperature of (a) 295 K and (b) 260 K.

> Under what conditions is the heat transfer relation valid for a heat exchanger?

> In the absence of compressed liquid tables, how is the specific volume of a compressed liquid at a given P and T determined?

> What are the two methods used in radiation analysis? How do these two methods differ?

> What are the common approximations made in the analysis of heat exchangers?

> What is a reradiating surface? What simplifications does a reradiating surface offer in the radiation analysis?

> Hot engine oil with a 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 exchanger is constructed of a 1.5-m-long copper pipe (k

> What are the radiation surface and space resistances? How are they expressed? For what kinds of surfaces is the radiation surface resistance zero?

> Reconsider Prob. 22–21. Using 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 0.0008 m2⋅K/W, and discuss the results. Data from Prob. 22-21: R

> How does radiosity for a surface differ from the emitted energy? For what kinds of surfaces are these two quantities identical?

> Repeat Prob. 22–20, assuming a fouling factor Rf, i = 0.0005 m2⋅K/W on the inner surface of the tube. Data from Prob. 22-20: Water at an average temperature of 110°C and an average velocity of 3.5 m/s flows through a 7 m-long stainless steel tube (k = 1

> Why do skiers get sunburned so easily?

> Water at an average temperature of 110°C and an average velocity of 3.5 m/s flows through a 7 m-long stainless steel tube (k = 14.2 W/m⋅K) in a boiler. The inner and outer diameters of the tube are Di = 1.0 cm and Do = 1.4 cm, respectively. If the convec

> It is well known that warm air in a cooler environment rises. Now consider a warm mixture of air and gasoline on top of an open gasoline can. Do you think this gas mixture will rise in a cooler environment?

> Why is the radiation analysis of enclosures that consist of black surfaces relatively easy? How is the rate of radiation heat transfer between two surfaces expressed in this case?

> When is a heat exchanger classified as being compact? Do you think a double-pipe heat exchanger can be classified as a compact heat exchanger?

> Two infinitely long parallel cylinders of diameter D are located a distance s apart from each other. Determine the view factor F12 between these two cylinders.

> A counterflow 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 use, scale buildup in the heat exchanger gives a fouling fa