Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)
8th Edition
ISBN: 9781305387102
Author: Kreith, Frank; Manglik, Raj M.
Publisher: Cengage Learning
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Chapter 2, Problem 2.45P
Heat is transferred from water to air through a brass wall
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A hot surface at 100°C is to be cooled by attaching 3-cm-long, 0.25-cm-diameter aluminum pin fins (k = 237 W/m·K) to it, with a center-to-center distance of 0.6 cm. The temperature of the surrounding medium is 30°C, and the heat transfer coefficient on the surfaces is 35 W/m2 ·K. Determine the rate of heat transfer from the surface for a 1-m x 1-m section of the plate. Also determine the overall effectiveness of the fins.
Consider a closed cylindrical reactor vessel of diameter D= 1 ft, and length L= 1.5 ft. The surface temperature of the vessel, T1, and the surrounding temperature, T2, are 390 deg. F and 50 deg. F, respectively. The convective heat transfer coefficient, h, between the vessel wall and surrounding fluid is 4.0 Btu/h . ft . ⁰F. Calculate the thermal resistance in ⁰F .h/Btu.
Two pin fins are identical, except that the diameter of one of them is twice the diameter of the other. For which fin is the (a) fin effectiveness and (b) fin efficiency higher? Explain.
Chapter 2 Solutions
Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)
Ch. 2 - A plane wall, 7.5 cm thick, generates heat...Ch. 2 -
2.2 A small dam, which is idealized by a large...Ch. 2 - 2.3 The shield of a nuclear reactor is idealized...Ch. 2 - A plane wall 15 cm thick has a thermal...Ch. 2 - 2.5 Derive an expression for the temperature...Ch. 2 - A plane wall of thickness 2L has internal heat...Ch. 2 - 2.7 A very thin silicon chip is bonded to a 6-mm...Ch. 2 - 2.9 In a large chemical factory, hot gases at 2273...Ch. 2 - 2.14 Calculate the rate of heat loss per foot and...Ch. 2 - 2.15 Suppose that a pipe carrying a hot fluid with...
Ch. 2 - Prob. 2.16PCh. 2 - Estimate the rate of heat loss per unit length...Ch. 2 - The rate of heat flow per unit length q/L through...Ch. 2 - A 2.5-cm-OD, 2-cm-ID copper pipe carries liquid...Ch. 2 - A cylindrical liquid oxygen (LOX) tank has a...Ch. 2 - Show that the rate of heat conduction per unit...Ch. 2 - Derive an expression for the temperature...Ch. 2 - Heat is generated uniformly in the fuel rod of a...Ch. 2 - 2.29 In a cylindrical fuel rod of a nuclear...Ch. 2 - 2.30 An electrical heater capable of generating...Ch. 2 - A hollow sphere with inner and outer radii of R1...Ch. 2 - 2.34 Show that the temperature distribution in a...Ch. 2 -
2.38 The addition of aluminum fins has been...Ch. 2 - The tip of a soldering iron consists of a 0.6-cm-...Ch. 2 - One end of a 0.3-m-long steel rod is connected to...Ch. 2 - Both ends of a 0.6-cm copper U-shaped rod are...Ch. 2 - 2.42 A circumferential fin of rectangular cross...Ch. 2 - 2.43 A turbine blade 6.3 cm long, with...Ch. 2 - 2.44 To determine the thermal conductivity of a...Ch. 2 - 2.45 Heat is transferred from water to air through...Ch. 2 - 2.46 The wall of a liquid-to-gas heat exchanger...Ch. 2 - Prob. 2.47PCh. 2 - The handle of a ladle used for pouring molten lead...Ch. 2 - 2.50 Compare the rate of heat flow from the bottom...Ch. 2 - 2.51 Determine by means of a flux plot the...Ch. 2 - Prob. 2.52PCh. 2 - Determine the rate of heat transfer per meter...Ch. 2 - Prob. 2.54PCh. 2 - 2.55 A long, 1-cm-diameter electric copper cable...Ch. 2 - Prob. 2.56PCh. 2 - Prob. 2.57PCh. 2 - Prob. 2.58P
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- Calculate the quantity of heat conducted per minute through a duralumin circular disc 119mm diameter and 22.65mm thick when the temperature drop across the thickness of the plate is 9.3°F take the coefficient of thermal conductivity of duralumin as 150 W/m-K. Answer: 22.833 kJ/minarrow_forwardCircular fins of uniform cross section, with diameter of 10 mm and length of 50 mm, are attached to a wall with surface temperature of 350°C. The fins are made of material with thermal conductivity of 240 W/m·K, and they are exposed to an ambient air condition of 25°C and the convection heat transfer coefficient is 250 W/m2·K. Determine the heat transfer rate and plot the temperature variation of a single fin for the following boundary conditions: (a) Infinitely long fin (b) Adiabatic fin tip (c) Fin with tip temperature of 250°C (d) Convection from the fin tiparrow_forwardThere are 3 windows in a room with a width of 100 cm and a height of 150 cm.There is a single glass (k=0. 9 W/mK) of 5 mm thickness in the windows initially. Instead of these glasses to save heatYou are considering replacing it with double glazing consisting of 5 mm glass and 12 mm air (k=0.022 W/mK). Indoor and outdoor environmenttemperatures are 20 0C and -10 0C, respectively, and the heat transfer coefficients are 7 W/m2 K and 25 W/m2 K. The total heat loss in the room is 3.5 kW.when switching to double glazing;a) Find the decrease in heat transfer. b) Considering that the heat given by the heaters remains 3.5 kW, what would the room temperature be?arrow_forward
- 2. A 15-cm X 20-cm hot surface at 85°C is to be cooled by attaching 4 cm-long aluminum (k = 237 W/m-°C) fins of 2-mm X 2-mm square cross section. The temperature of surrounding medium is 25°C and the heat transfer coefficient on the surfaces can be taken to be 20 W/m2-°C. If it is desired to triple the rate of heat transfer from the bare hot surface, determine the number of fins that needs to be attached.arrow_forwardA 50-meter-long cast iron pipe with a 10-centimeter outside diameter goes through a 288 K temperature open environment. The temperature of the pipe's outer surface is 423 K, and the combined heat transfer coefficient on the pipe's outside surface is 25 W/m2 K. Considering and stating the necessary assumptions determine,(a) The rate of heat loss from the pipe (b) The energy lost per year if the cost of the fuel is 0.52 $/therm ( 1 therm = 105,500 kJ) c) The thickness of the insulation if 98% of the energy loss is planned to be saved. Consider the conduction coefficient of the insulation is 0.035 W/mK.arrow_forwardA 50-meter-long cast iron pipe with a 10-centimeter outside diameter goes through a 288 K temperature open environment. The temperature of the pipe's outer surface is 423 K, and the combined heat transfer coefficient on the pipe's outside surface is 25 W/m2 K. Considering and stating the necessary assumptions determine, (5 marks) (a) The rate of heat loss from the pipe (b) The energy lost per year if the cost of the fuel is 0.52 $/therm ( 1 therm = 105,500 kJ) c) The thickness of the insulation if 98% of the energy loss is planned to be saved. Consider the conduction coefficient of the insulation is 0.035 W/mK.arrow_forward
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- The 4-mm-thick rear window of an automobile is defogged by passing warm air over its inner surface. Warm air temperature is at T,1 = 40C and corresponding convection coefficient is h1 =30 W/(m2·K). Outer ambient temperature T,2 = 5C and corresponding convection coefficient is h2 = 70 W/(m2·K). The size of the window is 0.5 m (height) 1.5 m (width). A. Draw two thermal circuits (one based on heat rate and one based on heat flux) considering the convection occurring over inner and outer surfaces and the conduction through the window. Show the equations for the thermal resistances in the circuits.B. Determine the total thermal resistance based on heat flux in m2K/W andoverall heat transfer coefficient U in W/m2K. Find the thermal conductivity of glass (sodalime at 300K)C. Determine the inner and outer temperatures of the glass (that are Ts,1 and Ts,2 shown above).arrow_forwardA 2 m X 1.5 m section of wall of an industrial furnace burning gas is not insulated, and the temperature at the outer surface of this section is measured to be 80oC. The temperature of the furnace room is 30oC, and the combined convection and radiation heat transfer coefficient at the surface of the outer furnace is 10 w/oC. It is proposed to insulate this section of the furnace wall with glass wool insulation (K=0.038 W/moC) in order to reduce the heat loss by 90 percent. Assuming the outer surface temperature of the section remains at about 80oC, determine i) the thickness of the insulation that is needed and ii) the outer surface temperature of the insulation after installation.arrow_forwardA plane wall (0.8 m x 0.6 m) at 10 oC is to be heated by attaching 7-cm-long, 3-mm-diameter pin fins (k=200 W/mK, ρ=5000 kg/m3) to it. nfin=200 fins are to be used in total. Temperature of the surrounding fluid is 100 oC, and the heat transfer coefficient on the surfaces is 35 W/m2K. Total (material + manufacturing) cost of the fins is 850 TL/kg. Fill the table below by neglecting heat transfer from the fin tips. nfin=? a) Fin efficiency b) Fin effectiveness c) Overall fin effectiveness d) Total cost of finsarrow_forward
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