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 2.38P
The addition of aluminum fins has been suggested to increase the rate of heat dissipation from one side ofan electronic device 1 m wide and 1 m tall. The fins are to be rectangular in cross section, 2.5 cm long and 0.25 cm thick, as shown in the figure. There are to be 100 fins per meter. The convection heat transfer coefficient, both for the wall and the fins, is estimated to be
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(a)
Consider a room with a 1.8-m-high and 2.0-m-wide double-pane window consisting of two 4-mm-thick layers of glass separated by a 10-mm-wide stagnant air space. The convection heat transfer coefficients on the inner and outer surfaces of the window are 12 W/m2 K and 25 W/m2 K, respectively, while the average thermal conductivity of glass is 0.78 W/m K; and the air, 0.026 W/m K.
If the room is maintained at 22 oC, the outside temperature is -4 oC and heat transfer due to radiation can be neglected, determine:
(i)
Draw the sketch and thermal resistance network;
(ii)
the total thermal resistance;
(iii)
the steady rate of heat transfer through this double-pane window;
(iv)
the temperature of the inner surface of the window.…
A long stainless-steel (AISI 316) steam pipe, with an inside diameter of 6.00 cm and an outside diameter of 8.00 cm, is covered with a layer of asbestos insulation (k = 0.150 W/m-K) 1.00 cm thick, which in turn is covered with foam insulation (k = 0.044 W/m-K) 6.00 cm thick. The inside surface temperature of the stainless-steel steam pipe is measured to be 250.0°C, while the outside surface of the foam is exposed to convection, T_inf = 25.0°C, h_inf = 15.0 W/m^2-K.
• Draw and label a sketch of this system. Include dimensions, known temperatures, etc.
• Draw and completely label the corresponding 1-D steady-state conduction resistor diagram.
• Determine the heat transfer rate through the pipe per unit length.
• Calculate the temperature at the asbestos/foam interface.
There 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?
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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- A 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_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_forwardA horizontal pipe having a surface temperature of 67 °C and diameter of 25 cm is buried at a depth of 1.2 m in the earth at a location where k = 1.8 W/m-°C. The earth surface temperature is 15 °C. Calculate the shape factor if the pipe length is 10 m.arrow_forward
- A person puts a few apples into the freezer at 15°C cool them quickly for guestswho are about to arrive. Initially, the apples are at a uniform temperature of 20°C,and the heat transfer coefficient on the surfaces is 8 W/m2·K. Treating the apples as9-cm-diameter spheres and taking their properties to be 840 kg/m3, Cp 3.81 kJ/kg·K, k = 0.418 W/m·K, and α =10-7 m2/s, determine the center and surface temperatures of the apples in 1 h. Also, determine the amount of heat transfer from each apple. Solve this problem using analytical one-term approximation method (notthe Heisler charts). Answer: Center: 11.2 ℃, Surface: 2.7 ℃, heat transfer: 17.2 kJarrow_forward2. 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_forwardCalculate 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_forward
- In a multilayered rectangular wall, the thermal resistance of the first layer is 0.005 °C/W, the resistance of the second layer is 0.2° C/W, and for the third layer it is 0.1 ° C/W. The overall temperature gradient in the multilayered wall from one side to another is 70° C. a. Determine the heat flux through the wall. b. If the thermal resistance of the second layer is doubled to 0.4° C/W, what will be its influence in % on the heat flux, assuming the temperature gradient remains the same?arrow_forwardA 5-m-wide, 4-m-high, and 40-m-long kiln used to cure concrete pipes is made of 20-cm-thick concrete walls and ceiling (k = 0.9 W/m · °K). The kiln is maintained at a surface temperature of 40°C. Determine the rate of heat loss from the kiln when the outside surface temperature is -4°Carrow_forward/ Hot square plate (1 m ×1 m) is to be cooled by attaching aluminum circular pin fins (D=0.25 cm, L= 3 cm) distributed with distance 0.6 cm as illustrated in Figs.(1-a) & (1-b). If the fin base temperature is 100°C, cooling air temperature is 30°C and h= 35 W/m. °C. Determine the total rate of heat transfer from the finned plate and the effectiveness of the fins? Assume k= 237 W/m.°C and nr=tanh mL/ mL.arrow_forward
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