A rectangular slab of butter which is 46.2 mm thick at a temperature of 277.6 K in a cooler is removed and placed in an environment at 297.1 K. The sides and bottom of the butter container can be considered to be insulated by the container sidewalls.

Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)

8th Edition

ISBN:9781305387102

Author:Kreith, Frank; Manglik, Raj M.

Publisher:Kreith, Frank; Manglik, Raj M.

Chapter1: Basic Modes Of Heat Transfer

Section: Chapter Questions

Problem 1.48P: A horizontal, 3-mm-thick flat-copper plate, 1-m long and 0.5-m wide, is exposed in air at 27C to...

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1. (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.…
The emissivity of galvanized steel sheet, a common roofing material, is ε = 0.13 at temperatures around 300 K, while its absorptivity for solar irradiation is αS = 0.65. Would the neighborhood cat be comfortable walking on a roof constructed of the material on a day when GS = 750 W/m2, T∞ = 16°C, and h = 7 W/m2 · K? Assume the bottom surface of the steel is insulated.
In a production facility, large brass plates of 4-cm thickness that are initially at a uniform temperature of 25°C are heated by passing them through an oven that is maintained at 455°C . The plates remain in the oven for a period of 7 min. Taking the combined convection and radiation heat transfer coefficient to be h = 120 W/m2·K, determine the surface temperature of the plates when they come out of the oven
The flames in an industrial furnace burn at 800°C on average and the convection coefficientbetween the hot gas and the inside wall of the furnace is ℎ1 = 30 W m2–K⁄ . The wall of thefurnace is made of steel (?? = 20 W m–K⁄ ) and is ? = 10 cm thick. To ensure nobody willburn themself on the exterior surface of the furnace, the steel is to be covered by aninsulating material with a low thermal conductivity (?? = 0.05 W m–K⁄ ). The airsurrounding the furnace is at 27°C and free convection on the exterior wall of the furnaceis expected to produce a convection coefficient of ℎ = 5 W/m2–K. Any radiation effects areexpected to be negligible in this analysis.a) If safety standards require that the outer surface of the furnace not exceed 65°C, howthick should the insulation layer be? This problem is most straightforward if youleverage the concept of thermal resistance.b) Using your result from part (a), calculate the overall heat transfer coefficient (?)from the furnace gas to the ambient…
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.
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.
Consider a 0.6-m * 0.6-m thin square plate in a room at 30°C. One side of the plate is maintained at a temperature of 90°C, while the other side is insulated. Determine the rate of heat transfer from the plate by natural convection if the plate is (a) vertical, (b) horizontal with hot surface facing up, and (c) horizontal with hot surface facing down.
A 5-mm-diameter spherical ball at 50 oC is covered by a 1-mm-thick plastic insulation (k=0.13 W/m.oC). The ball is exposed to a medium at 15 oC, with a combined convection and radiation heat transfer coefficient of 20 W/m2.oC. Determine if the plastic insulation on the ball will help or hurt heat transfer from the ball.
A person puts apples, whose initial temperature is 30 °C, into a 2 °C-cold room. If the heattransfer coefficient at the apples’ surface is 8 W/m2K, determine the center and surfacetemperatures of the apples after one hour. Assume the apples are spherical in shape with adiameter of 9 cm and also state your assumptions
A 2-m × 1.8-m section of wall of an industrial furnace burning natural gas is not insulated, and the temperature at the outer surface of this section is measured to be 80°C. The temperature of the furnace room is 30°C, and the combined convection and radiation heat transfer coefficient at the surface of the outer furnace is 10 W/m2·C. It is proposed to insulate this section of the furnace wall with perlite insulation (k = 0.052 W/m·C) in order to reduce the heat loss by 90 percent, Assuming the outer surface temperature of the metal section still remains at about 80°C, determine the thickness of the insulation that needs to be used.
How can we use the transient temperature charts when the surface temperature of the geometry is specified instead of the temperature of the surrounding medium and the convection heat transfer coefficient?
A 6-m-internal-diameter spherical tank made of 1.5-cm-thick stainless steel (k = 15 W/m·K) is used to store iced water at 0°C in a room at 20°C. The walls of the room are also at 20°C. The outer surface of the tank is black (emissivity « = 1), and heat transfer between the outer surface of the tank and the surroundings is by natural convection and radiation. Assuming the entire steel tank to be at 0°C and thus the thermal resistance of the tank to be negligible, determine (a) the rate of heat transfer to the iced water in the tank and (b) the amount of ice at 0°C that melts during a 24-h period. The heat of fusion of water is 333.7 kJ/kg.