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A 0.75-m x 1.5-m window is constructed of 6-mm-thick glass. On a cold night, the inside and outside surface temperatures of the glass are 16°C and -24°C, respectively. (a) What is the rate of heat loss through the glass?

A 0.75-m x 1.5-m window is constructed of 6-mm-thick glass. On a cold night, the inside and outside surface temperatures of the glass are 16°C and -24°C, respectively. (a) What is the rate of heat loss through the glass?

Elements Of Electromagnetics
Elements Of Electromagnetics
7th Edition
ISBN:9780190698614
Author:Sadiku, Matthew N. O.
Publisher:Sadiku, Matthew N. O.
ChapterMA: Math Assessment
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1. A 0.75-m x 1.5-m window is constructed of 6-mm-thick glass. On a cold night, the inside and outside surface temperatures of the glass are 16°C and -24°C, respectively. (a) What is the rate of heat loss through the glass? (b) The window is replaced by a double-paned window, in which two panes of glass are separated by an air space. If the spacing of the panes is 13 mm and the glass surface temperatures in contact with the interior air space are 12°C and -18°C, what is the new rate of heat loss from the window? (Hint: since the temperatures on the inside glass surfaces are given, you need only analyze conduction across the air gap.) 2. The convection heat transfer coefficient can have a great effect on how a person experiences temperature. Determine the convection heat flux from a person's hand in each of the circumstances below. In each case, the person's hand can be assumed to have a surface temperature of 30°C. (a) Hand outside the window of a car moving at 20 mph in air at -15°C with a convection coefficient of 40 W/m²-K. (b) Hand in a slow moving stream of water at 10°C with a convection coefficient of 900 W/m²-K. (c) Hand in still air in an air conditioned room at 20°C with a convection coefficient of 3 W/m²-K. 3. Both convection and radiation heat transfer can be important in situations where the heat transfer coefficient is relatively low. A steam pipe running through a factory is 30 m long and has a diameter of 15 cm. The steam maintains the outside surface temperature of the pipe at 165°C, and the emissivity of the pipe's surface is = 0.8. The natural convection heat transfer coefficient is 8 W/m²-K. Determine the heat loss rate from the pipe to the surrounding air and walls, both of which are at a temperature of 25°C. 4. The air temperature in a room is maintained at 20°C year-round, but the wall temperature is approximately 27°C in the summer and 14°C in the winter. Determine the total (convection + radiation) rates of heat transfer from a person in this room in both winter and summer if the exposed surface area, emissivity, convection coefficient, and the average outer surface temperature of the person are 1.8 m², 0.8, 4 W/m²-K, and 31°C, respectively.
Transcribed Image Text:1. A 0.75-m x 1.5-m window is constructed of 6-mm-thick glass. On a cold night, the inside and outside surface temperatures of the glass are 16°C and -24°C, respectively. (a) What is the rate of heat loss through the glass? (b) The window is replaced by a double-paned window, in which two panes of glass are separated by an air space. If the spacing of the panes is 13 mm and the glass surface temperatures in contact with the interior air space are 12°C and -18°C, what is the new rate of heat loss from the window? (Hint: since the temperatures on the inside glass surfaces are given, you need only analyze conduction across the air gap.) 2. The convection heat transfer coefficient can have a great effect on how a person experiences temperature. Determine the convection heat flux from a person's hand in each of the circumstances below. In each case, the person's hand can be assumed to have a surface temperature of 30°C. (a) Hand outside the window of a car moving at 20 mph in air at -15°C with a convection coefficient of 40 W/m²-K. (b) Hand in a slow moving stream of water at 10°C with a convection coefficient of 900 W/m²-K. (c) Hand in still air in an air conditioned room at 20°C with a convection coefficient of 3 W/m²-K. 3. Both convection and radiation heat transfer can be important in situations where the heat transfer coefficient is relatively low. A steam pipe running through a factory is 30 m long and has a diameter of 15 cm. The steam maintains the outside surface temperature of the pipe at 165°C, and the emissivity of the pipe's surface is = 0.8. The natural convection heat transfer coefficient is 8 W/m²-K. Determine the heat loss rate from the pipe to the surrounding air and walls, both of which are at a temperature of 25°C. 4. The air temperature in a room is maintained at 20°C year-round, but the wall temperature is approximately 27°C in the summer and 14°C in the winter. Determine the total (convection + radiation) rates of heat transfer from a person in this room in both winter and summer if the exposed surface area, emissivity, convection coefficient, and the average outer surface temperature of the person are 1.8 m², 0.8, 4 W/m²-K, and 31°C, respectively.
k (glass) = 1.4 W/m-K, from Table A.3 k (air) = 0.0239 W/m-K, from Table A.4, property evaluated @ 270 K
Transcribed Image Text:k (glass) = 1.4 W/m-K, from Table A.3 k (air) = 0.0239 W/m-K, from Table A.4, property evaluated @ 270 K
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