Thermodynamics HW Solutions 341

Thermodynamics HW Solutions 341 - k = 0.64 Btu/h.ft. F and...

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Chapter 4 Transient Heat Conduction 4-66 The walls of a furnace made of concrete are exposed to hot gases at the inner surfaces. The time it will take for the temperature of the outer surface of the furnace to change is to be determined. Assumptions 1 The temperature in the wall is affected by the thermal conditions at inner surfaces only and the convection heat transfer coefficient inside is given to be very large. Therefore, the wall can be considered to be a semi-infinite medium with a specified surface temperature of 1800 ° F. 2 The thermal properties of the concrete wall are constant. Properties The thermal properties of the concrete are given to be
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Unformatted text preview: k = 0.64 Btu/h.ft. F and = 0.023 ft 2 /h. Analysis The one-dimensional transient temperature distribution in the wall for that time period can be determined from = t x erfc T T T t x T i s i 2 ) , ( But, ) 85 . 2 ( 00006 . 00006 . 70 1800 70 1 . 70 ) , ( erfc T T T t x T i s i = = = (Table 4-3) 1800 F 70 F L =1.5 ft Q & Wall Therefore, min 181 = = = = = h 01 . 3 ) /h ft 023 . ( ) 85 . 2 ( 4 ft) 5 . 1 ( ) 85 . 2 ( 4 85 . 2 2 2 2 2 2 2 x t t x 4-52...
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This note was uploaded on 01/19/2012 for the course PHY 4803 taught by Professor Dr.danielarenas during the Fall '10 term at UNF.

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