Combined Convection, Radiation, and Conduction Heat Transfer in Constant-Rate Period

8 COMBINED CONVECTION, RADIATION, AND CONDUCTION HEAT TRANSFER IN CONSTANT-RATE PERIOD 

In Fig. 9,8-1 a solid material being dried by a stream of air is shown. The total rate of heat transfer to the drying surface is 

Note that in Eq. (4.10-10) T and Tj are in K. For the heat transfer by conduction from the bottom, the heat transfer is first by convection from the gas to the metal plate, then by conduction through the metal, and finally by conduction through the solid. Radiation to the bottom of the tray is often small if the tray is placed above another tray, and it will be neglected here. Also, if the gas temperatures are not too high, radiation from the top surface to the tray will be small. Hence, the heat by radiation should not be overemphasized. The heat by conduction is 

This equation can be compared to Eq. (9.6-7), which gives the wet bulb temperature when radiation and conduction are absent. Equation (9.8-8) gives surface temperature 7 greater than the wet bulb temperature. Equation (9.8-8) must also intersect the saturated humidity line at Tg and Hg, and Tg T andffg H r. The equation must be 

8 Combined Convection, Radiation, and Conduction Heat Transfer 

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