In a cross-circulation tray dryer, the equations for the constant-rate period neglect radiation and assume that the
Question:
In a cross-circulation tray dryer, the equations for the constant-rate period neglect radiation and assume that the bottoms of the trays are insulated so that heat transfer takes place only by convection from the gas to the surface of the solid where evaporation takes place. Under these conditions, evaporation occurs at the wet-bulb temperature of the gas when the moisture is water. In actual tray dryers, the bottoms of the trays are not insulated and heat transfer to the evaporating surface can also take place by convection from the gas to the tray bottom and thence by conduction through the tray and then through the wet solid. Derive an equation similar to (18-34) for the case where heat transfer by convection and conduction from the bottom side is taken into account. However, the conduction resistance of the tray bottom can be neglected. Show by combining your equation with the mass-transfer equation (18-35) that evaporation will now take place at a temperature higher than the wet-bulb temperature of the gas. What effect would heat transfer by radiation from the bottom surface of a tray to the tray below have on the temperature ofevaporation?
Step by Step Answer:
Subject Crosscirculation tray drying in the constantrate drying period Given Wet solid in a tray subject to heat transfer by convection to the bottom ...View the full answer
