Consider a drying batch operation in a tray-dryer as shown below. It contains the trays a tier of 10, each on racks 100mm apart, each tray 38mm deep and 1mm wide, with 14m2 of drying surface. The air entering the trays (see circled position 1) is to have a dry bulb temperature of 95C and humidity of 0.05 kg water/kg dry air. Atmospheric air enters at 25 and humidity of 0.01 kg water/kg dry air. The air velocity over the trays at the entrance to them is to be 3m/s. When the solid being dried is losing water at a constant rate of 7.5E-1 kg water/s, determine the percentage of recirculation of air and the conditions of the air in the various parts of the drier.

What is the humid volume at 1? What is the total available area for flow between the trays? What is the total air flow rate through the trays (m3 mixture/s)? What is the dry air mass flow rate through the trays (kg dry air/s)? What is the air-water mixture absolute humidity at 2? The air mixture leaving the trays is supposed to carry the most humidity. In other words, the mixture is expected to be saturated at the conditions in 2. The drierwalls are considered as thermal insulators so that this can be an adiabatic process. What is the adiabatic saturation temperature at 2 (dry bulb)? Make a mass balance to determine the volume of dry air per second passing through the trays (Gas flow rate)(Humidity at 2) - (Gas flow rate)(Humidity at 1) = Mass water evaporated/s What is the dry air mass flow rate at 3 and 4? What is the humid volume at 4? What is the mixture flow rate passing through the fan? What is the percentage of air leaving the tray dryer? The air not leaving the equipment is reused. What is the enthalpy at 1 and 2?

Make a plot of 1/W s X and estimate the are under the curve

\begin{tabular}{|l|l|l|l|} Parameter & Position \#1 & Position \#2 & Position \#3 \\ \hline AirabsolutehumidityY & & & \\ \hline Air velocity & & & \\ \hline & & & \\ \hline \end{tabular}