It is desired to dry two tons of wet product from an initial moisture of 70% (wet basis) to a final moisture of 10% (wet basis), using a cabinet dryer. The wet product has an initial density of 800 kg/m3, and is spread out on trays (2 cm thick) to be dried on one side only. Previous tests carried out in the laboratory have led to the following results: Equilibrium moisture: 0.03 kg/kg of dry solid Critical humidity: 1 kg/kg of dry solid Constant drying speed: 1 kg/m2 h The drying speed in a first period at decreasing speed has a linear relationship with humidity, until a humidity of 0.2 kg/kg of dry solid is reached, at which time the drying speed is 0.2 kg/m2 h. For the second decreasing period we have the following experimental data:

1. Calculate the drying time in the constant and decreasing periods, and the total total drying time.
2. What would be the total drying area (required area of trays)?
3. Air drying at 100C is used, which has been obtained by heating ambient air from a temperature of 25C (Tbh: 15) to 100C without humidity change. Hot air is injected into the dryer at a constant flow rate, determine: i. The minimum air flow to be introduced into the dryer considering that during the drying period at constant speed the air is humidified adiabatically. ii. What would be the humidity and temperature of the exhaust air when using a flow rate equal to twice the minimum?

\begin{tabular}{|l|l|} \hline Humidity (kg/kg s.s. ) & Drying speed (kg/m2h) \\ \hline 0.2 & 0.2 \\ \hline 0.15 & 0.10 \\ \hline 0.10 & 0.05 \\ \hline 0.05 & 0.03 \\ \hline \end{tabular}