708 Fermentation and Biochemical Engineering Handbook A Mass of liquid mass of dry solid Figure 1. Drying rate curve Moisture flow from within the material to the surface is fast enough to maintain a completely wet surface. The surface temperature reaches the wet bulb temperature. The rate of drying can be expressed where dw/dp is the rate of drying, i. e, change in moisture with time; Kp is the mass transfer coefficient, ps is the saturation vapor pressure of the liquid at the surface temperature, ts; and pa is the partial pressure of water vapor In addition, the following equation also applies dw ha do 1708 Fermentation and Biochemical Engineering Handbook T A I PON XI 6 IC Y M E A f Mass of liquid / mass of dry solid Figure 1. Drying rate curve. Moisture flow from within the material to the surface is fast enough to maintain a completely wet surface. The surface temperature reaches the wet￾bulb temperature. The rate of drying can be expressed as: Eq. 1 where dW/i+ is the rate of drying, Le., change in moisture with time; Kp is the mass transfer coefficient, ps is the saturation vapor pressure of the liquid at the surface temperature, fs; and pa is the partial pressure of water vapor. In addition, the following equation also applies: Eq. 2 (fa - ts) = Kp (ps - pa) dW ha dO A -=-