Higher temperatures result in faster drying in this region because the adiabatic saturation temperature of the air is higher and it can carry more water from the bed.
Before 25 minutes, the air reaching this depth is saturated, and the temperature is near the adiabatic saturation temperature.
The adiabatic saturation temperature (sometimes referred to as the thermodynamic wet-bulb temperature) is defined as the temperature obtained by an air-water vapor mixture if it becomes saturated with water vapor in an adiabatic process (ANSI/ASHRAE 1991).
The dew-point temperature along with the dry-bulb temperature and atmospheric pressure measurements were used to determine the "true" wet-bulb temperature and adiabatic saturation temperature associated with each test condition.
Wet-bulb temperature measurements were taken with the wet-bulb temperature sensor ("measured" wet-bulb temperature) over the entire range of test conditions and compared to the "true" wet-bulb temperature and adiabatic saturation temperature measurements, determined from the chilled mirror dew-point hygrometer.
Combining the uncertainty in these measurements to determine an uncertainty in the true wet-bulb temperature and in the adiabatic saturation temperature produced a total uncertainty in the range [+ or -] 0.
The measured wet-bulb temperature was also compared to the adiabatic saturation temperature (rather than the true wet-bulb temperature).
Figure 16 gives an important result, as it shows that the measured wet-bulb temperature provides a much better prediction of the adiabatic saturation temperature than of the true wet-bulb temperature.
The reason that the measured wet-bulb temperature is a better predictor of the adiabatic saturation temperature than the true wet-bulb temperature is because the adiabatic saturation temperature is larger than the true wet-bulb temperature by an amount that is almost exactly compensated for by the error associated with the parasitic heat transfer to the sensor.
As the bed temperature falls from room temperature to adiabatic saturation temperature of inlet air, the heat loss from the particles has negligible effect on the drying rate.
At equilibrium, the outlet air temperature would be same as the adiabatic saturation temperature of inlet air, which could be taken from psychometric charts (Keey, 1978).