The average mass flow rate of the drying medium calculated from
Eq. (1) showed that both air and nitrogen drying had the equal
average mass flow rates because of the close value of the density
(see Table 1). The dry and wet bulb temperatures of the inlet and
outlet of the drying chamber were measured and the relative humidity
computed using Eqs. (11)–(17). The relative humidity profile
at the inlet of the drying chamber for ginger drying in heat pump
dryer is shown in Fig. 5, and thus the humidity ratio can be computed
by Eqs. (7)–(10). The mass of evaporated water and the drying
time were known from the experiment, and thus the humidity ratio
of the outlet of the drying chamber was calculated by Eq. (2). The
humidity ratio profile for ginger drying in the heat pump dryer is
shown in Fig. 6; enthalpy was computed by Eqs. (4)–(6). The enthalpy
profile for ginger drying in the heat pump dryer is shown
in Fig. 7. Heat consumed at the drying chamber was calculated using
Eq. (22). The experiment showed that both air and nitrogen drying
required low heat shown in Table 2.