(1) input of drying air to the drying chamber to dry the products,
(2) input of moist products to be dried in the chamber,
(3) output of the moist air after taking the evaporated moisture from the products, and
(4) output of the dried products. In fact, their moisture contents are reduced to a certain level required for each commodity of the product.
In the analysis, the thermodynamic balance equations in terms of mass, energy, entropy and exergy for the drying system, as a control volume, as shown in Fig. 2 are first written for product, air and moisture content in the air. The comprehensive details of such an analysis are given elsewhere (Dincer & Rosen, 2007; Dincer & Sahin, 2004). Here, it is equally important to define both energy and exergy efficiencies of the drying system correctly. The energy efficiency is
defined as the ratio of net energy used for drying the product (e.g.,moisture evaporation) to the energy input supplied by the drying air and can be formulated as follows: