Energy and exergy analysis of a hybrid dryer with air/water solar collectors

Drying is essential to preserve food and agricultural products because reducing humidity prolongs their life without damaging their nutritional properties. Solar energy, an inexhaustible and friendly natural resource, can give a drying effect. This research paper studies the behaviour of a hybrid dryer activated with solar collectors of a) air, b) water, and c) air/water. The first and second laws of thermodynamics are used to determine the exergy efficiency and irreversibility for the main components and the whole system for every scenario. In the first analysis, solar radiation of 940 W/m2 is used with different mass flux rates and outlet temperatures in the solar collectors, heat exchanger and dryer. The results show that the finite heat transfer area and heat leaks in the solar collectors for all arrangements contribute to a low exergy efficiency due to the presence of high irreversibility (almost 90 % with air solar collectors, approximately 65 % with water solar collectors and, about 35 % with air/water solar collectors). Finally, the maximum exergy efficiency is obtained when the water solar collectors are used, reaching almost 4 %. For the second analysis, the performance of the three arrangements is analysed during the sunniest day with a solar radiation variation from 17.1 to 940.3 W/m2 given in Cuernavaca Morelos. Using air/water solar collectors, the dryer reaches outlet temperatures from 333.4 to 343.4 K and loads from 11.1 to 1 kW with solar radiation between 584.1 and 940.3 W/m2.