Thermography for performance evaluation of a compact, air disperser equipped hot air dryer

A hot air dryer has been developed for achieving uniform temperature distribution throughout the drying trays with the use of an air disperser. Comparative experiments were conducted with and without the use of the disperser. Then, 1 mm thick potato slices were dried at 50, 55, and 60°C and 1.5 m/s air velocity at different locales of the tray. Validation of drying rate uniformity was done by studying the temperature distribution on the drying tray using thermal imaging and measuring the chromatic, textural, and morphological properties of dried potato slices. Without the air disperser, the average temperature and average initial drying rate measured after 30 min at five different points on the bottom tray varied from 42.5 to 52.2°C and 0.086 to 0.185 g water/min, respectively, whereas the variation was only in the range of 49.0–49.6°C and 0.182 and 0.206 g water/min when the air disperser was used at a set dryer temperature of 50°C. Similarly, drying rates at all the positions in different trays were observed to be in close proximity throughout the drying period with the presence of air disperser; however, without it, the drying rate was found to be higher at the center of the tray than other four points. Similar observations were also made for all the qualitative parameters of potato slices at all drying temperatures. Practical Applications The dryer has provision for placement of different types of imaging devices and sensors for online monitoring of process parameters and the product being dried. It has been designed for nondestructive study of the drying progression using machine vision system. Such a dryer will be especially useful for controlled drying experiments and laboratory simulation of different hot air drying processes.