Thermal analysis of solar dryers

Abstract

A general purpose solar crop dryer for drying various agricultural products such as coffee, fruits, vegetables, medicinal plants, etc. is simulated. The simulated solar collector consists of the solar air heater (solar collector) which uses low-emissivity glass cover and an integral d1yer chamber attached to the collector where the products to be dried are placed, Fig. I. A thennal solar-collector model was developed to detennine the available useful energy for heating the ambiellt air from the available meteorological data such as global and diffuse radiation and ambient air temperatllre. Basic heat transfer equations for single-plane glass glazing are derived and techniques for the solution of these equations are presented. A computer programme was written to predict the collector outlet temperature, mass flow rate and other engineering variables from the input of the meteorological data and collector parameters. Results of the system simulation are presented in graphical fonn suitable for system pe1formance detennination. From the incident solar flux, ambient air temperature and solar collector parameters, the average yearly values of useful energy, the collector outlet air-temperature and air volume flow-rate are also predicted and presented graphically. In this paper, the theoretical analysis of the drying chamber was effected through an example, as it very much depends on experi~entally detennined parameters which also depend on the particular type of product to be dried.