Convective and evaporative heat transfer coefficients during drying of ivy gourd under natural and forced convection solar dryer.

Abstract

In the present work, a study on convective heat, mass transfer coefficients and evaporative heat transfer coefficient of the thin layer drying process of ivy gourd is performed. The experiment was conducted in three drying modes such as natural, forced convection solar dryer and open sun drying. The hourly data for the rate of moisture removal, sample temperature, relative humidity inside and outside the solar and ambient air temperature for complete drying have been recorded. The drying air temperature varied from 55, 65, 70 and 75°C, and the air velocity was 1, 1.5 and 2m/s. All the drying experiments had shown a falling rate period. The data obtained from experimentation have been used to evaluate the experimental constant values of C and n by simple regression analysis. Based on the values of "C" and "n", convective and evaporative heat transfer coefficients for ivy gourd were determined. The average convective heat and mass transfer coefficients varied between 2.64 and 8.30W/m2 °C and 0.0025 to 0.0076m/s for temperature ranges, at the different air velocities, respectively. The average evaporative heat transfer coefficient for ivy gourd varied from 181.89 to 421.84W/m2 °C. It was observed that convective and evaporative heat transfer coefficients increase with the increase in drying air temperature. The rate of increment of evaporative heat transfer coefficient is higher than the convective heat transfer coefficient. The intensity of heat and mass transfer during solar drying depends on the drying air temperature and velocity.