Dr. V P Sethi
Professor, Department of Mechanical Engineering, Punjab Agricultural University, India.

Speech title: Thermal Modeling Aspects of Solar Technologies for Greenhouse Microclimate, Solar Cooking and Crop Drying Applications

Abstract: In the first part, thermal modeling aspects of asymmetric overlap roof greenhouse (saw tooth design) is formulated and experimentally validated. A mathematical model for global solar radiation availability is utilized to compute hourly instantaneous solar radiation flux capture by the greenhouse and utilized in a dynamic thermal model to ascertain hourly plant and inside air temperature at each hour of the day during the sunshine hours. Asymmetric overlap roof shape is also compared with previously developed two best shapes of greenhouses viz. even-span and modified arch most suitable in terms of solar radiation capture, air and plant temperature in composite type of climate. The plant and air temperatures predicted by the model are in good agreement with measured values with root mean square error (RMSE) of 4.69 and 3.7 respectively. In this second part, thermal modeling aspects of an innovatively designed twin-chamber community solar cooker have been presented. Total solar radiation captured was utilized in the developed thermal model by writing and solving various energy balance equations and validating them for various cooker parameters such as; glass cover temperature, chamber stagnant air, absorber plate temperature during each hour of the selected day. For evaluation of thermal efficiency, overall heat transfer coefficient was also computed considering the effects of design parameters of solar cooker, air velocity and environmental conditions. Validation of thermal model for computing glass cover temperature, absorber plate temperature, utensil temperature and chamber air temperature was successfully performed. The model has been experimentally validated for solar radiation availability at 300N latitude (Ludhiana, India) and was found to be in close proximity with the expected values. Effect of booster mirror in enhancing the insolation availability on the cooker during different seasons and latitudes was also computed and presented. In the third part, thermal modelling aspects of a multi-shelf box type inclined solar cooker-cum-dryer (ISCCD) is presented and experimentally validated. The model validation was carried out for different ISCCD parameters such as; upper and lower glass cover temperature, chamber air temperature, absorber plate temperature and temperature of water in the cooking vessel. The heat transfer analysis of specialized design of parallelepiped cooking vessel is also performed for placement in inclined position of the cooker. The top, sides and bottom loss coefficients of ISCCD were calculated to find out overall heat loss coefficient which further used in evaluation of thermal efficiency. The cooking performance of ISCCD was tested as per BIS standards. Drying performance of ISCCD was evaluated by drying amla (gooseberry) under natural and forced convection modes at selective fan speeds. The drying data were fitted with four thin layer drying models namely Lewis, Henderson and Pebis, Modified Page and Logarithmic model. The Logarithmic model was found best fit by finding the determination of coefficient (R2) and standard error estimate (SEE). The designed ISCCD can be used as cooker as well as dryer and gives a year round performance under cooking as well as drying modes.