Thermal modeling and performance evaluation of north wall reflective multi-tray cabinet solar dryer
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Date
2019
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Punjab Agricultural University, Ludhiana
Abstract
In this study, an innovative design of front loaded multi-rack tray (MRT) solar cabinet dryer with north wall reflector (NWR) having two shelves and four trays (of 125 × 75 cm each) is presented for efficient drying operation at domestic and small scale commercial level. The total drying area of the polycarbonate sheet covered MRT solar cabinet dryer is 3.75 m2. Aluminized reflector sheet is used on the north wall of the dryer to enhance the solar radiation capture by utilizing the reflective component of the beam radiation particularly in winter conditions when conventional solar dryers are not able to perform the drying operation due to smaller solar radiation availability at latitudes of 30°N and above. The modified global solar radiation was developed to determine the effect of NWR onto the solar radiation capture by the dryer. A thermal model was also developed by writing energy balance equations for dryer chamber air (Tch) and crop surface temperature (Tc). Mathematical equations were solved using Modified Euler’s method by writing a computer program on FREEMAT software. The experiments were conducted under natural convection as well as under forced convection mode with and without using the NWR during winter and summer conditions in order to ascertain the effect of NWR on the performance of dryer. The validation of predicted results were performed using the experimental data generated in winter and summer conditions at Ludhiana climate (30.56°N latitude), India. Performance parameters such as; total heat loss coefficient, useful heat gain and thermal efficiency of the MRT solar cabinet dryer were also computed and compared with that of conventional dryer without using the NWR during winter as well as in summer. The results obtained showed that by using NWR, 37.5% solar radiation capture is enhanced in January month (at 30.56°N latitude) resulting in 4-7°C and 2-5°C higher chamber air temperature under natural and forced convection modes respectively. The total reduction in drying time for carrot drying was observed as 17.8% and 14.3% under natural and forced convection modes respectively by using NWR. The predicted and experimental values for crop surface and chamber air temperature were successfully validated with RMSE and 2 values ranging between 1.6 to 4.9. The Wang & Singh and Logarithmic drying models showed best adequacy of fit due to maximum value of R2 (0.991 to 0.999) and least value of SEE (0.002 to 0.004).
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