Evaluation studies of a mixed mode solar kiln with phase change material and distributed-type solar kiln

Abstract

The passive thermal performance of a distributed and mixed-mode model solar kiln was compared in the present study. The two kilns were made of double glazed flat plate thermal collector in which paraffin was used as the thermal storage medium. The range of ambient temperatures and daily radiation during the period when the study was carried out were 18.3–33.2 °C and 11.8–20.9 MJ m-2 respectively. The study revealed a peak cumulative efficiency of 44.3% and 40.7% for distributed kiln and 40.7% for mixed mode type. An average efficiency of 38.8% was obtained in the mixed-mode and 43.0% in the distributed type. The results show that low temperature operations such as drying of agricultural produce can conveniently be carried out with these solar kilns. The use of paraffin in the study ensured that the temperatures of the system were all time higher than the ambient temperature. Hence, when mixed-mode type is intended to be used at sun-sets, it is suggested that the top glazing of the working section should be covered with opaque materials to reduce the thermal loss as a result of the glazing to enhance efficient heat utilization.