Study on the Comparison of the Performance of a Glazed Transpired Collector and a Glazed Non-transpired Collector with Chimney in Natural Convection Mode
M. Ekoja *
Department of Mechanical Engineering, University of Agriculture, Makurdi, Nigeria.
S. O. Onyegegbu
Department of Mechanical Engineering, University of Nigeria, Nsukka, Nigeria.
O. V. Ekechukwu
Department of Mechanical Engineering, University of Nigeria, Nsukka, Nigeria.
*Author to whom correspondence should be addressed.
Abstract
Studies have shown that the glazed transpired solar collector (GTC) with a chimney has efficiencies higher than those obtained from a typical glazed non-transpired solar collector (GNTC) in natural convection mode. However, there has not been a direct comparison of the performance of the two collectors with chimneys in natural convection mode. This study experimentally compared the performance of a GTC with that of a GNTC with a chimney in natural convection mode. The two collectors were constructed and set up side-by-side for the study. Several absorbers were tested in the GTC with absorber hole diameters ranging from 1.0mm to 3.0mm. Data, including solar insolation, ambient temperature and wind speed, collector air temperature and velocity, and absorber plate temperature, were obtained at hourly intervals to characterise the collectors. Thereafter, 1 kg of freshly boiled paddy rice was dried in both collectors. Results showed that the thermal efficiency of the GTC for the absorber hole diameter range of 2.5 mm to 3.0 mm was higher than that of the GNTC, whereas for the diameter range of 1.0 mm to 2.0 mm, the thermal efficiency was lower than that of the GNTC, with a transition between 2.0 mm and 2.5 mm. The average efficiencies of the GTC with absorber hole diameters of 1.0 mm, 1.5 mm, 2.0 mm, 2.5 mm, and 3.0 mm were 3.4%, 11.9%, 47.9%, 56.9% and 74.3%, respectively, while the average efficiency of the GNTC was 50.8%. The GTC with an absorber plate having 3.0 mm diameter holes provided the best performance, with an average thermal conversion efficiency of 74.3%, and was used in the drying experiment for comparison with the GNTC. The relative drying rate of rice in the GTC was about 1.5 times higher than that in the GNTC. The study showed that the GTC with an absorber plate hole diameter of 3.0 mm had better overall performance than the GNTC and provided a better alternative to the GNTC for crop drying in natural convection mode.
Keywords: Glazed transpired collector, glazed non-transpired collector, natural convection, solar air heater, chimney, thermal efficiency, absorber hole diameter, crop drying, paddy rice, drying rate