Comparison of mixed-mode forced-convection solar dryer with and without stainless wire mesh in solar collector

Abstract

A mixed-mode forced-convection solar dryer (MMFCSD) is a device that utilizes both direct and indirect solar energy. The solar collector, which stores thermal energy for indirect solar uses, is an essential component of the dryer. Unfortunately, the thermal efficiency of this device is generally low. In this study, a technique was employed to improve the heat transfer of the solar collector in a MMFCSD. The technique involved adjusting the air flow pattern into a swirling flow to disturb the thermal boundary layer on the absorber plate under forced convection by using stainless wire mesh. The experiment was conducted under actual conditions and bananas were used as the drying sample. The experimental results of the thermal efficiency of the solar collector (ƞsolar) and the drying efficiency (ƞdrying) are presented. The results indicated that the air outlet temperature and ƞsolar of the solar collector with stainless wire mesh were higher than the case without stainless wire mesh, reaching a maximum temperature of 46.22°C and 37.97°C, and average ƞsolar of 0.26 ± 0.02 and 0.14 ± 0.01, respectively. The MMFCSD with stainless wire mesh had a higher ƞdrying than the case without stainless wire mesh, with values of 0.048 ± 0.004 and 0.039 ± 0.003, respectively, resulting in an ~23.07% increase. This was attributed to the air swirling flow through the stainless wire mesh and the heat accumulation in the drying chamber, which led to an increase in the drying chamber temperature from 54.03°C to 63.60°C, an increase in the effective moisture diffusivity from 7.28 × 10–7 to 1.19 × 10–6 m2/s and a decrease in the drying time of 5 h 30 min. However, further research is needed to investigate the quality of the dried samples and their economic value.