Mathematical modeling and performance investigation of mixed-mode and indirect solar dryers for natural rubber sheet drying

Smallholder rubber producers typically dry rubber in the open air, a process that takes about seven days, allowing the rubber to deteriorate and thus decreasing the price obtained by the producers. Solar dryers decrease the drying time by 2-3 days, thereby yielding a higher quality product. In this study, performances of mixed-mode and indirect solar drying systems have been investigated for 30 natural rubber sheets. Drying efficiency of the mixed-mode dyer is 15.4% which is higher than the indirect solar dryer (13.3%). The moisture contents of rubber sheets are reduced from 32.3 to 2.0% and 29.4 to 8.0% on a wet basis for mixed-mode and indirect solar drying, respectively, in 4 days. Hii et al. model is the combination of the Page and Two-term drying model. This model is found to best describe the natural rubber sheet drying behavior in both mixed-mode and indirect solar dryers. Coefficient of determination and root mean square error for mixed-mode and indirect solar drying of natural rubber are 0.998 & 0.0096 and 0.996 & 0.0109, respectively. Performance of the mixed-mode dryer is superior to the indirect solar dryer. Therefore, mixed-mode solar dryers are recommended for natural rubber sheet drying to smallholders.