PERFORMANCE OF DESICCANT SOLAR CROP DRYERS IN MAKURDI, NIGERIA

Dryers in humid tropical locations like Makurdi, Nigeria (Lat. 7 degrees 7'N), have not performed significantly better than the open air sun drying of crops because of the high ambient relative humidity that is often not less than 70% all year round, hence the need to use desiccant augmented dryers. The performance of three types of non-regenerative desiccant solar crop dryers was undertaken to determine the best performing dryer configuration for further improvement and use in the location. The dryers developed were the indirect-active desiccant dryer (IADD), direct-active desiccant dryer (DADD), and the direct-passive desiccant dryer (DPDD). The dryers were designed, constructed, and their performance evaluated and compared to open air sun drying (OASD). The drying rate (kg/h) and Dryer Performance Coefficient (DPC) were used to evaluate the performance of the dryers. The active dryers were operated at a fan speed of 1.2 m/s. Moisture absorption rate and % moisture absorbed to its weight were used to evaluate the performance of the desiccant. The desiccant used was a composite of rice husk ash (RHA) and calcium chloride binded with cement in the ratio of 1: 1: 1 by weight. The analysis of variance (ANOVA) at p <= 0.05 was used to determine if there was a significant difference in the measured parameters of the dryers. The Duncan's New Multiple Range Test (DNMRT) at p <= 0.05 was used to separate the means where there was a significant difference. The drying rates were 0.23, 0.19, 0.16, and 0.13 kg/h for the DADD, DPDD, IADD, and OASD, respectively. The drying rate of the OASD was not significantly different from that of the IADD. The DPC was 1.53, 1.40, and 1.15 for the DADD, DPDD, and IADD, respectively. The DPC of the dryers were significantly different. The direct active desiccant dryer had the highest temperature of 45 degrees C, the lowest relative humidity of 50% at the drying unit and the highest rate of moisture absorbed by the desiccant of 0.24 kg/h. The non-regenerative RHA desiccant had maximum moisture absorption of 28% of its weight. The direct active desiccant dryer is recommended for further development for use in humid tropical locations.