Testing the Performance of a Green House Effect (GHE) Solar Dryer.

by Emmanuel Menya
(Kampala, Uganda)


Coffee is one of the leading cash crops in Uganda contributing 27.6% of the total exports. Despite its economic importance, coffee is mainly dried on bare earth surfaces which have led to the drastic decline in its quality due to exposure to dust, rain, animals and insects hence low prices fetched by farmers.

The drawbacks however have been addressed through the development of the GHE solar dryer which in addition minimizes the need for labor to move the crop for safe storage at the end of the day.

Despite its development, the performance of the GHE solar dryer has not been critically analyzed such as the coffee quality analysis at the end of the drying period and not all the loading densities that can be subjected to the dryer have been tested for drying time.

The objective of this research was therefore to test and evaluate the performance of the GHE solar dryer that was constructed at MUARIK.

Three experimental runs were set up in the months of June and July which experienced average ambient temperature of 23.28oC resulting in an average dryer temperature of 35.68oC. The treatments were loading densities of 5,10 and 20kg/m2 each replicated thrice. The equations of the drying curves associated with the loading densities include; y = 65.565 e -0.333 x for the 5kg / , y = 68.965 e -0.3308 x for the 10 kg / and y = 59.218 e -0.2301 x for the 20 kg/ where x is time in days and y is the moisture content at that particular time.

The average drying time for the freshly harvested Robusta coffee at an average initial moisture content of 60.9%wb was 10days for 5kg/m2, 11days for 10kg/m2 and 12days for 20kg/m2.

When the t-test was used to analyze for any significant differences in terms of moisture content variations in the loading densities at the alpha-level of 0.05 using Microsoft SPSS software, the research showed no significant difference in the performance of the dryer. The coffee quality analysis showed that 20kg/m2 produces the best quality with an even roast while body and flavor were fair+ compared to 5 and 10kg/m2 that gave a silver skin roast while body and flavor were fair. Therefore for this particular research, 20 kg/m2 is the optimum loading density for the exhaustive utilization of the dryer although there is need for further research on cup tastes for higher loading densities.

Key words: Coffee quality analysis, GHE solar dryer, loading densities.

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