The Development and Testing of Low-Cost Heat Transfer Enhancements for Solar Dryers

Sammanfattning: In the mountainous regions of Bhutan and Nepal, post-harvest losses cause significant challenges for producers. Open air sun drying is usually used by farmers to preserve their produce. There are many disadvantages to this method. The Swedish Research Council is supporting a project called Solar Food: Reducing Post-Harvest Losses Through Improved Solar Drying, which aims to create a low-cost solar-powered food dryer to enhance the quality of food preservation in the Himalayas region. In this project, the thermal characteristics of various components of a solar dryer were analyzed at different air flows, including the heat exchanger, absorber, and drying chamber. The data is used to compute efficiency and heat fluxes, and drying rates are assessed to establish the optimum flow. The effect of adding a net as artificial roughness to the absorber was also examined to identify potential areas for improvement in thermal performance. The results indicate that increasing airflow reduces drying times, as higher flows facilitate faster moisture removal, resulting in shorter drying durations, Additionally, the study revealed a homogeneous drying process within the chamber, indicating that the samples dried uniformly. The study also demonstrated an inverse relationship between higher flow rates and lower heat exchanger efficiencies. Based on the results of the experiment evaluating the effectiveness of a chamber with holes in its walls, the chamber without holes performed slightly better than the chamber with holes. However, product thickness, sunlight, and wind may have impacted the measurements. In terms of absorber efficiency, the study reveals that flow has minimal impact within this project's scope. Nonetheless, it is inconclusive to compare the efficiency of solar dryer with and without a net on the absorber based on these tests because of the varying weather conditions. For a more accurate assessment of the impact of nets on absorber efficiency in the future, it is recommended to conduct experiments in a controlled environment. Furthermore, exploring the use of nets with various orientations on the surface of the absorber may reveal opportunities for enhancing heat transfer.