An experimental investigation has been carried out to study the effect of delta-shaped obstacles mounted on the absorber surface of an air heater duct with an aspect ratio 6 : 1 resembling the conditions close to solar air heaters. This study encompassed the Reynolds number (Re) ranging from 3400 to 27600, longitudinal pitch of the obstacle ($P_{\mathrm{l}}/e$ ) varied from 3/2 to 11/2, and relative obstacle height (e/H) varied from 0.25 to 0.75. The relative obstacle transverse pitch $(P_t/b)=7/3$ and the angle of attack of flow on obstacle = 90° are kept constant during the whole experimentation. By comparing the heat transfer data obtained from the obstacle-mounted duct with that of smooth duct under similar geometrical and flow conditions, the obstacle-mounted duct enhances the heat transfer by 3.6-times at Re = 7276.82, $P_l\mathrm{/e=}3/2$ , and $e/H=0.75$ .

An experimental investigation has been carried out to study the heat transfer augmentations by using delta-shaped obstacles mounted on the absorber surface of an air heater duct with an aspect ratio 6:1 resembling the conditions close to solar air heaters. The experiment encompasses the Reynolds number ranging from 3400 to 28,000, obstacle longitudinal pitch (P _l/e) varying from to and relative obstacle height (e/H) varying from 0.50 to 0.75, while relative obstacle transverse pitch and the angle of attack of flow on obstacle=90° are kept constant during the whole experimentation. The maximum heat transfer augmented by using an obstacle-mounted duct was 3.6 times higher compared with a smooth duct under similar geometrical and flow conditions. A numerical analysis using FLUENT software has also been done for further observation of heat transfer behaviour near the obstacles.

The main aim FIgure 9of this work is to design, develop and experimentally test the performance of an improved box-type solar cooker with thermal energy storage. The improvement features are the ability to concentrate solar rays and store thermal energy. The improved solar cooker became 20% less in inner surface area compared to the conventional solar cooker for the same intercept area of the sun. Experiments are conducted for stagnation test and load test followed by comparison of the thermal performance of improved solar cooker with conventional one. The performance testing parameters are used as per the Indian standard for box type solar cooker. Testing results showed that the averaged first figure of merits (F₁) is 0.115 for conventional and, 0.1349 for improved solar cooker with black stone as a thermal energy storage, 0.1238 for improved solar cooker with concrete as a thermal energy storage and 0.1453 for improved solar cooker without any thermal storage. As per the Indian standard for testing of box type solar cooker, the improved box-type solar cookers in all condition are found to be grade ‘A’ due to the fact that the first figure of merits (F₁) is greater than 0.12. Also the thermal energy storage materials used gives a remarkable storing capacity.

Postharvest crop losses, dependence on fossil fuels, and associated environmental consequences have emerged as critical global challenges. Drying is a food preservation method that consumes about 12%–15% of agricultural processing energy. A greenhouse solar‐based crop drying system uses solar energy to create controlled drying conditions, preserving crop quality and reducing drying time. Coffee, a cash crop and primary source of income for many developing countries, is facing considerable postharvest losses due to quality degradation from traditional drying methods. This review article identifies efficient and practical solar coffee dryers suitable for large‐scale producers in rural areas. It also examines the parameters for evaluating the performance of coffee drying systems. The review also highlighted the postharvest coffee processing techniques and drying kinetics. Based on the systematic selection method among the studies collected from three databases, 36 existing papers are included for comprehensive review. All the reviewed papers reported that solar‐based coffee dryers are promising alternative systems for coffee drying. The type of dryer, their configurations, air temperature, humidity, and airflow rate are the key factors that influence the coffee drying rate and the dryer’s overall performance. Among the classifications identified, direct‐type greenhouse solar dryers are found to be scalable and cost‐effective to use in developing countries. Furthermore, it was found that the design with an insulated north wall increased the air temperature for natural and forced convection modes by 1°C–6.7°C and 1°C–4.5°C, respectively.