Review on development, recent advancement and applications of various types of solar dryers

ABSTRACT

The demand for food is predicted to rise by 40–50% by 2030 due to the increasing population. The post-harvest losses need to be reduced by using advanced food processing techniques. Solar drying is one such ancient technique of food preservation. Lots of solar dryers are available now that not only dries food products at a faster rate but also maintains the texture and nutritious value of the product. Nowadays solar drying is not limited to the drying of agricultural products but also used in various sectors like poultry farms, rubber industry, milk industry, sludge drying, etc. The researches in direct, indirect, and mixed-mode dryers operating under active as well in passive modes are tabulated in the paper separately. The different modifications applied to the dryer for boosting their efficiency have also encapsulated in the paper. Further, the paper also covers the application of dryers in different sectors other than agricultural sectors. It is found that direct dryers are cheap and easy to installable at remote locations while indirect dryers give better control over drying rate and provide a better texture of crop due to no exposure to direct radiation. The mixed-mode dryer further reduces the drying time and hybrid dryers enable the drying process to be continued to off sunshine period also. It is also observed that drying rate depends largely on evaporative (h_e) and convective (h_c) heat transfer coefficients which vary with change in the quantity of drying crop inside the dryer, airflow rate, air inlet area, room temperature, and tray size. The value of h_c and h_e are found greater in the forced mode as compared to the passive mode for direct, indirect, and mixed-mode dryers.

KEYWORDS:

• Solar drying
• direct dryer
• indirect dryer
• hybrid dryer
• dryer modification
• dryer application

Additional information

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Notes on contributors

Pushpendra Singh

Pushpendra Singh (PhD Pursuing) Research Scholar in Department of Mechanical Engineering  at Madhav Institute of Technology and Science, Gwalior, India-474005.

Manoj Kumar Gaur

Manoj Kumar Gaur (PhD) Professor in Department of Mechanical Engineering at Madhav Institute of Technology and Science, Gwalior, India-474005.