Natural Convection Solar Dryers for Agricultural Products — A Comprehensive Exploration

Abstract

Objectives: To make review on passive solar dryers and its performance of drying agricultural products. Methods: This article focuses on the development in various categories of passive solar dryers in last six years. The different studies carried out in direct, indirect and mixed mode types of passive dryers for drying agricultural products in the year of 2014 to 2020 have been considered this review. Investigations on forced convection solar dryers have not been included in the current paper. The various experimental setups of solar dryers, specimens used for experimentation, measured output parameters and performance have been illustrated. The changes made in construction of solar dryers for improving the performance have also been reviewed. Findings:The mixed mode passive solar dryer is found to be superior in terms of drying time, better utilization of solar energy and efficiency compared to other passive dryers. Novelty: Several review articles have been published in solar dryers. Nevertheless, no comprehensive reviews have hitherto been published on passive dryers in particular. Hence, our current review article focuses on development in passive dryers and its advancements with emphasis on dryer design features, specimen and measured output parameters. Keywords: Passive solar dryers; Natural convection solar dryers; Direct solar dryers; Indirect solar dryers; Mixed mode solar dryers

Development and Performance Evaluation of a Novel Solar Dryer Integrated with Thermal Energy Storage System for Drying of Agricultural Products

“…It was calculated using eq 11, according to Fudholi, Othman, Ruslan, and Sopian. 35 = t t t Saving in drying time (%) OS SD OS (11) where t OS = time taken in (h) to dry a product under open sun, and t SD = time taken in (h) to dry a product in a solar dryer.…”

“…Depending on the mechanism of air flow, solar dryers can be divided into active and passive . Active solar dyers are generally incorporated with active components such as a fan or heat pump to move the heated air from the collector to the drying chamber, hence suitable for large-scale drying operations . Active solar dryers require substantial capital investments and burn significant amounts of fossil fuel, making them unsuitable for rural areas, particularly in sub-Saharan Africa, where the electrification rate is low and financial resources are limited .…”

“…Active solar dryers require substantial capital investments and burn significant amounts of fossil fuel, making them unsuitable for rural areas, particularly in sub-Saharan Africa, where the electrification rate is low and financial resources are limited . Passive solar dryers use only solar energy and do not use any active components, making them ideal for small-scale holders and agro-processors with limited resources, such as those in rural sub-Saharan Africa, due to attributes such as low capital investment and maintenance costs. , The most significant drawback of passive solar dyers is their intermittent nature, as they rely totally on the availability of sun radiation . Passive solar dryers are thus ineffective during cloudy days or nighttime, demanding alternative solutions to these limitations.…”

“…10 Active solar dyers are generally incorporated with active components such as a fan or heat pump to move the heated air from the collector to the drying chamber, hence suitable for large-scale drying operations. 11 Active solar dryers require substantial capital investments and burn significant amounts of fossil fuel, 12 making them unsuitable for rural areas, particularly in sub-Saharan Africa, where the electrification rate is low and financial resources are limited. 13 Passive solar dryers use only solar energy and do not use any active components, making them ideal for small-scale holders and agro-processors with limited resources, such as those in rural sub-Saharan Africa, due to attributes such as low capital investment and maintenance costs.…”

A Comprehensive State-of-the-Art Review on the Recent Developments in Greenhouse Drying

“…For a controlled airflow, vents of appropriate sizes and positions are incorporated into the dryer. The earliest types of passive solar greenhouse dryers are characterized by a large transparent cover of polyethene with an inclined glass roof to help allow direct solar radiation to cover the product [53]. The problems that arise from using natural convection greenhouse dryer include the holding capacity of the dryer, which results in low productivity; there is a risk of the air circulation failing, thus causing the drying products to spoil; and the exposure to solar radiation may result in vitamin loss and decolorization.…”