Design and Performance Evaluation of a Forced Convection Solar Dryer for Fig Dehydration

Abstract

Figs (Ficus carica), due to their high moisture content and perishability, require effective drying methods for preservation and storage. Traditional open sun drying, while cost-effective, suffers from major drawbacks such as long drying durations, microbial contamination, weather dependency, and poor product quality. This paper presents the design and implementation of a cost-efficient, forced convection solar dryer specifically developed for fig dehydration. The dryer features a black-painted metal chamber to maximize solar absorption, frontal air inlet vents for natural air intake, and a rear-mounted exhaust fan to maintain steady airflow. The system was experimentally tested in Pune, India, under varying ambient conditions. Observations were recorded for drying temperature, moisture removal, and weight reduction across specific time intervals. Compared to traditional drying, the proposed dryer demonstrated significantly reduced drying time, improved color retention, and enhanced product hygiene. Energy consumption was minimal, with the fan operating on solargenerated or battery-supported power. The results validate the efficiency of the forced convection mechanism in improving drying uniformity and minimizing energy costs. This system provides a sustainable and scalable solution for small and medium-scale fig processing units, contributing to improved post-harvest management and reduced wastage.

Introduction

Figs (Ficus carica) are classified as climacteric fruits, meaning they deteriorate quickly after harvest due to high moisture content and soft texture. Traditional sun drying methods, while inexpensive, suffer from major drawbacks—such as contamination, uneven drying, nutrient loss, and dependence on weather conditions—making them unsuitable for large-scale or hygienic processing.

To address these limitations, researchers have focused on advanced solar drying systems, particularly hybrid and forced convection solar dryers, which create controlled airflow and temperature conditions. These systems improve drying rates, preserve nutritional and sensory quality, and reduce microbial growth. Innovations such as solar thermal collectors, photovoltaic (PV) power, thermal insulation, and blackened absorber surfaces have further increased efficiency. However, little work has been specifically conducted on figs, especially for small-scale, low-cost applications.

This study presents the design, fabrication, and evaluation of a metal-based forced convection solar dryer optimized for fig dehydration under local climatic conditions (Pune, India). The aim is to create an affordable, energy-efficient, and scalable alternative to conventional drying methods.

Literature Review

Previous research emphasizes the shortcomings of open sun drying and the advantages of hybrid or forced convection systems for maintaining fig quality. Studies by Ustaoglu, Yaldiz, and Henriques demonstrated improved results with hybrid drying. Later works by Chouikhi, Komolafe, Ky, and others advanced forced convection and PV-powered designs, highlighting aspects such as airflow control, insulation, and energy autonomy. Modeling and simulation studies have also contributed to optimizing solar dryer efficiency. Despite progress, few studies target figs directly, underscoring the need for dedicated designs tailored to their high-moisture characteristics.

Methodology

The developed dryer employs forced convection driven by a 12V DC fan powered by a 10W solar panel and 12V battery. The system is designed around the greenhouse effect, where solar radiation enters through a 5 mm acrylic cover, heating the chamber’s interior. Warm air rises and exits through a rear vent, while fresh air enters through the front, carrying away moisture.

Key design features include:

• Metal structure (mild steel, 1.2 mm thick) coated in matte black paint for high absorptivity.

• Trapezoidal geometry (30° slope) optimized for maximum solar capture at Pune’s latitude.

• Internal aluminum foil lining for thermal reflection and uniform heat distribution.

• Stainless steel mesh drying tray allowing airflow and hygiene.

• Compact, modular build (15.5 kg) suitable for transport and small-scale use.

Results and Discussion

The system was tested over four days in Pune. Starting with 2 kg of fresh figs, steady moisture removal was observed, with approximately 150 g lost by the end of the first day. The study evaluates thermal behavior, moisture removal rates, and overall drying performance, confirming that the forced convection design effectively enhances drying uniformity and efficiency compared to passive sun drying.

Conclusion

This research primarily focuses on the design and testing of a forced convection solar dryer for fig dehydration in Pune, India, during summer conditions. This dryer employed acrylic sheets like glass, which reduced the weight of the dryer and made it more durable. An exhaust fan powered by solar energy facilitated effective air movement for better drying. Experimental results indicated that moisture content reduction for the figs during 9.0 hours of drying was approximately 7.5%, which is equivalent to removing 150 grams moisture from the initial weight of 2 kg. Maximum surface temperatures were attained within 64 degrees Celcius, while internal temperatures were kept between 45 and 52 degrees Celcius, short of optimal conditions for the dehydration of figs. The system\'s efficiency was consistent with literature benchmarks, confirming that the dryer’s performance in terms of drying time and energy consumption is suitable for small-scale rural applications. The results were further validated by a detailed comparison with traditional sun drying and hybrid solar dryers, where the proposed system outperformed passive solar drying methods and matched the performance of more complex hybrid systems. This research highlights the potential of low-cost, solarpowered drying solutions that are both sustainable and effective for agricultural post-harvest management, particularly in climates like Pune, where sunlight is abundant but electrical infrastructure is limited. The dryer can be easily replicated in similar regions, contributing to the improvement of food security and the preservation of agricultural products in rural and remote communities.

References

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Copyright

Copyright © 2025 Prof. Ganesh Korwar, Sankhya Desai, Samruddhi Deshmukh, Srushti Gade, Shramanraj Chikhale, Gaurav Deshpande. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.