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European Journal of Applied Sciences – Vol. 10, No. 2

Publication Date: April 25, 2022

DOI:10.14738/aivp.102.12077. Simate, I. N., & Simukonda, K. (2022). Photovoltaic Forced Convection Greenhouse Solar Dryer with an Integrated Vertical Solar

Collector for Mango Drying. European Journal of Applied Sciences, 10(2). 230-244.

Services for Science and Education – United Kingdom

Photovoltaic Forced Convection Greenhouse Solar Dryer with an

Integrated Vertical Solar Collector for Mango Drying

Isaac N. Simate

Department of Agricultural Engineering, School of Engineering

University of Zambia, Lusaka, Zambia

Kondwani Simukonda

Department of Agricultural Engineering, School of Engineering

University of Zambia, Lusaka, Zambia

ABSTRACT

The design and experimentation of a Photovoltaic forced convection greenhouse

solar dryer with a vertical solar collector incorporated inside the drying chamber

for mango drying is presented. The integrated vertical solar collector combined the

features of a south wall and a solar air heater to capture solar radiation that escapes

through the south wall (north wall for the northern hemisphere) and heat the air

before it enters the drying chamber. Mango drying experiments were carried out to

ascertain the performance of the dryer. The solar radiation at the beginning of the

experiments at 08:30 hours was 525.1 W/m2, reaching a maximum of 1,133.0 W/m2

shortly after midday and decreasing to 492.4 W/m2 at 16:30 hours when the

experiments were stopped. The ambient temperature and relative humidity ranged

from 28.4 0C to 36.4 0C and 19.9% to 37.8%, respectively. Under these conditions,

the air temperature inside the drying chamber was on average 14.7 0C above

ambient, resulting in high drying rates such that the mango reached the moisture

content of 13.7% wet basis after 7.5 hours of drying. The incorporation of a vertical

solar collector inside the drying chamber helped, through storing heat in its mass,

stabilise the drying chamber air temperature and made the forced convection dryer

more compact thereby reducing usage of the space outside the dryer and making it

available for other operations.

Keywords: Forced Convection, Greenhouse Solar Dryer, Mango Drying, Photovoltaic (PV),

South Wall, Vertical Solar Collector

INTRODUCTION

Fruit and vegetable post-harvest losses are estimated to be as high as 50% of their production

[1], and one way of reducing the losses is through solar drying. The advantages of solar drying

over open sun drying are well established in many studies [2,3,4,5] having been carried out on

different types of solar dryers. Among the advantages are that they have higher drying rates

and produce better quality food compared to sun drying. For instance, Simate and Cherotich [6]

carried out mango slices drying experiments in a natural convection solar tunnel dryer. The

moisture content of the slices was reduced from 85.5% (wet basis) to 13.0% (wet basis) in 9.5

hours, thus showing the effectiveness of the method in preserving the mango. According to

Simate [7] solar dryers can be broadly classified according to the method of heat transfer

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Simate, I. N., & Simukonda, K. (2022). Photovoltaic Forced Convection Greenhouse Solar Dryer with an Integrated Vertical Solar Collector for Mango

Drying. European Journal of Applied Sciences, 10(2). 230-244.

URL: http://dx.doi.org/10.14738/aivp.102.12077

(radiation, convection and conduction) to the drying material and the mode of airflow (natural,

forced) through the dryer.

In the recent past, greenhouse structures have been converted into solar dryers operating in

either natural or forced convection mode [8]. The conventional way of using the greenhouse as

a solar dryer is to have an entry for fresh ambient air on one side of the greenhouse structure

and an exit for warm humid air on the opposite side. This arrangement introduces cooler air

into the greenhouse which lowers the inside temperature thereby slowing down the drying

process.

Sahdev et al. [9] reviewed research on different types of greenhouse solar drying of various

foods. The studies reviewed covered subjects such as dryer thermal analysis, drying

characteristics of the foods, drying performance, energy and exergy analysis, and economic

aspects. The major findings were that greenhouse solar drying took less time to dry foods,

produced better quality foods and, had higher thermal efficiency than open sun drying. Gorjian

et al. [10] reviewed the advancements in technical design and thermal performance

enhancements of solar greenhouse dryers which include the integration with photovoltaic (PV)

modules, use of the north wall to reduce heat loss from the dryer, use of thermal storage

materials, and integration of solar air heaters for faster drying. The main findings of the review

were that the advancements resulted in reduced drying time and better quality dried products.

Sethi and Arora [11] incorporated an inclined north wall reflector to a conventional greenhouse

solar dryer to increase the solar radiation available on the drying food. The reflector was used

to capture radiation that was supposed to leave through the north wall of a conventional

greenhouse solar dryer. The addition of the reflector increased the air and crop temperature

which resulted in increased drying rate. Chauhan and Kumar [12] incorporated an insulated

wall on the northern side of a greenhouse dryer to capture the incident solar radiation that

escapes through the north wall. A further improvement on the dryer was the addition of a solar

collector made of a black PVC sheet placed inside, on the floor of the dryer to eliminate the heat

loss through the ground. The greenhouse dryer was operated under natural convection mode

and its performance with the solar collector installed was found to be better than earlier

developed greenhouse dryers. The highest temperature inside the greenhouse was 65.2 °C

while the lowest relative humidity was 4.4% which are suitable for drying most fruits and

vegetables. ELkhadraoui et al. [13] studied a solar greenhouse forced convection drying system

essentially consisting of two parts, a flat plate solar air collector and a chapel-shaped

greenhouse. The solar air collector was coupled to the greenhouse and supplied it with hot air.

With this arrangement, the temperature inside the greenhouse dryer was found to be much

higher than the ambient temperature while the relative humidity in the greenhouse was lower

than that in the ambient. The result was that the drying time was reduced by one day and two

days for red peppers and grape respectively. Román-Roldán et al. [14] carried out

computational fluid dynamics analysis of heat transfer in a chapel-type greenhouse solar dryer

coupled to an air solar heating system that heated the air before sending it to the greenhouse.

The arrangement resulted in an almost homogeneous temperature distribution in the entire

volume of the Greenhouse solar dryer making it suitable for good quality drying.

Among the thermal performance enhancements of solar greenhouse dryers, the use of an

insulated north wall to reduce heat loss from the dryer and, the integration of solar air heaters