Comparative Evaluation of a Square Shaped Mixed Mode Cabinet Solar Dryer with a Circular and Rectangular Cabinet Solar Dryer (PDF)


 – Comparative Evaluation of a Square Shaped Mixed Mode Cabinet Solar Dryer with a Circular and Rectangular Cabinet Solar Dryer –


Three different mixed mode solar dryers (square, circular and conventional) of the same volume and collector surface area were developed with available materials obtained from the market and evaluated.

The dryers were evaluated using crayfish (Procambarus clarkii), okra (Abelmoschus esculentus L.) and yam (Discorea rotunda) in order to evaluate their efficiencies.

1.5kg of crayfish was taken and prepared for the experiment. The material was divided into two, one half for the dryer, and the other for open air drying.


No load and loaded test was carried out for three days respectively. The moisture content of 78% (w.b) for 0.750kg of crayfish reduced to 12% (w.b) during the period of drying.

The drying rate in the circular mixed mode cabinet solar dryer was found to be higher than the conventional and the square shaped solar cabinet dryers.

During the course of drying, after the crayfish was put inside the drying chamber, the temperature of the drying was monitored at an hour interval as well as the relative humidity.

The water content of the product was also checked at an hour interval until there was no more change in the weight of the product.

It was observed that the product dried faster with the circular mixed mode cabinet solar dryer than with the conventional and square shaped cabinet solar dryer.

As a result of the highest temperature attained in the circular mixed mode cabinet solar dryer, it was evaluated that the rate of moisture removal of crayfish was highest in the circular dryer. All the dryers performed better than open air drying.


Certification     i

Dedication     ii

Acknowledgement   iii

Table of Content         iv

List of Figures    ix

Abstract    xi


1.1 Background of the study           1

1.1.1 Sun Drying               2

1.1.2 Solar Drying    3

1.2 Statement of the problem      4

1.3 Objective of the study     7

  • Scope of the study  7

1.5 Significance of the study    8


2.1 Theory of drying      9

  • Agricultural products drying mechanism  9
  • Economic and environmental benefits of solar dryers 10
  • Drying principles 11
  • Solar Drying Technology 12

2.6 Classification of solar dryers     12

2.7Application of solar dryers       14

2.7.1 Solar drying of agricultural products       14

  • Solar drying of marine products  17
  • Working Principle        18

2.8.1 Open Sun Drying (OSD)     18

  • Direct Solar Drying (DSD)  19
  • Indirect Solar Drying (ISD)  20


3.1 Materials     22

  • Study area 23
  • Materials used for the experiment 23 
  • Design considerations          23
  • Design calculation 24
  • Fabrication of machine  31
  • Machine description and operation 31

3.8 Method               36

3.8.1 Preparation of material (crayfish)   36

3.8.2 Evaluation performance of the dryer      36


4.1 Heated air rate curve    38

4.2 Loading Test   41

4.2.1 Diurnal variation of relative humidity       41

4.2.2 Diurnal variation in temperature curves for each day (crayfish)     44

4.3 Moisture Content Determination          46

4.4 Comparison of the square shaped dryer with the circular and conventional    dryer   47

4.4.1 Temperature variations   47

4.4.2 Diurnal relative humidity variations      50

4.5 Solar drying of crayfish   52

4.6 Solar drying of okra    54

4.7 Solar drying of yam        56


5.1 Conclusion      58

5.2 Recommendation         59



More than half of the energy in the world is gotten from the sun’s energy. Drying is one of the methods used to preserve food products for longer periods. The heat from the sun coupled with the wind has been used to dry food for preservation for several thousand years.

Solar thermal technology is a technology that is rapidly gaining acceptance as an energy saving measure in agriculture application (Ekechukwu, 2000). It is preferred to other alternative sources of energy such as wind and shale, because it is abundant, inexhaustible, and non-polluting.

Solar air heaters are simple devices to heat air by utilizing solar energy and it is employed in many applications requiring low to moderate temperature below 80°C, such as crop drying and space heating (Mujudar, 2007). Drying is the oldest preservation technique of agricultural products and it is an energy intensive process.

High prices and shortages of fossil fuels have increased the emphasis on using alternative renewable energy resources. Drying of agricultural products using renewable energy such as solar energy is environmental friendly and has less environmental impact.

Different types of solar dryers have been designed, developed and tested in the different regions of the tropics and subtropics (Norton, 2000).


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