INTRODUCTION:

Heat is not the only factor which is necessary for drying. The condition, quality and amount of air being passed over and through the pieces to be dried determine the rate of drying. The amount of moisture contained in the air to be used for drying is important and is referred to as absolute humidity. The common approach to drying fruits, vegetables and grains in many tropical countries is to spread them on mats or cloth just on the front porch. This can be seen in many places in India. In cities, they dry on the terrace floor. What is more, often times the grains are spread on the asphalt roads or sand to dry. One can see chillies and grains dried this way. This is sun drying.

Solar dryers are faster and more hygienic to dry using the sun. better quality product can be obtained. The basic principle of these dryers is simple: heat or warm the air above the ambient temperatures to about 50 to 60 deg. C and pass the air over the food items. In most cases, a natural convection current is used, the hot air goes upwards. So, keep the trays of food items above a black absorber plate, in an insulated box.

Figure of Experimental Setup

FABRICATION OF DOUBLE FLOW SOLAR AIR HEATER

1. Plywood frame:- It is used to fabricate wooden box which is used for storing purpose in solar air heater . It has dimension of 24 X 24 inch square block and thickness of 12 mm.

Reason for selecting plywood: It is resistant to many common annoyances found in solid wood, such as shrinking, cracking and twisting. Plywood is also a strong and durable material and it is more environmentally conserving.

2. Copper plate:- The purpose of the copper plate is to increase the temperature of atmosphere air to about 20°C-30°C. The copper plate used having dimension of 1 mm thick and area of 21 x 22 inches.

Reason for selecting copper plate:

- It is durable

- It is corrosion-resistant

- It is strong

- It has good thermal conductivity.

3. Glass :

It is mainly used for allowing the radiation from sun to enter and dimension of glass is 22 x 22 inches and thickness of 4 mm.

Reason for selecting glass:- Glass is transparent and amorphous material which can easily allow the radiation from sun in more effective manner.

4. Teak wood :

Concentration area of solar air heater is made up of teak wood. It has dimension of 25x25 inches.

Reason for selecting teak wood :- It is one of the hardest, strongest and most durable of all natural woods.

Resistant to rotting and to the effects of hot sun, rain, frost or snow, making it most suitable for outside.

5. Silicone sealant:- Silicon sealant is used to paste the glass over teak wood.

Reason for selecting silicone sealant.

- Good adhesion

- Good cohesion

- Good elasticity

- Good weathering characteristics

6. Stand:

The whole system of air heater is placed on the stand made up of mild steel having dimension 24x24 inches.

Reason for selecting mild steel :

It easy to weld.

- It is ductile.

- It is cheap.

7. Black paint :

- The whole system is painted black with copper plate except glass.

- Reason for selecting black paint :-

- It has good heat absorber as compared to any colour paint in the view of radiation.

8.Thermocol :-

Thermocol are used for insulating material in a wooden box.

Reason for selecting thermocol:-

- It reduces heat losses.

- It is foamed.

- It has low cost.

- It has less weight.

9. Shelves :-

Shelves are made-up of mild steel inside the wooden box.

Reason for selecting mild steel:-

- It easy to weld.

- It is ductile.

- It is cheap.

10. Blower :

It is just like a small fan consists of 3-4 blades having low rpm. Its purpose is to suck and circulate the air in proper manner. It also used for exhaust purpose. The hot air from the wooden box is exhaust to atmosphere for recirculation.

ACTUAL IMAGES OF PROJECT

WORKING

This solar air heater is the advanced modification of single flow solar air heater. In the single flow solar air heater, air flows through one side of copper plate whereas in this solar air heater air flow from both side of copper plate.

Atmospheric air is first entered through air filter which filtered dust particles. Then the atmospheric air passes over the blow the absorber plate. Thus the extremely hot air is entering the wooden box which is insulated. This collected hot air creates a high temperature in the wooden box. This high temperature is used for drying the crops, foods, household eatables and even clothes.

EXPERIMENTAL OBSERVATION.

Following parameters have been recorded

1. Atmospheric temperature

2. Temperature of copper plate

3. Temperature of wooden box.

Sample Reading

Time	T_∞	T_p1	T_p2	T_p3	T_box
11 AM	28 ^○C	49^○C	50.5 ^○C	52.5^○C	47^○C
12PM	30.55 ^○C	66^○C	68^○C	62.5^○C	53.5^○C
1PM	33^○C	73^○C	78^○C	74.5^○C	57^○C
2PM	34^○C	71.5^○C	79^○C	74^○C	60^○C
3PM	35.5^○C	74^○C	80^○C	72.5^○C	59^○C
4PM	31.5^○C	63^○C	65.5^○C	62.5^○C	50.5^○C

Where

T_∞: Atmospheric temperature of air

Tp₁ : Temperature of plate at initial point.

Tp₂ : Temperature of plate at mid point.

Tp₃ : Temperature of plate at end point.

T_box:Temperature of Wooden box

RESULT AND DISCUSSION:

The result obtained from this experimental investigation of thermal performance of solar air heater is that the force convection is better than natural convection in this investigation. The mass flow rate of natural convection is 3.997 x 10 -3 kg/s. The mass flow rate of forced convection is 0.0108 kg/s. which proves that the time required for drying purpose under this investigation is more better in the view of force convection.

CONCLUSION:

Under this experimental investigation of thermal performance of solar air heater gives the temperature difference of atmospheric air and wooden box of solar air heater of near about 20 to 25 0 C. on a moderate sunny day. It is suitable air heater for producing hot air of space heating and agricultural drying applications.

REFERENCES:

1. Foued Chabane, Noureddine Moummi and Said Benramache. Experimental Performance of Solar Air Heater With Internal Fins Inferior an Absorber Plate: in The Region of Biskra. International Journal of Energy and Technology. 2012; 4 (33): 1–6.

2. Pushkar Dwivedi, Shankar Singh. Review Paper on the Use of Artificial Roughness inside a Solar Air Duct to Increase the Heat Transfer Rate Inside It International Journal of Scientific Engineering and Technology. 2013; 2 (4): 307-310.

3. B.K. Maheshwari, Rajendra Karwa, R. Singhvi, A. Goyal, R.N. Kumawat, A. Sharma, R. Prajapat, D. Kumawat, M. Rankawat, N. Bhardwaj. Performance Study of Solar Air Heater with Baffled Duct IOSR Journal of Mechanical and Civil Engineering (IOSR-JMCE). 2012; 4(5): 52-56.

4. A. Sreekumar. Evaluation of a Roof-Integrated Solar Air Heating System For Drying Foodstuffs. International Journal of Emerging Technology and Advanced Engineering. 2013; 3 (3): 209-213.

5. P. Velmurugan and P. Ramesh. Evaluation of thermal performance of wire mesh solar air heater. Indian Journal of Science and Technology. 2011; 4(1).

6. Non Conventional Energy Sources by G.D. Rai Solar Energy By S. P. Sukhatme.

Received on 26.06.2015 Accepted on 25.07.2015

Research J. Engineering and Tech. 7(1): Jan. -Mar., 2016 page 07-10

DOI: 10.5958/2321-581X.2016.00002.7