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Mathematical Modelling and Experimental Validation of a Flat Plate Concentrating Solar Collector

Md. Ayub Hossain
Farm Machinery and Postharvest Process Engineering Division, Bangladesh Agricultural Research Institute. Gazipur-1701.

K. Gottschalk
lnstitute of Agricultural Engineering Potsdam-Bornim, Potsdam, Germany

M. B. Amer
Faculty of Agricultural Engineering, Cairo Agricultural University, Egypt

Abstract/ Executive Summary:

A flat plate concentrating solar collector was designed and constructed for agricultural product drying. The collector was tested in different weather and operating conditions such as day time heating using solar radiation and night time heating - without external heater, night time heating with hot water flow from the storage tank without water heater and night time heating with hot water flow using water heater. Day time average temperature rose at the outlet air of the collector was about 30°C over ambient air temperature and collector efficiency varied from 25 to 60%. Collector efficiency was increased by 10% using solar collector. A mathematical model was developed for a concentrative flat plate solar collector. One set of equations was developed to predict cover temperature, receiver (absorber) temperature and air temperature in the collector. These equations were solved iteratively. The simulated cover, air and receiver temperatures in the collector agreed well with the measured temperatures. This model can be used for providing design data of a solar drier.

Keywords: Solar collector, Mathematical, Validation

Location: Leibniz institut fur Agrartechnik Potsdam-Bornim, Germany

Start Date: 00-00-2005

End Date: 00-00-2006

Program Area: Farm Mechanization

Commodity: Pump

Objectives:

To develop a flat plate concentrating solar collector and a mathematical model for this collector and to validate the model with experimental data.

Methodology:

A flat plate concentrating solar collector was designed, constructed and tested at Leibniz institut fur Agrartechnik Potsdam-Bornim, Germany during 2005-06. The system basically consisted of a solar collector and a heat storage cum auxiliary heating unit. The dimensions of the horizontal solar collector were 2.5 m long, 1.8 m wide and 0.18 m high. The transparent cover of the collector was 4 mm thick glass. About 200 mm below the glass cover, 1.5 mm black painted corrugated iron sheet was used as an absorber plate. To increase the efficiency of the solar collector, flat type reflector made of brilliant aluminium was built on top of the collector. The dimensions of the reflector were the same as the solar collector so that it was used as a reflector in day time and a cover in night time. Six legs with 150 mm wheel were used to turn and move the solar collector horizontally and change its direction according to the change of the sun's angle during the day. A 0.75 kW centrifugal fan was connected in one side of the collector to draw the atmospheric air in the collector and to push out the heated air to the drier with a desired air velocity. There was an automatic air controlling system using three air dampers- inlet, mixing and outlet. The heat exchanger consisted of 15 mm copper tubes placed inside the solar collector, 100 mm below the glass cover and 100 mm above the absorber plate. One end of the copper tube was connected with the inlet end of a 500 liter insulated water tank and another end was connected with the outlet of the water tank through the insulated hose pipes. The heat exchanger gave a part of the heat collected during the sun shine by air inside the solar collector to the water inside the copper tubes. The heat was then carried by the water inside the tubes by using a small pump of a discharge capacity ranging from 5 to 50 liters per hour. The heat stored during the day in the water tank could be used in night time by recirculating the hot water from the water tank to the collector. The temperature of this water can also be raised by using water heaters (6 kW) located inside the tank. Flat plate collector is designed for appIications requiring moderate temperature not exceeding 100°C. It is relatively cheap and can be easily constructed. It uses both beam and diffuse solar radiation and is well suited for the drying of agricultural crops. The collector in this study is a concentrator type with a flat plate reflector. It may be termed as concentrator type flat plate air heater.

Source of Information: Journal of Agricultural Engineering The Institution of Engineers, Bangladesh, Vol. 33/ AE, December, 2007

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

Day time average temperature rose at the outlet air of the collector was about 30°C over ambient air temperature and collector efficiency varied from 25 to 60%. Collector efficiency increased by 10% using reflector. Collector cover, air and receiver temperatures and collector thermal efficiency were predicted along the length of the collector and their highest value were round at the end of the collector length. The predicted cover temperature, air temperature and relative humidity at outlet of the collector were validated with measured data and found to be agreed well with the measured data. This model can be used for providing design data of a solar drier.

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