Parametric modelling of a solar heater/dryer
Date
2011-08-19
Authors
Virdy, Satman Singh
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Abstract
A numerical model for determining the size of a forced - convection solar fish dryer
comprising of a drying bin (in which the fish is kept), aflat plate solar collector and a fan, has been developed. The model comprises of two sections with the first section calculating the technical parameters of the dryer and the second carrying out a cost analysis of the designed dryer. The model is in Delphi code and a number of simulations were carried out for Lusaka weather conditions.The results of the simulations are presented in two sections. In the first section, dryer
simulations are carried out for a design value of 100%-saturated air at the bin outlet whereas in the second, a design value of 80% saturation is used. The parameters studied in the first section include the monthly solar radiation received on both horizontal and inclined surfaces, the variation of collector area required for different seasons, radiation levels, and quantities offish; the bin size for different quantities of fish; the variation of air flow rate and heater power for different quantities offish; the
total system fan power and the drying times for different quantities of fish for the
months of July and October. In the second section, for the solar collector, the variation of collector area, dimensions, hydraulic diameter, efficiency, fan power, and drying time with the heat transfer coefficient were investigated. The drying times required for reducing the moisture content to various levels were studied for various batch sizes. A cost analysis of dryers has also been carried out in this section. For this section, all the
simulations were carried out for the month of October.For the first section, it was found that for a collector mounted in Lusaka, the orientation was only critical for the months of March to October during which it should face north.For the other months, this parameter is not critical. As expected, it was seen that' the collector area reduces with increasing radiation. It was also found that the solar collector area, the airflow rate and the heater power vary linearly with increasing fish quantity while the total system fan power varies almost linearly with increasing fish
quantity. As would be expected, the drying time in October is shorter than that in July
for the same fish quantity. The drying curve also provides a means of deducing the
optimum drying periods in a particular day. For the second section, it was found that
the collector area, collector width and the drying time show an exponential decrease
with increasing heat transfer coefficient. The collector hydraulic diameter however
shows a slight exponential decrease with the heat transfer coefficient. On the other
hand, the collector efficiency increases exponentially, while the collector fan power
increases parabollically with increasing heat transfer coefficient, and the drying time increases linearly with increasing batch size. A cost analysis to obtain the cost per unit of moisture evaporated and the optimum drying time in the day revealed that the cost per unit of moisture evaporated decreases to a minimum at around 15:00 hrs Zambian time which is also the optimum drying time of the day
Description
Keywords
Solar dryers , Food -- Preservation , Food -- Drying