| dc.description.abstract | Expressions
for the performance
of Solar
air
heaters operating in four modes
were
derived
and
solved using a computer
and
the
results
from a
series of experiments used to check the validity of
the expressions.
The expressions derived
were
simpler than the generally accepted exponential relationships but it was found that they described the performance of the col lectors reasonably we 11.
It was also found that the four modes differ in
their performances
over
the parameter ranges
considered. The parameters varied
were
mass flow
rate of the air, co I 1 ector length, flow channel
height and insolation. The four modes analysed were
single
pass,
double (top first> pass, double
(middle first) pass and triple pass.
In the single pass mode,
air
flowed between
the
absorber plate and the back plate. In the double
(top first) pass mode, air flowed between the two
covers in the first
pass
and then between
the
absorber plate and the back plate in the second
pass. In the double (middle f' i na t ) pass mode,
flowed between the lower
cover
and the absorber
.'
plate in the
first
pass and then between the
absorber plate and the back plate in the second
pass. In the triple pass mode, air
flowed
between
the two covers in the first pass, between the lower
cover and the absorber plate in the second pass and
then between the absorber plate and the back plate
in the third
pass.
It was found that at no added cost, the triple pass mode gave the best performance fa I lowed by the double (top first) pass mode and the double (middle first) pass mode. The single pass mode was found to give the most inferior performance as compared to other modes. This order of performance was found to be independent of the varied parameters. The gOO?
performance of the triple pass as compared to the
other modes and of the double (top first) pass mod~
as compared to the double (middle first) pass mode
were attributed to a lower
top cover
temperature
which. meant a lower heat loss to the surroundings. | en |
