Experimental and Numerical Analysis of a PCM-Supported ...

aspect ratio under constant bed volume in figure 7.4. For the higher mass flow rates,
there is a clear optimum aspect ratio lies between 0.4-0.5 at which the evaporation
rates peak. These findings indicate that no generalization can be made regarding the
optimum aspect ratio, but should be rather regarded as a case specific.
Figure 7.5: Effect of column aspect ratio on the evaporation rate,
H= 1m
7.2.3 Effect of inlet hot water temperature
The gas-solid heat flow direction depends on the quality of inlet heat capacity flow of
hot water relative to the heat capacity of the packing and the state of inlet gas
temperature to the column. As the ratio between water heat capacity and packing
heat capacity increases, evaporation rate is enhanced. This is because, as the water
to solid heat capacity ratio increases, both T s and thermal stratification increase and
the rate of heat transfer from the hot solid surface to the gas increases. Figure (7.7)
presents results for the influence of inlet hot water temperature on the evaporation
rate. This figure illustrates the dramatic difference between the behaviour of high and
low inlet hot water temperatures. As it can be seen in this figure, the response of the
system becomes more profound as the water load increases. The influence of
increasing the water load is three folds; the interfacial areas are changed due to
increasing the wetted area, the heat and mass transfer coefficients increase due to
varying the liquid and gas hold up, and the liquid-solid heat capacity ratio increases
as well. It can be clearly observed from the slopes, that the inlet hot water
temperature has the most significant effect on the evaporation rate with respect to
other parameters.
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