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

storage materials and thus it can help to find the optimum thermophysical properties
of the storage medium (e.g. optimum melting point range, heat capacity, heat of
fusion, etc.).
In order to study the
influence of the storage
material, one entire year
was simulated and weather
data for Al-Arish city was set
as boundary conditions.
Both sensible and latent
heat storage media were
simulated, see figure 8.9.
The effect of using water as
a sensible heat storage in
the external thermal buffer is
compared with that of PCM
spheres with a melting point
70ºC and other
thermophysical properties
indicated in table A.1 in the
appendix.
Figure 8.9: Comparison between water and
PCM as a storage medium
It is evident that the distillate rate using water spheres is typically the same as the
PCM storage for small collector area of 60 m 2 and small storage capacity up to 3m 3 .
Increasing the storage volume beyond the optimum capacity of 3m 3 with increasing
the solar collector area, the distillate rate of the HDH plant equipped with water
spheres provides more distillate rate than a PCM storage.
This behavior is explained as follows. Fixed-bed heat regenerators are usually
cycled between heat storing and heat releasing modes. First, a stream containing
charging heat is passed through the bed, where the heat is transferred to the
packing. Later a cold stream is passed through the hot bed in the reverse direction,
thereby heating the stream in the retrieval cycle. In this ideal arrangement, the
packing with the highest temperature in the regenerator contacts the fluid at the exit
from the store. Thus, temperature stratification is always desired to achieve high
thermal performance of the cyclic regenerators as it allows the highest attainable
inlet fluid temperature at the interface with the load.
Due to the proposed unidirectional or once-through flow arrangement through the
storage tank, the collector output continuously charges storage and energy is
simultaneously withdrawn to handle the demand for the HDH cycle. Under the
transient and low solar irradiation intensity at Al-Arish, the daily average inlet hot
water temperature to the storage is relatively low compared to the melting
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