الفهرس 
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Abstract
The present experimental study aims to improve the productivity of a stepped
solar still. To investigate this idea, a stepped solar still using PCM as latent store
materials with internal reflectors integrated with an evacuated tube collector (first
case) and a stepped solar still using a graphite and PCM as hybrid store materials
with internal reflectors integrated with an evacuated tube collector (second case) was
designed, implemented and operated at Tanta University under the climatic
conditions of Egypt to obtain the better configuration. This study illustrated to effects
the graphite, PCM, internal reflectors, and evacuated tube solar collector on the
stepped solar still performance. The results show that the daily distillate production
was varied between 11.24-11.29 and 13.6-13.62 L/m
2
day for the first case and
second case, respectively. The daily efficiency was varied between 42.55 -42.62%
and 51.7-51.82% for the first case and second case, respectively. This results
indicated that the second case is more effective than the first case, the percentage
improved in the daily productivity for second case as compared to first case varied
between 20.64-21.05%. Also, the percentage improved in a daily efficiency for
second case compared to first case varied between 21.48-21.64%. For increase the
hot brackish water from rate from 15-35 ml/h, the daily productivity increases from
10.54-12.08 l/m
2
and 12.88-14.42 l/m
2
for the first case and second case,
respectively. .