Improvement of the tilted wick solar still by using a flat plate reflector

140
reflector on the solar radiation absorbed on the
basin liner of the basin still.
Furthermore, we proposed a newly designed
solar still [15], which consists of a vertical
multiple-effect diffusion still and a flat plate
reflector, and we presented a geometrical method
for calculating the direct and diffuse solar radiation
directly absorbed on the vertical surface as
well as the radiation reflected by the flat plate
reflector and absorbed on the vertical surface. We
performed outdoor experiments [16] under solar
isolation in Kurume (33EN latitude), Japan, to
validate the geometrical method, and the results
show that direct, diffuse and reflected radiation
absorbed on the vertical surface can be adequately
calculated with the geometrical method
we presented.
The geometrical method for calculating the
effect of external reflector for the basin still as
well as the vertical still can be easily modified to
the tilted wick still. Therefore, in this paper, the
objective of the study is to theoretically find the
effect of the vertical flat plate external reflector
on the amount of solar radiation absorbed on the
evaporating wick as well as the distillate productivity
of a single slope tilted wick still at 30EN
latitude. Finally, we give the optimum inclination
of the tilted wick still with and without an external
reflector.
2. Solar radiation absorbed on the evaporating
wick of a single slope tilted wick still with a
vertical flat plate external reflector
The proposed still is shown in Fig. 1. The still
consists of a glass cover, evaporating wick and a
vertical flat plate external reflector of highly
reflective materials such as a mirror finished
metal plate. Saline water is fed to the wick constantly.
The direct and diffuse solar radiation and
also the reflected solar radiation from external
reflector are transmitted through the glass cover
and absorbed onto the wick.
H. Tanaka, Y. Nakatake / Desalination 216 (2007) 139–146
Fig. 1. Schematic diagram of tilted wick still with vertical
flat plate external reflector.
To simplify the following calculation to determine
the absorption of solar radiation on the
wick, the walls of the still are disregarded, since
the height of the walls (10 mm) is negligible in
relation to the still’s length (1 m) and width
(1 m).
Fig. 2 shows a schematic diagram of the
shadows of the glass cover (as well as the evaporating
wick) and the external reflector on a
horizontal surface caused by direct solar radiation.
Since the walls disregarded as mentioned
above, the shadows of the glass cover and the
evaporating wick would be exactly the same. l s is
the length of the still (ABCD), l m is the height of
the external reflector (ADEF), w is the width of
both the still and reflector and θ is the angle of
the still from horizontal. γ is the azimuth angle of
the still and is always set as 0 o (still is oriented
due south) in this paper, and ϕ and φ are the
azimuth and altitude angle of the sun.
The direct solar radiation absorbed on the
evaporating wick, Q sun,dr, can be determined as the
product of the direct solar radiation on a horizontal
surface, G dr, the shadow area of the still on