Parametric investigation of a vertical multiple-effect diffusion solar still coupled with a tilted wick still

doi:10.1016/j.desal.2017.01.019

Desalination

Volume 408, 15 April 2017, Pages 119-126

https://doi.org/10.1016/j.desal.2017.01.019 Get rights and content

Highlights

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Vertical multiple-effect diffusion solar still coupled with tilted wick still
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Parametric investigation was performed to determine optimum conditions.
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Design and operation conditions were analyzed theoretically.
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Distillate productivity is equivalent to other types of multiple-effect stills.

Abstract

A parametric investigation was performed theoretically for a solar still consisting of a vertical multiple-effect unit (MEU) and a tilted wick unit (TWU). Thermal input to MEU is the latent heat of vapor from TWU and solar radiation directly incident on MEU. Parameters analyzed in this study were the inclination angle of TWU, the ratio of the height of MEU to the length of TWU, air gap sizes in double glass covers of MEU and TWU, and the distance between the plates and number of plates used in MEU. Each parameter was analyzed to find the optimum value to produce the maximum daily production of distilled water. With optimum conditions, the total daily production of the still would be competitive with other types of multiple-effect stills. Outdoor experiment with 4-effect MEU was also performed, and it was found that the discrepancy between experimental and theoretical results was about 10%.

Graphical abstract

Introduction

MEDS (multiple-effect diffusion solar still) is constructed from a number of plates. Each plate has a wick which works as an evaporating surface. All plates are arranged parallel to each other with small gaps. Evaporation and condensation are repeated in MEDS by recycling the latent heat from condensation. As a result, MEDS has been found to produce a greater amount of distilled water than other types of solar still experimentally and theoretically [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25], [26], [27], [28], [29], [30]. These studies were reviewed by Rajaseenivasan et al. [31] and also in a past paper [32].

For this research, a new kind of MEDS was introduced and its basic behavior was analyzed numerically [33], and validated in outdoor experiments with a single-effect unit instead of a multiple-effect unit (MEU) [32]. MEU was set vertically and works together with a tilted wick unit (TWU) as shown in Fig. 1. The double glass covers insulate MEU and TWU, and form a connected and sealed humid air layer enclosed by four surfaces; the wick of TWU (wk), the first plate of MEU (p1) and the inner surfaces of the double glass covers of MEU (gmi) and TWU (gti). The vapor from wk is distributed to and condenses on the other inner surfaces, i.e., p1, gmi and gti. The thermal input to MEU is not only the sunlight directly incident on p1 but also the latent heat released from the vapor from wk and condensed on p1. Therefore, it is preferable to increase the ratio of condensation on p1 in order to increase the thermal energy delivered to MEU.

In this study, some parameters which affect the total daily production of distilled water and/or the ratio of condensation on p1 to the total amount of vapor from wk were analyzed numerically to determine the optimum conditions. Outdoor experiment with 4-effect MEU was also performed to validate the theoretical results.

Section snippets

Theoretical analysis

Theoretical analysis of the proposed still was performed [33]. Listed in Table 1 are the conditions and physical properties determined in this study. In the parametric study, all parameters were set at the values listed in Table 1 except for each single parameter which was varied to determine its effect on production. Parameters analyzed in this study are shown as red letters in Fig. 1. The parameters are inclination angle of TWU, θ_t; length ratio, l_m/l_t (l_m is height of MEU and l_t is length of

Theoretical analysis

The total daily production of distilled water (sum of the daily production from the entire still for a whole a day), Σm_d,still; varying with θ_t on four solstice and equinox days, are shown in Fig. 2. The average value for the four days is also shown. The unit area of Σm_d,still was the area of the double glass cover of TWU. Σm_d,still shows gentle peaks at around 35^o in spring and autumn and around 60^o in winter, while it decreases with an increase in θ_t in summer. Fig. 3 shows the horizontal

Conclusions

Some parameters affecting the daily production of distilled water from a solar still combining MEU and TWU were analyzed numerically to determine the optimum design and operational conditions for the four solstice and equinox days at Kurume, Japan (33^oN latitude), and outdoor experiment with 4-effect MEU was performed. A summary of this work is as follows:

1)
θ_t has an optimum value for each season, and should be at about 30^o if θ_t cannot be changed.
2)
Σm_d,still can be increased by increasing l_m/l_t

References (36)

M.M. Elsayed et al.
Performance of multiple effect diffusion stills
Desalination
(1984)
T. Kiatsiriroat et al.
Performance analysis of multiple effect vertical still with a flat plate solar collector
Solar Wind Technol.
(1987)
S. Toyama et al.
Dynamic characteristics of a multistage thermal diffusion type solar distillator
Desalination
(1987)
R.C. Ouahes et al.
A hardy, high-yield solar distiller of brackish water
Desalination
(1987)
G.N. Tiwari et al.
Analytical study of multi-effect solar still
Energy Convers. Manag.
(1989)
K. Ohshiro et al.
A compact solar still utilizing hydrophobic poly (tetrafluoroethylene) nets for separating neighboring wicks
Desalination
(1996)
B. Bouchekima et al.
Performance study of the capillary film solar distiller
Desalination
(1998)
H.M. Yeh et al.
Energy and mass balances in multiple-effect upward solar distillers with air flow through the last-effect unit
Energy
(2000)
H. Tanaka et al.
A highly productive basin-type — multiple-effect coupled solar still
Desalination
(2000)
H. Tanaka et al.
Parametric investigation on a basin-type — multiple-effect coupled solar still
Desalination
(2000)

H. Tanaka et al.

Experimental study of basin-type, multiple-effect, diffusion-coupled solar still

Desalination

(2002)

H. Tanaka et al.

A vertical multiple-effect diffusion-type solar still coupled with a heat-pipe solar collector

Desalination

(2004)

H. Tanaka et al.

Indoor experiments of the vertical multiple-effect diffusion-type solar still coupled with a heat-pipe solar collector

Desalination

(2005)

H. Tanaka et al.

A simple and high productive solar still: a vertical multiple-effect diffusion-type solar still coupled with a flat plate mirror

Desalination

(2005)

H. Tanaka et al.

Numerical analysis of the vertical multiple-effect diffusion solar still coupled with a flat plate reflector: optimum reflector angle and optimum orientation of the still at various seasons and locations

Desalination

(2007)

H. Tanaka et al.

Outdoor experiments of a vertical diffusion solar still coupled with a flat plate reflector

Desalination

(2007)

H. Tanaka

Experimental study of vertical multiple-effect diffusion solar still coupled with a flat plate reflector

Desalination

(2009)

T. Nosoko et al.

Theoretical analysis of a multiple-effect diffusion still producing highly concentrated seawater

Desalination

(2005)

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Parametric investigation of a vertical multiple-effect diffusion solar still coupled with a tilted wick still

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Theoretical analysis

Theoretical analysis

Conclusions

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