Performance evaluation of a vertical rotating wick solar still

doi:10.1016/j.psep.2021.02.004

Process Safety and Environmental Protection

Volume 148, April 2021, Pages 796-804

https://doi.org/10.1016/j.psep.2021.02.004 Get rights and content

Abstract

In this work, a new solar still desalination system named vertical rotating wick solar still (VRWSS) was investigated experimentally. The experiments were performed under different operating conditions. The performance of VRWSS was investigated under different wick belt materials (jute and cotton cloth), belt rotational speeds (0.02, 0.05, 0.1, 0.2, and 0.3 rpm), and rotating directions (clockwise and counterclockwise) with and without solar tracking. The VRWSS features are its small size (small horizontal area), fast water evaporation and condensation due to the low thermal capacity and large condensation area. The results revealed that the jute wick obtained higher productivity than the cotton wick at all belt rotational speeds except that at 0.02 rpm. Additionally, the water production for VRWSS-counterclockwise movement increased from 4350 mL/m².day at 0.02 rpm to 5800 mL/m².day at 0.05 rpm, then, the productivity started to decrease with increasing the speed. Furthermore, VRWSS productivity with counterclockwise movement was always larger than that with clockwise direction at all rotational speed except at 0.02 rpm. Besides, the solar tracking for VRWSS (jute wick-counterclockwise-0.1 rpm) increased the freshwater productivity by about 37% with a thermal efficiency of 51%. The cost of produced freshwater from VRWSS was 0.02 $/L.

Introduction

Shortage of freshwater can be considered as the main issue in many developed and developing countries. With overpopulation, industrial evolution and agriculture progress this issue is heightened. It is expected that the freshwater resources will be deficient by 40% in 2030 (Rijsberman, 2006). An efficient solution to overcome this problem, is to desalinate the saline, brackish, or even contaminated water. Solar energy is renewable energy source that can be collected using simple, cheap, and available technology to drive the thermal desalination systems. Solar still (SS) desalination systems can be considered as the most cheapest, easiest and available systems in thermal desalination family (Kabeel et al., 2015; Omara et al., 2015). The main drawback of any SS desalination system is its low daily production of freshwater (Abdullah et al., 2020b; Kabeel et al., 2012b). Many research works were carried out to maximize the productivity of SS systems by minimizing the basin water depth (Kabeel et al., 2012b; Omara et al., 2013a; Ward, 2003), increasing the feed water temperature by employing solar water heaters (Al-harahsheh et al., 2018; Elbar and Hassan, 2020; Eltawil and Omara, 2014; Kabeel et al., 2019), integrating reflectors to enlarge the incident solar energy to the SS (Bataineh and Abbas, 2020; El-Samadony et al., 2015; Kabeel and Abdelgaied, 2019; Mu et al., 2019; Omara et al., 2013b, 2014). Additionally, the wick materials and extended trays were used to increase the evaporation area (Abdullah et al., 2020a, b; Agrawal and Rana, 2019; Modi and Modi, 2020), adding rotating elements to maximize the evaporation area as well as the exposed area to solar energy and to break the basin water surface tension (Abdullah et al., 2019a, b; Abdullah et al., 2021; Essa et al., 2020, 2021; Haddad et al., 2017; Kabeel et al., 2012a).

Employing wick material to the solar stills enlarges the evaporation area, minimizes the water thickness, and reduces the heat capacity inside the SS. Subsequently, the produced freshwater of the SS increased. Omara et al. (Omara et al., 2013a) studied the performance of wick solar stills with various base inclination angels, wick thicknesses, and shapes. Results indicated that the single- and double- layer wick solar stills provided 90% and 114% higher freshwater productions than the conventional SS. Additionally, floating wick (V-shaped) was applied into SS to raise the rate of evaporation due to the increase in evaporation area by 26% (Agrawal and Rana, 2019). Besides, the jute wick was employed with concave base SS with pyramid condensation surface to enlarge the evaporation and condensation rates of SS system (Kabeel, 2009). Besides, the performance of double slope stepped SS was studied by integrating linen wick and carbon nanoparticles (Sharshir et al., 2020). The experiments indicated that, adding linen wick and carbon nanoparticles increased the freshwater production of the SS by 81% and 111% compared with conventional SS, respectively. Munisamy et al. (Karthick Munisamy et al., 2019) investigated the effect of various wick materials (polyester, fur fabric, jute cloth and terrycloth) on the performance of a tilted wick SS. The results indicated that, fur fabric was the best wick for the SS performance. Saravanan and Murugan (Saravanan and Murugan, 2020) investigated the effect of employing different vertical wick matters on the performance of square pyramid SS. The results indicated that the woolen fabrics had superior performance with the SS compared with polyester, terry cotton and jute cloth. Haddad et al. (Haddad et al., 2017) employed a vertical rotating belt made of black jute cloth to augment the performance of SS. The measurements showed an increase in the SS daily production by 15% and 51% in winter and summer, respectively. Abdullah et al. (Abdullah et al., 2019a) investigated the performance of SS with employing a jute cloth rotating belt (vertically and horizontally). The effects of belt OFF times at constant belt ON time of 5 min were investigated. The best performance of SS was at 30 min OFF time. The experiments showed that, the daily freshwater distillate of rotating wick belt was 300% greater than that of conventional SS with a thermal efficiency of 82%.

In this study, a new decorative vertical rotating wick SS is studied. The new SS can be fixed on the outside walls of buildings. The main aim of this study is to design and build high productivity and effective SS occupying minimum horizontal space. In this work the performance of a vertical wick SS with enhanced evaporation technique and large condensation area is investigated. The main advantages of VRWSS are its small size, fast water evaporation due to low thermal capacity and fast condensation along with fast collecting of condensed water droplets due to large vertical condensing surfaces. The experimental measurements are performed to investigate the effect of the following points on the performance of VRWSS.

1
Different belt rotational speeds (0.02, 0.05, 0.1, 0.2, and 0.3 rpm).
2
Different wick belt rotational directions (clockwise and counterclockwise)
3
Different wick materials (cotton wick and jute wick).
4
Solar tracking of the of VRWSS.

Section snippets

Materials and methods

The studied SS desalination system is vertical rotating wick SS (VRWSS). The vertical rotating wick SS is in the form of cuboid as presented in Fig. 1. The VRWSS consists of water basin, glass sheets, two stainless steel rollers, a DC motor, a wick belt and a PV system. The dimensions of the VRWSS base were 50 cm × 14 cm with 100 cm sides height, as shown in Fig. 1. Besides, five glass sheets of 4 mm thickness are used to form the VRWSS sides. Two stainless steel rollers of 6 cm diameter were

Experimental error analysis

The uncertainty in the measured data was estimated using the method proposed by Holman (Holman, 2012). Assume that a set of measurements was carried out to determine “n” number of experimental parameters. Let ‘R’ be the desired experimental result obtained based on these measurements.

Thus;R = R(X₁, X₂, X_3, ………….., X_n)

Let the uncertainty in the result was W_R and W₁, W₂, W₃, ………, W_n were the uncertainties in the independent variables. Hence, W_R could be computed using the proposed equation by

Results and discussion

The performance of VRWSS was investigated under various operating conditions. Different belt materials, various belt rotational speeds, and belt rotating direction were considered.

Comparison between the present study and the previous investigations

To estimate the performance of VRWSS, a comparison between the thermal effeciency of the present work and prevous works has been presented in Table 2. From the table, it can be concluded that, VRWSS thermal effeciency is comparable with the previous works. Besides, the comparison obtained that using rotating wick belt, considering the rotating direction and sun tracking enhance significantly the performance of VRWSS. Aditionally, the advantages of the present VRWSS are its small size (occupies

Cost evaluation of the VRWSS

Cost analysis has been considered for VRWSS. The fabrication cost has been presented in Table 3. The cost analysis equations are shown below (Abdullah et al., 2020b):

The total annual cost (TC) is predicted as follows: $T C = F A C + A M C - A S V$ where:

$F A C$ , $A M C$ , and $A S V$ are the annual fixed cost, annual maintenance cost and annual salvage cost, respectively. $F A C = P (\frac{i {(1 + i)}^{n}}{{(1 + i)}^{n} - 1})$ Where, P is the capital cost of SS ($) $A M C = 0.15 (P (\frac{i {(1 + i)}^{n}}{{(1 + i)}^{n} - 1}))$ $A S C = 0.2 P (\frac{i}{{(1 + i)}^{n} - 1})$ Where, i is the annual interest rate

Conclusions

The performance of a new vertical rotating wick SS has been investigated experimentally. The objective is to introduce a small size, high evaporation/condensation area and high productivity/efficiency SS. The main advantages of VRWSS are its small size, fast water evaporation due to low thermal capacity, and fast condensation along with fast collecting of condensed water droplets due to large vertical condensing surfaces. The experimental measurements have been performed to investigate the

Declaration of Competing Interest

The authors report no declarations of interest.

Acknowledgements

This project was supported by the Deanship of Scientific Research at Prince Sattam Bin Abdulaziz University, Saudi Arabia under the research project number 2020/01/17122.

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Performance evaluation of a vertical rotating wick solar still

Abstract

Introduction

Section snippets

Materials and methods

Experimental error analysis

Results and discussion

Comparison between the present study and the previous investigations

Cost evaluation of the VRWSS

Conclusions

Declaration of Competing Interest

Acknowledgements

Alexandria Eng. J.

Energy Convers. Manage.

J. Energy Storage

Sol. Energy

Sol. Energy

Heliyon

Desalination

Appl. Therm. Eng.

Sol. Energy

Sol. Energy

Desalination

J. Clean. Prod.

Process. Saf. Environ. Prot.

Desalination

Energy

J. Clean. Prod.

Desalination

Renewable Sustainable Energy Rev.