Global Journal of Researches in Engineering, A: Mechanical & Mechanics, Volume 22 Issue 1

Performance of a Modified Stepped Solar Still Ali. F. Muftah Abstract- Distillation represents one of the earliest methods of treating water, and it remains as such in many parts of the world. A basin type solar still remains the simplest desalination technology, made up of a hermetic basin that is covered with a transparent airtight material such as glass or plastic. The system is simple, easy to construct, requires minimal maintenance, and cost effective. It is difficult maintaining minimum depth in conventional basin type solar still, as the area is large. However In an attempt to increase production per unit area by decreasing the thermal inertia of the water mass, this can be achieved in basin-type stepped solar still in which the area of the basin is minimized by having small trays. The purpose of this study were to design, fabricate and evaluate the performance of a modified stepped solar still. The theoretical analysis was conducted to determine the optimum design of the basin. The productivity and solar still efficiency were obtained by solving the energy balance equations for the absorber plate, saline water and glass cover, temperature difference between saline water and the glass cover. The results indicated that, the productivity of the modified stepped still is higher than that for conventional solar still approximately by 103%. Keywords: solar desalination, stepped solar still, solar thermal energy. I. I ntroduction esalination is one of the most primitive forms of water treatment, and it is still a popular treatment solution throughout the world. Desalination methods utilize large amount of energy (fossil fuels) to remove a portion of pure water from seawater. The fossil fuels create pollution on environment. A solar still is a device, which used in solar desalination process to produce drinkable water from brackish and saline water by using solar energy. Although solar still is a very simple device, easy to fabricate and require less maintenance, it is economical and not familiarly used because of its lower productivity. Numerous solar distillation systems were developed over the years using the above principle for water purification in many locations in the world. Many researchers analyzed the works carried out on the solar still to augment the productivity of the simple solar still. [Sebaii et al. 2009], [Madhlopa and Johnstone 2011]. Glass, rubber and pebble are some of materials that used as thermal storage materials [Abdel-Rehimaand Lasheen 2005], [Nafey et al. 2001]. A solar still was tested with a special phase changing material as energy storage media at its base. [Naim and Abd El Kawi 2002], [Bassam and Author: College of Mechanical Engineering Technology, Benghazi, Libya. e-mail: ali.f.muftah@ceb.edu.ly Himzeh 2003] reported that, as providing of energy storing materials, wick materials, reducing water depth in basin increases the output. The productivity of a solar still increased from 18% to 27% with different size sponge cubes placed in the basin. [Velmurugan et al. 2008], [Velmurugan et al. 2009a] designed and analyzed a stepped still. Where a maximum increase in output of 98% is reported in stepped solar still when fin, sponge and pebbles are used in this basin. As well as [Velmurugan et al. 2009b] studied the augmentation of salt water streams in solar stills integrated with a mini solar pond. a highest production of 100% was obtained when the fin type solar still was integrated with pebble and sponge. When solar pond, basin type stepped solar still and a single basin solar still are located in series, a highest productivity of 80% is found, when fins and sponges are used in both the solar stills. When solar pond, stepped solar still and wick type solar still are coupled in series, It is found that maximum productivity of 78% occurred, when fins and sponges are used in the stepped solar still. [Tabrizi et al. 2010] Constructed two cascade solar stills with and without latent heat thermal energy storage system (LHTESS). It was observed that the total productivity of still without LHTESS is slightly higher than the still with LHTESS. II. T heoretical A nalysis Theoretical analysis have been performed at the same conditions for two types of the solar still included modified stepped solar still and conventional solar still. The schematic diagram of the conventional solar still is shown in Figure 1. Basin area of conventional solar still (single basin solar still) 1 m² (0.5 m×2.0 m) Basin of the still fabricated from a black painted galvanized iron sheet to increase the absorptivity. The cover of the still is made up of glass. Figure 2 shows the schematic diagram of stepped solar still. The stepped still has the same dimension and construction of conventional still. As well as absorber plate of stepped still is made up of 5 steps, (each of size 0.1 m×2 m). the stepped solar still integrated with an external condenser to increase the evaporation, fins to increase the absorptivtiy, and an external and an internal mirrors to increase the solar radiation on the still. The water vapour inside the still condensed on the cooler inner surface of the glass, thus, forming droplets and running down the glass. The covering glass prepares the smooth surface to flow the condensate. The distilled water dripped into tilted troughs attached to the lower edges of the glass cover. The condensed water was collected in the V-shaped D Global Journal of Researches in Engineering (A ) Volume XxXII Issue I Version I 13 Year 2022 © 2022 Global Journals