Author Topic: Effect of Nanofluids in a Vacuum Single Basin Solar Still  (Read 6030 times)

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Effect of Nanofluids in a Vacuum Single Basin Solar Still
« on: February 18, 2012, 02:30:23 am »
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Author : M. Koilraj Gnanadason, P. Senthil Kumar, G.Jemilda, S.Raja Kumar
International Journal of Scientific & Engineering Research Volume 3, Issue 1, January-2012
ISSN 2229-5518
Download Full Paper : PDF

Abstract — Clean water is a basic human necessity and without water life will be impossible. The provision of fresh water is becoming an increasingly important issue in many areas of the world. Among the non-conventional methods to desalinate brackish water or seawater, is solar distillation. The solar still is the most economical way to accomplish this objective. Tamilnadu lies in the high solar radiation band and the vast solar potential can be utilized to convert saline water to potable water. Solar distillation has low yield, but safe and pure supplies of water in remote areas. The attempts are made to increase the productivity of solar still by using different absorbing materials, depths of water, heat storage medium, nanofluids and also by providing low pressure inside the still basin. Heat transfer enhancement in solar still is one of the key issues of energy saving and compact designs. The use of additives is a technique applied to enhance the heat transfer performance of water in the still basin. Recently, as an innovative material, nanosized particles have been used in suspension in conventional solar still water. The fluids with nanosized solid particles suspended in them are called “nanofluids.” The suspended metallic or nonmetallic nanoparticles change the transport properties, heat transfer characteristics and evaporative properties of the base fluid. Nanofluids are expected to exhibit superior evaporation rate compared with conventional water. The aim of this paper is to analyze and compare the enhanced performance in a vacuum single basin solar still using nanofluids with the conventional water. They greatly improve the rate of evaporation and hence the rate of condensation on the cooler surface.

Keywords— Solarstill; Nanofluid ;Nanoparticles; productivity.

1     INTRODUCTION
Water is essential to life. The origin and continuation of mankind is based on water. The supply of drinking water is an important problem for the developing countries. The increasing world population growth together with the increasing industrial and agricultural activities all over the world contributes to the depletion and pollution of fresh water resources. Worldwide drought and desertification are expected to increase the problem [1]. The importance of supplying potable water can hardly be overstressed. Water is an abundant natural resource that covers three quarters of the earth’s surface. However, only about 3% of all water sources is potable. Less than 1% fresh water is within human reach and the rest is ice. Even this small fraction (ground water, lakes and rivers) is believed to be adequate to support life and vegetation on the earth. About 25% of the world does not have access to quality and quantity of fresh water and more than 80 countries face severe water problem [2]. In some instances, the salinity is probably too high for water to be considered as fresh drinking water; instead it is called brackish water. Salinity is usually expressed in parts per million (ppm). In such cases, fresh water has to be either transported for long distances or connected with an expensive distribution water network at extremely high cost for a small population [3]. Solar distillation is one of the available methods for water distillation and sunlight is one of the several forms of heat energy that can be used to power that process. Solar stills can easily provide enough water for drinking and cooking needs of the family. Also distilled water can be used for industrial purpose as it is cleaner [4].
 In this context, distilled water evaporation rate is enhanced by using solar still made up of Copper sheet instead of Cast Iron. The attempts are also made to increase the productivity of water by painting black coating inside the basin and providing low pressure inside the still. But the novel approach is to introduce the nanofluids in solar still with conventional water. The poor heat transfer properties of these conventional fluids compared to most solids are the primary obstacle to the high compactness and effectiveness of the system. The essential initiative is to seek the solid particles having thermal conductivity of several hundred times higher than those of conventional fluids. An innovative idea is to suspend ultrafine solid particles in the fluid for improving the thermal conductivity of the fluid [6]. The fluids with solid-sized nanoparticles suspended in them are called nanofluids. The suspended metallic or nonmetallic nanoparticles change the transport properties, heat transfer characteristics and evaporative rate of the base fluid. The carbon nanotube (CNT)-based nanofluids are expected to exhibit superior heat transfer properties compared with conventional water in the solar still and other type of nanofluids and hence the increase in the productivity and efficiency of the solar still [7].

2    SOLAR STILL
As the available fresh water is fixed on the earth and its demand is increasing day by day due to increasing population and rapidly increasing of industry, hence there is an essential and earnest need to get fresh water from the saline/brackish water present on or inside the earth. This process of getting fresh water from saline/ brackish water can be done easily and economically by desalination [3]. The solar stills are simple and have no moving parts and it can be used anywhere with lesser number of problems. The operation of solar still is very simple and no special skill is required for its operation and maintenance [4]. The use of solar energy is more economical than the use of fossil fuel in remote areas having low population densities, low rain fall and abundant available solar energy. Various parameters affect both efficiency and the productivity of the still.  The distilled water production rate can be increased by varying design of the solar still, depths of water, salt concentration, location and different absorbing materials, evaporative techniques and use of nanofluids [9].

2.1  Distillation is the same as Rainwater Process
Desalination is the one of the most important methods of getting potable water from brackish and sea water by using the free energy supply from the sun.  In nature, solar desalination produces rain when solar radiation is absorbed by the sea and causes water to evaporate. The evaporated water rises above the earth’s surface and is moved by the wind. Once this vapor cools down to its dew point, condensation occurs, and the fresh water comes down as rain. The same principle is used in all manmade distillation systems using simple scientific principle of Evaporation and condensation. There are several types of solar stills, the simplest of which is the single basin still. But the yield of this is low and falls in the range of 3-4 litres per day per square metre [5].

2.2   Working of Solar Still
In conventional basin type solar still, the still consists of a shallow airtight basin lined with a black, impervious material, which contains Brackish or saline water. Solar radiation received at the surface is   absorbed effectively by the black surface and heat is transferred to the water in the basin. Temperature of the water increases and it increases the rate of evaporation. A sloping transparent glass cover is provided at the top. Water vapour produced by evaporation rises upward and condenses on the inner surface of the glass cover which is relatively cold. Condensed water vapour trickles down into the trough and from there it is collected in the storage container as distilled water.  The distilled water from a solar still has excellent taste when compared with commercially distilled water since the water is not boiled (which lowers pH). They are made of quality materials designed to stand up to the harsh conditions produced by water and sunlight. Provision is made to add water in the stills. Purified drinking water is collected from the output collection port as distillate.

3    EXPERIMENTAL SETUP
3.1   Solar Still Made Up of Copper
 As shown in the figure 1, solar still consists of a shallow triangular basin made up of Copper sheet instead of Cast Iron. As Copper has higher thermal conductivity of 401 W/mK comparatively higher than Cast Iron, rate of heat transfer to water in the still is more. The bottom of the basin is usually painted black to absorb sun’s heat which in turn increases the evaporation rate. Top of the basin is covered with a glass of 4mm thick. Tilted fixed 32o so as to allow maximum transmission of solar radiation and helps the condensed vapour to trickle down into the trough, built in channel in the still basin. The edge of the glass is sealed with a tar tape so as to make the basin airtight. Entire assembly is placed on a stand structure made up of M.S angles. The outlet is connected to   a   storage container through a pipe.
The   basin   liner   is   made   of   a copper   sheet   of 900x400x50mm and 1.5 mm thickness.  The copper sheet is painted by red-lead primer then by matt-type black paint. used in the still.
 
Fig. 1. Experimental setup

Glass  cover  has  been  sealed  with  silicon  rubber which plays an important role to promote efficient operation as  it  can  accommodate  the  expansion and contraction between dissimilar materials. A thermo cool of 2.5 cm thickness with thermal conductivity of 0.045W/mK is used as insulating material to reduce the heat losses from the bottom and the side walls of the solar still.  The still is filled with the brackish water in a thin layer. The outer box is made by plywood. When sun radiation is coming on the solar still, the glass cover is heated. And due to heating of glass cover temperature of the water inside the solar still is increases and it forms vapour.  Such vapour has low density so goes upward and sticks to glass cover means it condenses. And due to slope it will go downward and collect in glass. Researches in heat transfer have been carried out over the previous several decades, leading to the development of the currently used heat transfer enhancement techniques. The use of additives is a technique applied to enhance the heat transfer performance of water in the still basin. Recently, as an innovative material, nanosized particles have been used in suspension in conventional solar still [7]. The fluids with nanosized solid particles suspended in them are called “nanofluids”. The suspended metallic or nonmetallic nanoparticles change the transport properties and heat transfer characteristics of the water in the still. Thus the water temperature in the basin increases. The carbon nanotube (CNT)-based nanofluids are expected to exhibit superior heat transfer properties compared with conventional water and other type of nanofluids [8].

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samantha_9

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Re: Effect of Nanofluids in a Vacuum Single Basin Solar Still
« Reply #1 on: December 07, 2013, 05:48:13 am »
Nice!