Enhancing of solar still productivity using vacuum technology

In this study the effect of applying vacuum inside the solar still on its productivity is presented. The effect of vacuum inside the still is to avoid any heat transfer due to the convection in the still. So the heat loss from the water in an insulated still is due to the evaporation and radiation only. Hence, the air mass transfer is not included in the analysis. In presence of vacuum the effect of the non-condensable gas which reduces the rate of condensation is also avoided. The results show that applying vacuum inside the solar still increases the water productivity about 100%, i.e. enhancing the efficiency about 100%. This can be considered as the maximum increase in the productivity of the still up to now.     

A multistage solar still with photovoltaic panels and DC water heater using a pyramid glass cover enhanced by external cooling shower and PCM

A novel multistage solar desalination system with a photovoltaic heater was manufactured. The base of the down basin of the solar still had a layer of paraffin wax with a mass of 13 kg as a phase change material. The system has been studied to evaluate the enhancement of freshwater. Saltwater was heated by solar radiation and by a direct current water heater. The surfaces of condensation vapor, such as the pyramid glass cover and lower surface of two stacked trays, were designed. This is to improve the productivity of freshwater by decreasing the resistance of condensation. The high temperature of the glass cover is modified by using a cooling water shower, especially at the highest intensity. The study includes parameters, such as cooling water shower flow rate, down basin water level, and the effect of the heater. It is observed that the novel solar desalination is proportional to solar radiation, paraffin wax, the heat input from a heater, cooling water shower flow rate, and down basin water level. The Multiple Stage Effect Photovoltaic Heater (MSEPVH) can produce 15 L/day of distilled water. The excellent flow rate of cooling water, the total freshwater, and the efficiency of MSEPVH for the optimal day were mathematically and experimentally determined.     

Increase in distillate productivity by inclining the flat plate external reflector of a tilted-wick solar still in winter

This paper presents a theoretical analysis of a tilted-wick solar still with an inclined flat plate external reflector on a winter solstice day at 30°N latitude. The daily amount of distillate of a still with an inclined reflector would be about 15% or 27% greater than that with a vertical reflector when the reflector’s length is a half of or the same as the still’s length.     

A new type of solar water heater

This investigation reports a new type of solar water heating system without water pipes on the collector surface or a separate storage tank. The water to be heated continuously flows perpendicularly from an upper transparent cover to a porous absorber and is stored in a small volume beneath this assembly. Three different systems were designed, manufactured and tested but only one proved to be successful; this design indicated higher thermal efficiency compared to conventional collectors at high flow rates whereas at low flow rates the opposite is true.     

Experimental study and exergetic analysis of a CPC-type solar water heater system using higher-temperature circulation in winter

The common solar water heater system can meet low temperature requirements, but exhibits very low efficiency in attaining higher water temperatures (55–95 °C). In the current paper, a compound parabolic concentrator (CPC)-type solar water heater system experiment rig with a U-pipe was set up, and its performance in meeting higher temperature requirements was investigated. The experiments were conducted in December at Hefei (31°53′ N, 117°15′ E), in the eastern region of China. The system showed steady performance in winter, with overall thermal efficiency always above 43%. The water in the tank was heated from 26.9 °C to 55, 65, 75, 85, and 95 °C. Through the experimental study and exergetic analysis of the solar water heater system, results of the five experiments showed thermal efficiency of above 49.0% (attaining 95 °C water temperature) and exergetic efficiency of above 4.62% (attaining 55 °C water temperature). Based on these results, the CPC-type solar water heater system with a U-pipe shows superior thermal performance in attaining higher temperatures and has potential applications in space heating, heat-powered cooling, seawater desalination, industrial heating, and so on.     

Performance of a collector-cum-storage type of solar water heater

An inexpensive solar water heater of about 701 capacity, combining collection and storage, has been tested. The blackened plate (1.5 m²) of the collector-cum-storage unit of this heater absorbs solar energy and transfers it to the water stored in its enclosure (140 × 90 × 5.5 cm), the water being in direct contact with the absorber plate. The collector-cum-storage unit is enclosed in a wooden box with 10 cm thick glass wool insulation at the bottom and one glass cover.Experiments have been carried out to test the performance of the water heater under four different modes of operation: (a) water circulation with a small pump (b) natural convection conditions (c) water draw-offs taking place when the water is around 50–60°C (d) water flowing continuously past the absorber plate with flow rates of 38, 60, and 75.9 kg/hr. The day-long collection efficiency under the first two modes has been ascertained to be around 50–53 per cent for a rise in water temperature of 57-50°C. For water temperatures between 60 and 70°C, the collection efficiency is around 65-58 per cent. No appreciable difference in the collection efficiencies has been observed under the first two modes of operation. The average collection efficiency under the third mode of testing has been found to be 64.8 per cent with 202.61 of water heated from 38.5 to 58°C. In continuous flow of water past the absorber plate, a collection efficiency as high as 71.8 per cent was attained at the mass flow rate of 75.9 kg/hr, when tested under steady flow conditions. If no water is drawn off during the day, temperatures between 50 and 60°C are reached at about 11 a.m.–12 noon, 60–70°C at 12 noon–1 p.m., and 70–80°C at about 1–2 p.m., the maximum being as high at 86°C by about 3.30 p.m.In addition a theoretical calculation based on Hottel and Woertz equation for the overall heat loss coefficient between the absorber plate and the surroundings for the hourly rise in water temperature shows a very good agreement with the experimentally measured values of water temperatures.     

闷晒式全玻璃真空管太阳能热水器

太阳能热水器主要由集热器与水箱两部分组成。集热器把太阳能转变为热能,靠自然对流或强迫对流把热能储存在水箱中,并有效地防止热损失。评价太阳能热水器性能的好坏,主要看集热器吸热量的多少和水箱散热损失的多少。集热器的吸热量越多,水箱的散热损失越少,其性能越好。不管是平板型的太阳能热水器,还是真空管     

Thermal performance of a solar still coupled with an inexpensive ground water heater

This paper presents the results of investigations carried out over a solar still coupled with an inexpensive solar ground water heater. The explicit expressions for water temperature at the outlet of water heater, glass and water temperatures in the case of a solar still in which the hot water is flowing at a constant rate, have been derived. To appreciate the enhancement in the still productivity, numerical calculations have also been carried out for two typical days at Delhi, India.     

Year-round performance of an improved collector-cum-storage type solar water heater

Systematic studies have been carried out on collector-cum-storage type solar water heaters, and efforts were made to minimise heat losses so that this type of water heater can be used for getting hot water at 40°–45°C for taking baths in the early morning hours of the next day. This paper reports year round performace, the performance equation and economics of this new improved solar water heater. This heater can supply 100 litres of hot water at 60°–70°C in the afternoon, and 40°–45°C temperature can be retained till next day morning. Its efficiency is 70.1%.     

Experimental studies of a new solar water heater system using a solar water pump

The research goal was to develop a new solar water heater system (SWHS) that used a solar water pump instead of an electric pump. The pump was powered by the steam produced from a flat plate collector. Therefore, heat could be transferred downward from the collector to a hot water storage tank. The designed system consisted of four panels of flat plate solar collectors, an overhead tank installed at an upper level and a large water storage tank with a heat exchanger at a lower level. Discharge heads of 1, 1.5 and 2 m were tested. The pump could operate at the collector temperature of about 70–90 °C and vapor gage pressure of 7–14 kPa. It was found that water circulation within the SWHS ranged between 12 and 59 l/d depending on the incident solar intensity and system discharge head. The average daily pump efficiency was about 0.0014–0.0019%. Moreover, the SWHS could have a daily thermal efficiency of about 7–13%, whereas a conventional system had 30–60% efficiency. The present system was economically comparable to a conventional one.     

Desalination of effluent using fin type solar still

In this work, an attempt is made to produce potable water from industrial effluents. An ordinary basin type solar still integrated with fins at the basin plate is used for experimentation. Since industrial effluent is used as feed, before this still, an effluent settling tank is provided to get clarified effluent. This effluent settling tank is fabricated with three chambers, consists of pebble, coal and sand for settling the impurities and removing the bacteria in the effluents. Sponges, pebbles, black rubber and sand are used in the fin type single basin solar still for enhancing the yield. Results show that the productivity increases considerably due to this modification. A theoretical analysis is also carried out which, closely converges with experimental results. The economic analysis proved that the approximate payback period of such kinds of still is 1 year.     

Study of a solar water heater using stationary V-trough collector

There are various types of solar water heater system available in the commercial market to fulfill different customers’ demand, such as flat plate collector, concentrating collector, evacuated tube collector and integrated collector storage. A cost effective cum easy fabricated V-trough solar water heater system using forced circulation system is proposed. Integrating the solar absorber with the easily fabricated V-trough reflector can improve the performance of solar water heater system. In this paper, optical analysis, experimental study and cost analysis of the stationary V-trough solar water heater system are presented in details. The experimental result has shown very promising results in both optical efficiency of V-trough reflector and the overall thermal performance of the solar water heater.     

Effect of inclination of external flat plate reflector of basin type still in winter

This paper presents a theoretical analysis of a basin type solar still with an internal reflector (two sides and back walls) and an inclined flat plate external reflector on a winter solstice day at 30° N latitude. We are proposing a new geometrical method for calculating the solar radiation reflected by the inclined external reflector and then absorbed on the basin liner. Using this method, we performed a numerical analysis of heat and mass transfer in the still in order to determine the effectiveness of the inclination of the external reflector. We found that the benefit of a vertical external reflector would be smaller or even negligible for a still with a larger value for the glass cover angle, while an inclined external reflector can increase the distillate productivity of the still at any glass cover angle, and the external reflector angle should be set at about 15° from vertical on a winter solstice day. The daily amount of distillate of the still with the inclined external reflector would be about 16% greater than that with the vertical external reflector, and about 2.3 times as large as that of the still with neither the internal nor the external reflector on a winter solstice day.     

板式高层住宅应用太阳能热水器的建筑策略

太阳能热水器已在建筑中大量应用,但与高层住宅的结合问题一直没有得到较好的解决。文章分析了当前高层单元式住宅的设计问题和热水器利用的现状,从建筑设计角度提出南向楼梯与太阳能热水器结合的应用方案,分别从系统形式、集热器安装、水箱设置、管道井设置等方面介绍了具体做法和优缺点。     

Theoretical and experimental studies on collector/storage type solar water heater

Extensive theoretical and experimental studies on a built-in-storage solar water heater which was developed earlier by Garg in India, are carried out. In this water heater the absorber plate performs the dual function of absorbing the solar energy and storing the heated water. In the theoretical study, the transient performance of the system is predicted by solving the mathematical models consisting of energy balance equations which are written on different collector nodes by considering their capacity effects and various heat loss effects. These equations are converted in the finite difference form and then solved by digital computer. Solar radiation and ambient temperature are represented by Fourier series in the theoretical analysis. Its night cooling drawback is somehow checked by covering the collector system by an insulation cover during cooling hours and also by using a insulated baffle plate inside the tank adjacent to the absorber plate. It is observed that by using the insulation cover, the collector performance can be improved by 70 per cent. Use of baffle plate improves the performance during day as well as night time.     

新型整体式太阳能热水器的优化设计和实验研究

本文的新型焖晒式热水器主要有两个特点 :一是水箱采用倒三角形且水平横向长纵向短的设计方式 ,以减少水箱中的死水和承压问题 ;二是在玻璃盖板和吸热面之间覆盖透明V形槽或透明蜂窝 ,该种透明隔热构件既有较高的太阳透过率又有较好的隔热性能 ,虽然减少了到达吸热面上的太阳辐射能 ,但保温性能提高了 1～ 2倍。该种热水器热效率接近真空管热水器 ,但成本低 ,且不怕冻冰 ,是我国大部分地区全年可用的低成本高效率的热水器。     

Effects of external reflector and glass cover cooling on thermo-enviro-economic performance of a stepped solar still

In the current research work, performance enhancement of stepped solar still (SSS) having an external reflector (ER) and glass cover cooling (GCC) arrangements is presented. The individual and combined effects of ER and GCC on the performance of SSS have been evaluated and compared with simple SSS. The GCC reduces the glazing temperature significantly and results in increased distillate. The ER reflected the solar radiation inside the basin that increases the water temperature, consequently increasing distillate. The SSS having ER and GCC (SSS-ER-GCC) gave a maximum distillate of 4.340 kg/m² which was observed, respectively, 12.43%, 3.21%, and 1.36% higher than that of simple SSS, SSS with ER (SSS-ER) and SSS with GCC (SSS-GCC). The average energy efficiency of SSS-ER-GCC was evaluated as 40.78%, which was found to be 14.36%, 7.84%, and 10.64%, respectively, higher than that of simple SSS, SSS-ER, and SSS-GCC. The carbon credits earned and CO₂ mitigation were found the maximum for SSS-ER-GCC having values $65.96 and 4.40 tons, respectively. The economic payback period was found the minimum (490 days) for SSS-ER-GCC.     

太阳热水器技术讲座(六)太阳热水器技术经济分析

能量是物质运动的一般量度。能量有机械能、分子内能、电能、化学能、原子能、太阳能、生物质能等。     

Experimental investigation of the effect of using the cylindrical parabolic collector,different solar panels and their cooling on seawater desalination in double-slope solar still

ABSTRACT

The present study was aimed at examining the effect of using solar panels and cylindrical parabolic collectors, or CPCs, on solar still unit. Cooling of the solar panels up to 25°C has been also conducted in order to rise the amount of produced freshwater. In the first setup, the solar still unit has been made up of 300 W and 600 W solar panels along with the CPC devices of lengths 1 m and 2 m outside for water heating. The second setup was designed in a way that water is heated by the solar panels as well as the CPC device with the copper pipe circulation inside the solar still unit, so the hot water within the pipe has raised the temperature of the water as a heat exchanger inside the solar still. Based on the results, the second setup had a higher efficiency than the first setup. Moreover, the highest amount of fresh water was 4.215 kg and 5.091 kg during one day in the first setup and the second setup, respectively. Cases 1 to 6 are related to the first setup and cases 7 to 12 are related to the second setup. The lowest fresh water production in case 1 was 2.852 kg. the highest water temperature in experimental setup 1 was 71.9 °C and in experimental setup 2 was 84.8°C.     

The effect of aging on a 22-year-old solar water heater

Collector thermal performance tests on a 22-year-old double-glazed black painted solar water heater indicate that the degradation in its performance is due mainly to glazing seal failure allowing moisture into the insulation. The effect of dirt on the covers does not appear to have adversely affected its thermal performance.