Assessment of convective heat transfer coefficient and mass of water evaporated from a single-slope passive solar still by different thermal models: an experimental validation

In this paper, an effort has been made to evaluate the convective heat transfer coefficient and mass of water evaporated from a single-slope passive solar still for different water depths (0.01, 0.015, 0.02 and 0.025?m) by various thermal models, namely Dunkle’s model, Chen et al.’s model, Clark’s model, Adhikari et al.’s model, Kumar and Tiwari’s model, Zheng Hongfei et al.’s model and Tsilingiris’s model. These models were studied and compared with our experimental work. Also, the energy and exergy efficiency were calculated and the percentage deviation between experimental and theoretical prediction is also listed out. The experimental validation of energy and exergy efficiency of single slope passive solar still using different thermal models was carried out at Chennai, Tamil Nadu, India. By comparing the theoretical values of the hourly yield with the experimental data it was found that Dunkle’s, Chen et al.’s and Tsilingiris’s models gave better conformity between the forecasted and experimental results. Kumar and Tiwari’s model yield is very high, whereas Clark’s model, Adhikari et al.’s model and Zheng Hongfei et al.’s model predict lower values as compared with our experimental results.     

Energy and exergy analysis of single slope single basin solar still

A single slope basin type solar still has been designed and fabricated. The still is provided with a dripping arrangement to pour saline water drop by drop in the basin. Thermal modelling has been proposed based on the energy balance equations of the temperature elements of the still. A computer program has been written for the analytical solutions for the temperature of glass cover, water and basin, respectively, and numerical results are validated with the experimental for one of the typical days in summer and winter (2 October 2010 and 30 May 2011). The numerical results are in close agreement with the experimental results. Also exergy and energy analysis have been carried out to find the parametric influence on the performance of the still and to evaluate the fractional exergy and energy, instantaneous exergy and energy efficiency of the still.     

Solar energy performance analysis of basin-type solar still under the effect of vacuum pressure

ABSTRACT

This paper deals with a solar still for distilled water, using the heat of the sun to evaporate, cool and then collect the water. They are used in areas where drinking water is unavailable, so that clean water is obtained from dirty water or from plants by exposing them to sunlight; vacuum pressure is delivered to still-type solar. The reason for selecting vacuum pressure is that during the monsoon and cloudy days, solar intensity will not be high as it leads to evaporation at lower temperature saline water under the soar still. The basin area for the production of 5 litres per day of fresh water is determined as 1.44?m²and the solar still basin area of 1.44?m² and 21.5° tilt angle are designed. Solar energy be may used full to alternate in electrical power and to purify water in future. Finally, the performance was analysed for the solar still with a vacuum pressure at 0.6 bar. The outcome of the theoretical analysis shows that adoption of 0.6 bar pressure inside the solar still improves the average performance by 30%. In order to overcome this problem, vacuum could be applied for the better performance of the solar still during the low solar intensity periods.     

Experimental investigation of a passive solar still with and without tetrahedral sponge in basin

In this work, an experimental study is carried out to investigate the influence of the presence of porous media on the performance of solar still. Two different shapes of sponge pieces, namely cube and tetrahedron, are considered for this study. Experiments are conducted on a single-slope solar still with condensing cover of 30° inclination. This study was performed in Indian coastal climatic condition for 24?h. The experimental study emphasises on the overall distillate yield, and the efficiency of the still with sponge cubes and tetrahedrons is compared with the conventional still. The size of the pieces is selected such that the volume of both shapes is the same. As the surface area to volume ratio is more for tetrahedral sponge piece, the highest distillate production is observed in that of sponge cube. It is observed that the maximum distillate yield is produced at optimum values of water depth at 5?cm, single piece sponge volume of 216?cm³ and sponge volume of 30% of the basin water volume. The increase in yield is due to the capillary effect and high evaporation rate and it varies from 45% to 219% with tetrahedral sponge pieces when compared to conventional still.     

Economic and exergy investigation of triangular pyramid solar still integrated to inclined solar still with baffles

This paper presents the detailed exergy and economic investigation of triangular pyramid solar still under passive and active mode of operation. For validation, experiments were carried out at different water depth maintained inside the basin under a continuous flow of water from an inclined solar still. Results confirm that the effect of integration rises the exergy efficiency during the offshine period, whereas during the sunshine hours the exergy efficiency decreases when the maintained the depth of water inside basin decreases. Similar study on economic analysis shows that the net pay back period increases from 5.6 to 11.4 with an increase in the water depth at an average selling price of water Rs 5/kg in a standalone triangular pyramid solar still.     

Performance analysis on improved efficiency in a hybrid solar still and solar heater

ABSTRACT

This paper deals with solar still. Today fresh water demand is increasing continuously, because of the industrial development, intensified agriculture, improvement of standard of life and increase in the world population. Only about 3% of the world water is potable and this is not evenly distributed on the earth. On deserts and islands, underground water is not readily available and the cost of shipping to other places is high, it is worthwhile to consider producing potable water from saline water using solar energy that is in abundant in deserts. The efficiency of the solar still can be increased by increasing the evaporation rate and by minimising the convective and radioactive losses in still. The evaporation rate can be increased effectively by coating the still base with photocatalyst materials or by pre-heating the inlet water of still. The easily available GAC is one of the best photocatalyst materials suitable for the solar still for enhancing the evaporation rate. Solar-still technology is a renewable and efficient technology for pre-heating the inlet water to solar still. Hence the combination of GAC coating and solar-still technology can increase the evaporation rate and efficiency of solar still.     

Experimental study on improving the performance of solar still using air blower

Water is a basic necessity of man. Economical and efficient production or recycling of water is very much needed in today's world. Solar still has emerged as a life-saving technology to distil brackish water and produce drinkable water using solar energy. The aim of this project was to improve the performance of solar still by adding an air blower which creates a bubbling effect in the still due to which the evaporation rate increases. The bubbling effect using the blower makes the raw water to circulate and to distribute heat energy equally. The evaporated raw water was collected in the glass plate as drop particles. The drop condenses due to ambient air and finally distillate output is collected in the jar, which is placed outside the still. The solar still with air blower arrangement gave higher difference in efficiency and higher distilled output when compared with solar still without an air blower.     

Effect of forced cover cooling technique on a triangular pyramid solar still

In the present study a triangular pyramid solar still is theoretically analysed by flowing air over the entire surface of the glass from the top to analyse the improvement in yield of fresh water. The effect of water mass and wind velocity was theoretically analysed. The results show that there is a significant improvement in the yield of fresh water to about 10.1?kg/m² with a maximum velocity of air (U?=?40?m/s) at a least water mass of 20?kg inside the basin. For practical cases the yield of fresh water depends on naturally occurring wind velocity and the results show that the improvement in yield is 104% with an increase in velocity from 0.5 to 4?m/s.     

Annual performance analysis of various energy storage materials in the upper basin of a double-basin solar still with vacuum tubes

ABSTRACT

A double-basin solar still with vacuum tubes showed impressive distillate output due to getting potable water from lower and upper basins. But it is also true that distillate output of the upper basin is lower compared with that of the lower basin. Hence, work is required to increase distillate output of the upper basin. In the present work, the upper basin was used with various energy-absorbing materials like black granite gravel, pebbles and calcium stones. The main purpose of using absorbing materials is to store excess energy during sunshine hours and release during off-sunshine hours. Therefore, the distillate output of the upper basin is increased compared with a still with only an upper basin. Hence, continuous work on a double-basin solar still with vacuum tubes (DBSWVT) by putting above energy absorbing materials is carried out during clear sky days of July 2014 and in June 2014. For comparison of a still with energy-absorbing materials, experimental readings of three days of May 2014 (1st, 5th and 9th) are chosen to determine the performance output of the present still with the said energy-absorbing materials. At last, yearly average distillate output of DBSWVT is carried out with said energy absorbing materials, cost of potable water/INR, energy payback time found 0.509 and 109 days. Also, on comparison with other researchers’ work in terms of percentage increment in distillate output 229.2% increment was found compared with a passive solar still.     

Effect of flat plate collectors in parallel on the performance of the active solar still for Indian coastal climatic conditions

The effect of flat-plate collectors (FPCs) when connected in parallel on, in particular, the heat transfer coefficients and, in general, distillate output and the efficiency of solar still has been studied in the active mode. The solar still has an effective basin area of 1?m² and fixed cover inclination of 30°. Each FPC with an effective area of 2?m² is attached to the solar still. An effective collector inclination of 5° is used. Experiments have been conducted for 24?h in summer for the active solar distillation system at Kakinada (16°.93′N/83°.33′E), India, which has coastal climatic conditions. The aim of the present work is to study the variation in internal heat transfer coefficients with respect to the number of FPCs coupled with the solar still in parallel. It is understood that the heat transfer coefficients depend significantly on the size of the collector. The size of the collector is increased by increasing the number of collectors. It is also observed that this leads to an increase in distillate output but a decrease in efficiency of the solar still.     

A comparative performance analysis of solar heat exchangers for solar hot water application under controlled laboratory conditions

The paper presents the experimental performance evaluation of a novel retrofit heat exchanger (‘SolaPlug’) developed for solar hot water storage applications. The performance of this system was compared with a traditional dual-coil (‘Coil’) solar cylinder under controlled operating conditions. The tests were conducted under different solar-simulated conditions with a 30 and 20 evacuated tube collector. The results showed that after a 6-h test period, the average water temperatures within the store for the ‘SolaPlug’ system were 58.8°C and 40.5°C at 860 and 459?W?m^?2, respectively, and for the ‘Coil’ system were 60.5°C and 40.6°C when a 30 tube collector was used. The performance of the ‘SolaPlug’ system was marginally better than the ‘Coil’ system under the low solar input condition. Under high insolation condition, the overall ‘SolaPlug’ system efficiency was found to be 4.3% lower than that of the ‘Coil’ system. The ‘SolaPlug’ heat exchanger rating was 222?W?K^?1.     

Enhancing the productivity of double-slope single-basin solar still with internal and external modifications

The major task before us is to increase the performance of solar stills. Researchers have done many modifications to enhance the productivity of solar stills. In this article, the authors have attempted to improve the performance of solar stills. Instead of a conventional solar still, a double-slope single-basin solar still was fabricated. It was internally modified by spreading pebbles at the bottom. External modification was attempted by fitting an external mirror. Internal modification enhanced the production marginally. Significant improvement in production was witnessed when both internal and external modifications were attempted. The performance of the double-slope single-basin solar still with internal and external modifications was 40.86% higher than that of the solar still without any modification.     

利用被动太阳能改善中部地区城镇住宅室内热环境

从应用动态软件进行围护结构热工性能参数研究，并从优化设计着手，利用被动太阳能技术实现水平室内热舒适环境条件，试点建筑科夏季实测，证明达到预期目标。     

槽式太阳能集热器传热模型及性能分析

槽式太阳能集热器一维和二维传热数学模型是一组非线性代数方程,为改进求解的稳定性和计算精度,将槽式太阳能集热器一维和二维传热模型的求解看作有约束优化问题,建立了集热器传热过程求解的有约束优化数学模型,应用MATLAB软件优化函数fmincon进行求解。分析了传热流体入口温度及太阳能辐射热流密度变化对集热器性能的影响。采用fmincon函数求解集热器传热过程,计算速度快,计算过程稳定。分析表明,传热流体温度变化对集热器效率的影响大于太阳能辐射热流密度对集热器效率的影响。     

Impact of magnetic field on the enhancement of performance of thermal solar collectors using nanofluids

A numerical mathematical model has been developed to predict the thermal behaviour of thermal solar collectors using nanofluids under different magnetic fields. The model is based upon energy conservation equations for nanofluids flow, heat transfer for different nanofluids and magnetic field. The thermal behaviour of the solar collectors during charging phase has been studied, predicted numerically and analysed using different nanofluid materials and magnetic fields. Comparisons were made against literature data for validation purposes of the predictive model. The model fairly predicted heat absorbed and solar panel efficiency under different nanofluids conditions, magnetic fields and compared well with existing data on the subject.     

关于热泵一次能源利用率的计算与分析

发电环节按燃煤电厂考虑,针对空气源热泵热水供热系统进行了一次能源热效率和[火用]效率的计算和分析,结果表明:热泵机组COP分别为3和4时,其一次能源热效率均大于100%,但热泵机组的一次能源[火用]效率、热泵供热系统的一次能源[火用]效率都远小于100%。热泵供热系统的一次能源[火用]效率表征了热泵供热系统对一次能源[火用]价值的利用程度,可称为热泵供热系统的一次能源利用率。而热泵机组的COP及其一次能源热效率虽然不能直接反映一次能源价值的利用程度,但它们都与热泵供热系统的一次能源[火用]效率呈正比关系,所以也都可以用于对热泵供热系统进行能效比较和评价。合理降低热泵机组输出水温可以提高机组的COP,从而提高热泵供热系统的一次能源[火用]效率,实现相同供暖目标的一次能源消耗量减少。     

Life-cycle assessment of a 100% solar fraction thermal supply to a European apartment building using water-based sensible heat storage

Providing 100% of a building's heating and hot water using a solar thermal system in a European climate has been shown to be both practically feasible and functionally successful for a new apartment building in Switzerland. The research conducted a life cycle assessment of the solar thermal system and compared the results with an air-source heat-pump, ground-source heat pump, natural gas furnace, oil furnace and a wood-pellet furnace. Using a range of lifetime scenarios it was found that the solar thermal system displays potentially significant advantages over all other systems in terms of reductions for purchased primary energy (from 84 to 93%) and reductions in GHG emissions (from 59 to 97%). However, due to the heavy industrial processes and the particular metals used in manufacturing, the solar thermal system was shown to have a higher demand for resources which, in relation to the natural gas system, can be by a factor of almost 38. Potential impacts on ecosystem quality were marginally worse than for the heat-pump and fossil fuel systems due to resource use impacts whilst potential human health impacts were similar to the heat pump systems but better than the fossil and biomass fuelled systems.     

Build-up and performance test of a novel solar thermal roof for heat pump operation

Global increase in energy demand and fossil fuel prices loaded ever-increasing pressure on identifying and implementing new means to utilise clean and efficient energy resources. Due to the environmental benefits, technical and economic possibilities of Solar-Assisted Heat Pump Systems, there has been a growing interest for such hybrid systems with a variety of system configurations for various climates. International Energy Agency Task 44 of the Solar Heating and Cooling Programme has recently started working on finding methods to most effectively use solar heat pump systems for residential use. In the present study, a novel solar thermal roof collector was developed by primarily exploiting components and techniques widely available on the market and coupled with a commercial heat pump unit. The proposed indirect series Solar-assisted Heat Pump system was experimentally tested and system performance was investigated. Yet, the analysis based on indoor and outdoor testing predominantly focuses on the solar thermal roof collector. A detailed thermal model was developed to describe the system operation. Also, a computer model was set up by using Engineering Equation Solver to carry out the numerical computations of the governing equations. Analyses show that the difference in water temperature could reach up to 18°C while maximum thermal efficiency found to be 26%. Data processing of the series covering the test period represents that Coefficient Performance of the heat pump (COP_HP) and overall system (COP_SYS) averages were attained as COP_HP?=?3.01 and COP_SYS?=?2.29, respectively. An economic analysis points a minimum payback period of about three years for the system.     

Investigation on performance analysis of a novel design of the vacuum tube-assisted double basin solar still: an experimental approach

In this present work, the lower basin is connected to the conventional vacuum tubes, hence the temperature of water remains higher throughout the day and the distillate output also remains higher and always releases the latent heat of condensation to the upper basin for heating of water and enhancement of the distillate output. In this research paper, the double basin solar still with vacuum tubes fabricated wastested in climate conditions of Mehsana, (23.6000°N, 72.4000°E), Gujarat, with three different water depths 0.03, 0.04 and 0.05 m inside the lower basin and upper basin for one year time period of January 2012 to December 2012. It has been found that the double basin solar still with 0.03 m depth produced more compared with 0.04 kg and 0.05 m. It has also found that the average distillate output of the present system was found to be 8 with the monetary value of produced water being around 0.37 Rs/kg.     

中空窗玻璃贴低辐射膜的性能研究

热阻和太阳能透过率是分别反映窗玻璃热工性能和光学性能的参数.在不贴膜和室内贴低辐射膜2种情况下,对中空窗玻璃的热阻和太阳能透过率进行实验研究,分析和比较2种情况下的窗玻璃性能及其对节能性的影响.结果表明,实验所用中空窗的固定窗和推拉窗2部分,贴膜后传热阻分别增大31.1%和40.7%,传热系数分别降低23.7%和28.8%.对于玻璃的太阳能透过率,贴膜后从40%减少到28.6%,透过玻璃的辐射热减少28.5%.