A low cost collector-cum-storage type solar water heater

A low cost collector-cum-storage type solar water heater has been developed. The cost of the heater is reduced by replacing window glass cover with 0.2 mm thick PVC film to avoid glass breakage in transportation and maintenance. In this paper the performances of solar water heaters having double glazing of PVC and glass have been compared. It was found that their performances are similar. Moreover, by providing an insulating cover in the night, the water remains warm till next morning for taking a bath etc. in the early hours when there is no sunshine.     

Enhancement of daily yield in a double basin solar still

A straightforward transient analysis of a double basin solar still has been presented, incorporating the effect of water flow over the glass cover and flow of hot water in the lower basin by a flat plate collector. It is concluded that, for higher daily yield, the collector should be disconnected from the still during off-sunshine hours.     

Performance of an inexpensive rural solar collector

In this paper we discuss an inexpensive solar collector in which the heat storage material is sand or sand mixed with iron filings. The heat is absorbed by the blackened portion of the heat storage material. The heat is withdrawn from the system by water flowing through a network of plastic pipes buried in the heat storage material at an appropriate depth. The large efficiency is obtained when the material is sand mixed with iron filings. It is shown that the efficiency of the system can be judged from the glass cover temperature. As the glass cover temperature decreases, the efficiency of the system increases.     

Short communication simple transient thermal model for solar colector/storage water heaters

This note presents a simple transient model for predicting the thermal performance of some novel solar water heaters which combine both collection and storage of solar energy. These heaters consist of either (i) an insulated rectangular tank whose top surface is blackened and suitably glazed, or (ii) an insulated open shallow tank with black bottom/inner sides and a top glass cover (shallow solar pond). the heaters are adequately covered with an insulation during the night to reduce the heat losses. the proposed model is based on different characteristic equations during sunshine and off-sunshine hours. It is seen that the model predicts the water temperature in close agreement with the experimental observations and earlier theoretical investigations.     

Validation of CFD simulation for flat plate solar energy collector

The problem of flat plate solar energy collector with water flow is simulated and analyzed using computational fluid dynamics (CFD) software. The considered case includes the CFD modeling of solar irradiation and the modes of mixed convection and radiation heat transfer between tube surface, glass cover, side walls, and insulating base of the collector as well as the mixed convective heat transfer in the circulating water inside the tube and conduction between the base and tube material. The collector performance, after obtaining 3-D temperature distribution over the volume of the body of the collector, was studied with and without circulating water flow. An experimental model was built and experiments were performed to validate the CFD model. The outlet temperature of water is compared with experimental results and there is a good agreement.     

An investigation of the parameters involved in simple solar still with inclined yute

Desalination of water has been one of the most important technological work undertaken in many countries, in particular Middle East. For this purpose, solar energy is the attractive familiar way in producing such fresh water where the cost of other energy is continuously increased. This paper represents the experimental results carried out with a solar still with inclined evaporating yute to study the effects of air gap, base slope angle and glass cover slope angle on the performance of the still. In order to investigate the parameters involved in the still, three models have been designed, manufactured and tested against some experimental measurements on a still having 1m × 1m basin area. The models have been designed in a way that it can give different base slope angle and glass slope angle. A comparison between the three models has been made for three glass slope angles. The test results show that the model with base slope of 15° and glass slope of 35° gives the best results. It gives a daily desalinated water quantity of 5.6 liter/m².day.     

System design, operation and performance of roof-integrated desalination in greenhouses

This paper is focused on applications in remote and arid locations where the source water is assumed to be brackish. In this concept the roof transmission is reduced as solar irradiation is absorbed by flowing water on a glass sheet covered by a top glass sheet. Fresh water is evaporated, condensed on the top glass and collected at the roof eaves.For the assessment of this concept compared to conventional, single glassed greenhouses, extensive computer simulations and field experiments were performed in Tunisia. Considerably less extreme climate conditions were registered in an experimental greenhouse with roof desalination compared to a conventional house. The simulation inaccuracy was around 5% for the water demand and production. In a more general analysis, various design cases, including crop cultivation examples were simulated. A system integrated in 50% of the roof area had the capacity to cover the annual demand for a low canopy crop. A similar capacity for a high canopy crop requires asymmetrical roof design and desalination system in the whole roof area.The yield problem could be solved with more light selective glass materials (NIR-absorption). Interesting future prospects are expected for electrochromic glasses with dynamic absorptance control. This could improve crop yields and eliminate the seasonal storage demand.     

Physics of shallow solar pond water heater

This communication presents a theoretical analysis of a shallow solar pond water heater, which is in good agreement with the experiments of Kudish and Wolf (1979) and the authors. the heater consists of an insulated metallic rectangular tank with black bottom and sides and a transparent cover at the top. After the collection of solar energy during sunshine hours the heater stores a substantial amount of heat because the top glass cover is covered by an adequate insulation in the night. Analytical expressions for the transient rise of temperature of water in the tank have been derived taking into account the appropriate heat transfer processes during day and night. These experimental results as well as those of Kudish and Wolf (1979) have been found to be in good agreement with the theory presented in this paper. the effects of one more glass cover on the top, and of the thickness of the bottom and side insulation and tank depth on the water temperature have also been studied.     

Transient analysis of double basin solar still

The effect of water flowing over the upper glass cover of a double basin solar still on its transient performance has been presented. A comparative study of the daily distillate production of a double basin solar still with and without water flowing over the upper glass cover has been made, and some interesting conclusions have been drawn. Numerical calculations have been made for a typical hot day (viz 2 May 1980) in Delhi.     

Analysis of heat transfer coefficients and evaporation in a solar still

The dependence of the glass cover temperature, the individual heat transfer coefficients, the overall upward heat flow factor, the fraction of upward heat flow utilized for evaporation, and the rate of water evaporation on the basic parameters has been studied. A semi-empirical equation for estimation of the glass cover temperature has recently been proposed by the authors. An analysis has been made of the capability of the new method to compute accurately the glass cover temperature, the overall upward heat flow factor, the rate of water evaporation, the fraction of upward heat flow utilized for evaporation over an extensive number of combinations of the basic parameters.     

Thermal modeling of passive and active solar stills for different depths of water by using the concept of solar fraction

This communication presents the thermal analysis of passive and active solar distillation system by using the concept of solar fraction inside the solar still with the help of AUTOCAD 2000 for given solar azimuth and altitude angle and latitude, longitude of the place. Experiments have been conducted for 24 h (9 am to 8 am) for New Delhi climatic conditions (latitude 28°35′N, longitude 77°12′E) during the months of November and December for different water depths in the basin (0.05, 0.1 and 0.15 m) for passive as well as active solar distillation system. Analytical expressions for water and glass cover temperatures and yield have been derived in terms of design and climatic parameters. It is observed that

(i) the solar fraction plays a very important role at lower values of solar altitude angle;

(ii) the internal convective heat transfer coefficient decreases with the increase of water depth in the basin due to decrease in water temperature;

(iii) there is a fair agreement between the experimental observation and theoretical prediction during daytime as compared to that during the night.

Transient analysis of solar still

This paper presents an analysis of the transient performance of a basin type mounted still; explicit expressions for hourly variation of temperature of glass cover and water in the basin and distillate output have been obtained. The results of the analysis are in good agreement with experiments.     

Effect of Water Flow over the Glass on the Performance of a Solar Still Coupled with a Flat Plate Solar Collector†

In this communication a transient analysis of a solar distillation system with water flow over the glass cover is presented. The system comprises of a single basin solar still coupled with a flat plate solar collector. Due to the increased difference between water and glass temperatures the yield of this system is significantly increased. The performance of this system has been compared with that of a simple single basin solar still (SBSS), SBSS with water flow over it and SBSS coupled with a flat plate collector; and it is concluded that a SBSS with water flow over it shows the best performance.     

Monthly optimum inclination of glass cover and external reflector of a basin type solar still with internal and external reflector

In this report, we present a theoretical analysis of a basin type solar still with internal and external reflectors. The external reflector is a flat plate that extends from the back wall of the still, and can presumably be inclined forwards or backwards according to the month. We have theoretically predicted the daily amount of distillate produced by the still throughout the year, which varies according to the inclination angle of both the glass cover and the external reflector, at 30°N latitude. We found the optimum external reflector inclination for each month for a still with a glass cover inclination of 10-50°. The increase in the average daily amount of distillate throughout the year of a still with inclined external reflector with optimum inclination in addition to an internal reflector, compared to a conventional basin type still was predicted to be 29%, 43% or 67% when the glass cover inclination is 10°, 30° or 50° and the length of external reflector is half the still’s length.     

Photothermal performance of selective black nickel coatings

Selective black nickel coatings with solar absorptance (αs = 0·94) and thermal emittance (ε = 0.08) at 100°C have been developed on galvanized steel using electroplating and chemical conversion techniques. Thermal performance tests have been conducted on selective and non-selective collectors with single glass cover. A suitable collector test assembly has been constructed for thermal performance study. Measurements have been made under clear sky conditions over a wide range of inlet temperatures. For comparison, measurements have been carried out on an identical collector painted black. Thermal efficiencies of about 28 per cent at an operating water temperature =100°C ambient temperature =35°C and incident insolation =1000 W/m2 have been obtained.     

Thermal modeling of a combined system of photovoltaic thermal (PV/T) solar water heater

In this paper, an integrated combined system of a photovoltaic (glass–glass) thermal (PV/T) solar water heater of capacity 200 l has been designed and tested in outdoor condition for composite climate of New Delhi. An analytical expression for characteristic equation for photovoltaic thermal (PV/T) flat plate collector has been derived for different condition as a function of design and climatic parameters. The testing of collector and system were carried out during February–April, 2007. It is observed that the photovoltaic thermal (PV/T) flat plate collector partially covered with PV module gives better thermal and average cell efficiency which is in accordance with the results reported by earlier researchers.     

Critical evaluation of solar chimney power plant performance

This paper evaluates the influence of a recently developed convective heat transfer equation, more accurate turbine inlet loss coefficient, quality collector roof glass and various types of soil on the performance of a large scale solar chimney power plant. Results indicate that the new heat transfer equation reduces plant power output considerably. The effect of a more accurate turbine inlet loss coefficient is insignificant, while utilizing better quality glass enhances plant power production. Models employing Limestone and Sandstone soil produce virtually similar results to a Granite-based model. The plant collector height is found to differ from previously obtained optimal values.     

Theory and experimental investigation of a weir-type inclined solar still

A weir-type solar still is proposed to recover rejected water from the water purifying systems for solar hydrogen production. This consists of an inclined absorber plate formed to make weirs, as well as a top basin and a bottom basin. Water is flowed from the top basin over the weirs to the bottom collection basin. A small pump is used to return the unevaporated water to the top tank. Hourly distillate productivity of the still with double- and single-pane glass covers was measured and the latter showed higher production rates. The average distillate productivities for double- and single-pane glass covers are approximately 2.2 and 5.5 l/m²/day in the months of August and September in Las Vegas, respectively. Mathematical models that can predict the hourly distillate productivity are developed. These compared well with the experimental results. Productivity of the weir-type still with a single-pane glass was also compared with conventional basin types tested at the same location. The productivity of the weir-type still is approximately 20% higher. The quality of distillate from the still is analyzed to verify the ability of the still to meet the standards required by the electrolyzers.     

Theoretical study of tilted solar still as a regenerator for liquid desiccants

A closed type (tilted solar still) solar regenerator has been studied in application to regeneration with liquid desiccants. Essentially, it consists of a flat blackened, tilted surface with a transparent glazing as a covering. The absorbent solution which is to be regenerated trickles down as a thin film over the absorber and is heated by solar energy. The water vapor that evaporates from the liquid film is condensed on the under side of the glass cover and the solution leaving the regenerator becomes strong. A simple expression is derived, in this paper, to estimate the mass of water evaporated from the weak absorbent solution as a function of climatic conditions and initial conditions of the absorbent solution. A comparison is also made with a forced flow air circulation regenerator, and it was found that the closed type regenerator may be used for regeneration only in hot, humid climates.     

A three-dimensional performance analysis of all-glass vacuum tubes with coaxial fluid conduit

The thermal performance of a solar system composed of parallel, all-glass (double skin) vacuum tubes has been investigated by using a three-dimensional analytical model. Each vacuum tube is equipped with a coaxial fluid conduit for water to flow through and collect the sun's thermal energy. The space between the exterior of the fluid conduit and the glass tube is filled with antifreeze solution to facilitate heat transfer from the solar heated absorber surface to water and to prevent the functional problems due to freezing in frigid weather conditions. Different from one-dimensional analytical models, the three-dimensional model considered in the present analysis enables the prediction of spatial variation of water temperatures as it flows through the coaxial conduit. This is quite useful in extracting major variables for the operation of the solar system using all-glass vacuum tubes as considered in the present investigation.