Performance study on basin type double slope solar still with different wick materials and minimum mass of water

Solar still is one of the best solutions to solve water problem in remote arid areas. This device is not popular because of its lower productivity. One of the methods to increase the productivity is by decrease the volumetric heat capacity of the basin. A layer of water with wick material in the basin will increase the evaporation area and enhance the production.A basin type double slope solar still with mild steel plate was fabricated and tested with minimum mass of water and different wick materials like light cotton cloth, sponge sheet, coir mate and waste cotton pieces in the basin. Still with aluminium rectangular fin arranged in different configurations and covered with different wicks were also tested. It was found that, the still with light black cotton cloth is the effective wick material. The still with rectangular Aluminium fin covered with cotton cloth and arranged in length wise direction was more effective.The still was theoretically modeled. The variation in transmittance of the cover was considered in the proposed model. The total radiation on the covers was taken as input. Theoretical values of water and glass temperatures using proposed model were compared with theoretical values obtained by Dunkle model and actual experimental values. It was found that the theoretical production rate using the proposed model were close to the experimental.     

Application of high-density daylight for indoor illumination

A fiber optic solar concentrator system with a simple parabolic profile is designed and fabricated to deliver a stream of high-density solar flux into the interior of a building for indoor illumination. The system consists of a small dish concentrator (30 cm in diameter), an optical fiber cable and a diffuser at the end. A series of tests are performed using a goniophotometer and spectrometer to investigate the photometric characteristics of the system in terms of luminous intensity distribution and spectral radiance, which are used in link with the actual photometric measurements for a lightless mock-up space of 4.9 m × 4.9 m × 2.6 m. The illuminance on the working plane was continuously monitored at 25 points by using photometric sensors. Measurements clearly indicate the photometric characteristics of the present system where a constant level of indoor illumination is observed depending on the sky clearness.     

Performance of a solar chimney

A mathematical model of a solar chimney was proposed in order to predict its performance under varying ambient and geometrical features. Steady state heat transfer equations were set up using a thermal resistance network and solved using matrix inversion. Existing correlations of heat transfer coefficients were utilised. Property values for the air flow in the duct were based on mean bulk or film temperatures. The performance of the chimney was evaluated by predicting the temperatures of the glass glazing and the heat-absorbing wall and also the temperature and velocity of the induced air flow in the chimney. The effects of air gap and solar radiation intensity on the performance of different chimneys were investigated. In order to verify the theoretical model, experiments were conducted on a 2 m high×0.45 m wide physical model with air gaps of 0.1, 0.2 and 0.3 m. Experiments were carried out outdoors on the roof and the experimental model exposed to both direct and diffuse solar radiation. Air velocities between 0.25 m s⁻¹ and 0.39  m s⁻¹ for radiation intensity up to 650 W m⁻² were obtained. No reverse air flow circulation was observed even at the large gap of 0.3 m.     

Estimation of internal heat transfer coefficients of a hybrid (PV/T) active solar still

In this paper, an attempt is made to estimate the internal heat transfer coefficients of a deep basin hybrid (PV/T) active solar still. The estimation is based on outdoor experimental observation of hybrid (PV/T) solar still for composite climate of New Delhi (latitude 28°35′N and longitude 77°12′E). The internal heat transfer coefficients are evaluated by using thermal models proposed by various researchers. The comparison of hourly yield predicted using various thermal models to the experimental has also been carried out by evaluating the correlation coefficient and percentage deviation. It is observed that, Kumar and Tiwari model (KTM) better validate the results than the others model. The average annual values of convective heat transfer coefficient for the passive and hybrid (PV/T) active solar still are observed as 0.78 and 2.41 W m⁻² K⁻¹, respectively at 0.05 m water depth.     

Optimization of number of collectors for integrated PV/T hybrid active solar still

The aim of this paper is to optimize the number of collectors for PV/T hybrid active solar still. The number of PV/T collectors connected in series has been integrated with the basin of solar still. The optimization of number of collectors for different heat capacity of water has been carried out on the basis of energy and exergy. Expressions of inner glass, outer glass and water temperature have been derived for the hybrid active solar system. For the numerical computations data of a summer day (May 22, 2008) for Delhi climatic condition have been used. It has been observed that with increase of the mass of water in the basin increases the optimum number of collector. However the daily and exergy efficiency decreases linearly and nonlinearly with increase of water mass. It has been observed that the maximum yield occurs at N = 4 for 50 kg of water mass on the basis of exergy efficiency. The thermal model has also been experimentally validated.     

Performance study of the inverted absorber solar still with water depth and total dissolved solid

In this communication, an experimental study of inverted absorber solar still (IASS) and single slope solar still (SS) at different water depth and total dissolved solid (TDS) is presented. Experiments are conducted for the climatic condition of Muscat, Oman. A thermal model is also developed for the IASS and validated with experimental results. A fair agreement is found for the daytime operation of the IASS. It is observed that higher water temperature can be achieved by using the IASS in comparison to the SS. The daily yield obtained from the IASS are 6.302, 5.576 and 4.299 kg/m²-day at water depths (d_w) 0.01, 0.02 and 0.03 m respectively. At same respective water depths, the daily yield obtained from the SS are 2.152, 1.931, 0.826 kg/m²-day respectively lower than that of the IASS. It is observed that for climatic condition of Muscat, Oman, the optimum water depth for the IASS is 0.03 m above which the addition of reflector under the basin does not affect its performance much more in comparison to that of the SS for sea water. The feed saline water and yielded distilled water are also compared for different TDS values, pH, and electrical conductance. On the basis of economic analysis of IASS, it is found that the annualized cost of distilled water in Indian rupees for Muscat climatic condition is Rs. 0.74, 0.66 and 0.62 (conversion factors: $ 1 = Rs. 50 and 1 OMR = Rs. 120) for the life time of 15, 20 and 25 years respectively.     

Performance analysis of double basin solar still with evacuated tubes

Solar still is a very simple device, which is used for solar distillation process. In this research work, double basin solar still is made from locally available materials. Double basin solar still is made in such a way that, outer basin is exposed to sun and lower side of inner basin is directly connected with evacuated tubes to increase distillate output and reducing heat losses of a solar still. The overall size of the lower basin is about 1006 × 325 × 380 mm, the outer basin is about 1006 × 536 × 100 mm Black granite gravel is used to increase distillate output by reducing quantity of brackish or saline water in the both basins. Several experiments have conducted to determine the performance of a solar still in climate conditions of Mehsana (latitude of 23°59′ and longitude of 72°38′), Gujarat, like a double basin solar still alone, double basin solar still with different size black granite gravel, double basin solar still with evacuated tubes and double basin solar still with evacuated tubes and different size black granite gravel. Experimental results show that, connecting evacuated tubes with the lower side of the inner basin increases daily distillate output of 56% and is increased by 60, 63 and 67% with average 10, 20 and 30 mm size black granite gravel. Economic analysis of present double basin solar still is 195 days.     

Determination of the thermal transport properties of ammonia borane and its thermolysis product (polyiminoborane) using the transient plane source technique

Reliable thermal property data are necessary to improve the fidelity of chemical hydride thermal decomposition models. The thermal diffusivity and conductivity of ammonia borane (NH₃BH₃) and its partial thermolysis product (polyiminoborane) were measured at various packing densities using a transient plane source technique under ambient conditions. The particle size of the ammonia borane powder was between 200 and 600 μm, while the particle size of the polyiminoborane powder was between 10 and 30 μm. The thermal diffusivity and conductivity of the ammonia borane increased from 0.17 to 0.24 mm²/s and 0.19 to 0.44 W/m K (±10%), respectively, when its packing density was increased from 0.37 to 0.58 g/cm³. The increase in thermal conductivity is due to the increase in contact area between particles and the increase in the thermal diffusivity is related to an increase in density and volumetric heat capacity caused by compaction. The thermal conductivity of the polyiminoborane powder was approximately three times lower, likely due to its higher porosity. The thermal diffusivity and conductivity of this product changed from 0.21 to 0.12 mm²/s and 0.068 to 0.23 W/m K (±10%), respectively, when its packing density was increased from 0.13 to 0.96 g/cm³.     

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.

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.     

A new version of a solar water heating system coupled with a solar water pump

This research target was to improve the thermal efficiency of a solar water heating system (SWHS) coupled with a built-in solar water pump. The designed system consists of 1.58-m² flat plate solar collectors, an overhead tank placed at the top level, the larger water storage tank without a heat exchanger at the lower level, and a one-way valve for water circulation control. The discharge heads of 1 and 2 m were tested. The pump could operate at the collector temperature of about 70–90 °C and vapor gage pressure of 10–18 kPa. It was found that water circulation within the SWHS ranged between 15 and 65 l/d depending upon solar intensity and discharge head. Moreover, the max water temperature in the storage tank is around 59 °C. The max daily pump efficiency is about 0.0017%. The SWHS could have max daily thermal efficiency of about 21%. It is concluded that the thermal efficiency was successfully improved, except for the pump one. The new SWHS with 1 m discharge head or lower is suitable for residential use. It adds less weight to a building roof and saves electrical energy for a circulation pump. It has lower cost compared to a domestic SWHS.     

Helium dispersion following release in a 1/4-scale two-car residential garage

A series of experiments are described in which helium was released at a constant rate into a 1.5 m × 1.5 m × 0.75 m enclosure designed as a 1/4-scale model of a two-car garage. The purpose was to provide reference datasets for testing and validating computational fluid dynamics (CFD) models and to experimentally characterize the effects of a number of variables on the mixing behavior within an enclosure and the exchange of helium with the outside surroundings. Helium was used as a surrogate for hydrogen, and the total volume released was scaled as the amount that would be released by a typical hydrogen-fueled automobile with a full tank. Temporal profiles of helium were measured at seven vertical locations within the enclosure during and following 1-h and 4-h releases. Idealized vents in one wall sized to provide air exchange rates typical of actual garages were used. The effects of vent size, number, and location were investigated using three different vent combinations. The dependence on leak location was considered by releasing helium at three different points within the enclosure.     

A new 500 m paraboloidal dish solar concentrator

The Australian National University (ANU) has worked for many years on paraboloidal dish solar concentrators and demonstrated a 400 m² system in 1994. The commercialization of this technology has involved a re-design of the Big Dish concept for mass production. The new design is a 500 m² concentrator with 13.4 m focal length and altitude-azimuth tracking. It uses 380 identical spherical 1.17 m × 1.17 m mirror panels, which incorporate the Glass-on-Metal Laminate mirrors. Construction of a first prototype on the ANU campus began in the first quarter of 2008. The first on sun test was carried out on 29 June 2009.     

Phase separated thermotropic layers based on UV cured acrylate resins - Effect of material formulation on overheating protection properties and application in a solar collector

This paper focuses on the effect of material composition on the overheating protection properties of thermotropic systems with fixed domains for solar thermal collectors. Numerous functional layers were prepared by a variation of base resin (polyester-, epoxy- or urethane-acrylate) and of thermotropic additives (non-polar and polar waxes) as well as by additive concentration (5 and 7 wt%). A detailed investigation of optical properties, switching temperature and switching process was performed applying UV/Vis/NIR spectroscopy. Thermal transitions of both the thermotropic layers and the additives used were determined by Differential Scanning Calorimetry (DSC). The capability of the produced thermotropic layers to reduce stagnation temperatures in an all-polymeric flat plate collector was evaluated by theoretical modeling. The thermotropic layers showed a hemispheric solar transmittance between 76% and 87% in clear state. Above the switching threshold this transmittance changed by 1-16% to values between 62% and 85%. The layers exhibited switching temperatures between 33 and 80 °C. The transition is fully completed within a temperature frame of 10-25 °C. Resin types with higher glass transition temperatures were detected to benefit the reduction of the hemispheric solar transmittance above the switching threshold. This reduction was also found to increase with increasing molecular weight of the non-polar additive types. The comparison of the switching performance with the thermal transitions of the additives revealed a good correlation. Theoretical modeling showed that by the use of selected thermotropic layers in the glazing the maximum absorber temperatures can be limited to temperatures below 130 °C.     

Practical application of a sea-water battery in deep-sea basin and its performance

Stable power supply is essential for various long-term sea floor geophysical observations. Due to a simple structure and a large energy capacity, sea-water batteries have been developed and used for such observations. However, the characteristics of sea-water batteries have not been well known in the case of installations at depths more than 5000 m in deep-sea basin. In 2000, a sea floor borehole broadband seismic observatory was installed in the northwestern Pacific basin where the water depth is 5577 m. For electric power supply, a Sea-Water Battery (SWB) system with monitoring and control was developed and used. The SWB system consists of four sea-water battery cells, a DC/DC converter, the Power Control System, the Data Logger, and an accumulator. The conditions of the SWB system were recorded more than 1 year, and the monitoring data was recovered. The SWB system generated enough power for the observation system consuming power of 6 W in average and continued to supply power for at least 5 years. From the monitoring data, the SWB can supply up to the long-term average of at least 13 W. The energy density is estimated to be 318 Wh kg⁻¹. The sea-water battery is useful for application of long-term power consumption even in the deep-sea basin.     

Energy efficiency enhancement of natural rubber smoking process by flow improvement using a CFD technique

A non-uniform flow and large temperature variation in a natural rubber smoking-room cause an inefficient use of energy. Flow uniformity and temperature variation can be improved by using a computational fluid dynamics (CFD) simulation. The effects of the size, position and number of gas supply ducts and ventilating lids which were at the inlets and the outlets of the smoking-room were investigated. The optimal rubber smoking-room of size 2.6 m × 6.2 m × 3.6 m contains 154 50 mm-diameter hot gas supply ducts, and four 0.25 × 0.25 m and four 0.25 × 0.20 m ventilating lids. The velocity distribution of this model in the rubber-hanging area was rather uniform. The average monitoring temperature of 54 positions was 62.1 °C. This model could reduce the temperature variation by a factor of three from the original room model, i.e., from 15 to 5.5 °C. In a further study, the heat input of an appropriate room model was finely adjusted to obtain a suitable temperature (60 °C) for the smoking process. It was found that an appropriate heat supply at this temperature is 11 kW. At this rate, the temperature variation is 5.3 °C. This improved model should help the rubber smoking cooperatives to achieve at least a 31.25% saving in energy.     

Life cycle cost analysis of single slope hybrid (PV/T) active solar still

This paper presents the life cycle cost analysis of the single slope passive and hybrid photovoltaic (PV/T) active solar stills, based on the annual performance at 0.05 m water depth. Effects of various parameters, namely interest rate, life of the system and the maintenance cost have been taken into account. The comparative cost of distilled water produced from passive solar still (Rs. 0.70/kg) is found to be less than hybrid (PV/T) active solar still (Rs. 1.93/kg) for 30 years life time of the systems. The payback periods of the passive and hybrid (PV/T) active solar still are estimated to be in the range of 1.1–6.2 years and 3.3–23.9 years, respectively, based on selling price of distilled water in the range of Rs. 10/kg to Rs. 2/kg. The energy payback time (EPBT) has been estimated as 2.9 and 4.7 years, respectively.     

Prospectives for China's solar thermal power technology development

China's total installed electrical power capacity reached 700 GW by the end of 2007 and is predicted to surpass 900 GW in 2010. The rapid increase in energy demand and increasing global warming have both pushed China to change its current electrical power structure where coal power accounts for nearly 75% of the total electric power generation. China has already become the world's largest solar water heater producer and user. However, there is still much to be done in the solar thermal power field before its commercialization. Solar thermal power technologies including solar power towers, solar parabolic trough concentrators, solar dish/stirling systems, linear Fresnel reflectors, and solar chimneys have been studied in China since the 1980s. A 10 kW dish/stirling project was funded by the Ministry of Science and Technology (MOST) during 2000–2005 with a 1 MW solar power tower and research of trough concentrator metal–glass evacuated tubes supported during 2006–2010. This paper describes a continued solar thermal power development roadmap in China in 5-year intervals between 2006 and 2025.     

Productivity enhancements of compound parabolic concentrator tubular solar stills

The performance of compound parabolic concentrator assisted tubular solar still (CPC-TSS) and compound parabolic concentrator-concentric tubular solar still (CPC-CTSS) (to allow cooling water) with different augmentation systems were studied. A rectangular saline water trough of dimension 2 m × 0.03 m × 0.025 m was designed and fabricated. The effective collector area of the still is 2 m × 1 m with five sets of tubular still – CPC collectors placed horizontally with north-south orientation. Hot water taken from the CPC-CTSS was integrated to a pyramid type and single slope solar still. Diurnal variations of water temperature, air temperature, cover temperature and distillate yield were recorded. The results showed that, the productivity of the un-augmented CPC-TSS and CPC-CTSS were 3710 ml/day and 4960 ml/day, respectively. With the heat extraction technique, the productivity of CPC-CTSS with a single slope solar still and CPC-CTSS with a pyramid solar still were found as 6460 ml/day and 7770 ml/day, respectively. The process integration with different systems cost was found slightly higher but the overall efficiency and the produced distilled water yield was found augmented.     

Simple multiple wick solar still: Analysis and performance

This paper presents the design, analysis and performance of a multiple wick solar still, in which blackened wet jute cloth forms the liquid surface which can be oriented to intercept maximum solar radiation and attain high temperatures on account of low thermal capacity. The wet surface consists of a series of jute cloth pieces of increasing length separated by thin black polythene sheets, resting on foam insulation supported by a net of nylon ribbon; these pieces are arranged along an incline and their upper edges are dipped in a saline water tank. Suction by the cailliary action of the cloth fibre provides a thin sheet of liquid on the cloth; the arrangement ensures that all the surface, irradiated by the sun is wet at all times. The results of an analysis based on Dunkle's relation[16] are in excellent agreement with the observed performance of the still. On a typical cold sunny day in Delhi (viz. 6 February 1980) the distillate output was 2.5 l/m² day, corresponding to an overall efficiency of 34 per cent (as compared to a maximum of 30 per cent for basin type still). The still costs less than half of the cost of a basin type still of same area and provides a higher yield of distillate.