Design and performance characteristics of honeycomb solar pond

This paper presents the design and performance characteristics of a honeycomb solar pond. It considers natural convection suppression in an air layer incorporating a cellular array and points out that a cell of size 1.25 cm × 1.25 cm matches quite well with temperatures operational in a solar pond. Honeycomb transmittance to incident radiation is calculated by taking into account the refraction, scattering and absorption by vertical walls. Results corresponding to a wide range of angles of incidence are presented. Honeycomb effectiveness on heat loss reduction and solar collection efficiency is investigated. Explicit results on optimization of system efficiency are presented. It is found that a honeycomb depth of 12–17 cm is optimum. An efficiency of 40–60% is predicted at a collector temperature of 90°C. The results of earlier workers are discussed.     

The daily performance of a solar pond integrated with solar collectors

The present study deals with heat storage performance investigation of integrated solar pond and collector system. In the experimental work, a cylindrical solar pond system (CSPS) with a radius of 0.80 m and a depth of 2.0 m and four flat plate collectors dimensions of 1.90 m × 0.90 m was built in Cukurova University in Adana, Turkey. The CSPS was filled with salty water of various densities to form three salty water zones (Upper Convective Zone, Non-Convective Zone and Heat Storage Zone). Heat energy collected by collectors was transferred to the solar pond storage zone by using a heat exchanger system which is connected to the solar collectors. Several temperature sensors connected to a data acquisition system were placed vertically inside the CSPS and at the inlet and outlet of the heat exchanger. Experimental studies were performed using 1, 2, 3 and 4 collectors integrated with the CSPS under approximately the same condition. The integrated solar pond efficiencies were calculated experimentally and theoretically according to the number of collectors. As a result, the experimental efficiencies are found to be 21.30%, 23.60%, 24.28% and 26.52%; the theoretical efficiencies to be 23.42%, 25.48%, 26.55% and 27.70% for 1, 2, 3 and 4 collectors, respectively. Theoretical efficiencies were compared with the experimental results and hence a good agreement is found between experimental and theoretical efficiency profiles.     

Natural brine solar pond: an experimental study

The South East of Tunisia is a sunny region. This area contains many mineral reserves of natural brine, which currently are not well exploited. These reserves are estimated to several millions of cubic metres. The abundance of solar energy and salt has led us to test the collection and storage of solar energy by a salt gradient solar pond. A small laboratory solar pond of dimensions 2 m×2 m×1 m, excavated from the ground, has been constructed at ENIT (National School of Engineers of Tunis). The salt utilised in the pond is a natural brine which comes from south of Tunisia. Temperature and solar radiation measurements have been carried out over 8 weeks to evaluate the efficiency of this pond.     

Mathematical modelling of salt gradient solar pond performance

This paper presents a mathematical model of the performance of the salt gradient solar pond. A lumped parameter model of the upper convective zone, non-convective zone and lower convective zone is used. This model enables the temperatures of the upper-convective zone and the lower convective zone of the solar pond to be predicted. The experimental results agree well with theoretically predicted values. The major error in the theoretical results is due to the difference between the theoretical value of the solar radiation inside the water and that observed experimentally. It is found that the experimental value of the solar radiation at a depth of 90 cm is approximately 26 per cent of the total solar radiation falling on the solar pond surface, whereas the corresponding theoretical value is found to be 33 per cent. The results conclude that the lumped parameter model can be used as a simple model to predict the performance of the solar pond.     

Spectral calculation of the thermal performance of a solar pond and comparison of the results with experiments

This paper deals with a method and the result of the spectroscopic calculation on heat balance of a salt-gradient solar pond under the conditions of spectral solar radiation. Furthermore, reflection of the ray incident upon the surface of the pond water, refraction of the rays within the salt-water layer and diffusion of salt in the pond water are considered. On the other hand, in order to make a clear mechanism of the heat collection and heat storage of the solar pond, we conducted an indoor experiment and a numerical analysis on a small scale model of the salt-gradient solar pond with 2 m² surface area and 1.6 m depth, under the incident rays from a Xe-lamp solar simulator. According to the above experimental analysis, we made a simulation model of thermal performance for a solar pond and carried out the calculation from the heat balance. We found that the simulation calculations correspond well to the experimental results, so that our thermal simulation model and method might be correct. We also did the thermal calculation by changing the incident rays from a Xe-lamp into natural ray (Moon’s spectrum) and Halogen lamp. As a result, it was found that the temperature distributions in the solar pond were notably different due to spectral characteristics of the incident ray. Therefore, the spectroscopic consideration for thermal performance of any solar pond is necessary to obtain a correct solution under the spectral incidence with special wavelength distributions.     

配合集热器的盐梯度太阳池热性能实验与分析

构建表面积为1.50 m×1.50 m的小型实验用盐梯度太阳池,并与平板太阳能集热器配合使用,分别对普通太阳池和集热增强型太阳池进行了储热、放热实验。实验研究与理论分析表明:单独盐梯度太阳池的放热量为3.5×103k J,热效率为13.6%;集热增强型太阳池放热量可以达到4.8×103k J,且热效率增至28.1%。另外后者下对流层温度最高可提升10℃以上,从而证明太阳能集热器可以有效提高太阳池热效率,增加下对流层储热量。此外,考虑了放热过程换热器对太阳池下对流层的扰动,对比实验前后的溶液浓度,可以看出实验后太阳池盐度曲线合理,非对流层呈良好梯度分布,太阳池稳定性并未遭到破坏。     

Theoretical and experimental study of solar dryer

Certain agricultural products need to be dried (fruits, fodder, cereals, etc.) in order to avoid deterioration when they are exposed to the elements. Solar air collectors have been optimized in previous studies resulting in a clear enhancement of their thermal performances in relation to the flat plate. In this comparative study, a flat plate and offset plate fin absorber-plate collectors are used, as a heat source and are linked to the forced dryer. The performance of the solar dryer has improved remarkably, in relation to the use of the solar dryer with a flat-plate collector and the drying time is consequently reduced. In the present paper, a summary theoretical analysis is given and experimental results are established.     

Numerical and experimental analysis of a salt gradient solar pond performance with or without reflective covered surface

An experimental salt gradient solar pond having a surface area of 3.5 × 3.5 m² and depth of 2 m has been built. Two covers, which are collapsible, have been used for reducing the thermal energy loses from the surface of the solar pond during the night and increasing the thermal efficiency of the pond solar energy harvesting during daytime. These covers having reflective properties can be rotated between 0° and 180° by an electric motor and they can be fixed at any angle automatically. A mathematical formulation which calculates the amount of the solar energy harvested by the covers has been developed and it is adapted into a mathematical model capable of giving the temporal temperature variation at any point inside or outside the pond at any time. From these calculations, hourly air and daily soil temperature values calculated from analytical functions are used. These analytic functions are derived by using the average hourly and daily temperature values for air and soil data obtained from the local meteorological station in Isparta region. The computational modeling has been carried out for the determination of the performance of insulated and uninsulated solar ponds having different sizes with or without covers and reflectors. Reflectors increase the performance of the solar ponds by about 25%. Finally, this model has been employed for the prediction of temperature variations of an experimental salt gradient solar pond. Numerical results are in good agreement with the experiments.     

On the performance of a salt gradient solar pond

The performance of a laboratory-scale salt-gradient solar pond is described in this paper. Different methods of saline injection to the bottom layer and corresponding temperature and concentration profiles as a function of depth are reviewed and compared with experimental results. A time history of the development of temperatures, salinities and elevations of the lower and upper layers at various climatological situations is reported. The ‘dynamic stability’ and ‘equilibrium boundary criterion’ are discussed and verified experimentally for the lower and upper gradient interfaces.     

非对流层数对太阳池性能的影响

盐梯度太阳池是一种兼具集热与蓄热功能的太阳能利用设施。在太阳池的工程应用中,非对流层(NCZ)层数对太阳池性能影响问题十分重要,然而以往对这方面的研究较少。文章通过构建小型太阳池,设置不同的NCZ层数,分析其对太阳能集热和储热性能的影响。研究结果显示:随着NCZ层数增加,太阳池集热性能减弱;无NCZ太阳池平均每小时的集热量分别是含有1,2,3层NCZ太阳池集热量的1.11倍、2.52倍和4.03倍,热效率分别是其1.39倍、2.86倍和5.21倍;NCZ层数增加,夜间散热量减小,无NCZ太阳池中,夜间平均散热量是含3层NCZ太阳池散热量的3.56倍。在构建太阳池时,应充分考虑当地的气候条件和实际用途,设置适当的NCZ层数,方可发挥太阳池的最大功效,达到最大经济效益。     

Thermal performance modeling of the reverse absorber shallow solar pond

Reverse absorber type shallow solar ponds are proposed as being capable of attaining higher temperatures and still higher efficiencies than the conventional type due to convection suppression and elimination of top radiative losses. The theoretical thermal analysis and simulation of the performance of two configurations of the reverse absorber shallow solar pond (RASSP); one with the top insulated and the other with top exposed, are presented. The ensuing model equations were solved to obtain the desired performance parameters. For a pond depth of 0.10 m, results of the simulations show that water temperatures up to 70°C could be obtained in a RASSP with double glass covers, higher than could be gotten in either an RASSP with top insulation or a conventional SSP of equal depth. The effect of pond depth on the proportions of the radiation incident on the RASSP that is either collected as thermal energy or lost was studied. The average transmissivity-absorptivity products, (τα), overall heat loss coefficients, UL and optimal pond depths were also computed.     

Comparative performance evaluation of fertiliser solar pond under simulated conditions

An experimental test rig for solar pond simulation was developed to study the chosen fertiliser salt, Muriate of Potash (MOP) for use in a solar pond under simulated conditions with provisions to vary the heating input and maintain a particular lower convective zone temperature. The performance, in terms of temperature and density profiles, was studied for MOP and was compared with that of sodium chloride and saltless solar ponds for different heating regimes and lower convective zone temperatures. The formation of three zones viz., upper convective zone, nonconvective zone, and lower convective zone was distinct at all heating combinations for both MOP and sodium chloride salts under simulated conditions. The temperature and density gradients were not affected significantly by intermittent no-heating spells of the solar ponds. Maintaining lower convective zone temperature of 70 °C and above led to the initiation of minor internal convective zone under simulated conditions. The temperature decay of lower convective zone (LCZ) was at lesser rate for different LCZ temperatures associated with both the heating regimes, for a MOP pond over a 24 h period of cessation of heating as compared to sodium chloride and saltless ponds.     

Thermal behaviour of a coffered solar pond: An experimental study

The construction of conventional solar ponds usually involves highly expensive excavations. So the widespread adoption of this type of solar-energy collector and store has been severely inhibited. Thus the use of the coffered solar pond was proposed. For a laboratory-sized coffered solar pond, experimental thermal behaviour data have been obtained and compared with computer predictions. Hence the mathematical model employed has been validated.     

Theoretical performance of cylindrical parabolic solar concentrators

This is a theoretical study of the performance of cylindrical parabolic solar concentrators under ideal conditions. Particular attention is given to the application of this type of concentrator in the intermediate temperature range, where wide targets are used.Suitable indices that describe the performance are defined and calculated, and the effects of the different parameters are studied. In particular, the energy available at the focal plane and the distribution of its intensity are determined. All ranges of rim angles are studied: less than 90°, more than 90°, and the whole range of 0–180°.The performances obtained are the best possible and can, therfore, be used as a standard of reference for the appraisal of actual concentrators of the type studied.     

Applicability of steady state equations for solar pond thermal performance predictions

The steady state thermal performance of solar ponds is compared with hourly numerical simulation results and limitations of the steady-state equations are discussed. The approach to steady-state is described by the definition of a time constant. Based on numerical simulation results, a simple way of evaluating monthly performance is given. The concept of utilizability is extended to solar ponds and it is shown that the yearly utilizability curve is independent of location.     

An experimental study on a modified design compact shallow solar pond

In this study a design of compact shallow solar pond modified from that of Kudish (Kudish and Wof, 1978) is studied experimentally. The difference between this design and that of Kudish is that the water depth is allowed to be changed from 2–15 cm and is not fixed as in the mentioned reference design. The thermal insulation of the cover is installed between the reflector and the inner surface of the wooden cover. In the design of the reference (Kudish and Wof, 1978), the insulation is fixed on the outer surface of the cover, where it will probably be damaged by water, wind, dust etc. Also in our design, the level of water in the bag is measured using a static pressure manometer. The tests were carried out both in winter and in summer whereas they have been done only in summer in the mentioned reference. The results show that the compact shallow solar pond can provide a suitable water temperature to be used for low and moderate temperature applications even in a cold winter and with 10 cm water depth.     

Effect of the gap spacing on the shallow solar pond performance

It is stated by Garg et al. [Energy Convers. Mgmt 22, 117 (1981)] that, for a shallow solar pond where the gap spacing is large (300 mm), the convective heat loss is somewhat lower than for a conventional collector with a shorter gap spacing (20 mm). How much the total heat transfer coefficient is lowered, and what is the effect of the gap spacing on the performance of the shallow solar pond were not mentioned. In this study, the effect of gap spacing on shallow solar pond performance is studied. For this purpose, a computer program is constructed and is experimentally tested using a shallow solar pond of 6.6 m² area. It is concluded from the results that the effect of gap spacing on the top loss coefficient is independent of the temperature difference between the upper film of the water bag and the glazing of the shallow solar pond. The results also show that the change in gap spacing of the shallow solar pond has not an important effect on the pond performance. Hence, the large gap spacing in the conventional design shallow solar pond (300 mm) cannot be considered as a major difference with the flat plate collector design (20 mm), as Garg et al. stated.     

Theoretical and experimental analysis of a novel low emissivity water pond in summer

The present study focuses on the research of a new passive roof cooling technique, based on the combination of low emissivity materials and water. A novel roof pond is chosen as the most advantageous in terms of both energy efficiency and less maintenance or functional demands. The pond – referred as “Roof Pond with Gunny Bag” (RPWGB) – is covered by a cloth floating on water level, encouraging evaporative heat losses. A mathematical model describing the energy flux through the RPWGB is developed. The following sensitivity analysis marks the parameters that reduce bottom pond temperature thus improving the efficiency of the system. The experimental study analyses alternative ways to reduce bottom pond temperature. For this purpose, the low emissivity material is placed in different positions, above, below and floating on water level. Heat dissipation occurs by means of radiation losses and water evaporation.     

Theoretical and experimental studies of an ethanol basin solar still

A transient-state mathematical model for an ethanol basin solar still based on Spalding's work was developed. Driving force B was defined based on the mass balance between the evaporating (S) and condensing (G) surfaces. Mass transfer conductance (g) was obtained from an indoor experiment. Then productivity could be calculated. In order to validate the model an ethanol basin solar still was tested under outdoor conditions. The model had RMSEs of 4% and 23% of the measured mean temperature and productivity. The mean productivity was 0.33 kg/h when the mean solar radiation input was 1.95 MJ/m²/h. The simulated distillate concentrations were 74, 59 and 24%v/v for ethanol solution concentrations of 50, 30 and 10%v/v. The monthly means of the simulated daily productivity and total daily solar radiation were linearly correlated.

An indoor experimental equipment of the same type as that used for the outdoor experiments was constructed. Ethanol solutions with concentrations of 10–100%v/v were distilled. The ethanol solution temperature varied between 40 and 70 °C. The experimental data from the still was then used to find the g used for the above mathematical model. The still height had a slight effect on the productivity. Increasing the ethanol solution concentration by not more than around 80% v/v could improve the still productivity.