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Abstract Phase effect of bismuth vanadate (BiVO4) nanostructured catalysts for the photoelectrochemical (PEC) solar water oxidation, removal of toxic organic pollutants from wastewater, and electrochemical storage were reported. The monoclinic (BV-M) and tetragonal (BV-T) crystal structured BiVO4 photocatalysts were synthesized using a facile hydrothermal route without the support of any template. The BV-T photoelectrode also exhibits lower charge transfer resistance compare to BV-M photoelectrode. The BV-T photoelectrode showed a remarkable photocurrent density (0.4249 mAcm−2) over BV-M photoelectrode (0.0702 mAcm−2), which is about 6 times greater than BV-M photoanode. Furthermore, BV-T sample showed 17 times superior electrochemical capacitance over BV-M sample at the scan rate of 10 mVs−1. The photocatalytic analysis has also shown that the BV-T photocatalyst revealed greater photocatalytic activity for the methyl orange under visible light, about 87.8% of the MO was degraded within 80 min.

Current solar hot water (SHW) system modelling techniques, as applied in Australia, are inadequate for the demands of programs and policies that aim at widespread usage of SHW. Two major problems with current modelling techniques are the coarseness of modelling in a spatial context and the use of only two hot water load categories. These problems are described and suggestions are offered for improved modelling processes. Geographical information systems can be used in conjunction with existing SHW performance evaluation tools to produce models with much finer spatial resolution than those currently in use. It is recommended that categories used for evaluating SHW systems should be based upon household size. Methodologies for modelling SHW system performance that conform to these recommendations are described in this paper.

This paper describes the development, validation and use of a design and simulation tool for modeling the performance of a salinity gradient solar pond. An experimental solar pond pilot plant was constructed in central Catalonia (NE part of the Iberian Peninsula). The body of the pond is a cylindrical reinforced concrete tank, with 3 m height, 8 m diameter and total area of 50 m2. The lateral tank wall has been insulated with 60 mm of rock wool. The gradient in the solar pond was settled and maintained since 30 September 2009 to date. The developed tool was validated by comparing simulation results to experimental data collected from the experimental solar pond from November 2009 until August 2011. The resulting first-order differential equations describing the overall energy balance in the pond were solved numerically using a finite-difference method. The temperature profiles of the pond were properly described, especially at lower subzones of the non-convective zone (NCZ) and the lower convective zone (LCZ). The higher errors between experimental and predicted values were found in the upper convective zone (UCZ). Once validated, successfully, the model was used to predict the thermal performance of pre-industrial solar pond to be constructed and operated in Granada, SW of Spain. The thermal profiles predicted temperature differences between surface and bottom of around 40 °C during summer time, with a maximum temperature of 75 °C. The energy efficiency of the LCZ was anticipated to range between 12% and 25% along one year operation, resulting in 16% of incoming radiation to be extractable for site application. Peer Reviewed

Abstract Many natural systems such as oceans, lakes, etc.…, are influenced by the effect of double-diffusive convection. This phenomenon, which is a combination of heat and mass transfer, can destroy the stability of system-flows. In the case of solar ponds the middle layer, that is linearly stratified, acts as a thermal and mass insulator for the lower layer. This middle layer, called the Non-Convective Zone (NCZ), needs special care to avoid convection and to maintain its stability. In fact, due to an excess of heat stored, a thermal gradient occurs within the NCZ. A convective movement appears at the bottom of the stratified-layers and then grows to a double-diffusive convection movement. This movement transforms the stratified-layers into a well mixed layer, reducing the storage capacity of the pond. Laboratory small-scale pond and middle-scale outdoor solar ponds were designed and built to provide both quantitative data and to study the dynamic processes in solar ponds, including the behavior of the gradient zone. Particle Image Velocimetry (PIV) visualization-experiments carried out in the mechanical and energetic laboratory in the engineering school of Tunisia and experiments in the field showed that the instability of solar ponds could be limited by using porous media placed in the lower layer of the stratification.

Abstract This paper describes the performance analysis of a cross-flow type plate heat exchanger for use as a liquid desiccant absorber (dehumidifier) and indirect evaporative cooler. The proposed absorber can be described as a direct contact, cross-flow, heat and mass exchanger, with the flow passages separated from each other by thin plastic plates. One air stream (primary air) is sprayed by liquid desiccant solution, while the other stream (secondary air) is evaporatively cooled by a water spray. Each thin plate, besides separating the water/air passage from the solution/air passage, also provides the contact area for heat and mass transfer between the fluids flowing in each passage. A parametric study for the primary air stream at 33°C, 0.0171 kg/kg humidity ratio and secondary air stream at 27°C and 0.010 kg/kg humidity ratio using calcium chloride solution was performed in this study. The results showed a strong dependence on the heat and mass transfer area, solution concentration and ratio of secondary to primary air mass flow rates. However, negligible differences were found between the performance of a counter flow and a parallel flow arrangement. The results demonstrate that the proposed absorber will not offset both the latent and sensible load of the primary air and, therefore, an auxiliary cooler or more dehumidification/indirect evaporative cooling stages will generally be required to meet the sensible and latent load in a typical comfort application.

The method of heat recovery from the ground below solar ponds is investigated in the present brief note. Solar ponds lose considerable amount of heat from its bottom to the ground due to temperature gradient between them. This waste heat from ground, which is at different temperature at different depths decreasing downwards from the bottom of the solar pond, can be extracted to enhance the thermal performance of the solar pond. This note addresses the technique to remove heat from ground and shows the enhancement of the heat removal and efficiency in doing so. Thermal performance of solar ponds is investigated and compared for the cases where the heat extraction fluid (HEF) flux through the LCZ and ground is constant and when they are different. Results show that constant HEF flux through LCZ and ground is a preferable option for heat removal. Also it is evident that the heat recovered from ground may reach a significant quantity which may almost be equal to the heat extracted from LCZ. Hence not recovering heat from ground leads to loss of upto 50% thermal energy.

Abstract This paper presents the results of a thermal performance analysis of a phase change thermal storage unit. The unit consists of several parallel flat slabs of phase change material (PCM) with a liquid heat transfer fluid (HTF) flowing along the passages between the slabs. A validated numerical model developed previously to solve the phase change problem in flat slabs was used. An insight is gained into the melting process by examining the temperatures of the HTF nodes, wall nodes and PCM nodes and the heat transfer rates at four phases during melting. The duration of the melting process is defined based on the level of melting completion. The effects of several parameters on the HTF outlet temperature, heat transfer rate and melting time are evaluated through a parametric study to evaluate the effects of the HTF mass flow rate, HTF inlet temperature, gap between slabs, slab dimensions, PCM initial temperature and thermal conductivity of the container on the thermal performance. The results are used to design a phase change thermal storage unit for a refrigerated truck.

Abstract In operation of a closed-cycle salt-gradient solar pond (CCSGSP) system, fresh or low salinity water is supplied at the surface of the solar pond (SP) as make-up for evaporation losses as well as for surface washing. In the present investigation the surface water is flushed to an evaporation pond (EP) and concentrated for reinjection at the bottom of the SP. A 20 m2 SP incorporating an EP for concentrating brine, has been established. Theoretical modelling of the CCSGSP is presented. Results from the initial operation of the SP show that wind action and convective mixing caused some erosion of the gradient layer thereby increasing the surface layer thickness. Salt flux to the surface was found to be approximately 19 kg/m2 per year. Sodium hypochlorite solution proved successful as shock treatment during severe algal bloom. The result of acidification was less promising in maintaining pond clarity. Occasional addition of alum helped in settling some of the suspended particulates in the pond.