Designing a cost-effective phase change thermal storage system involves two challenging aspects: one is to select a suitable storage material and the other is to increase the heat transfer between the storage material and the heat transfer fluid as the performance of the system is limited by the poor thermal conductivity of the latent heat storage material. When used for storing energy in concentrated solar thermal power plants, the solar field operation temperature will determine the PCM melting temperature selection. This paper reviews concentrated solar thermal power plants that are currently operating and under construction. It also reviews phase change materials with melting temperatures above 300 °C, which potentially can be used as energy storage media in these plants. In addition, various techniques employed to enhance the thermal performance of high temperature phase change thermal storage systems have been reviewed and discussed. This review aims to provide the necessary information for further research in the development of cost-effective high temperature phase change thermal storage systems.

Review on storage materials and thermal performance enhancement techniques for high temperature phase change thermal storage systems

Developing heat transfer in rectangular channels with rib turbulators

Heat transfer and friction in solar air heater duct with V-shaped rib roughness on absorber plate

High performance heat transfer ducts with parallel broken and V-shaped broken ribs

Phase change materials (PCMs) can be applied to several different solar energy systems for the extended heat energy storage which is quite useful as the solar energy is intermittent in nature and is unavailable during the night period Application of PCMs in solar energy systems allows the solar energy to be used at any time even in the absence of the natural solar radiation Thus, the use of PCMs in the solar energy systems can bridge the demand and supply gap of the normal electrical energy This paper deals with the recent advances in PCMs application in different solar energy systems and presents almost all of the emerging areas where the applications of PCM in solar energy systems are urgently required The novel and most recent developments of PCMs in solar thermal energy systems, such as, solar thermal power plants, solar air heater, solar water heater and solar cooker have been duly covered Furthermore, the application of PCMs in heating and cooling of buildings have been presented as well as the investigation of the PCM application in the solar photovoltaic systems for the performance enhancement of PCMs Intrinsically important, from the study it has been found that PCMs have been in use in almost all of the solar energy systems even though their uses are still limited and commercially not available due to several economic and environmental constraints Thus, the paper attempts to present recent and novel approaches by the authors around the world on PCMs applications in the solar energy in well documented forms Based on the findings, future recommendations have also been given to provide the idea and pragmatic concepts for the researcher to work on the areas of research for further improvements in the systems

Novel approaches and recent developments on potential applications of phase change materials in solar energy

The continuous increase in the level of green house gas emissions and the increase in fuel prices are the main driving forces behind efforts to more effectively utilize various sources of renewable energy. In many parts of the world, direct solar radiation is considered to be one of the most prospective sources of energy. Among the different energy end uses, energy for cooking is one of the basic and dominant end uses in developing countries. Energy requirement for cooking accounts for 36% of total primary energy consumption in India. Hence, there is a critical need for the development of alternative, appropriate, affordable mode of cooking for use in developing countries. However, the large scale utilization of this form of energy is possible only if the effective technology for its storage can be developed with acceptable capital and running costs. Thermal energy storage is essential whenever there is a mismatch between the supply and consumption of energy. Latent heat storage in a phase change material is very attractive because of its high storage density with small temperature swing. The choice of PCM plays an important role in addition to heat transfer mechanism in the PCM. In this present work a review has been made to study all the research and development work carried out in the field of solar cooker in particular the storage type solar cookers. A novel concept of PCM-based storage type solar cooker is also presented which is under experimental investigation.

Solar cookers with and without thermal storage—A review

Turbulent flow heat transfer and fluid friction in helical-wire-coil-inserted tubes

Etude experimentale du coefficient de frottement et de transfert de chaleur pour des ecoulements turbulents d'un melange 50-50 d'eau et de glycerol dans des tubes a cannelures en spirales pour differentes configurations et des valeurs du nombre de Reynolds de 5000 a 80000. Comparaison avec des tubes lisses. Etablissement de correlations

Turbulent Flow Friction and Heat Transfer Characteristics of Single- and Multistart Spirally Enhanced Tubes

Cashew nut shell, a waste product obtained during deshelling of cashew kernels, had in the past been deemed unfit as a fuel for gasification owing to its high occluded oil content. The oil, a source of natural phenol, oozes upon gasification, thereby clogging the gasifier throat, downstream equipment and associated utilities with oil, resulting in ineffective gasification and premature failure of utilities due to its corrosive characteristics. To overcome this drawback, the cashew shells were de-oiled by charring in closed chambers and were subsequently gasified in an autothermal downdraft gasifier. Equilibrium modeling was carried out to predict the producer gas composition under varying performance influencing parameters, viz., equivalence ratio (ER), reaction temperature (RT) and moisture content (MC). The results were compared with the experimental output and are presented in this paper. The model is quite satisfactory with the experimental outcome at the ER applicable to gasification systems, i.e., 0.15 to 0.30. The results show that the mole fraction of (i) H2, CO and CH4 decreases while (N2 + H2O) and CO2 increases with ER, (ii) H2 and CO increases while CH4, (N2 + H2O) and CO2 decreases with reaction temperature, (iii) H2, CH4, CO2 and (N2 + H2O) increases while CO decreases with moisture content. However at an equivalence ratio less than 0.15, the model predicts an unrealistic composition and is observed to be non valid below this ER.

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R. Sethumadhavan

Papers

Solar cookers with and without thermal storage—A review

Turbulent flow heat transfer and fluid friction in helical-wire-coil-inserted tubes

Turbulent Flow Friction and Heat Transfer Characteristics of Single- and Multistart Spirally Enhanced Tubes

Performance prediction and validation of equilibrium modeling for gasification of cashew nut shell char

Gasification Facets of Cashew Nut Shell Char Vis-à-Vis Casuarina Wood—An Experimental Analysis