The use of a latent heat storage system using phase change materials (PCMs) is an effective way of storing thermal energy and has the advantages of high-energy storage density and the isothermal nature of the storage process. PCMs have been widely used in latent heat thermal-storage systems for heat pumps, solar engineering, and spacecraft thermal control applications. The uses of PCMs for heating and cooling applications for buildings have been investigated within the past decade. There are large numbers of PCMs that melt and solidify at a wide range of temperatures, making them attractive in a number of applications. This paper also summarizes the investigation and analysis of the available thermal energy storage systems incorporating PCMs for use in different applications.

Review on thermal energy storage with phase change materials and applications

A review on phase change energy storage: materials and applications

The continuous increase in the level of greenhouse gas emissions and the climb in fuel prices are the main driving forces behind efforts to more effectively utilise 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. However, the large-scale utilisation of this form of energy is possible only if the effective technology for its storage can be developed with acceptable capital and running costs. One of prospective techniques of storing solar energy is the application of phase change materials (PCMs). Unfortunately, prior to the large-scale practical application of this technology, it is necessary to resolve numerous problems at the research and development stage. This paper looks at the current state of research in this particular field, with the main focus being on the assessment of the thermal properties of various PCMs, methods of heat transfer enhancement and design configurations of heat storage facilities to be used as a part of solar passive and active space heating systems, greenhouses and solar cooking.

Solar energy storage using phase change materials

Impact of water droplets on a flat, solid surface was studied using both experiments and numerical simulation. Liquid–solid contact angle was varied in experiments by adding traces of a surfactant to water. Impacting droplets were photographed and liquid–solid contact diameters and contact angles were measured from photographs. A numerical solution of the Navier–Stokes equation using a modified SOLA‐VOF method was used to modeldroplet deformation. Measured values of dynamic contact angles were used as a boundary condition for the numerical model. Impacting droplets spread on the surface until liquid surface tension and viscosity overcame inertial forces, after which they recoiled off the surface. Adding a surfactant did not affect droplet shape during the initial stages of impact, but did increase maximum spread diameter and reduce recoil height. Comparison of computer generated images of impacting droplets with photographs showed that the numerical model modeled droplet shape evolution correctly. Accurate predictions were obtained for droplet contact diameter during spreading and at equilibrium. The model overpredicted droplet contact diameters during recoil. Assuming that dynamic surface tension of surfactant solutions is constant, equaling that of pure water, gave predicted droplet shapes that best agreed with experimental observations. When the contact angle was assumed constant in the model, equal to the measured equilibrium value, predictions were less accurate. A simple analytical model was developed to predict maximum droplet diameter after impact. Model predictions agreed well with experimental measurements reported in the literature. Capillary effects were shown to be negligible during droplet impact when We≫Re1/2.

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Capillary effects during droplet impact on a solid surface

Thermal energy storage technologies and systems for concentrating solar power plants

In the present study, the performance of a heat storage unit consisting of number of vertical cylindrical capsules filled with phase change materials, with air flowing across them for heat exchange has been analyzed. Earlier theoretical models did not consider temperature distribution in the radial direction within the capsules, an assumption that limits their applications for small diameter capsules. The mathematical model developed in this work is based on solving the heat conduction equation in both melt and solid phases in cylindrical coordinates, taking into account the radial temperature distribution in both phases. Heat flux was then evaluated at the surface of the first row of the capsules to determine the temperature of the air leaving that row by a simple heat balance. It was found that such computation may be carried out for every few rows rather than for a single row to minimize computer time. The simulation study showed a significant improvement in the rate of heat transfer during heat charge and discharge when phase change materials with different melting temperatures were used. Air must flow in the direction of decreasing melting temperature during heat charge, while it must be reversed during heat discharge.

Thermal Performance of a Heat Storage Module Using PCM’s With Different Melting Temperatures: Mathematical Modeling

A latent heat storage module with rapid charging and discharging rates has been developed. The heat storage module consisted of horizontal cylindrical capsules filled with three types of PCM with different melting temperatures. A numerical model has been developed to predict the transient behavior of the heat storage module. Both the experimental and numerical results showed some improvements in charging and discharging rates by use of a “three-type” PCM

Enhancement of charging and discharging rates in a latent heat storage system by use of PCM with different melting temperatures

Deformation and solidification of a droplet on a cold substrate

The exergy efficiency, as well as the charging and discharging rates, in a latent heat storage system can be improved by use of the PCMs having different melting points. The melting point distribution of the PCMs has substantial effects on the exergy efficiency. The optimum melting point distribution of the PCMs has been estimated from numerical simulations and also from simple equations. The fast charging or discharging rate leads to high exergy efficiency.

Second law optimization of a latent heat storage system with PCMS having different melting points

Dichlorodifluoromethane was decomposed by a thermal argon plasma generated by a DC are discharge. The experiments and the kinetic calculations showed that the complete decomposition of the chlorofluorocarbon proceeded with the simultaneous additions of hydrogen and oxygen. Both the expertimental and calculated results confirmed that it is favorable, for the decomposition, not to quench the products but to add an excess of hydrogen over the stoichiometric amount, which leads to a reduction in chlorine formation.

Atsushi Kanzawa

Papers

Thermal Performance of a Heat Storage Module Using PCM’s With Different Melting Temperatures: Mathematical Modeling

Enhancement of charging and discharging rates in a latent heat storage system by use of PCM with different melting temperatures

Deformation and solidification of a droplet on a cold substrate

Second law optimization of a latent heat storage system with PCMS having different melting points

Thermal plasma decomposition of chlorofluorocarbons