Thermal Performance Of Phase Change Materials Research Articles

The experimental exploration of sodium chloride solution on thermal behavior of phase change materials

Phase change materials (PCMs) are the effective substances for thermal energy storage. Unfortunately, various problems such as high supercooling degree, low crystal growth rate and poor thermal conductivity greatly hinder the large-scale utilization of PCMs. The present study focuses on improving the crystallization and decreasing supercooling degree by adding various proportions of NaCl/NaCl solutions into the n-octadecane-based PCMs for thermal energy storage. The experimental results show that 20wt% NaCl solutions have the greatest effect on the thermal performance of PCMs. The supercooling degree has been minimized up to 6°C with the addition of NaCl. It can not only promote crystallization under 1wt% addition rate, but also enhance latent heat storage performance. Such observations have been verified by the kinetics of crystallization. The researches on supercooling could advance the application of PCMs on solar energy.

Role of Melt Convection on Optimization of PCM-Based Heat Sink Under Cyclic Heat Load

In this article, we study the thermal performance of phase-change material (PCM)-based heat sinks under cyclic heat load and subjected to melt convection. Plate fin type heat sinks made of aluminum and filled with PCM are considered in this study. The heat sink is heated from the bottom. For a prescribed value of heat flux, design of such a heat sink can be optimized with respect to its geometry, with the objective of minimizing the temperature rise during heating and ensuring complete solidification of PCM at the end of the cooling period for a given cycle. For given length and base plate thickness of a heat sink, a genetic algorithm (GA)-based optimization is carried out with respect to geometrical variables such as fin thickness, fin height, and the number of fins. The thermal performance of the heat sink for a given set of parameters is evaluated using an enthalpy-based heat transfer model, which provides the necessary data for the optimization algorithm. The effect of melt convection is studied by taking two cases, one without melt convection (conduction regime) and the other with convection. The results show that melt convection alters the results of geometrical optimization.

Centralized latent heat thermal energy storage system: Model development and validation

Centralized latent heat thermal energy storage (LHTES) system offers potential benefits in energy efficiency, in load shifting, and in emergency heating/cooling load systems. A three-dimensional heat transfer model of a LHTES is developed to investigate the quasi-steady state and transient heat transfer of phase change materials (PCMs). The prediction of model is in good agreement with the experimental data. The effect of convective heat transfer on the melting rate of PCM is assessed. Through a parametric study, the effect of the temperature, PCM phase change temperature range, and the temperature difference of the incoming air and PCM melting temperature on thermal performance of PCM is undertaken. The temperature difference between the air as a heat transfer fluid (HTF) and the PCM melting point has a significant effect on the performances of a LHTES system. The thermal energy retrieved from the centralized LHTES system is the highest when the inlet air temperature is about 10K higher than the PCM mean melting temperature. Correlations are obtained for the distribution of melting front and solid fraction as a function of time during charging and discharging of LHTES. These correlations can be used for further component optimization and design of cooling and heating systems.

A multi-level modelling and evaluation of thermal performance of phase-change materials in buildings

Integration of phase-change materials (PCMs) in building envelopes is a way to enhance heat storage capacity of buildings and thereby to rationalize the use of energy for heating and cooling of buildings. This work presents a numerical model of a building envelope with PCMs, verifications of the model according to a normative benchmark and measurements and a tentative case study that exemplifies the effects of such a building envelope on the thermal performance of a whole building. Simulations have been carried out using a modular environment of the International Building Physics Toolbox in Simulink®. As for the effects of PCMs in buildings, it is concluded that they are rather case sensitive; in the tentative case study, the annual savings of total energy for heating and cooling vary between 5% and 21%, depending mainly on the thermal comfort and the placement of PCM in the building envelope.