This paper reviews the development of latent heat thermal energy storage systems studied detailing various phase change materials (PCMs) investigated over the last three decades, the heat transfer and enhancement techniques employed in PCMs to effectively charge and discharge latent heat energy and the formulation of the phase change problem. It also examines the geometry and configurations of PCM containers and a series of numerical and experimental tests undertaken to assess the effects of parameters such as the inlet temperature and the mass flow rate of the heat transfer fluid (HTF). It is concluded that most of the phase change problems have been carried out at temperature ranges between 0 °C and 60 °C suitable for domestic heating applications. In terms of problem formulation, the common approach has been the use of enthalpy formulation. Heat transfer in the phase change problem was previously formulated using pure conduction approach but the problem has moved to a different level of complexity with added convection in the melt being accounted for. There is no standard method (such as British Standards or EU standards) developed to test for PCMs, making it difficult for comparison to be made to assess the suitability of PCMs to particular applications. A unified platform such as British Standards, EU standards needs to be developed to ensure same or similar procedure and analysis (performance curves) to allow comparison and knowledge gained from one test to be applied to another.

A review of materials, heat transfer and phase change problem formulation for latent heat thermal energy storage systems (LHTESS)

The flow of homogeneous fluids through porous media: analogies with other physical problems

Thermal energy storage has recently attracted increasing interest related to thermal applications such as space and water heating, waste heat utilization, cooling and air-conditioning. Energy storage is essential whenever there is a mismatch between the supply and consumption of energy. Use of phase change material (PCM) capsules assembled as a packed bed is one of the important methods that has been proposed to achieve the objective of high storage density with higher efficiency. A proper designing of the thermal energy storage systems using PCMs requires quantitative information about heat transfer and phase change processes in PCM. This paper reviews the development of available latent heat thermal energy storage technologies. The different aspects of storage such as material, encapsulation, heat transfer, applications and new PCM technology innovation have been carried out.

Heat transfer characteristics of thermal energy storage system using PCM capsules: A review

Successful utilization of the latent heat energy storage system depends considerably on the thermal reliability and stability of the phase change materials (PCMs) used. Thermal stability of phase change material can be established by measuring the thermo-physical properties of the PCM after a number of repeated thermal cycles. A comprehensive knowledge of thermal stability of the PCMs as functions of number of repeated thermal cycles is essential to ensure the long-term performance and economic feasibility of the latent heat storage systems. In this paper, a detailed review is reported for thermal stability of different groups of PCMs. The PCMs are categorized as organic (paraffins and non-paraffins), inorganic (salt hydrates and metallics) and eutectics (organic eutectics and inorganic eutectics). Further, a broad database of different PCMs is developed for which thermal cycling tests were carried out by different researchers and reported in the literature. Some conclusions are derived after critical evaluation of thermal stability of different groups of PCMs. This review will assist to identify the most reliable PCM to be used for a particular application of latent heat energy storage system.

Thermal stability of phase change materials used in latent heat energy storage systems: A review

Numerical and experimental study of melting in a spherical shell

Heat transfer characteristics of the latent heat thermal energy storage capsule

The melting phenomena of a solid, pressed on a surface with the temperature higher than the melting point, were analyzed and calculated numerically The analytical results concerning non-dimensional heat flux agreed well with experimental results for water and octadecane shown in the former report Then, an approximate formula relating non-dimensional heat flux with Stefan number and non-dimensional contact pressure was proposed The liquid layer thickness distribution between the heat transfer surface and the melting solid, besides the distributions of pressure, velocity and temperature within the liquid layer, was also calculated and discussed

On the Contact Heat Transfer with Melting : 2nd report: Analytical Study

The phase change process of a melting solid pressed on a hot heat transfer surface was investigated experimentally, as a basic research of the heat storage process in a latent heat TES (thermal energy storage) capsule. Along with measurements for various conditions, the physical parameters deciding the phenomena were analyzed, normalizing the basic equations and boundary conditions. It was shown as the result that the nondimensional heat flux expressed as a function of the Stefan number and the nondimensional contact pressure. Based on the experimental results, the relation among the bove nondimensional quantities was shown by a simple formula.

On the Contact Heat Transfer with Melting : 1st Report: Experimental Study

The frost formation process consists of three periods : "crystal growth period", "frost layer growth period" and "frost layer full growth period". This paper studies the process in the frost layer full growth period, which is characterized by the phenomena of water permeation and freezing in the frost layer. It was shown experimentally that this process could be classified largely into two frost formation patterns, depending on the diffusion rate of water vapour. The position of the freezing interface in the frost layer was related to the water quantity held on the frost surface by surface tension and the heat flux in frost layer. Further, the frost structure in this period was composed of a freezing layer and a porous layer, and the frost properties could be estimated from this structure.

A Study on Frost Formation : The Process of Frost Formation involving the Phenomena of Water Permeation and Freezing

A latent heat thermal energy storage capsule, having a horizontal heat transfer surface at the bottom and storing the energy by contact melting, is prepared. The time-dependency of the storage heat flux is measured, using n-octadecane as the phase change material. Next, the non-dimensional formula for the contact melting heat flux in the steady state is derived, based on the results of the previous papers. Using the above formula, the time-dependency of the heat flux in the storage process is analyzed generally and the approximate solution is shown to agree well with the experimental results. Then, the effects of the PCM properties and the capsule specifications on the average heat flux are summarized.

Kozo Katayama

Papers

Heat transfer characteristics of the latent heat thermal energy storage capsule

On the Contact Heat Transfer with Melting : 2nd report: Analytical Study

On the Contact Heat Transfer with Melting : 1st Report: Experimental Study

A Study on Frost Formation : The Process of Frost Formation involving the Phenomena of Water Permeation and Freezing

Basic research on the latent heat thermal energy storage utilizing the contact melting phenomena