Belén Zalba

Review on thermal energy storage with phase change: materials, heat transfer analysis and applications

Abstract Thermal energy storage in general, and phase change materials (PCMs) in particular, have been a main topic in research for the last 20 years, but although the information is quantitatively enormous, it is also spread widely in the literature, and difficult to find. In this work, a review has been carried out of the history of thermal energy storage with solid–liquid phase change. Three aspects have been the focus of this review: materials, heat transfer and applications. The paper contains listed over 150 materials used in research as PCMs, and about 45 commercially available PCMs. The paper lists over 230 references.

Determination of enthalpy-temperature curves of phase change materials with the temperature-history method: improvement to temperature dependent properties

The temperature-history method, proposed by Yinping et al, is a simple and economic way to determine the main thermophysical properties of materials used in thermal energy storage based on solid–liquid phase change. It is based on comparing the temperature history of a phase-change material sample and a sample of a well known material upon cooling down. In this paper we describe a further developed evaluation procedure to determine cp and h as temperature dependent values which was not the case in Yinpings method, based on the same experimental procedure. Given the suitability of these properties to calculate thermal energy storage using these materials, the method is proposed to present the results obtained in the form of enthalpy–temperature curves. A discussion about the errors produced by this method and an experimental improvement are proposed too.

Verification of a T-history installation to measure enthalpy versus temperature curves of phase change materials

Phase change materials (PCM) are able to store thermal energy in small temperature intervals very efficiently due to their high latent heat. Accurate knowledge of the enthalpy as a function of temperature, or the storage capacity at each temperature, is the key to design any application. Conventional methods for thermal analysis however often lack sufficient accuracy or sample size to be applied to PCM. The T-history method is a simple method to determine the storage capacity of PCM and allows the use of large sample sizes. The experimental setup and methods of data analysis have been significantly improved in recent years. In this paper, a proper methodology to verify the correct setup and data analysis method of a T-history installation using standard materials with known properties is described and tested. The implementation of the T-history method has been done at the ZAE-Bayern. Three standard materials, gallium, water and hexadecane, were measured, as well as two commercial PCM, RT27 and sodium acetate trihydrate graphite compound (SAT+G). The obtained results confirm that the T-history installation can be used to analyse different PCM.

An experimental study of thermal energy storage with phase change materials by design of experiments

Abstract Accurate theoretical modelling and simulation of thermal energy storage (TES) by means of phase change materials (PCM) is very complex and its results are not close enough to experimental values. This paper presents the empirical study of a thermal storage unit operating with a commercial PCM called RT25. The study is carried out by means of the statistical procedure, Design of Experiments. This methodology has rarely been used in the analysis of heat transfer problems. The present study has allowed us to investigate the phenomena involved and to design an actual system. We show the whole procedure followed in order to design the set-up, to run the experiments with a 23 factorial design, to compare its results with a numerical simulation and to get the empirical model by regression. Its results have been used to design actual installations aimed at free-cooling or maintaining the temperature constant in rooms where thermal security is necessary.

A theoretical study on the accuracy of the T-history method for enthalpy–temperature curve measurement: analysis of the influence of thermal gradients inside T-history samples

The present work analyses the effect of radial thermal gradients inside T-history samples on the enthalpy temperature curve measurement. A conduction heat transfer model has been utilized for this purpose. Some expressions have been obtained that relate the main dimensionless numbers of the experiments with the deviations in specific heat capacity, phase change enthalpy and phase change temperature estimations. Although these relations can only be strictly applied to solid materials (e.g. measurements of shape stabilized phase change materials), they can provide some useful and conservative bounds for the deviations of the T-history method. Biot numbers emerge as the most relevant dimensionless parameters in the accuracy of the specific heat capacity and phase change enthalpy estimation whereas this model predicts a negligible influence of the temperature levels used for the experiments or the Stefan number.

PCM-Air Heat Exchangers: Slab Geometry

Energy efficiency and the search for new energy sources and uses are becoming main objectives for the scientific community as well as for society in general. This search is due to various environmental issues and shortages of conventional and non-sustainable energy resources, for example fossil fuels, that are essential to industrial development and to daily life. Free-cooling in buildings, bioclimatic architecture applications, demand and production coupling in renewable energy sources, as solar energy, are examples of thermal energy storage contributions to achieve these objectives. The application of Phase Change Materials (hereafter PCM) in Thermal Energy Storage (hereafter TES) is an expanding field due to the variety of materials being developed. There are four critical considerations for the technical viability of these applications: 1) The features of both the PCM and the encapsulation material must be stable during the system lifetime; 2) A reliable numerical model of the system to simulate different operational conditions; 3) The thermophysical properties of the PCM; 4) The cost of the system.