An approximate analytical solution for the movement of the phase change front in latent thermal energy storage heat exchangers

Simulation study on the effect of fins on the heat transfer performance of horizontal dual-inner-tube latent thermal energy storage heat exchangers

In this study, the shrinking solid regime is investigated in a high aspect ratio tube-in-tube latent thermal energy storage (LTES) heat exchanger by tracking the phase change front evolution. In the setup, water flows through the inner tube as heat transfer fluid (HTF) and the shell contains a paraffin RT35HC as phase change material (PCM). A series of melting experiments have been performed in which the HTF mass flow rate, HTF inlet temperature and initial PCM temperature were varied. During each experiment, the movement of the phase change front was tracked using a camera placed next to the PCM tube. The front position as a function of time follows an S-shape curve. The effect of the operating conditions on the evolution of the phase change front is analysed. It is found that the temperature difference between the HTF and PCM exerts a more pronounced influence on the front position compared to the HTF Reynolds number. Finally, a correlation was developed to determine the temporal evolution of the front position. This research contributes to a deeper understanding of phase change phenomena in LTES systems and the found correlation can be a valuable tool for predicting and optimizing the performance of tube-in-tube LTES heat exchangers.

Standardised methods for the determination of key performance indicators for thermal energy storage heat exchangers

Estimating the state of charge in a latent thermal energy storage heat exchanger based on inlet/outlet and surface measurements

Thermal performance of a plate-type latent heat thermal energy storage heat exchanger - An experimental investigation and simulation study

A charging time energy fraction method for evaluating the performance of a latent thermal energy storage heat exchanger

Thermal energy storage (TES) technology is considered to have the greatest potential to balance the demand and supply overcoming the intermittency and fluctuation nature of real-world heat sources, making a more flexible, highly efficient and reliable thermal energy system. This article provides a comprehensive state-of-the-art review of latent thermal energy storage (LTES) technology with a particular focus on medium-high temperature phase change materials for heat recovery, storage and utilisation. This review aims to identify potential methods to design and optimise LTES heat exchangers for heat recovery and storage, bridging the knowledge gap between the present studies and future technological developments. The key focuses of current work can be described as follows: (1) Insight into moderate-high temperature phase change materials and thermal conductivity enhancement methods. (2) Various configurations of latent thermal energy storage heat exchangers and relevant heat transfer enhancement techniques (3) Applications of latent thermal energy storage heat exchangers with different thermal sources, including solar energy, industrial waste heat and engine waste heat, are discussed in detail.

Characterization of a latent thermal energy storage heat exchanger using a charging time energy fraction method with a heat loss model

Latent thermal energy storage can be a key technology for a green energy transition by matching fluctuating heat demand and supply. In order to implement a storage system, it needs to be designed which requires estimating the outlet temperature of a system for a given geometry and time history of the heat transfer fluid’s mass flow rate and inlet temperature. Currently, design methods are either overly simplistic, focusing solely on e.g. the phase change time or requiring the solution of partial differential equations which can be computationally expensive. The present paper proposes a novel approach where a latent thermal energy storage system is decomposed into a heat transfer fluid vessel, a sensible storage system and a storage system with only latent heat. Computationally inexpensive models are available for all three of these sub heat exchangers. A heat exchanger model is obtained by connecting the sub heat exchangers in parallel. This novel approach is used to model an industrial scale shell and tube latent thermal energy storage heat exchanger. The predicted outlet temperature is compared to the measured outlet temperature and the design model obtains good agreement.

Effect of inner-tube spacing on charging and discharging performance of latent energy storage heat exchangers

A predictive method for pipe in pipe, cylindrical modules and spherical packed bed latent thermal energy storage systems

Optimizing phase change composite thermal energy storage using the thermal Ragone framework

Compressed Air Energy Storage is a promising large-scale storage system in part because of its high power rating during discharge. But it is not the cleanest way of storing energy due to the necessity of an external heat source (typically the combustion of natural gas) to heat the air at the turbine inlet. This problem can be overcome with Thermal Energy Storage by storing the thermal energy of air at the compressor exhaust in order to be used for heating air before turbine. In this study, a numerical transient heat transfer model of Thermal Energy Storage is developed and the performance of Thermal Energy Storage is investigated based on heat storage capacity, required time to store unit amount of energy and air temperature profiles at the outlet of Thermal Energy Storage during discharge for the system. High heat storage per volume is necessary for more compact systems. Required time to store unit amount of energy is desired to be short for a fixed volume Thermal Energy Storage in order to maintain continuous operation; on the other hand, air at the outlet (turbine inlet) should be at a high temperature for the longest time possible to supply hot air to turbine. In order to investigate the effects of operating parameters, different volumes of Thermal Energy Storage tank filled with different storage mediums of various sizes are explored. Latent Heat and Sensible Heat Thermal Energy Storage systems are compared using magnesium chloride hexahydrate, paraffin, myristic acid and naphthalene as phase change materials and rock as sensible storage medium. Results show that Latent Heat Thermal Energy Storage gives a better performance than Sensible Heat Thermal Energy Storage. Among phase change materials, magnesium chloride hexahydrate provides the highest heat storage per volume. Required time to store unit amount of energy are comparable among the phase change materials. Magnesium chloride hexahydrate seems promising considering the discharge temperature profile at the Thermal Energy Storage outlet. Capsule size should be kept as small as possible which can be challenging in terms of manufacturing.

ABSTRACTThe application of a phase change material (PCM) as thermal energy storage observed unprecedented growth due to its large latent heat storage capacity at a constant temperature. However, the design of an energy storage heat exchanger is a challenging task because of the poor thermal conductivity of PCMs. In an effort to improve the heat exchanger design, this paper presents a numerical performance investigation of a PCM-based multitube heat exchanger incorporated with two new fin configurations. The analysis of the results shows that the placement of fins is one of the important aspects, which needs to be cogitated in the design of heat exchangers.

The latent thermal energy storage (LTES) technology has advantages of high thermal energy storage density, system volume saving, and easy installation, which is of great significance for improving the flexibility of thermal energy supply in the background of renewable energy utilization. The process of storing/releasing thermal energy of LTES systems mainly relies on heat exchangers, one special device for exchanging heat between heat transfer fluids (HTFs) and phase change materials (PCMs). The inherent liquid-solid phase change process of PCMs in the device makes this kind of heat exchanger urgently needed for more efficient design and optimization. In this chapter, working materials, device types, design forms, heat transfer enhancement methods, and some actual applications for heat exchangers are introduced. The present problems of the heat exchanger development are also discussed. The purpose of this chapter is to attempt to help the readers obtain key knowledge and design points for potential better applications of the LTES heat exchangers.