Phase Change Material Melting Process in a Thermal Energy Storage System for Applications in Buildings

Abstract

The development of thermal energy storage systems is a possible solution in the search for reductions in the difference between the global energy supply and demand. In this context, the ability of some materials, the so-called phase change materials (PCMs), to absorb and release large amounts of energy under specific periods and operating conditions has been verified. The applications of these materials are limited due to their low thermal conductivity, and thus, it is necessary to associate them with high-conductivity materials, such as metals, to make the control of energy absorption and release times possible. Bearing this in mind, this paper presents a numerical analysis of the melting process of a PCM into a triplex tube heat exchanger (TTHX) with finned copper tubes, which allowed for the heat transfer between a heating fluid (water) and the phase change material to power a liquid-desiccant air conditioning system. Through the analysis of the temperature fields, liquid fractions, and velocities, as well as the phase transition, it was possible to describe the material charging process; then, the results were compared with experimental data, which are available in the specialized literature, and presented mean errors of less than 10%. The total required time to completely melt the PCM was about 105.5 min with the water being injected into the TTHX at a flow rate of 8.3 L/min and a temperature of 90 °C. It was observed that the latent energy that accumulated during the melting process was 1330 kJ, while the accumulated sensitive energy was 835 kJ. The average heat flux at the internal surface of the inner tube was about 3 times higher than the average heat flux at the outer surface of the TTHX intermediate tube due to the velocity gradients that developed in the internal part of the heat exchanger, and was about 10 times more intense than those observed in the external region of the equipment.

Application of Phase Change Material-Based Thermal Capacitor in Double Tube Heat Exchanger—A Numerical Investigation

“…Constant temperature and flow were defined at the inlet of the cold stream. The velocity of the cold stream was set such that the mass flow rate of water was the same as that in the hot stream and is reported in Table 5.ṁ =ṁ in , T = T c,in (14) At the wall between the hot stream and the PCM, a no-slip condition was specified with a coupled wall. Similarly, the wall between the cold stream and the PCM was specified as no-slip and with coupled heat transfer.…”

“…To develop a better understanding of the application of PCMs as thermal capacitors, the present study is conducted to numerically investigate the performance of a triplex heat exchanger with an integrated PCM. Previous authors studied this configuration at larger scales and demonstrated that is well suited for use as a thermal energy storage device [14]. The scope of this study is first limited to the laminar regime to better understand the possible temperature gradients that can be generated from the system.…”

Preparation and characterization of a form-stable phase change hydrogel for heat-protective clothing

“…15–18 Compared to organic PCMs, inorganic PCMs have the advantages of a small volume change, higher thermal conductivity, and a wider operating temperature range. 14,19–21 Inorganic PCMs include crystalline hydrated salts, molten salts, metals, their alloys, etc . 22–25 Among them, hydrated salts are the most widely used inorganic PCMs due to their advantages such as non-combustibility, high latent heat density, and low cost.…”

Recent Advances in CFD Simulations of Multiphase Flow Processes with Phase Change

“…Numerical modeling based on computational fluid dynamics (CFD) is increasingly applied to gain a better understanding of the complex transfer and reaction behaviors of multiphase flow with phase change . The spatial details of the heat transfer coefficient, temperature, velocity, and phase fraction can be extracted from the numerical data, which are difficult to obtain from experiments. , The inner mechanisms of various phase change flows can be divided into processes with gas–liquid, liquid–solid, and both gas–liquid and liquid–solid phase changes. Previous publications have extensively reviewed the application and numerical simulation of the pure gas–liquid phase change flows ,− or pure liquid–solid phase change flows, − while little attention has been devoted to the hybrid phase change systems .…”