Numerical simulation and parametric analysis of latent heat thermal energy storage system

This paper presents the numerical analysis of the transient performance of the latent heat thermal energy storage unit established on finite difference method. The storage unit consists of a shell and tube arrangement with phase change material (PCM) filled in the shell space and the heat transfer fluid (HTF) flowing in the inner tube. The heat exchange between the HTF, wall and PCM has been investigated by developing a 2-D fully implicit numerical model for the storage module and solving the complete module as a conjugate problem using enthalpy transforming method. A comparative investigation of the total melting time of the PCM has been performed based on natural convection in liquid PCM during the charging process. The novelty of this paper lies in the fact it includes convection in PCM and this investigation includes a detailed parametric study which can be used as a reference to design latent heat storage. The results indicate that natural convection accelerates the melting process by a significant amount of time. In order to optimize the design of the thermal storage unit, parametric study has been accompanied to analyze the influence of various HTF working conditions and geometric dimensions on the total melting time of the PCM. Another important feature considered in this work is the influence of the inner wall of the tube carrying the HTF on the entire melting time of the PCM. An error of around 7.2% is reported when inner wall of the tube is ignored in the analysis.

     

Computational study of a latent heat thermal energy storage system enhanced by highly conductive metal foams and heat pipes

Numerical simulations are performed to analyze the thermal characteristics of a latent heat thermal energy storage system with phase change material embedded in highly conductive porous media. A network of finned heat pipes is also employed to enhance the heat transfer within the system. ANSYS-FLUENT 19.0 is used to create a transient multiphase computational model to simulate the thermal behavior of the storage unit. Copper foam is the porous medium used to enhance the heat transfer and is impregnated with the phase change material, potassium nitrate (KNO₃). The effects of the porosity of the metal foam and the quantity of heat pipes on the thermal characteristics of storage unit have been investigated. The results indicated that increasing the quantity of the embedded heat pipes leads to drastic acceleration of both charging and discharging process. Impregnating the copper foam with potassium nitrate phase change material significantly affects the total charging and discharging times of the storage unit. It was shown that the porosity of the metal foam plays a key role in the thermal behavior of the system during the charging and discharging processes.

     

High-conductivity nanomaterials for enhancing thermal performance of latent heat thermal energy storage systems

Journal of Thermal Analysis and Calorimetry - Dispersing high-conductivity nanomaterials into phase change materials (PCM) of latent heat thermal energy storage systems (LHTESS) is expected to...     

Thermoanalytical investigation of sodium acetate trihydrate for application as a latent heat thermal energy storage material

The thermal behaviour of sodium acetate trihydrate (NaAc · 3H₂O) was investigated by DTA, Q-TG and measurements of the solubility properties. The nucleation efficiency of Na₄P₂O₇ · 10H₂O for the crystallization of NaAc · 3H₂O melts is not stable over long periods. Stratification can be ascribed to the formation of anhydrous sodium acetate in the supercooled melts. Under static heat storage conditions, NaAc · 3H₂O and Na₄P₂O₇ · 10H₂O do not exhibit stable behaviour.

---

Zusammenfassung Das thermische Verhalten von Natriumacetat-trihydrat (NaAc · 3H₂O) wurde durch DTA, Q-TG und Löslichkeitsmessungen untersucht. Der Keimbildungseffekt von Na₄P₂O₇ · 10H₂O gegenüber NaAc · 3H₂O ist über längere Zeit nicht stabil. Die Schichtbildung kann zurückgeführt werden auf die Bildung von wasserfreiem NaAc in unterkühlten Schmelzen. Unter statischen Bedingungen der Wärmespeicherung zeigen NaAc·₃H₂O und Na₄P₂O₇ · 10H₂O kein stabiles Verhalten.

---

, Q- . Na4P2O7 · 102, . . .

     

Numerical simulation of nanofluid turbulent flow in a double-pipe heat exchanger equipped with circular fins

Journal of Thermal Analysis and Calorimetry - In this study, the thermal and flow characteristics of a nanofluid were evaluated numerically in a circular finned double-pipe heat exchanger. A 3D CFD...     

DSC study of melting and solidification of salt hydrates

Most salt hydrates, especially those proposed for thermal-energy-storage applications, melt incongruently. In static systems, this property often leads to differences between the enthalpy of fusion and enthalpy of solidification. By means of differential scanning calorimetry (DSC), these differences have been determined for several salt hydrates. For Na₂SO₄ · 10 H₂O, the enthalpy of solidification at or near the peritectic temperature is never more than 60% of the enthalpy of fusion; further cooling leads to a second phase transition at a temperature corresponding to eutectic melting of mixtures of ice and this hydrate. This asymmetrical melting and freezing behavior of Na₂SO₄ · 10 H₂O decreases its potential as an energy-storing medium and also limits its usefulness for temperature calibration of DSC instruments. Sodium pyrophosphate decahydrate, Na₄P₂O₇ · 10 H₂O, although in some ways a higher temperature analog of Na₂SO₄ · 10 H₂O, exhibited a smaller discrepancy between the enthalpies of fusion and of solidification; its relatively high transition temperature permits a more rapid solidification reaction than is the case for Na₂SO₄ · 10 H₂O. For Mg(NO₃)₂ · 6 H₂O, a congruently melting compound, the magnitude of ΔH of crystallization equalled ΔH of fusion, even when supercooling occurred; a solid-state transition at 73°C, with ΔH = 2.9 cal g^?1, was detected for this hydrate. MgCl₂ · 6 H₂O, which melts almost congruently, exhibited no disparity between ΔH of crystallization and ΔH of fusion. CuSO₄ · 5 H₂O and Na₂B₄O₇ · 10 H₂O exhibited marked disparities. Na₂B₄O₇ · 10 H₂O formed metastable Na₂B₄O₇sd 5 H₂O at the phase transition; this was derived from the transition temperature and verified by relating the observed ΔH of transition to heats of hydration. Peritectic solidification of hydrates can be viewed as a dual process: crystallization from the liquid solution and reaction of the lower hydrate (or anhydrate) with the solution; where ΔH of solidification appears to be less in magnitude than the ΔH of fusion, the difference can be attributed to slower reaction rate between solution and the lower hydrate. New or previously unreported values for ΔH of fusion obtained in this study were, in cal g^?1: Mg(NO₃)₂ · 6 H₂O, 36; Na₄P₂O₇ · 10 H₂O, 59; CuSO₄ · 5 H₂O, 32; Na₂B₄O₇ · 10 H₂O, 33.     

Application of PCM thermal energy storage system to reduce building energy consumption

The building sector is known to make a large contribution to total energy consumption and CO₂ emissions. Phase change materials (PCMs) have been considered for thermal energy storage (TES) in buildings. They can balance out the discrepancies between energy demand and energy supply, which are temporally out of phase. However, traditional PCMs need special latent storage devices or containers to encapsulate the PCM, in order to store and release the latent heat of the PCM. The proper design of TES systems using a PCM requires quantitative information and knowledge about the heat transfer and phase change processes in the PCM. In Korea, radiant floor heating systems, which have traditionally been used in residential buildings, consume approximately 55% of the total residential building energy consumption in heating. This article reviews the development of available latent heat thermal energy storage technologies and discusses PCM application methods for residential building using radiant floor heating systems with the goal of reducing energy consumption.     

Influence of thermal transport properties of NEPCM for cool thermal energy storage system

Journal of Thermal Analysis and Calorimetry - The present work deals with thermal energy storage behavior of the nano-enhanced phase change materials (NEPCMs) for building space cooling...     

Evaluation of adsorbent materials for heat pump and thermal energy storage applications in open systems

The evaluation of solid adsorbents in open sorption systems for heating, cooling and thermal energy storage (TES) applications is crucial for the ecological and economical performance of these systems. An appropriate adsorbent has to reach the temperature limit given by the heating/cooling system of the consumer. It has to provide high energy efficiency and a high energy density for storage applications. A method for an easy evaluation of different adsorbents for a specific application has been developed. The method is based on the adsorption equilibrium of the adsorbent and water vapor. The crucial property for the discussed field of applications is the differential heat of adsorption. Criteria for the evaluation of the adsorbent are the breakthrough curves (responsible for the dynamics of the process), the possible temperature lift (or the dehumidification) of the air, the thermal COP and the storage capacity.     

Charging process of thermal energy storage system under varying incident heat flux: interaction the fluid neighbour nodes and particles in order to heat transfer

Journal of Thermal Analysis and Calorimetry - A numerical study of a charging process of thermal energy storage (TES) system with solar tower receiver was investigated under real environmental...     

Synthesis and thermal energy storage properties of a calcium-based room temperature phase change material for energy storage

Journal of Thermal Analysis and Calorimetry - In order to obtain a low-cost, high latent heat and thermostable phase change material with a phase change temperature between 18 and...     

Comparison of different approaches for thermal performance improvement of a phase change energy storage system

Journal of Thermal Analysis and Calorimetry - Performance improvement of a phase change material (PCM) thermal storage system is numerically investigated. A finite volume solver is employed to...     

Experimental study on novel phase change composites for thermal energy storage

Journal of Thermal Analysis and Calorimetry - In this study, beeswax is studied as a phase change material (PCM) to store heat due to its high latent heat. The disadvantages of using beeswax were...     

Preparation and mechanical properties of thermal energy storage microcapsules

A series of heat energy storage microcapsules was prepared using melamine-formaldehyde resin as the shell material and the mechanical properties of the shell were investigated. A phase change material whose melting point was 24 °C was used as core and the quantity of heat involved in phase transition was 225.5 J/g. Average diameter of the microcapsules varied from 5 to 10 μm, and the globular surface was smooth and compact. The mechanical properties of the shell were evaluated by observing the surface morphological structure change after application of pressure by means of scanning electron microscopy. When the mass ratio of the core and shell material is 3:1, a yield point of about 1.1×10⁵ Pa was found and when the compression was increased beyond this point the microcapsules showed plastic behavior. This has been attributed to the cross-link density and to the high degree of reaction of the shell material. Different yield points subsequently reflected differences in the mechanical behavior. It was also found that the mechanical intensity of double-shell microcapsules was better than that of single shelled ones.     

Effect of iron scrap additives in stearic acid as PCM for thermal energy storage system

Journal of Thermal Analysis and Calorimetry - The thermal energy storage (TES) system is used to store the heat energy for longer periods and retrieve the heat energy as and when required....     

Effect of the inclination angles on thermal energy storage in a quadrantal cavity

A free-base tetra sodium meso-tetra (p-sulphonatophenyl) porphyrin (TPPS₄) and its corresponding metalloporphyrins (MTPPS₄), where M?=?Co, Ni and Zn were synthesized and characterized by UV?Cvisible spectroscopy, infra red spectroscopy and ¹H nmr spectroscopy. Thermal studies of these porphyrins were conducted in synthetic air from room temperature to 800?°C. The residues of MTPPS₄ were qualitatively analyzed which showed the presence of corresponding metal oxides and Na₂SO₄. Further, the above porphyrins were subjected to TG-EGA-MS analysis in argon atmosphere to study the evolved gases/species during the thermal events. This information is useful to know the ring opening sequence of these porphyrins at corresponding temperatures.     

Thermodynamic and thermal energy storage properties of a new medium-temperature phase change material

Journal of Thermal Analysis and Calorimetry - Phase change materials (PCMs) that can store the heat energy obtained from intermittent solar irradiation are very important for solar energy...     

Thermal energy storage materials — a DSC study

A DSC investigation of a thermal energy storage, first-order phase change system has been carried out. The material is a borax—common salt modified sodium sulfate decahydrate system, distributed throughout a fumed silica supporting matrix. The qualitative features of the thermal behavior of the material can be explained in terms of the phase diagram of the sodium sulfate—water peritectic system, modified by the presence of a low-temperature eutectic. Fusion and recrystallization enthalpies have been measured as a function of cycle number. The thermal conversion efficiency of the system is high. Combining these data with specific heat measurements, the calculated storage capacity is in good agreement with published engineering information.