Latent Heat Storage Material Research Articles

Numerical simulation for fin effect of a rectangular latent heat storage vessel packed with molten salt under heat release process

The present numerical study has dealt with the enhancement of latent heat Release by using plate type fins mounted on the vertical cooling surface in the rectangular vessel packed with molten salt as a latent heat storage material. It was found that the fin thickness and pitch exerted an influence on solidification heat transfer in a liquid layer of a nitric molten salt. The numerical results elucidated the flow pattern, velocity profile and heat transfer rate in the melted liquid layer.

The capric and lauric acid mixture with chemical additives as latent heat storage materials for cooling application

The mixture of capric acid and lauric acid (C-L acid), with the respective mole composition of 65% and 35%, is a potential phase change material (PCM). Its melting point of 18.0°C, however, is considered high for cooling application of thermal energy storage. The thermophysical and heat transfer characteristics of the C-L acid with some organic additives are investigated. Compatibility of C-L acid combinations with additives in different proportions and their melting characteristics are analyzed using the differential scanning calorimeter (DSC). Among the chemical additives, methyl salicylate, eugenol, and cineole presented the relevant melting characteristics. The individual heat transfer behavior and thermal storage performance of 0.1 mole fraction of these additives in the C-L acid mixture are evaluated. The radial and axial temperature distribution during charging and discharging at different concentrations of selected PCM combinations are experimentally determined employing a vertical cylindrical shell and tube heat exchanger. The methyl salicylate in theC-L acid provided the most effective additive in the C-L acid. It demonstrated the least melting band width aimed at lowering the melting point of the C-L acid with the highest heat of fusion value with relatively comparable rate of heat transfer. Furthermore, the thermal performance based on the total amount of transferred energy and their rates, established the PCM’s latent heat storage capability.

Thermal performance evaluation of a latent heat storage unit for late evening cooking in a solar cooker having three reflectors

In this paper, a phase change material (PCM) storage unit for a solar cooker was designed and developed to store energy during sunshine hours. The stored energy was utilised to cook food in the late evening. Commercial grade acetanilide (melting point 118.9 °C, latent heat of fusion 222 kJ/kg) was used as a latent heat storage material. Evening cooking experiments were conducted with different loads and loading times during the winter season. The experimental results showed that late evening cooking is possible in a solar cooker having three reflectors to enhance the incident solar radiation with the PCM storage unit.

Thermodynamics and dynamics of the Mg–Fe–H system and its potential for thermochemical thermal energy storage

The reversible Mg 2FeH 6 and the mixed Mg 2FeH 6–MgH 2 hydride systems [ Eqs. (1) and (2)] turned out to be highly suitable materials for thermochemical thermal energy storage at around 500 °C, for example as the storage of solar or excess industrial heat. The systems are characterized by a high gravimetric and volumetric thermal energy density in comparison to sensible or latent heat storage materials ( Table 1) and have excellent stability in cycle tests. Further advantages include low price of the starting materials, a free choice and constancy of the heat delivery temperature by controlling the applied hydrogen pressure, and the absence of heat losses with time. By means of combined TEM–EDX investigations essential features of the initial formation and the subsequent de- and rehydrogenation processes of Mg 2FeH 6 could be elucidated on a micro- or nanoscale level.

Performance investigation of the capric and lauric acid mixture as latent heat energy storage for a cooling system

The thermal performance of the capric acid and lauric acid mixture (C–L acid) in the respective composition of 65% and 35% by mole was investigated for its cooling capacity. Pentadecane was used for comparison. A vertical cylindrical storage capsule was employed for the study. The temperature distribution of the C–L acid during charging and discharging inside a vertical tube was experimentally determined in both radial and axial directions. A melting point of 18–19.5°C was observed. This value corroborates with the DSC-obtained values for the C–L acid. The calculated stored energy based on the radial temperature distribution during charge and discharge processes indicates that the C–L acid is a potential latent heat storage material.

The capric–lauric acid and pentadecane combination as phase change material for cooling applications

The mixture of 65 mol% capric acid and 35 mol% lauric acid (C–L acid) is a potential latent heat storage material. However, its melting temperature of 18.0°C is quite high for low-temperature thermal energy storage. Addition of pentadecane, with a melting point of 9.9°C, is proposed. The thermal characteristics of the combination of the C–L acid with pentadecane (CL:P) in different volume ratio are investigated employing the DSC analysis. The actual thermal performance of each CL:P combination is further determined from their radial and axial temperature distribution employing a fabricated thermal storage capsule. The 90:10 CL:P combination manifests an improvement in the melting characteristic of the C–L acid.

Direct Contact Cold Heat Extraction from Water Mixture of Gel Type Latent Heat Storage Material to Air Bubbles.

This paper has dealt with cold heat extraction characteristics from the gel latent-cold-heat storage-material suspension with surfactant to air bubbles. The gel latent-cold-heat storage-material consisted of n-paraffin as the core latent-cold-heat storage-material and water as a heat transfer medium. The relationship between outflow air temperature in latent-cold-heat release process and various parameters was examined experimentally. As a result, especially concentration of the gel latent material added to water exerted an influence on gas holdup and cold heat extraction characteristics to air bubbles. The non-dimensional correlation equations for the temperature effectiveness of latent-heat storage process were derived in terms of the ratio of water layer height to diameter of latent heat material, Reynolds number of air flow, Stefan number and modified Stefan number including air humidity.

D207 数値計算による矩形状中温潜熱蓄熱槽の特性(オーガナイズドセッション14 : 固・液相変化を伴う熱・物質移動及び流動の基礎と応用)

The present study deals with the characteristics of the heat storage vessel packed with rectangular phase change materials by numerical analysis. The latent heat storage materials in the vessel are heated by utilizing the natural convection of the heat transfer medium, which flow the interval of the latent heat storage materials. The interval of rectangular latent heat storage materials is greatly related to natural convection of the heat transfer medium. Numerical results revealed temperature profiles and flow patterns of the heat transfer medium affected the heat storage characteristics.

Natural Convection Behavior in an Inclined Rectangular Latent Heat Storage Vessel Having One Heating Wall with Plate Fins.

The present paper has dealt with the natural convection heat transfer in a melted liquid layer appeared in the inclined rectanglar latent heat storage vessel having one heating wall with plate fins. The effects of plate fin length, inclination angle of the rectangular vessel and heat wall temperature on the melting behavior of paraffin wax as a latent heat storage material. and natural convection heat transfer were investigated experimentally under a heat storage process. As a result, non-dimentional correlation equations of natural convection heat transfer were derived in terms of some non-dimentional parameters.

Thermal cycle test of urea for latent heat storage applications

Accelerated thermal cycle tests for melt/freeze cycles of urea were conducted. Urea has shown a very high degradation in its latent heat and melting point within the first few cycles and did not melt after a few cycles. It is recommended that urea should not be used as a latent heat storage material. Copyright © 2001 John Wiley & Sons, Ltd.

Heat Storage Characteristics of Latent-Heat Microcapsule Slurry Using Hot Air Bubbles by Direct-Contact Heat Exchange.

This study deals with the heat storage characteristics of latent-heat microcapsule slurry consisting of a mixture of fine microcapsules packed with latent-heat storage material and water. The heat storage operation for the latent-heat microcapsules was carried out by the direct-contact heat exchange method using hot air bubbles. The latent-heat microcapsule consisted of n-paraffin as a core latent-heat storage material and melamine resin as a coating substance. The relationship between the completion time of latent-heat storage and some parameters was examined experimentally. The nondimensional correlation equations for temperature efficiency, the completion time period of the latent-heat storage process and variation in the enthalpy of air through the microcapsule slurry layer were derived in terms of the ratio of microcapsule slurry layer height to microcapsule diameter, Reynolds number for airflow, Stefan number and modified Stefan number for absolute humidity of flowing air.

Design, development and performance evaluation of a latent heat storage unit for evening cooking in a solar cooker

In this paper, a PCM storage unit for a solar cooker was designed and developed to store solar energy during sunshine hours. The stored energy was utilised to cook food in the evening. Commercial grade acetamide was used as a latent heat storage material. Cooking experiments were conducted with different loads and loading times during the summer and winter seasons. The thermal performance of a solar cooker with the PCM storage unit was compared with a standard solar cooker. The experimental results showed that evening cooking is possible with a solar cooker having the PCM storage unit and is not possible in a standard solar cooker.

00/01062 Measurements of transmittance of solar radiation through stearic acid: a latent heat storage material

00/01062 Measurements of transmittance of solar radiation through stearic acid: a latent heat storage material

Heat Storage Characteristics of Latent Microcapsules Using Hot Air Bubbles by Direct Contact Heat Exchange.

This paper has dealt with the heat storage characteristics of fine microcapsules packed with latent heat storage material in the water layer. The heat storage operation to the latent microcapsules was carried out using hot air bubbles by direct contact heat exchange. The microcapsule consists of n-paraffin as a core latent-heat storage material and melamine resin as a coating substance. The relation of the completion time of latent-heat storage to some parameters was examined experimentally. The non-dimensional correlation equations for the completion time of latent-heat storage process had were derived in terms of the ratio of water layer height to diameter of microcapsule, Reynolds number for air flow, Stefan number and modified Stefan number for absolute humidity of flowing air.

Thermodynamics of crystallization of sodium sulfate decahydrate in H 2O–NaCl–Na 2SO 4: application to Na 2SO 4·10H 2O-based latent heat storage materials

In this paper, we present a methodology for the prediction of the crystallization enthalpy of mirabilite (Na 2SO 4·10H 2O) from supersaturated H 2O–NaCl–Na 2SO 4 solutions. Required thermodynamic properties of H 2O–NaCl–Na 2SO 4 such as dissolution enthalpies, phase equilibria and heat of hydration of Na 2SO 4 are represented or determined using Pitzer’s ion-interaction model. Measurements of crystallization enthalpies at various temperatures and concentrations were made in a SETARAM C80D calorimeter by mixing H 2O–Na 2SO 4 and H 2O–NaCl–Na 2SO 4 solutions supersaturated relatively to mirabilite with a seed crystal of Na 2SO 4·10H 2O once the thermal equilibrium was reached. Good agreement was obtained between experimental and predicted values of crystallization enthalpies. Furthermore, we have studied the influence of NaCl used as an additive regarding the heat storage capacity of supersaturated H 2O–Na 2SO 4 solutions.

Measurements of transmittance of solar radiation through stearic acid: a latent heat storage material

This paper presents the experimental measurements of the transmittivity of commercial grade stearic acid. The effects of temperature and thickness on transmittance have been studied. The study indicates that the effect of temperature on the transmittance of stearic acid in the liquid phase is not significant. However, it is highly dependent on temperature during the solidification process. Because of its low thermal conductivity and high transmittivity, it can be used as a transparent insulating material.

HEAT TRANSFER ENHANCEMENT IN A LATENT HEAT STORAGE SYSTEM

Commercial acceptance and the economics of solar thermal technologies are tied to the design and development of efficient, cost-effective thermal storage systems. Thermal storage units that utilize latent heat storage materials have received greater attention in the recent years because of their large heat storage capacity and their isothermal behavior during the charging and discharging processes. One major issue that needs to be addressed is that most phase-change materials (PCM) with high energy storage density have an unacceptably low thermal conductivity and hence heat transfer enhancement techniques are required for any latent heat thermal storage (LHTS) applications. In the present paper the various heat transfer enhancement methods for LHTS systems are discussed. Three different experiments to augment heat transfer were conducted and the findings are reported.

Heat Release Characteristics of Middle Temperature Latent Heat Storage Vessel by Means of Direct Contact Heat Exchange Method.

Experiment has been performed of heat transfer characteristics of the middle temperature latent heat storage system of the direct-contact heat transfer by using m-E (meso-Erythritol, melting point of 119°C, latent heat of 375 kJ/kg) droplets as a latent heat storage material and silicone oil as a heat transfer medium. In the present study the liquid m-E was injected into the heat tranfer medium through a circular nozzle. The m-E droplets changed from liquid to solid phase during falling in the heat transfer medium at low temperature. From the measuring results of m-E droplet diameter, falling velocity, and solidification rate, the nondimensional empirical equations of the arithmetic mean diameter of the droplets and falling velocity, the solidification rate and the overall heat transfer coefficient were derived as a function of the characteristic arithmetic mean diameter, the terminal velocity, temperature and physical properties.

Physical properties and thermorheological behaviour of a dispersion having cold latent heat-storage material

A dispersion of n-alkanes in water has been elaborated for thermal energy storage and transport. Quantitative results regarding the thermophysical properties of the material are presented and compared with results obtained from correlations based on combination of the properties of the suspending phase and the dispersed phase. Thermorheological investigations of the material at various temperatures have shown a shear-thinning behaviour. The temperature dependence of the viscosity exhibits a slight jump near 9.5°C, corresponding to the phase change temperature. This deviation is interpreted in terms of a change in the particle state near the phase change temperature. This thermorheological behaviour obeys a power law model in which the parameters are temperature dependent. Its range of viscosity and its high heat capacity render the material particularly attractive in cooling and air conditioning processes.

Heat Storage Characteristics of an Inclined Rectangular Heat Storage Vessel Packed with Plate Type of Shape-Stabilized Phase Change Material.

The present study deals with the heat storage characteristics of the inclined rectangular vessel packed with spape-stabilized paraffin plates as a latent heat storage material by numerical analysis. It was found that the heat storage characteristics were remarkedly affected by the inclination angle of the rectangular vessel and the heat transfer medium flow direction, due to the presence of natural convection in the fluid flow channel between the paraffin plates. Numerical results revealed flow patterns, temperature profiles and heat storage characteristics for various inclination angles, inlet velocities and temperatures of the heat transfer medium fluid, and widths of the fluid flow channel.