Latent Heat Storage Material Research Articles

Experience in the Application of Latent Heat Storage Material LC‐58

AbstractDie effiziente und wirtschaftliche Speicherung von Wärmeenergie steht in engem Zusammenhang mit der Nutzung von Solarenergie. Es wurden mit dem Latentwärmespeichermaterial LC‐58 gefüllte Versuchsspeicher verschiedener Größen entwickelt, die ein neues innovatives System zur Speicherung solarthermischer Energie darstellen. Zur Abdichtung gegen Wasser wurde das korrosive LC‐58 makroverkapselt.

Investigation on heat transfer properties of slurry of stabilized paraffin during a melting process

This paper is presented in the framework of the increasing interest for the use of latent heat transfer slurries for cooling processes. Paraffin serves as a latent heat storage material and a polymer network acts as the supporting material. The phase change material melts around 7 °C with a latent heat of fusion of 115 kJ/kg. A special experimental device is realized which permits the recording of the temperature in a single slurry undergoing a phase change in an agitated bath. Analysis of data permits to develop a phenomenological correlation adapted to the millimetric dimension of the slurry, leading to an estimation of the melting phase change time duration of a particle as a function of the main parameters of the problem.

Development and testing of PCM doped cool colored coatings to mitigate urban heat island and cool buildings

In this study the performance of organic PCMs used as latent heat storage materials, when incorporated in coatings for buildings and urban fabric, is investigated. Thirty six coatings of six colors containing different quantities of PCMs in different melting points were produced. Accordingly, infrared reflective (cool) and common coatings with the same binder system and of the same color were prepared for a comparative thermal evaluation. The samples were divided in six groups of different color and eight samples each: three PCM coatings of different melting temperatures (18 °C, 24 °C, 28 °C) each one of two different PCM concentrations (20% w/w, 30% w/w), an infrared reflective and a common coating of matching color. Surface temperature of the samples was recorded at a 24 h basis during August 2008. The results demonstrate that all PCM coatings present lower surface temperatures than infrared reflective and common coatings. Analysis of the daily temperature differences showed that peak temperature differences occur between PCM and common or cool coatings from 7 am to 10 am. Investigating the temperature gradient revealed that for this time period the values for PCM coatings are lower compared to infrared reflective and common. From 10 am to 12 pm, temperature gradients for all coatings have similar values. Thus coatings containing PCMs store heat in a latent form maintaining constant surface temperatures and discharge with time delay. PCM doped cool colored coatings have the potential to enhance thermal inertia and achieve important energy savings in buildings maintaining a thermally comfortable indoor environment, while fighting urban heat island when applied on external surfaces.

Study on polyethylene glycol/epoxy resin composite as a form-stable phase change material

Form-stable polyethylene glycol (PEG)/epoxy resin (EP) composite as a novel phase change material (PCM) was prepared using casting molding method. In this new material, PEG acts as the latent heat storage material and EP polymer serves as the supporting material, which provides structural strength and prevents the leakage of the melted PEG. The structure and morphology of the novel composite were observed using Fourier transformation infrared spectroscope (FTIR) and scanning electronic microscope (SEM). The thermo-mechanical property and transition behavior were characterized by polarizing optical microscope (POM), static thermo-mechanical analysis (TMA) and differential scanning calorimeter (DSC). The experimental results show that, as a result of the physical tangled function of the epoxy resin carrier to the PEG segment, the composite macroscopically presents the solid–solid phase change characteristic.

916 液相状態における相変化蓄熱媒体の熱流動特性に関する研究(OS12-(2)オーガナイズドセッション《流体工学・熱流体》)

916 液相状態における相変化蓄熱媒体の熱流動特性に関する研究(OS12-(2)オーガナイズドセッション《流体工学・熱流体》)

Development of PCM Reactor for Methane Steam Reforming

This paper describes the experimental investigation of a new methane steam reformer utilizing waste heat through the latent heat storage material called “phase change material (PCM)”. The intermittently released waste heat such as steelmaking off gas was first converted to a continuous, constant temperature heat source in the form of latent heat of the PCM. Then, the stored heat in the PCM was supplied to methane to induce an endothermic steam-reforming reaction. In the experiments, a laboratory scale reformer in which packed beds of nickel porous catalyst was circumferentially covered by PCM of copper was intermittently heated from outside by a burner and the transient local temperatures were monitored. The results revealed that the PCM temperature was constant in spite of intermittent heating and that hydrogen was generated continuously. The proposed system could possibly produce hydrogen with less CO2 emission than that produced by a conventional hydrogen generator. This could allow the integration of two processes in the steelmaking and hydrogen production industries.

Development of PCM Storage for Process Heat and Power Generation

The increased interest in solar thermal systems using steam as a working medium either for power generation or process heat applications gave rise to a growing demand for latent heat storage units. Essential for the development of cost-effective latent heat storage systems is the achievement of a sufficient power level in spite of the characteristic low thermal diffusivities of latent heat storage materials. The sandwich concept using fins made either from graphite or aluminum has been identified as the most promising option for latent heat storage systems. The feasibility of this approach has been demonstrated by three prototypes using graphite and one prototype using aluminum fins. The prototype with aluminum fins was filled with sodium nitrate and was operated for more than 4000 h without degradation of power. The volume specific average power density is in the range 10–25 kW/m3, so it is proven that the major problem of phase change material (PCM) storage of low heat transfer rates has been overcome and high-temperature PCM storage with large capacity factor is possible.

B133 固液潜熱蓄熱体の熱媒体との直接接触による蓄放熱挙動(固液相変化を伴う伝熱現象II)

The purpose of this study is the development of the latent heat storage system using erythritol as a latent heat storage material. In this study, the direct contact melting and solidification behaviors of erythritol were visualized in order to investigate the heat storage and release characteristics of erythritol. The experimental results show that the melting and solidification characteristics of erythritol were influenced with the heating medium (oil) temperature and velocity. And the heat release speed influenced flowing quantity of oil and height of erythritol, there may be a limit in high-speed heat release experiment.

Study of an Optical Non-Contact Measurement Technique of the Solidification Rate for Latent Heat-Storage Materials

A new technique is developed for the measurement of the solidification rate for a latent-heat storage material that consisted of spherical n-paraffin particles and water (emulsion slurry). This method utilizes the correlation between the optical characteristics of the slurry and the solidification rate of the paraffin particles. From experiment, it was shown that the increase in the solidification rate of the particles causes the rise in the transimissivity and the drop in the reflectivity of the slurry. Each paraffin particles has a conical crater on the surface when it solidifies. Based on these observations, a new radiative transfer model has been developed for a transparent particle with a conical crater and a three-dimensional radiative transfer model for a particulate medium by the Monte Carlo method. The analytical results for the slurry using the model well agreed with the experimental ones. From the analysis, it was shown that the crater on the particle surface makes the forward scattering weak and scattering in the backward and the lateral direction strong. Therefore, it was concluded that the rise in the transmissivity and decrease in the reflectivity of the slurry by the increase in its solidification rate is caused by the craters on the particle surfaces due to their phase-change.

High latent heat storage and high thermal conductive phase change materials using exfoliated graphite nanoplatelets

Using exfoliated graphite nanoplatelets (xGnP), paraffin/xGnP composite phase change materials (PCMs) were prepared by the stirring of xGnP in liquid paraffin for high electric conductivity, thermal conductivity and latent heat storage. xGnP of 1, 2, 3, 5 and 7 wt% was added to pure paraffin at 75 °C. Scanning electron microscopy (SEM) morphology showed uniform dispersion of xGnP in the paraffin wax. Good dispersion of xGnP in paraffin/xGnP composite PCMs led to high electric conductivity. The percolation threshold of paraffin/xGnP composite PCMs was between 1 and 2 wt% in resistivity measurement. The thermal conductivity of paraffin/xGnP composite PCMs was increased as xGnP loading contents. Also, reproducibility of paraffin/xGnP composite PCMs as continuous PCMs was manifested in results of electric and thermal conductivity. Paraffin/xGnP composite PCMs showed two peaks in the heating curve by differential scanning calorimeter (DSC) measurement. The first phase change peak at around 35 °C is lower and corresponds to the solid–solid phase transition of the paraffin, and the second peak is high at around 55 °C, corresponding to the solid–liquid phase change. The latent heat of paraffin/xGnP composite PCMs did not decrease as loading xGnP contents to paraffin. xGnP can be considered as an effective heat-diffusion promoter to improve thermal conductivity of PCMs without reducing its latent heat storage capacity in paraffin wax.

Thermal cycle testing of calcium chloride hexahydrate as a possible PCM for latent heat storage

In order to study the changes in latent heat of fusion and melting temperature of calcium chloride hexahydrate (CaCl 2·6H 2O) inorganic salt as a latent heat storage material, a thousand accelerated thermal cycle tests have been conducted. The effect of thermal cycling and the reliability in terms of the changing of the melting temperature using a differential scanning calorimeter (DSC) is determined. It has been noticed that the CaCl 2·6H 2O melts between a stable range of temperature and has shown small variations in the latent heat of fusion during the thermal cycling process. Thus, it can be a promising phase change material (PCM) for heating and cooling applications for various building/storage systems.

Preparation and performance of form-stable polyethylene glycol/silicon dioxide composites as solid–liquid phase change materials

This work mainly involved the preparation and characterization of form-stable polyethylene glycol (PEG)/silicon dioxide (SiO 2) composite as a novel solid–liquid phase change material (PCM). In this study, the polyethylene glycol/silicon dioxide composites as form-stable, solid–liquid phase change material (PCM) was prepared. In this new material, the polyethylene glycol acts as the latent heat storage material and silicon dioxide serves as the supporting material, which provides structural strength and prevents the leakage of the melted polyethylene glycol. Results indicated that the composite remained solid when the weight percentage of silicon dioxide was higher than 15%. Moreover, the polyethylene glycol was observed to disperse into the network of the solid silicon dioxide by investigation of the structure of the composite PCMs using a scanning electronic microscope (SEM). The properties of the porous materials and phase change materials were characterized using Fourier transformation infrared spectroscope (FTIR). The transition process was observed using polarizing optical microscope (POM) and dynamic thermo mechanic analysis (DMA). The melting temperatures and latent heats of the form-stable PEG/SiO 2 composite PCMs were determined using differential scanning calorimeter (DSC).

Fatty Acid/Expanded Graphite Composites as Phase Change Material for Latent Heat Thermal Energy Storage

The fatty acid/expanded graphite (EG) composites as phase change material (PCM) for latent heat thermal energy storage were prepared by means of vacuum impregnation method and their thermal properties and heat charging/discharging characteristics were determined. In the composites, the fatty acids (capric, lauric, and myristic acids) act as a phase change latent heat storage material, and the EG serves like an absorptive material that penetrates melted fatty acid into its porous structure. The maximum fatty acids absorption of EG was found as 80 wt% without melted fatty acid oozing from the composites. Thermal properties of fatty acid/EG composites were measured by differential scanning calorimetry (DSC) method. DCS results indicated that the melting and solidification temperatures of the composite PCMs were almost the same as those of fatty acids, and the latent heats of composites were little less than those of the pure fatty acids. The heat charging and discharging rate of the composites were obviously increased due to expanded graphite that had a high thermal conductivity. The prepared fatty acid/EG composites as PCM have great potential for thermal energy storage applications in terms of their satisfactory thermal properties, improved thermal conductivity, and good heat charging and discharging characteristics.

Can latent heat safely warm blood? – in vitro testing of a portable prototype blood warmer

BackgroundTrauma/retrieval patients are often in shock and hypothermic. Treatment of such patients usually involves restoring their blood volume with transfusion of blood (stored at 2°C – 6°C) and/or crystalloids or colloids (stored at ambient temperature). Rapid infusion of these cold fluids can worsen or even induce hypothermia in these patients. Warming of intravenous fluids at accident sites has traditionally been difficult due to a lack of suitable portable fluid warmers that are not dependent on mains electrical or battery power. If latent heat, the heat released when a liquid solidifies (an inherently temperature limiting process) can warm intravenous fluids, portable devices without a reliance on electrical energy could be used to reduce the incidence of hypothermia in trauma patients.MethodsRapid infusion of red cells into patients was timed to sample typical clinical flow rates.An approved dry heat blood warmer was compared with a prototype blood warmer using a supercooled liquid latent heat storage material, to warm red cells whilst monitoring inlet and outlet temperatures. To determine the effect of warming on red cell integrity compared to the normal storage lesion of blood, extracellular concentrations of potassium, lactate dehydrogenase and haemoglobin were measured in blood which had been warmed after storage at 2°C – 6°C for 1 to 42 days.ResultsA prototype latent heat fluid warmer consistently warmed red cells from approximately 4°C to approximately 35°C at typical clinical flow rates. Warming of stored blood with latent heat did not affect red cell integrity more than the approved dry heat blood warmer.ConclusionUsing latent heat as an energy source can satisfactorily warm cold blood or other intravenous fluids to near body temperature, without any adverse affects.

Numerical heat transfer studies of PCMs used in a box-type solar cooker

Theoretical investigations on the phase change materials (PCMs) used as the heat storage media for box-type solar cookers have been conducted in this study. The selected PCMs are magnesium nitrate hexahydrate, stearic acid, acetamide, acetanilide and erythritol. For a two-dimensional simulation model based on the enthalpy approach, calculations have been made for the melt fraction with conduction only. Different materials such as glass, stainless steel, tin, aluminum mixed, aluminum and copper are used as the heat exchanger container materials in the numerical calculations. The large value of thermal conductivity of heat exchanger container material did not make a significant contribution on the melt fraction except for at very low thermal conductivities. Based on the theoretical results, stearic acid and acetamide are found to be good compatibility with latent heat storage system. It is also found that the initial temperature of PCM does not have very important effects on the melting time, while the boundary wall temperature plays an important role during the melting and has a strong effect on the melt fraction. The results also show that the effect of thickness of container material on the melt fraction is insignificant. The results obtained in this paper show that in a box-type solar cooker, acetamide and stearic acid should be used as a latent heat storage materials.

Preparation of shape-stabilized phase change materials as temperature-adjusting powder

The shape-stabilized phase change materials (PCMs) composed of paraffin wax and silica were prepared in O/W emulsion with cetyl trimethylamine bromide as emulsifier and n-pentanol as assist emulsifier. The paraffin wax (with melting temperature of 29°C, crystallizing temperature of 26°C and latent heat of 142 J/g) served as latent heat storage material and the silica as supporting material, which prevented the leakage of the melted paraffin wax. Silica supporting material was formed in situ via hydrolysis and condensation from low-cost sodium silicate solution with chlorhydric acid and ammonium bicarbonate as neutralizing agent. The thermogravimetry (TG) curves show that the composite has a thermal stability superior to that of paraffin wax and that the content of paraffin wax in the composite is 65wt%. The maximum latent heat and its relevant melting point of composite are 95 J/g and 30°C, respectively.

A Study on Supercooling Characteristics of Clathrate Compounds with Concentration of TMA

Ice storage system that water is used as low temperature latent heat storage material, refrigerator capacity is increased and COP is decreased because refrigerator is operated at low temperature due to supercooling of water in the course of phase change from solid to liquid. This study is investigated the cooling characteristics of the TMA-water clathrate compound including TMA (Tri-methyl-amine, (CH3)3N) of 20~25 wt% as a low temperature latent heat storage material at -5°C, cooling source temperature. The results showed that the phase change temperature, the specific heat is increased and the supercooling degree is decreased as the weight concentration of TMA became higher. Especially, low temperature latent heat storage material containing TMA 25 wt% has the average of phase change temperature of 5.8°C, supercooling degree of 8.0°C and specific heat of 4.099kJ/kgK in the cooling process. Phase change temperature higher than that of water and inhibitory effect against supercooling can be confirmed through experimental study on cooling characteristics of TMA-water clathrate compound.

Design, Development of a Solar Chimney with Built-in Latent Heat Storage Material for Natural Ventilation

A prototype of a solar chimney with a built-in latent heat storage system for prolonging ventilation system operation until evening/night or even 24 hours was designed and developed. Sodium Sulfate Decahydrate “Na2SO4.10H2O” (melting point 32°C, latent heat of fusion 126 kJ/kg) was used as a Phase Change Material (PCM) for latent heat storage. Experiments have been carried out with the air gap of 0.20 m and 45 degree inclination angle of solar chimney. Results showed that integration of PCM storage inside the solar chimney is positive and supplies a constant airflow rate of 155 m3/h in evening and night periods. Description of the fabricated prototype solar chimney with PCM storage, thermal analysis to predict the air flow rate, and temperatures of the component of the system with experimental results are presented.

Shape‐Stabilized Phase Change Materials: Frozen Gel fom Polypropylene and n‐Octadecane for Latent Heat Storage

AbstractWe prepared polymer‐PCM gels such as prepared frozen gel from polypropylene and n‐octadecane for thermal storage and release materials, their basic properties and possible applications especially in latent heat storage. The preparation methods are used to melting method and absorption method respectively. The composition and properties of prepared frozen gels from polypropylene and n‐octadecane were observed by DSC, WAXD, FT‐IR spectra, ARES and Elemental analysis. We can prepare frozen gels in different temperature for latent heat storage materials as controlling composition of phase change material as well as using different incorporating phase change materials. These frozen gels can be used to latent heat storage materials for several applications.

High Density Polyethylene/Paraffin Composites as Form-stable Phase Change Material for Thermal Energy Storage

This article focuses on the preparation and thermo-physical properties of paraffin/high density polyethylene (HDPE) composites as form-stable solid-liquid phase change material (PCM) for thermal energy storage. In the paraffin/HDPE blend, the paraffin (P) dispersed into the HDPE serves as a latent heat storage material when the HDPE, as a supporting material, prevents the melted paraffin leakage thanks to its structural strength. Therefore, this type composite is form-stable and can be used as a PCM without encapsulation for thermal energy storage. In this study, two paraffins with melting temperatures of 48°C–50°C and 63°C–65°C were used. The mass percentages of paraffins in the composites could go high as 76% without any seepage of the paraffin in melted state. The dispersion of the paraffin into the network of the solid HDPE was investigated using scanning electronic microscope (SEM). The melting temperatures and latent heats of the form-stable P1/HDPE and P2/HDPE composite PCMs were determined as 44.32°C and 61.66°C, and 179.63 and 198.14 Jg−1, by the technique of differential scanning calorimetry (DSC), respectively. Furthermore, the thermal conductivity of the composite PCMs were improved as about 33.3% for the P1/HDPE and 52.3% for the P2/HDPE by introducing the expanded and exfoliated graphite to the samples in the ratio of 3 wt%. The results reveal that the prepared form-stable composite PCMs have great potential for thermal energy storage applications in terms of their satisfactory thermal properties, improved thermal conductivity and cost-efficiency because of no encapsulation for enhancing heat transfer in paraffin.