Phase Change Thermal Storage Research Articles

Experimental studies on cycling stable characteristics of inorganic phase change material CaCl2·6H2O-MgCl2·6H2O modified with SrCl2·6H2O and CMC

By means of mass ratio method, binary eutectic hydrated salts inorganic phase change thermal energy storage system CaCl2·6H2O-20wt% MgCl2·6H2O was prepared, and through adding nucleating agent 1wt% SrCl2·6H2O and thickening agent 0.5wt% carboxy methyl cellulose (CMC), inoganic phase change material (PCM) modified was obtained. With recording cooling-melting curves simultaneously, this PCM was frozen and melted for 100 cycles under programmable temperature control. After per 10 cycles, the PCM was charaterized by differential scanning calorimeter (DSC), X-ray diffraction (XRD) and density meter, then analysing variation characteristics of phase change temperature, supercooling degree, superheat degree, latent heat, crystal structure and density with the increase of cycle index. The results showed that the average values of average phase change temperature for cooling and heating process were 25.70°C and 27.39°C respectively with small changes. The average values of average supercooling and superheat degree were 0.59°C and 0.49°C respectively, and the maximum value was 1.10°C. The average value and standard deviation of latent heat of fusion were 120.62 J/g and 1.90 J/g respectively. Non-molten white solid sediments resulted from phase separation were tachyhydrite (CaMg2Cl6·12H2O), which was characterized by XRD. Measuring density of the PCM after per 10 cycles, and the results suggested that the total mass of tachyhydrite was limited. In summary, such modified inoganic PCM CaCl2·6H2O-20wt% MgCl2·6H2O-1wt% SrCl2·6H2O-0.5wt% CMC could stay excellent circulation stability within 100 cycles, and providing reference value in practical use.

Experimental investigation of a solar cooker based on evacuated tube collector with phase change thermal storage unit in Indian climatic conditions

Experimental investigation of a solar cooker based on evacuated tube collector with phase change thermal storage unit in Indian climatic conditions

Development and performance evaluation of phase change thermal storage heat exchange system

Development and performance evaluation of phase change thermal storage heat exchange system

D-mannitol for medium temperature thermal energy storage

D-mannitol is a sugar alcohol with a melting temperature of approximately 167°C. It has been identified as a phase change material for storing heat at a temperature range of about 150–180°C. The outcome of the published research on its applicability for this purpose is inconsistent and sometimes contradictory. We identified that there is a need for further study on the material to overcome such uncertainty. Thus we conducted a series of thermal measurements to quantify its properties and suitability for a phase change thermal storage. Our differential scanning calorimetric measurements showed that the material has a melting temperature of 167°C and fusion heat of 297kJ/kg. However, our accelerated thermal cycling test revealed that this value decreases logarithmically to 249 and 240kJ/kg after 100 and 200 cycles respectively. The material shows a significant level of sub-cooling in DSC measurement with a solidification temperature of approximately 110–120°C which can render the material unsuitable for thermal storage purposes. However, our secondary measurement with a large quantity of D-mannitol shows that such level of sub-cooling is unlikely to occur in a macro-scale sample. We built and tested a thermal storage system containing 3.8kg of D-mannitol to investigate its performance in larger quantities and evaluate the heat transfer properties of the heat exchanger mechanism in the storage system. We show that the material releases significant heat when it is cooled down to 150°C which means implies the occurrence of solidification at a temperature above 150°C.

A thermal management system using ammonium carbamate as an endothermic heat sink

The issue of managing low-quality waste heat onboard modern high-performance aircraft represents a critical performance limitation that can severely restrict flight envelopes, preclude the integration of high-power electronics, or compromise system reliability. The principal engineering challenges to the thermal systems engineer are the large quantities of heat involved, low (and carefully controlled) coolant temperatures required, and the limited availability of heat sinks to which the waste heat must ultimately be rejected. The use of endothermic chemical reactions to serve as controllable, flight envelope-independent heat sinks has considerable potential in addressing the latter of these engineering challenges, but must be integrated as part of a systems-level approach in order to address all three - acquisition, control, and rejection. In this paper, we introduce and demonstrate a thermal management system (TMS) architecture integrating a vapor compression heat pump, phase change thermal energy storage, and heat exchanger-reactor (HEX reactor) to utilize the endothermic decomposition of ammonium carbamate as an expendable heat sink. An experimental proof-of-concept study was conducted to demonstrate acquisition of both static and time- variant thermal loads, coolant temperature regulation typical of electronics cooling applications, and rejection of the thermal load to an expendable heat sink. The proposed TMS successfully managed pulsed and steady thermal loads while maintaining a coolant temperature within 1°C of the target set point. During steady-state operation, the TMS was able to achieve coefficients of performance (COP) in the neighborhood of 3 with nearly 100% efficiency in expendable heat sink utilization; when subjected to dynamic heat loads, the use of a thermal energy storage material allowed simple control schemes to be used to maintain TMS stability.

Two-Phase Anaerobic Digester Combined with Solar Thermal and Phase Change Thermal Storage System in Winter

Using solar energy as the heat source for biogas improvement of the anaerobic digester is an effective method. However, intermittent solar radiation and low ambient temperature in the winter make it difficult to maintain a steady fermentation temperature. In this study, a pilot-scale two-phase anaerobic digester combined with solar thermal and phase change thermal storage (PCTS) system has been constructed. A set of comparative field studies were carried out during the winter in Maanshan City, Anhui Province, China; these periods of study included no heating mode (P1), heated with solar thermal and PCTS system (P2), and conventional solar heating mode (P3). The comparison shows that methane yields and the energy conversion rate of the substrates of P2 were 12.33 m3 and 48.6%, respectively, both of which increased by 5.65 and 1.01 times, compared with that of P1 and P3, respectively. The statistical coefficients of variation for the fermentation temperature were 2.5% in P2 and 6.6% in P3, which means that ...

Preparation research of novel composite phase change materials based on sodium acetate trihydrate

As phase change thermal storage material, sodium acetate trihydrate (SAT) exhibits certain problems such as large undercooling, stratification in phase change, and small thermal conductivity. To overcome these problems, in this study, a new composite phase change thermal storage material was prepared by adding a certain amount of nucleating agent, thickening agent, and high thermal conductivity medium. The research results showed that addition of an appropriate proportion of nucleating agent disodium phosphate dodecahydrate(DSP) and thickening agent carboxymethyl cellulose(CMC) or gelatin led to a good restrain to the undercooling of SAT, while maintaining the heat storage capacity of sample, and avoiding the phenomenon of phase stratification at room temperature cooling. A certain proportion of expanded graphite could also be used in combination with the thermal storage materials, which resulted in relatively small undercooling of the SAT thermal storage materials and a relatively large thermal conductivity.

Analysis on Cascade Heat Utilization of Solar Energy in Building Heating Based on Phase Change Thermal Storage

Solar energy is a clean and renewable energy for building heating, it is an environmentally friendly technology which can effectively reduce building energy consumption. However, so-lar energy has the characteristics of low distribution density, discontinuity and instability due to the changeable weather condition, moreover, there is a contradiction in time between the building heating demand in night and the solar energy collection in day. Therefore, a cascade utilization of solar energy with solar heat collection process, phase change heat storage process and capillary radiation heating process is presented in this study. Firstly, a low temperature phase change material is tested and used as an energy storage pool, secondly, the capillary radiation heating is adopted as the terminal heating mode due to its features of low temperature operation mode, large heat transfer area and higher thermal comfort, finally, the performance of the system is calculated and analyzed. The results show that the cascade utilization of solar energy system can store and transfer solar energy from day to night, and it has higher efficiency compared with traditional heat sink mode.

Effect of Alloy Element Al on the Corrosion Behavior of Ni-10wt%Fe Based Alloy in Molten NaCl

NaCl and its mixed salt have many advantages as a medium of solar energy phase change thermal storage at moderate and high temperature. But molten chloride has sharp corrosive action on metal thermal storage vessel. The corrosion behavior of three kinds of Ni-10 wt% Fe based alloy (1#, 2# and 3#) in 850 °C molten NaCl was studied. The content of Al in 1#, 2# and 3# sample was 0.0 wt%, 5.0 wt% and 10.0 wt%, respectively. The components of NaCl after corroding and corrosion products on samples surface were analyzed. Elements change trend and corrosion characteristics on cross section of the three samples were contrasted. Corrosion mechanisms were discussed finally. Results show that the kinetics curves of the three kinds of sample obey a liner rule. The average mass loss rate declines when Al is added in the sample. The rate of 2# and 3# is only 12% and 20% of that of 1#, respectively. There are two reasons for the value reduction: firstly, Al will be oxidized prior to oxidization of Fe or Ni, and the atomic mass of Al is small; secondly, Al 2 O 3 is very stable at high temperature as corrosion products. However, when the content of Al is very high (for example 10 wt% in here) in Ni-10 wt% Fe based alloy, Al oxidized on sample surface provides a convenient condition for Al atom transmission from sample inside to surface. Al 2 O 3 film becomes thick and exfoliates easily. The exfoliation increases the average mass loss rate in turn.

低位熱エネルギー回収向け相変化蓄熱式熱交換器の熱輸送機構

低位熱エネルギー回収向け相変化蓄熱式熱交換器の熱輸送機構

Characterization of phase change thermal storage heat exchanger

Characterization of phase change thermal storage heat exchanger

Experimental Investigation of the a Solar Cooker based on Evacuated Tube Collector with Phase Change Thermal Storage unit in Indian Climatic Conditions

A solar cooker based on evacuated tube collector with phase change thermal storage unit is investigated. The water is used as a working fluid, and it is filled in the evacuated tubes. The energy stored by the acetanilide (PCM) during the daytime can be transferred to the cooking vessel entirely throughout the day up till the late evening time. Daytime and evening cooking processes are carried out separately at different loads. To enhance the performance of the solar cooker, the reflector is used beneath the evacuated tube collector. It is observed that in case of the high load, the solar cooker gives better performance with reflector as compared to without reflector. The maximum increase in the temperature of the working fluid, PCM and cooking vessel with reflector is 18.3%, 20.4% and 20.8% respectively. Also, the cooking time is reduced to 30 minutes with the reflector. It is found that evening cooking using PCM heat storage unit is faster than daytime cooking at low load.

Preparation and characterization of composite material Na2SO4·10H2O - KAl(SO4)2·12H2O for thermal storage

In the present paper, the preparation and characterization of composite material Na2SO4·10H2O - KAl(SO4)2·12H2O for thermal storage are reported. The co - melting method is employed to perform the preparation. The thermal properties and the step cooling behaviors of the composites are studied. The results show that: the phenomenon of phase separation disappears in the composite system with the mass ratio of 1 : 9 to 3 : 7 (Na2SO4·10H2O: KAl(SO4)2·12H2O), and the optimized mass ratio is about 2 : 8, which results in the lowest phase change temperature, the longest heat releasing platform of 41 min and a higher latent heat of 819.93J/g at 72.7 °C; the enthalpy remains higher value after 50 thermal cycles. Thus, this composite material has a potential as the phase change thermal storage material for low temperature application.

Experimental Study on Phase Change Thermal Storage of Crystalline Hydrated Salt Applied in Solar Thermal Utilization

The building energy consumption is 28 percent of the total energy consumption in China, especially in winter building heating. The solar energy is a high quality clean and renewable energy for building energy conservation, however, the solar energy is easily affected by the weather and the demands of heating is often in the light. Therefore, the thermal storage technology can solve these two contradictions and can be used as energy storage pool in order that it can storage solar energy in day and release heat in night. In this study, the phase change thermal storage material of crystalline hydrated salt Na2HPO4•12H2O is adopted as the basic thermal storage material, additionally, different content of alumina powder and sodium carboxymethyl cellulose are added in the basic thermal storage material as nucleating agent and thickening agent, according to the tests, the step curve, the subcooling curve and the latent heat curve are obtained. The results show that the phase change thermal storage material is better in stability when the ratio is that the water 30%, the alumina powder 2%, the sodium carboxymethyl cellulose 5% and the Na2HPO4•12H2O 63%, the phase change temperature is around 36.0℃, the subcooling temperature is 4.6℃, and the phase change latent heat is 182.4kJ/kg.

Research on Thermal Storage Performance of Solar Phase Change Thermal Storage Integrated Device

In this paper, an integrated device of solar energy thermal storage is proposed. The utility model avoids the problem of excessive energy loss of the heat exchange system caused by the separation of the collector and the phase change heat storage device. The mathematical model of the device is established and verified by experiments. The comparison between the experimental results and the calculated results shows that numerical analysis method is feasible and accurate. Based on the model, the effects of the thermal conductivity, the convective heat transfer coefficient and the flow rate of heat transfer fluid on the heat storage efficiency were analyzed.

Thermal cycling stability of Mg-25Al-15Zn-14Cu PCM

Thermal cycling tests of repeated melting/freezing processes were performed to check the thermal stability of Mg-25Al-15Zn-14Cu alloy as phase change thermal storage material(PCM). Latent heat storage capacity and phase transition temperature of the PCMs were determined by differential scanning calorimetry (DSC) technique as a function of repeated thermal cycles such as 0, 100, 200, and 1000. The present work also comprised the investigation of the density and microstructure of Mg-25Al-15Zn-14Cu alloy before and after thermal cycles by using the hydrostatic method and optical microscopy (OM), X-ray diffraction (XRD), and electron probe microanalysis (EPMA), respectively. The results show that the melting temperature of alloy after 1000 thermal cycles is 415.1 °C and the latent heat value is 190.4 J/g. Compared with the original alloy, the phase transition temperature will increase by 1.87% and the value of phase change latent heat will decrease by 7.35%, which are in a suitable range. Therefore, Mg-25Al-15Zn-14Cu alloy has a good thermal reliability in terms of the change in its thermal properties with respect to thermal cycling for 1000, and can be used for a middle-temperature thermal storage utility.

Experimental study of an externally finned tube with internal heat transfer enhancement for phase change thermal energy storage

After having presented the design of a latent heat thermal energy storage system (LHTESS) for district heating, experimental results of a vertical tube-in-shell LHTESS are discussed. The tube is radially finned on its external wall to enhance the heat transfer in the phase change material. The test rig is operated with flow conditions corresponding to the proposed design. As the internal flow of heat transfer fluid (HTF) appears to be laminar and is highly influenced by buoyancy forces, which results in mixed convection regime, cross-sectional area reducers are installed inside the HTF tube in order to reduce the Rayleigh number and thus natural convection. Experimental results are presented for two finned tubes, with and without internal heat transfer enhancement respectively.

Numerical simulation on heat transfer enhancement of phase change thermal storage devices for low-middle temperature

Using Ba(OH)2·8H2O as phase change material (PCM) and water as heat transfer fluid (HTF), we numerically simulated annular finned-tube heat exchangers. In order to measure and analyze the impact of parameters in the heating/cooling process, temperature changes of different monitoring points, fin widths, and fin pitches as key parameters were considered and applied. The experimental results show that the heat exchange process can be divided into three stages within a certain time. The faster heat transfer rate is associated with the greater temperature difference between PCM and HTF. Furthermore, fins width and pitch affect dramatically the heat charging/discharging rate. The large fins width or small fins pitch is beneficial for extending the heat exchange surface, leading to improve heat transfer efficiency.

Numerical simulation on heat transfer characteristics of the storage tank for concentrating solar power plant

Concentrating solar power plant coupling with energy storage is a new and emerging technology, which can solve two issues, that is, low flux density and intermittent of solar energy. Heat transfer characteristics of the storage tank in this system have a key effect on the system’s efficiency and cost. In this article, the heat transfer performance of a phase change thermal storage tank has been proposed, and the temperature distribution and liquid fraction of phase change material in the tank has numerically been investigated. The results show that the temperature increases with the increasing charge time. The results also show that there is a phase change process at the charge time of 200 min, and no phase change for the charge time of 250 and 300 min. The results of this article can provide a reference for future design and optimal operation of the storage tank in concentrating solar power plant.

Investigation of diffusional transport of heat and its enhancement in phase-change thermal energy storage systems

Thermal energy storage in general, and phase-change materials (PCMs) in particular, have been a major topic of research for the last thirty years. Due to their favorable thermo-dynamical characteristics, such as high density, specific heat and latent heat of fusion, PCMs are usually employed as working fluids for thermal storage. However, low thermal conductivities of organic PCMs have posed a continuous challenge in its large scale deployment. This study focuses on experimental and numerical investigation of the melting process of industrial grade paraffin wax inside a semi-cylindrical enclosure with a heating strip attached axially along the center of semi-cylinder. During the first part of the study, the solid-liquid interface location, the liquid flow patterns in the melt pool, and the spatial and temporal variation of PCM temperature were recorded. For numerical simulation of the system, open source library OpenFOAM® was used in order to solve the coupled Navier-Stokes and energy equations in the considered system. It is seen that the enthalpy-porosity technique implemented on OpenFOAM® is reasonably well suited for handling melting/solidification problems and can be employed for system level design. Next, to overcome the inherent thermal limitations of PCM storage material, the study further explored the potential of coupling the existing heat source with copper-water heat pipes, so as to help augment the rate of heat dissipation within the medium by increasing the effective system-level thermal conductivity. Integration of heat pipes led to enhanced transport, and hence, a substantial decrease in the total required melting time. The study provides a framework for designing of large systems with integration of heat pipes with PCM based thermal storage systems.