Phase Change Heat Storage Research Articles

Delignified wood/polyethylene glycol-based material with BN as thermal conductive filler for thermal energy storage

In this work, phase change energy storage wood ([email protected]) was obtained by injecting PGMA into the porous tissue of wood by high temperature and high pressure method, and the BN grafted with KH550 and DA (KH550-DA-BN) was synthesized to improve the heat transfer rate. Studies have found that PGMA has good thermal conductivity in the cavities of woody cells. After adding KH550-DA-BN to PGMA, the KH550-DA-BN combines with PGMA in a physically dispersed manner and the crystal structure of PGMA does not change. When the filling amount of KH550-DA-BN is 6 wt%, the thermal conductivity of [email protected] increases to 0.4185 W/(m·K), its melting enthalpy and solidification enthalpy are all maintained at 103.40 J/g and 100.20 J/g, respectively. The [email protected] shows efficient solar-to-thermal energy conversion and a lasting heat storage capacity under simulated sunlight. After 200 cycles of cooling and heating, the melting enthalpy and solidification enthalpy of [email protected] are both above 120 J/g, indicating that [email protected] has good stability in use. There is no leakage of 6 % [email protected] after heated at 80 °C for 4 h, due to the interpenetrating network structure between PGMA and wood components. The phase change heat storage wood prepared in this research increases the potential of wood for temperature regulation in fields such as building materials, furniture and aerospace.

Performance analysis of the phase-change heat-storage tank based on numerical simulation

Phase-change heat storage system contributes to the smooth operations of building energy supply and demand. In this paper, the numerical model of the heat-storage tank with phase change material blocks is established. The charge and discharge process of the heat-storage tank is analyzed with the numerical model. The performances of the heat-storage tank with and without phase change material blocks are compared by experiment and numerical simulation. The effects of structural parameters of phase change material blocks on the heat storage and release rate are comprehensively discussed, including the number and size of phase change material blocks. The results indicate that under the experimental conditions, the charge capacity and duration of the tank with phase change material blocks are extended by 7.43% and 8.3% respectively under the condition of replacing 6.75% volume of hot water with phase change material. The thermal stratification phenomenon in the heat-storage tank without phase change material blocks is more obvious. For certain volume of the phase change material, the performance analysis of three cases with different amount and size of phase change material blocks is investigated. The results show that the phase change material blocks with number and size of 24 and 0.45 m × 0.1 m × 0.1 m reduces the charge and discharge duration by 2.47% and 3.78% compared with those of 12 and 0.9 m × 0.1 m × 0.1 m.

Study on Energy Flow Characteristics of Solar–Gas Combined Heating System for Settling Tank of Oilfield

Heating furnaces fueled by fossil fuels are commonly utilized in oilfields to provide heat to the settling tank, which heats the layer of crude oil. However, this traditional heating method consumes a significant amount of oil and gas resources, resulting in low energy utilization and environmental pollution. As the water content of the extracted crude oil increases over time, the operating costs of the settling tanks also continue to increase. Therefore, it is crucial to develop and implement clean and efficient heating technologies to facilitate the efficient operation of settling tanks. This paper proposes a solar–gas combined heating technology for settling tanks. A simulation model for the solar–gas combined heating system for the settling tank is constructed, considering the overall perspective of the system. The simulation model analyzes the impact of the control strategy for the oil collection period of the settling tank on the system performance. This analysis covers various aspects including the heat collection of the solar collector, the heat supply of the gas boiler, and the heat storage and release of the phase-change heat storage tank. The results demonstrate that when the oil collection cycle is Scheme E (4:00–8:00), the collector achieves the highest annual cumulative heat collection, the gas boiler provides the lowest annual total heat supply, and the phase-change heat storage tank exhibits the highest heat storage and release efficiency. Over the course of the system’s 15 year service life, the settling tank solar–gas combined heating system saves 727,988.69 MJ of energy annually, resulting in total energy-saving costs of CNY 397,007. The dynamic investment payback period is estimated at 9.14 years, and the system reduces CO2 emissions by 753,069.8 kg.

Microencapsulated waste cooking oil derivatives for building thermoregulation

The utilization of waste resources and the intelligence of building materials are of great significance to the sustainable development of human society. A novel type of microencapsulated phase change material (MPCM) with a phase change heat storage capability was prepared in this paper through the suspension polymerization method using methyl palmitate (MP) derived from waste cooking oil as core materials. Meanwhile, the response of foamed concrete containing MPCM to ambient temperature change was investigated. According to the experimental findings, the MPCM's phase change temperature, phase change enthalpy, and decomposition temperature are respectively 20 °C, 68 J/g, and 215 °C, which is extremely suitable for the external walls of buildings to adjust the indoor temperature. Moreover, the particle size of the MPCM is about 100 μm-220 μm, which can fill part of the voids in foam concrete to increase its strength. Additionally, the infrared thermal imaging experiment indicates that the foam concrete containing 10 wt% MPCM can maintain 4 °C-5 °C gap with the ambient temperature, which demonstrates that the MPCM can significantly mitigate the impact of ambient temperature on buildings. The findings of the study contribute to the intellectualization of building materials and the recycling of waste resources.

Collaborative configuration and optimal operation of cogeneration system based on phase change heat storage

Given the low efficiency of heating and power supply caused by the low temperature in the Northeast during the heating process of the solar heat pump, the article first adds phase change hot storage device based on time-sharing control based on the traditional PVT collector — heat pump, and constructs a flexible thermoelectric coupling multi-energy system by shifting the peak and filling the valley; Secondly, based on TRNSYS software, the simulation model of PVT collector-heat pump-phase change heat storage-electrical coupling combined supply system is built. By comparing with the heat storage system using an ordinary heat storage tank, the results show that the phase change water tank system can significantly improve the system performance. Finally, Hooke-Jeeves is used to optimize the inclination angle, area, volume of the tank, and heating capacity of the air source heat pump of the PVT collector of the thermal-electric coupling system, to increase the system’s one-year operation.

Influence of different rotational speeds of inner and outer tubes on phase change heat storage: An optimization study

The implementation of the solar phase change heat storage evaporation heat pump system with a latent heat energy storage system has shown promising potential in enhancing solar heating and facilitating the efficient utilization of solar energy. Nevertheless, the utilization of a heat storage medium phase change material with low thermal conductivity in the latent heat energy storage system has hindered its broad-scale application. This present study focuses on a triplex-tube latent heat energy storage unit with N-eicosane serving as the phase change material. A subzone rotation strategy has been developed to improve the melting properties of the unit, and a numerical model of the energy storage unit has been constructed and authenticated. The Taguchi method has been utilized to examine the effect of inner tube speed, outer tube speed, and fin/wall material on melting properties, and the interaction between control variables has been scrutinized. The research findings indicate that the optimized structure, according to the Taguchi method, significantly shortens the melting time by 26.22%, and increases the average rate of temperature response and average heat storage rate by 22.98% and 32.39%, respectively. It should be noted, however, that there is a certain decrease in the total heat absorption during the melting period. By examining the internal dynamic temperature/velocity response, this study displays that the augmentation of the rotation speed in the zone improves the overall convective intensity and heat transfer performance in the unit.

Effect of phase change heat storage tank with gradient fin structure on solar energy storage: A numerical study

In this paper, the heat storage process of a latent heat thermal energy storage (LHTES) tank is studied numerically. A new type of gradient fin is added to the heat storage process in a latent heat storage tank to improve the heat transfer performance of the internal phase change material (PCM). The numerical model is verified by the experimental data. The influences of different structures on the melting rate, temperature distribution, velocity distribution, and maximum melting rate of PCM in LHTES tank are investigated, and the influence of natural convection on the energy storage system is further quantified. The results show that the melting time can be significantly reduced by 16.9% by using the four straight fins with gradient shape, and the melting time can be further reduced by 41.1% by reconstruction of the gradient fin position. The deformation in the opposite direction will slow down the melting speed and extend the melting time by more than 4.66 times. The convection criterion for judging the buoyancy convection of the melt in this paper shows that natural convection is dominant in both the upper and lower part of the melt. The closer the convection coefficient is to the overall heat transfer coefficient, the better the melting efficiency and energy efficiency will be.

Utilization of mine waste heat in phase change rechargeable battery

Mine geothermal energy has been recognized as “heat hazard”, which is harmful to the health of miners and causes disasters. In order to realize the transformation of mine geothermal energy and waste heat from “hazard/waste” into “treasure”, this paper analyzes the distribution characteristics and genesis of mine geothermal energy with the field geothermal temperature monitoring data, evaluates geothermal reserves, and reveals the mutual influencing mechanism of stratified exploitation of two-layer geothermal reservoir and the law of thermal energy conduction and evolution in the stope of geothermal-coal synergetic mining (GE-COSM), using numerical models verified by experiments. In the end, the improvement effect of mine waste heat on the development potential of geothermal-coal mine (G-CM) was analyzed. The result shows that: The present geothermal field distribution characteristics of Anju Mine are high in the north and low in the south, high in the east and low in the west. There are two layers of zoned reservoir, with the temperatures of 43 °C and 54 °C respectively, the average heat flow value 70.1 mW/m2 and 80.9 mW/m2 respectively, and the geothermal water type SO42--Na+·Ca2+. The simultaneous exploitation of the two geothermal reservoirs will form a Coal-Austria geothermal reservoir joint influence area(C-Area) with lower temperature, which reduces the harm of “heat hazard” to miners. But the phase change heat storage function of functional cemented paste backfill material for phase change heat storage (F-CBM) is not fully utilized in the late stage of geothermal exploitation. The mine generates 4.6 × 1011 J of waste heat per day, and according to the type of heat source of mine waste heat can be continuously “heat charging” for a conventional backfill working face. Moreover, under the action of high temperature surrounding rock, the thermal energy recovery rate is greater than 1, and under the action of “heat charging”, the average maximum value of solid phase ratio is greater than 70 %. Therefore, the phase change rechargeable battery mode creatively proposed by this paper is significantly better than the traditional rock layer heat storage mode and is worth vigorously popularizing.

Preparation and characterization of phase change capsules containing waste cooking oil for asphalt binder thermoregulation

The green utilization of waste is of great significance to the sustainable development of human society. In this work, a new kind of capsule with the phase change heat storage function was prepared using waxy components extracted from waste cooking oil (WCO) as core material for the thermoregulation of asphalt binder. The differences in waxy components before and after hydrolysis treatment were studied including functional groups, phase transition temperature, and phase transition enthalpy. Meanwhile, the surface morphology, thermodynamic properties, and mechanical properties of the phase change capsules (PCCs) were also characterized comprehensively. Additionally, the effect of PCCs on asphalt thermoregulation was also examined in the laboratory. The results indicate that the waxy components after hydrolysis treatment are more suitable for asphalt binder thermoregulation in terms of the phase transition temperature, phase transition enthalpy, and thermal stability. According to the results of differential scanning calorimeter and thermogravimetric experiments, it can be calculated that the ratio of wall material and core material in PCCs is about 1:1, which endows the capsule with excellent heat storage properties (125 J/g), mechanical properties (>13 N), and thermal stability (>190 ℃). With the help of the temperature sensor, it is found that PCCs can delay the change rate of asphalt temperature with the environment by undergoing a phase transition to mitigate the damage of asphalt pavement in extremely hot climates. However, the performance of PCCs in asphalt mixtures still needs to be further explored. Overall, the findings of this research can further promote the green utilization of WCO and the functionalization of construction and building materials.

Experimental and numerical investigation of a rectangular finned-tube latent heat storage unit for Carnot battery

Latent heat storage technology has a great potential in Carnot battery systems, and its thermal performance directly affects the system performance. In this paper, a rectangular phase change heat storage unit with finned-tube structure is designed and manufactured, and polyethylene wax/expanded graphite is adopted as the composite phase change material. The thermophysical properties of the polyethylene wax are characterized by experiments first, and then the heat transfer performance of the unit is investigated through varying inlet mass flow rates and inlet temperature on the test rig. Meanwhile, the detailed evolution of the phase change process is visualized and obtained by corresponding numerical simulations. Furthermore, the effects and selection principle of fin number, thickness, and material on the melting process are clarified by numerical simulations. Results shows that the influence of the inlet temperature is more significant than the mass flow rate on the melting/solidification time, however, changing the inlet temperature and mass flow rate has little effect on melting/solidifying the last 10 % of PCM. Heat conduction dominated the heat transfer process due to the high viscosity of polyethylene wax, inducing little stratification of the temperature distribution in the regions bounded by fins. The regions close to the corners and sidewalls are the primary factors delaying melting/solidification rate. Increasing fin number and thickness can effectively decrease the melting/solidification time at the expense of the heat storage capacity. Compared to selecting only high thermal conductivity fin materials, adopting fins with high thermal conductivity, low density, and low specific heat is a better approach for achieving higher heat storage capacity and shorter melting time. The present study explores candidate materials for medium-low temperature latent heat storage and potential applications of traditional finned-tube heat exchangers in medium-low temperature latent heat storage.

Heat transfer characteristics of triple-tube latent heat storage system placed horizontally and vertically

Phase change heat storage technology can realize the utilization of thermal energy across time and space, which is of great significance for solving the problem of mismatch between supply and demand of renewable energy and promoting the energy structure adjustment of our country. However, the low thermal conductivity of phase change materials (PCM) severely limits the application and development of PCM technology. Compared with the traditional two-tube phase change heat storage system, the three-tube latent heat storage system (TTLHSS) has the advantages of large heat transfer area and good heat transfer uniformity. However, there is a lack of comparative research on the heat storage and release performance of the triple tube phase change heat storage system placed horizontally and vertically. Based on the above, this paper studies the heat transfer characteristics of the triple tube phase change heat storage system placed horizontally and vertically, and compares the influence of the tube length on the heat storage and release performance. The coagulation/melting model and Boussinesq model of Fluent software were used to calculate the coagulation and melting process of lauric acid with the same structural parameters placed horizontally and vertically. The results show that when the tube length is 250 mm, the solidification and melting time of lauric acid in the case of horizontal placement is less than that in the case of vertical placement, decreasing by 8 % and 45.9 %, respectively. In addition, it is found that the natural convection has little influence on the axial heat transfer, so the tube length has little influence on the horizontally placed TTLHSS, which can be simplified to a two-dimensional structure for calculation. Due to the phenomenon of temperature stratification in the heat storage process in the case of vertical placement, the heat storage performance will decrease significantly with the increase of tube length, so the tube length has a certain impact on the heat storage and release performance of the triple tube phase change heat storage system placed vertically.

Machine learning and multilayer perceptron enhanced CFD approach for improving design on latent heat storage tank

Solid-liquid phase change heat storage is an important method to solve the mismatch of the generation and usage of waste heat, which is conducive to decarbonization and energy conservation. However, there always exists inhomogeneity for the melting and temperature of the phase change material (PCM) in solid–liquid phase change heat storage. Changing the shape of the heat storage tank will change the distance of heat transfer to the phase change material, thus changing the heat storage performance. Therefore, this paper designed ten shapes of trapezoidal tank with different proportions of upper and lower radius. And the heat storage performance of ten cases were investigated through the designed numerical model, whose accuracy is convinced through comparison with experimental results. Many indexes are proposed to evaluate the properties of the latent heat thermal energy storage (LHTES) from the view of whole region, uniformity among subregions, and the storage heat performance of integrity. Except for drawing mass fraction, temperature, and streamline contours, the temperature proportion and the average velocity are proposed to quantitatively evaluate the temperature distribution and convection intensity. The results showed that the cases with larger upper radius are shorter than cases with larger lower radius. In addition, the shortest melting time is 17210 s, which is about 39.2% shorter by 11080 s than that of basic case. The evaluation from the view of uniformity also indicated that properly increasing the PCM amount is beneficial for improving the melting uniformity. The most uniform temperature and mass fraction are case 5 and case 4, respectively, with 12.92% and 38.28% improvement. Finally, one multilayer perceptron (MLP) network model is built to predict the melting fraction and total heat storage. After training, one model with a deviation lower than 10% between simulation and prediction is set up.

Analysis of melting and solidification performance of bionic snowflake fin horizontal Triplex-tube latent heat storage system based on response surface method

For the low thermal conductivity of phase change materials and other characteristics, a crossed snowflake fin Triplex-tube thermal energy storage (TTES) is proposed, and the analysis of melting and solidification of phase change material (PCM) by applying the numerical simulation method in the comprehensive thermal performance study. The three-casing phase change heat storage unit filled with RT55 is the object of this paper, and firstly, the cross distribution of snowflake fins into 8 fins is studied, and in the analysis of the thermal performance of TTES, the integrated heat storage (release) time, heat storage (release) and heat storage (release) temperature are used as evaluation indicators. By investigating the melting and solidification properties of PCM, the bifurcation angle of the best thermal performance is 60°, and the best fin profile is obtained by reasonable simplification for the purpose of maximum heat storage. The response surface method (RSM) is then used to optimize the size structure of the fins for the purpose of maximum melting heat storage and maximum solidification heat release of TTES, and the heat function equations of the melting and solidification processes of PCM are fitted, and the optimal regions of the melting and solidification processes of TTES are obtained. Finally, the optimization results show that when the length of the fin is 11 mm and the width of the fin is 0.8 mm, TTES has the best overall thermal performance. Compared with before optimization, the heat of PCM melting accumulation increased by 3.92 kJ and the heat of PCM solidification exotherm increased by 5.773 kJ.

Studying the performance of phase change heat storage enhanced by ultrasonic energy

The ultrasonic wave could propagate in elastic media and bring ultrasonic flow which could effectively strengthen the convective heat transfer. Thus, various research works have been carried out on the enhancement effect for its potential future application. This work studied the influence of the acoustic flow effect on the melting process of phase change material. For the first, the influence of ultrasonic acting position on enhancement effect was examined. Then, the effectiveness of ultrasonic energy on enhancing heat storage process was discussed. The present work was also compared with other representative studies. The results show that when the side surface of the container is a constant temperature heating surface, the ultrasonic vibration surface at the bottom of the container has best melting performance of phase change heat storage. Then, a new evaluation method of heat transfer enhancement was proposed. The new method cannot only measure the improvement of melting performance, but also clearly measure the relationship between the improvement of melting performance and the consumption of ultrasonic energy. Finally, by contrast and analysis with representative studies, the development potential and further research direction of ultrasonic enhanced phase change heat storage are clarified. This work can provide reference for the further application of active heat transfer enhancement technology in the field of phase change heat storage.

Optimal rule based double predictive control for the management of thermal energy in a distributed clean heating system

Solar energy coupled with electric heat storage is a kind of promising energy saving technology for distributed building heating. Precise and quick heat load prediction for the demand side of heating system and renewable energy prediction for the supply side are imperative in realizing the flexibility of building clean energy supply systems. A predictive control based on back propagation (BP) artificial neural network is built to predict the demand heat load of an office building and the heat supply quantity of solar collector (SC) system. The heat dissipation of the SC system is considered to improve the prediction accuracy of its heat supply quantity. A double predictive (DP) control is introduced and combined with dynamic adjustment to optimize the operation of renewable energy, phase change heat storage and valley electric heating system. The results indicate that predictive model is of high precision and the variation coefficient of root mean squared errors corresponding to each prediction parameter are all greater than 0.9. Furthermore, the optimization results indicate that the DP control would save, in March, about 59.3% of charge heat quantity of phase change material (PCM) tank and terms of cost (30.4%). Meanwhile, maintaining indoor temperature between 20 °C and 22 °C.

Progress in the Study of Enhanced Heat Exchange in Phase Change Heat Storage Devices.

In comparison with sensible heat storage devices, phase change thermal storage devices have advantages such as high heat storage density, low heat dissipation loss, and good cyclic performance, which have great potential for solving the problem of temporal and spatial imbalances in the transfer and utilization of heat energy. However, there are also issues such as the small thermal conductivity of phase change materials (PCMs) and poor efficiency in heat storage and release, and in recent years, enhanced heat transfer in phase change thermal storage devices has become one of the research hotspots for optimizing thermal storage devices. Although there have been reviews of enhanced heat transfer technology for phase change thermal storage devices in the literature, there is still insufficient research on the summarization of the enhanced heat transfer mechanism, structural optimization, and applications of phase change thermal storage devices. This Review provides a review of enhanced heat transfer in phase change thermal storage devices from two aspects: internal structure enhanced heat transfer and heat exchange medium flow channel enhanced heat transfer. It summarizes the enhanced heat transfer measures of various types of phase change thermal storage devices and discusses the role of structural parameters in enhanced heat transfer. It is hoped that this Review will provide some references for scholars engaged in research on phase change thermal storage heat exchangers.

Research on performance of radiant floor heating system based on heat storage

With the development of the economy, improving energy efficiency and saving energy have become important issues that need to be addressed. In terms of building energy efficiency, combining phase change heat storage material with floor radiation heating is an effective way to improve energy utilization efficiency. In this paper, a composite phase change heat storage material used in radiant floor heating was introduced. Based on the selected materials, experiments on floor radiation heating system based on heat storage in different environments during the heating season were conducted. The results showed that thermal conductivity of composite phase change heat storage material increased by a maximum of 97.2%, and the maximum heat release time can be obtained 6 h. By using this radiant floor heating system, a balance between heating comfort and economy has been achieved, so this system will have a good applied foreground.

Feasibility Analysis of a Direct-drive PV Heat Pump System Based on Phase Change Heat Storage

A direct-drive PV pump system based on phase change heat storage is proposed to address the current building energy consumption problem in heating/cooling. The system can solve the problems of unstable solar energy, high battery cost, and short battery service life. Taking a 45m 2 office in Shanghai as the research object, the annual dynamic simulation model of the system is built through TSNSYS. The linear weighted evaluation function method is used for multi-objective optimization analysis of system performance and cost. The results show that the selection scheme with a PV area of 26 m2, a phase change volume of 0.14 m3, and a valley electricity storage ratio of 1 has the best-combined performance and cost of the system.

A route of polyethylene glycol-based phase change heat storage wood with AlN as the thermal conductive filler

Wood is a great natural material with good energy storage and temperature adjustment for the energy crisis. In this study, wood was delignified, and the PEG-based eutectic polymer (PGMA) was impregnated into the delignified wood, and styrene (SM) grafted AlN was selected as thermal conductive filler to synthesize a stable phase change heat storage wood. The result shows that the styrene (SM) polymerized on the surface of AlN to form polystyrene (PS), and the dispersion of AlN was enhanced. The thermal stability and loss resistance of PCES-Wood are improved for the penetration of PS-AlN into the cavities, which is attributed to the PS-AlN playing a “limiting” role in the crystallization of PGMA. When the content of PS-AlN is 6%, the thermal conductivity of PCES-Wood reaches 0.5148 W/(m·K). 4% PS-AlN-PCES@Balsa has the lowest undercooling and heat loss rate, and the melting enthalpy and solidification enthalpy reach 125.60 J/g and 120.30 J/g, respectively. The phase change temperature range is between 19.59 and 33.87 °C, which is in the comfortable temperature range for humans. Under the illumination of the simulated solar light source, the surface temperature of PS-AlN-PCES@Balsa rises rapidly and shows a lasting heat storage capacity at low temperatures compared with the original wood. After 200 cold and hot cycle tests, the phase change enthalpy of PS-AlN-PCES@Balsa is still high, and there is a slight leakage phenomenon. The phase change wood prepared in this study shows that it is a potential material to store and release solar energy in practical applications.

Integration of phase change thermal storage system with vertical solar Chimney In Greenhouse

The performance stability of the system can be improved by incorporating a solar chimney with a phase-change material (PCM). It is recommended that instead of using the traditional multi-curved trough air collectors for solar greenhouses, a solar phase change thermal storage wall construction system with vertical air channels be employed. Solar thermal utilization of the rear wall. In order to verify feasibility of the construction system, a multi-curved trough air collector test system for solar greenhouse and a phase-change heat storage wall test system with vertical air channels were built respectively. The air velocity in the heater, the air flow parameters (air velocity, air channel spacing, air flow direction) in the sensible heat storage wall layer in the solar greenhouse, etc. The study’s findings indicate that the collector performs at its peak level of total heat absorption when its air velocity is between 1.4 and 1.8 m/s, and that heat absorption rises as solar radiation intensity rises. The suggested system design orientation offers an efficient way to raise the thermal performance of the system with the least amount of work and expense for practical applications.