Solar Phase Change Research Articles

Studying the Improvement of Solar Collector Mechanism with Phase Change Materials

This study delves into the integration of phase change materials (PCM) in solar thermal collector systems to address this challenge. By incorporating nano encapsulated PCMs, researchers have mitigated concerns surrounding PCM leakage, revolutionizing the potential of solar collector systems to elevate energy efficiency, diminish carbon emissions, and yield manifold benefits. This article comprehensively investigates the design and utilization of solar phase change energy storage devices and examines the transformative impact of employing nano-coated phase change materials (Nano capsules) to augment solar collector performance. The integration of paraffin-based PCM and the insulation of the collector system have been crucial in optimizing heat retention and operational efficacy. The composition of the PCM involves a balanced blend of octadecane phase-change particles and water as the base fluid, designed to maximize thermal performance. Analysis of the experimental findings demonstrates the dynamic thermal behavior of the nano encapsulated phase change material, revealing distinctive temperature profiles about fluid dynamics and absorbent characteristics. Notably, the study emphasizes the nuanced trade-offs associated with the conductivity and melting temperature of the Nano encapsulated PCM, yielding valuable insights into energy storage capacity limitations and thermal performance variations throughout diurnal cycles. Central to the investigation, the optimal nanoparticle proportion is elucidated, shedding light on its pivotal role in modulating PCM performance. Furthermore, findings underscore the complex interplay between nanoparticle volume fraction and thermal fluid temperature, providing critical perspectives on optimizing PCM-enhanced solar collector systems.

Thermal performance study of a solar-coupled phase changes thermal energy storage system for ORC power generation

The current solar organic Rankine cycle power generation (ORC) system cannot run smoothly under the design conditions due to the shortcomings of solar fluctuations, and thermal energy storage (TES) can effectively buffer the fluctuations of solar energy. Cascaded heat storage (CLTES) has been shown to be more suitable for solar heat storage than single-stage heat storage (LTES). The main objective of this study is to analyze the thermal storage characteristics of thermal storage systems under real-time solar energy fluctuations, and to improve the thermal storage efficiency and total thermal storage capacity of solar phase change thermal storage systems in distributed scenarios. The current research on solar CLTES system needs to focus on the heat storage characteristics under the actual solar fluctuations to provide guidance for the design and practical operation of CLTES system. Analyzing the effect of solar fluctuations on thermal storage performance is the focus of solar thermal storage research, which can provide guidance for the design and actual operation of CLTES systems. However, the current research on solar CLTES system lacks the analysis of thermal storage characteristics under typical solar energy fluctuations. Therefore, a simplified two-dimensional enthalpy-dynamic model of heat transfer for shell-and-tube latent heat storage system is developed in this paper to simulate the heat storage characteristics of single-stage and cascade heat accumulators containing different phase change materials (PCMs) at a fixed temperature of the heat source, and the heat storage performance of the system is simulated based on the solar fluctuations of typical four seasons. Finally, based on the shortcomings of large-capacity thermal storage, a dual-tank recirculation thermal storage model is proposed and the thermal storage characteristics of the improved recirculation model are analyzed. The results show that the optimized cycle heat storage mode can bring about a minimum of 10 % and a maximum of 17.2 % thermal efficiency improvement. On a typical summer day with the most abundant solar energy resources, four times of complete phase change heat storage and one incomplete phase change heat storage were completed (melting fraction = 81.83 %), and on a typical winter day with the least solar energy resources, two times of complete phase change heat storage and one incomplete phase change heat storage were completed (melting fraction = 75.81 %). The maximum difference of heat storage between them is 45.38 %.

Thermal storage characteristics of microencapsulated phase change material coatings in low-energy rural prefabricated building walls

ABSTRACT Prefabricated buildings in rural areas of China waste a large amount of energy due to poor thermal insulation. Phase change materials (PCMs) are able to stabilize room temperature by latent heat absorption and release during the phase change process. This study incorporated PCMs in the form of microcapsules into the interior wall coatings of prefabricated buildings, and by taking advantage of PCMs’ energy storage capacity, the thermal storage characteristics of PCM-coated bricks were investigated. The results show that microencapsulated phase change material(MPCM) coatings for prefabricated walls exhibit excellent thermal stability properties and effectively reduce the heat flux of prefabricated walls, with coatings having a MPCM mass fraction of 15% and a thickness of 5 mm providing the highest overall benefits. By fitting the numerical simulation results with experimental data, a novel multifunctional passive solar phase change heat collection and storage wall system was developed. This study innovatively combines energy storage materials with interior wall coatings in prefabricated walls of modular buildings investigating how it enhances the thermal stability of the external insulation walls and effectively reduces the reliance on heating equipment for auxiliary heating in rural residences. This essay aims to provide feasible recommendations for optimizing the dual-stage energy-saving and carbon reduction goals in both the construction and operation of rural areas.

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.

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.

Performance improvement and investigation of radiation heat transfer of chloride salt as high-temperature heat storage medium

• Synthesis of carbon doped molten salt composites by reaction method. • High absorptivity material combined with translucent molten salt. • Research on radiation heat transfer based on Finite Element Method (FEM). • Molten salts exhibit good thermal conductivity and radiative properties. The development of solar phase change thermal storage technology is significant for the efficient use of energy. In this study, molten chloride salt was used as a high-temperature phase change thermal storage material to improve the heat transfer performance of the chloride salt by reacting citric acid with sodium chlorite to generate a flaky carbon morphology in the molten salt. The results indicated that the carbon generated by the reaction was uniformly distributed in the molten salt matrix, and the modified molten salt obtained a high latent heat of phase change with a maximum latent heat of phase change of 227.3 J·g –1 , which was 13.7% higher than that of the undoped molten salt, and the maximum thermal conductivity could reach 2.313 W·m –1 ·K –1 , which effectively improved the applicability range. In addition, the combination of ANSYS simulations and the constructed temperature measurement platform showed that the radiation heat transfer effectively improved the temperature distribution of the molten salt in the high-temperature stage. This study may promote the research of the heat transfer behavior of molten salt at high temperature and play an important role in concentrated solar power generation.

A stable new composite phase change material based on H2C2O4⋅2H2O-NH4Al(SO4)2⋅12H2O binary eutectic into ZrO2 modified expanded graphite

As energy shortage intensifies, improving energy efficiency and reducing energy consumption have become essential topics. Herein, a form-stable composite phase change material (FCPCM) consisting of modified expanded graphite (MEG) and eutectic hydrate was designed as a reliable and efficient thermal energy storage medium. Firstly, novel binary eutectic hydrate involving oxalic acid dihydrate (H2C2O4.2H2O) and ammonium aluminum sulfate dodecahydrate (NH4Al(SO4)2.12H2O) served as an excellent thermal energy storage guest. Zirconium dioxide (ZrO2) was used as a hydrophilic modifier because of its high heat resistance, high inertness, corrosion resistance, non-toxicity and countless hydrophilic groups. Therefore, the hydrophilic modified expanded graphite (MEG) as a supporting host was constructed by dip-coating of nano ZrO2 sol on the surface of expanded graphite (EG), which improved its hydrophilicity and compatibility with a eutectic guest. Compared with the original EG (83.05°), the contact angle of MEG containing 10 % ZrO2 on the water was decreased to 37.95°. In addition, the adsorption rate and capacity of MEG to binary eutectic were much faster and larger, reaching an approximate saturation (65.58 %) within 40 min, which was three times that of the untreated EG (23.10 %) in the same adsorption time. The resultant FCPCM containing 24 wt% MEG exhibited a good phase transition temperature (54.10 °C), high phase transition enthalpy (168.5 J/g), as well as excellent anti-leakage behavior. After 100 hot and cold cycles, the thermal performances of FCPCM kept relatively stable, which guaranteed its sustained thermal benefits. It provides a potential application in the field of solar phase change heat exchangers.

An Experimental Study of the Heat Storage and the Discharge Performance and an Economic Performance Analysis of a Flat Plate Phase Change Material (PCM) Storage Tank

Solar heating technology has the advantages of being high efficiency, energy-saving, and environment protecting; however, the instability of solar energy and its mismatch with the variation characteristics of building heat load have caused great difficulties in the design and the efficient operation strategy of a solar system. A heat storage tank is an important part of a solar hot water system. In order to improve system efficiency, this paper proposes a flat plate PCM storage tank, establishes a mathematical model, and conducts experimental verification under different working conditions. Experiments show that in the heat storage process, the phase change material (PCM) only accounts for less than 20% of the space of the PCM storage tank, and its heat storage can reach 50% of the total heat storage of the tank. In the discharge process, the water temperature of the ordinary tank decreases by 20 °C within 1.5 h, and the phase change process lasts approximately 3 h, with the water temperature remaining at 45~50 °C during this period. In the natural cooling process, the heat discharge of the two water tanks at night was similar, while the temperature of the ordinary water tank decreased by 12 °C and that of the phase change water tank decreased by 7 °C. By simulating the dynamic simulation model of the composite solar phase change thermal storage combined with an air-cooled heat pump system, the results show that the solar heating system with a PCM storage tank (SHS-PCM) saves 34% more energy than a solar heating system with a common tank (SHS-without PCM), and the volume of the PCM storage tank is reduced to 1/5 of the ordinary tank. The investment payback period method of energy saving reconstruction is used to analyze the economy of the SHS-PCM and the SHS-without PCM, the initial investment cost of the SHS-PCM is CNY 9858 higher than the SHS-without PCM, but the annual operation cost is saved by CNY 12,100, and the project investment payback period is 0.81 years, which has energy-saving potential and economic benefits.

Simulation of an improved solar absorption refrigeration system with phase change materials

Aiming at the problems of low solar energy utilization rate, poor intermittent, low stability and poor energy saving effect in traditional solar absorption refrigeration system, a lithium bromide-water absorption refrigeration system driven by solar in Tai’an was taken as the research object. An improved solar absorption refrigeration system with phase change was presented. In typical day and whole refrigeration period, the traditional solar absorption refrigeration system with and without phase change were simulated by TRNSYS transient simulation software. Their collector efficiency, unit cooling capacity and COP were comparatively analyzed. The results showed that the collector efficiency of the improved solar absorption refrigeration system with phase change was 4.2% higher than that of the traditional solar absorption refrigeration system without phase change. The unit cooling capacity was 2.8% lower than that of the traditional system, which store the excess cooling capacity with the help of PCMs. The average COP of traditional absorption system and improved solar absorption refrigeration system were 0.737 and 0.679, respectively. This manuscript provides a theoretical basis for the development of solar phase change heat storage absorption refrigeration system.

Numerical simulation study on heat transfer characteristics and parameter optimization of solar phase change energy storage fresh air preheating system

In cold regions, indoor fresh air preheating in winter has received much attention. An improved fresh air preheating system using solar energy and phase change energy storage technology is proposed in this study to solve the problem of insufficient fresh air supply in cold regions. This study establishes two-dimensional mathematical model for air-type phase change energy storage device, and compares the error between them and the experimental results. The results show that the comparison between the simulated and experimentally measured is in good agreement. This study explores the effects of velocity of hot air, temperature of fresh air and temperature of hot air during simultaneous heat storage and discharge conditions by using numerical simulation method. The results show that the designed system has the ability to preheat fresh air at 4.5 °C for more than 4 hours under the condition of outdoor average temperature of -10 °C at night, and has practical promotion value. All three parameters affect the thermal performance of the system. When the hot air velocity increases from 1.5 m / s to 2.25 m / s, the liquid fraction increases by 5.16 %, 10.11 % and 14.52 % respectively. Different fresh air temperatures determine the heat storage capacity of the system under the condition of simultaneous heat storage and heat release.

Preparation and properties of composite phase change material based on solar heat storage system

Solar phase change hot water storage tank is a kind of storage / exothermic system with solar energy as heat source and phase change heat storage material. It can store heat during the day, continue to operate at night with stored heat without consuming other energy. Because of the poor thermal conductivity of solid-liquid phase heat storage materials, carbon fiber is added to enhance the thermal conductivity of phase change materials. Stearic acid is used as phase change material, carbon fiber as heat transfer material and ethyl cellulose as auxiliary material to prepare carbon fiber / stearic acid composite phase change material. Carbon fiber / stearic acid in the mass ratio of 7.5:92.5 is the optimal material and the chemical compatibility, phase change temperature, phase change latent heat, thermal conductivity and thermal stability of carbon fiber / stearic acid are measured by using SEM, XRD and DSC. From the DSC test, the latent heat capacity was determined as 192.6 J/g and the phase change temperature as 67.7°C. Thermal conductivity was measured as 0.4011 W/m⋅K. The storage / exothermic experimental system of carbon fiber / stearic acid composite phase change material is built. The melting process and solidification process of the composite phase change material are tested, and the storage / exothermic characteristics are analyzed. SEM and DSC analysis results revealed that the PCM had high thermal stability. XRD revealed that the binary eutectic mixture had good chemical stability. Thus, the new PCM possessed high latent heat with good thermal and chemical stabilities making it a potential phase change material for solar heat storage applications.

A Review on Thermal Properties Improvement of Phase Change Materials and Its Combination with Solar Thermal Energy Storage

This article summarizes measures to enhance the solar phase change thermal energy storage (TES), starting from two key points in solar phase change TES research: solar phase change materials (PCM) and solar phase transition devices. First, different types of PCM and their advantages and disadvantages are introduced. To improve thermal performance, the research progress of different dimensional thermal conductivity additives, photothermal composite phase change materials (CPCM), and phase change microcapsules is reviewed. Then, the characteristics of commonly used solar phase transition TES devices and the research status of solar energy device improvement with fins and multistage phase transition TES are summarized for the past few years. It is hoped to provide methods and ideas for the design and research of solar phase change TES systems, and to increase the overall heat transfer properties through the combination of multiple optimization methods. Finally, the future direction and research focus of solar phase change TES technology are put forward.

Experimental research on solar phase change heat storage evaporative heat pump system

With increase in global temperature, worsening of environmental conditions and a shortage of energy resources, countries around the world are actively developing the use of renewable energy sources. The technology of combining solar energy and heat pumps is an important direction for the development of new energy utilization technologies. In this paper, a solar phase change heat storage evaporative heat pump system (SPHP) is designed. The system uses a phase change heat storage tank as the connection center, and is coupled with a solar system and a heat pump system. The phase change heat storage tank is filled with ammonium aluminum sulfate dodecahydrate /stearic acid composite phase change heat storage material. The system was experimentally studied, and the analysis of a system simulation was performed using TRNSYS. The results show that the heating electricity consumption of the system is about 72.8% of that of a single heat pump, the daily operating cost is only 41.2% of that for a single heat pump heating system, the average system coefficient of performance (COP) reaches 3.79, the average heat collection efficiency of the solar collector can reach 59.8%, and the system solar energy proportion of heat supply is 27.2%. There was good agreement between the experimental and simulation results for the system COP and temperature of the heating end equipment.

Study on heat transfer enhancement of solar finned tube phase change regenerator

Based on the problems of heat storage in the process of solar energy utilization and the advantages of finned tube heat exchanger, the finned tube is applied into the solar phase change heat accumulator and the heat storage process of the phase change material is simulated numerically. The results show that the use of finned tube instead of smooth tube in solar phase change heat accumulator can effectively improve the heat transfer intensity of the outside of the tube during phase change heat storage, thus enhancing the heat transfer capacity of the whole heat accumulator and shortening the heat storage time. In the simulation range of this paper, the optimum structure parameter of finned tube is: finned outer diameter of D2=28mm, fins thickness of t=1mm, fins number of c=13, spacing between fins of h=25mm.

Experimental study of a modified solar phase change material storage wall system

Aiming at satisfying demands of buildings in hot summer and cold winter regions, this work proposed a dual-channel and thermal-insulation-in-the-middle type solar phase change material storage wall system. The system has four independent functions: passive solar heating, heat preservation, heat insulation, and passive cooling, and it can agilely cope with requirements of climatization of buildings in different seasons throughout the year. The analysis of measured data from comparative tests on a hot-box test platform, shows that in summer, the daily average temperatures in the experimental room are 29.8 °C, 30.9 °C and 31.0 °C respectively, while those in the reference room are 29.6 °C, 30.7 °C and 30.8 °C, and thereby the difference is small. The south-facing wall with solar collector module shows reduction in peak temperature and delay phenomenon compared with that without solar collector module. These aspects highlighted by the results together indicate that effective prevention from summer overheating problem can be achieved by this system. In winter, by comparison with the ambient temperatures and those of the reference room, the air temperatures in the experimental room, both its maximum and average, raise greatly showing good heating effect. In addition, some distinct thermal characteristics of the system operated in summer or winter are obtained.

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.

Experimental investigation and feasibility analysis on a capillary radiant heating system based on solar and air source heat pump dual heat source

Due to sustainable development, solar energy has drawn much attention and been widely applied in buildings. However, the application of solar energy is limited because of its instability, intermittency and low energy density in winter. In order to use low density and instable solar energy source for heating and improve the utilization efficiency of solar energy, a solar phase change thermal storage (SPCTS) heating system using a radiant-capillary-terminal (RCT) to effectively match the low temperature hot water, a phase change thermal storage (PCTS) to store and continuously utilize the solar energy, and an air source heat pump (ASHP) as an alternate energy, was proposed and set up in this research. Series of experiments were conducted to obtain the relation between the solar radiation utilization rate and the heating supply temperatures, and to evaluate the performance of the RCT module and the indoor thermal environment of the system for its practical application in a residential building in the north-western City of Xi’an, China. The results show that energy saving of the solar heating system can be significantly improved by reducing the supplied water temperature, and the supplied water temperature of the RCT would be no more than 35°C. The capillary radiation heating can adopt a lower water temperature and create a good thermal comfort environment as well. These results may lead to the development of designing and distributing the solar energy for building heating during winter.

Short Term Ionospheric Variability in the Northern Hemisphere for Two Consecutive Solar Cycles

Hourly values of the total electron content (TEC-Faraday content) collected at five stations in the northern hemisphere extending from the low to high latitudes lying in the narrow longitude zone of (270 ± 20) °E during the solar maximum years 1981 and 1989 respectively of the last 21 and 22nd solar cycles and also during the common solar minimum year 1985 are used to study the latitudinal variations of the day to day TEC variability. The effect of solar phase change in the variability is found to be the least for the midlatitude station of Boulder and most during the nighttime for the high latitude station of Goose bay. The magnetic disturbance generally enhances the TEC variability for the five stations during the three seasons of both solar phases and this effect seems to be somewhat higher for the mid and high latitudes during the equinox season of the solar maximum years. A spectral investigation of the TEC variability reveals narrowing of the spectrum from low to high latitudes during the solar minimum phase while the reverse seems to be the case during the solar maximum. While the low latitude TEC variability spectrum is not correlated to either the variability spectrum of S10.7 solar flux or to the mean equatorial Dst variations, the mid latitude TEC variations show a good positive correlation with the variability of Ap and the higher latitude TEC variations are negatively correlated with the variability spectrum of the daily mean Auroral electrojet (AE) indices.