Conductivity Of Phase Change Materials Research Articles

Study on thermal performance of a new optimized snowflake longitudinal fin in vertical latent heat storage

Taking the casing phase change heat storage unit filled with RT55 as the research object. According to the low thermal conductivity of phase change materials, we propose a Phase Change Material (PCM) sleeve with snowflake longitudinal fin structure to improve the melting performance of vertical latent heat storage system (LHTES), and the phase change heat transfer process is simulated by numerical simulation. We studied the enhanced heat transfer characteristics of the snowflake-shaped fin structure to the casing PCM unit, and compared with the ordinary rectangular longitudinal fin and the improved snowflake-shaped longitudinal fin. The results show that the combined mechanism of snowflake finned tube structure and local heat transfer of phase change materials can significantly shorten the charging time, which is 45.59% lower than that of traditional fin melting time. Reasonable changes in fin length, width, shape and angle structure can shorten the charging time, but reduce the heat storage. We analyzed the thermal performance of the heat storage system by taking the charging time, heat storage capacity and average heat flux as evaluation indexes, and discussed the effects of flow temperature in the tube, fin material and longitudinal fin shape on the melting performance of the system.

A novel design of discrete heat and cold sources for improving the thermal performance of latent heat thermal energy storage unit

The low thermal conductivity of phase change materials (PCMs) severely limits the operating efficiency and flexibility of the latent heat thermal energy storage (LHTES) unit. In this study, a novel LHTES unit with discrete heat and cold sources was proposed and investigated numerically, including symmetrical and staggered arrangements with side-heat and bottom-heated LHTES units. The consecutive and simultaneous heat storage and release processes of the seven developed models were comprehensively considered and compared for the first time. The results show that with the discrete arrangement of source, the additional heat conduction effect and natural convection in the side-heated LHTES unit would be significantly improved. More importantly, the heat storage and release cycle of the side-heated and symmetrical arrangement was shortened by 49.9%, the steady-state time was advanced by 46.6%, the steady-state liquid fraction was increased by 4.2%, and the heat transfer rate was increased by 22.3%. The discrete source arrangement had no obvious improvement on the performance of the bottom-heated LHTES unit. In addition, energy analysis showed that the side-heated LHTES unit stored more sensible heat. The discrete heat and cold sources effectively improved the thermal performance and flexibility of the LHTES unit.

Melting performance assessments on a triplex-tube thermal energy storage system: Optimization based on response surface method with natural convection

The low thermal conductivity of phase change materials significantly affects the heat storage and release performance for a phase change energy storage system. To alleviate this issue, a novel triplex-tube latent heat thermal energy storage system is designed and the melting behavior of phase change materials is studied numerically. On the premise of a fixed total volume of phase change material, the multi-parameter optimization design of the system is carried out by the response surface method. The fluid-structure coupling function of each parameter is fitted. Compared with the original model for the triplex tube, the melting performance of the optimized model is improved by 23.87%. The internal temperature fluctuation is found by dynamic temperature response, and the mechanism is explained by dynamic flow rate study. The improvement of melting performance by natural convection after optimization is also studied. The influences of the physical parameters (fin length, initial temperature of phase change material, inner and outer tube wall temperature, and fin material) of the optimization model on the melting performance of the system are quantified, as well. The effect of fin length (30-35-40 mm) on melting performance is found to be less than 11.47% and the effect of thermal conductivity of fin on the melting process is not obvious.

Functional Unit Construction for Heat Storage by Using Biomass-Based Composite.

How to construct a functional unit for heat storage by using biomass materials is significant for the exploration of phase change materials (PCMs). In this work, we try to design and construct a functional unit for heat storage by employing a vacuum impregnation method to prepare sugarcane-based shape stabilized phase change materials (SSPCMs) for improving the thermal conductivity of phase change materials (PCMs) and preventing the liquid state leakage of PCMs. The morphologies of the prepared materials are characterized by Scanning electron microscope (SEM) as containing a unique channel structure which is viewed as the key factor for heat storage. X-ray diffractometry (XRD), Fourier transform infrared spectroscopy (FT-IR), and thermogravimetric analysis (TGA) were used to characterize the prepared materials. The results indicated that no chemical reaction occurred between PEG and sugarcane-based biomass during the preparation process and SSPCMs showed great thermal stability. Their thermal properties are measured by using the differential scanning calorimetry (DSC) characterization and show a high melting enthalpy of 140.04 J/g and 94.84% of the relative enthalpy efficiency, illustrating the excellent shape stabilized phase change behavior. Moreover, the highest thermal conductivity of SSPCMs is up to 0.297 W/(mK), which is 28.02% higher than that of the pristine PEG. The excellent capability for thermal energy storage is attributed to the directional thermal conduction skeletons and perfect open channels and the unique anisotropic three-dimensional structure of the SSPCMs. Hence, the unique structure with PEG is testified as the functional unit for heat storage. Comprehensively considering the excellent properties of sugarcane-based materials—providing cheap raw materials via green preparation—it is conceived that sugarcane-based materials could be applied in many energy-related devices with reasonable function unit design.

Evaluation of different melting performance enhancement structures in a shell-and-tube latent heat thermal energy storage system

Latent heat thermal energy storage employing phase change materials is widely used in energy storage systems. To further improve the low thermal conductivity of phase change materials in these systems, it is essential to investigate different thermal enhancement techniques. In this work, two principal thermal enhancement techniques (i.e., finned tubes and conductive metal foams) are numerically investigated for melting processes in a shell-and-tube latent heat thermal energy storage system. Topology optimised structures are used as fins, and the simulation predictions are validated by experimental results using additive manufactured topology optimised fins. For metal foams, different filling ratios (i.e., whole-foam structure and half-foam structure) are considered. Compared to the configuration without enhancement, the thermal energy storage rates are 3.3–5.8 times higher. In addition, the results show that the topology optimised fins can achieve the best performance, but can only be an economical solution when the unit price ratio between the enhancement technique and the phase change materials is less than 6. For the first time, the thermal enhancement performance and economic efficiency of these two principal techniques are quantitatively analysed. The results would be useful for appropriate energy storage design solutions in practice.

Optimization of an innovative hybrid thermal energy storage with phase change material (PCM) wall insulator utilizing Taguchi method

Most studies considered low conductivity of phase change material as negative point on its application in hybrid thermal storage. However, it has hidden potential to be used as an effective insulation for thermal storage while at the same time acts as energy storage medium. Based on our literature survey, no previous study investigating this configuration has been reported. This experimental study are thus conducted to evaluate the energy storage performance of the Hybrid TES with PCM layer as insulation wall and energy storage, and to assess the effect of several key geometry and operating parameters on the performance of the Hybrid TES. To achieve these objectives, an experimental setup consisting of hybrid TES tank with PCM embedded in the wall and flow loop for heat transfer fluid is prepared. Insulation tests are carried out to evaluate its PCM wall insulation effectiveness. During charging and discharging cycle, k-type thermocouples connected with datalogger are utilized to measure and record the temperature profile of the working fluid and PCM layer with TES. Three important parameters of the proposed Hybrid TES including the ratio of PCM volume to heat transfer fluid (HTF) volume, inlet temperature and volumetric flow rate of the HTF, are studied to evaluate their influence on the Hybrid TES performance. Taguchi statistical method is adopted to minimize the number of experiments whilst securing all important information and parameter interaction. Based on the experimental results, it was found that Hybrid TES with PCM wall layer offers better insulation, indicated by higher retained temperature within the storage, than its conventional sensible TES counterpart. In addition, TES heat storing capacity is increased by introducing the PCM wall. Among the investigated parameters, HTF inlet temperature has the most significant positive effect on the performance of Hybrid TES. This study signifies the potential of PCM wall incorporation into TES as wall insulation and additional thermal energy storage medium.

Ultra-high thermal conductivity and mechanical properties of a paraffin composite as a thermal conductive phase change materials for novel heat management

Because of their large latent heat, phase change material (PCM) composites have received much attention for thermal energy storage and heat management applications. However, the intrinsically low thermal conductivity of PCMs remains a challenge for efficient heat management. In this study, a mixed matrix composed of stearic acid-grafted bisphenol A (SABPA) and paraffin was filled with a porous expanded graphite network impregnated with alkylated boron nitride; the resulting composite showed an ultrahigh through-plane thermal conductivity of 7.21 W/mK, mechanical property (tensile strength and elongation at break) improvements of 470 and 568% compared to pure paraffin, and a latent heat of 93.506 J/g. When the PCM composite was applied in electrical devices, we observed heat buffering caused by the large latent heat of PCM, in contrast with existing conductive polymer composites. This novel thermal management approach, combining heat storage and heat dissipation, makes the SABPA/paraffin composites promising materials for thermally conductive PCM composites and advanced electronic packaging.

Effect of copper metal foam proportion on heat transfer enhancement in the melting process of phase change materials

• The greater proportion of copper metal foam affords greater heat transfer. • Natural convection is the major heat transfer mechanism with low metal foam proportion. • The heat storage capacity first increases and then decreases with increasing metal foam proportion. • The heat storage rate increases with increasing copper metal foam proportion. • A copper metal foam proportion of 1.28% exhibit the best heat storage performance. Phase change materials can overcome the low energy density and utilisation efficiency of solar energy. However, the low thermal conductivity of phase change materials significantly affects the thermal efficiency of solar devices; thus, improving the thermal conductivity of phase change materials has been the focus of many recent studies. Using paraffin wax and copper metal foam, copper metal foam composite phase change materials were prepared in this study. The effect of the copper metal foam proportion on heat transfer enhancement in the melting process of phase change materials was analysed using visualisation heat storage experimental equipment. The integrated heat transfer coefficient of the copper metal foam composite phase change materials was obtained. The experimental results showed that as the copper metal foam proportion increased from 0% to 2.13%, the melting time of the copper metal foam composite phase change materials decreased from 901 s to 791 s, and the heat storage rate and integrated heat transfer coefficient increased from 21.81 J/s to 25.08 J/s and 1.26 W/(m K) to 4.16 W/(m K), respectively. The heat storage capacity first increased and then decreased. The minimum temperature gradient of 5.2 K was reached when the copper metal foam proportion was 2.13%. More important, natural convection is the major heat transfer mechanism in the melting process of composite phase change materials with a low copper metal foam proportion; heat conduction plays a primary role in the melting process of composite phase change materials with a high copper metal foam proportion. The best heat storage and heat storage rate for copper metal foam composite phase change materials were 20260.49 J and 24.38 J/s, respectively, achieved with a copper metal foam proportion of 1.28%.

Thermal energy storage characteristics of packed bed encapsulating spherical capsules with composite phase change materials

• Experiments were conducted on a solar heating system with a PBTESD. • The PA/EG/CF composite phase change material were prepared. • Models were developed for the dynamic processes of the packed bed. • Temperature field and dimensionless parameter analysis was conducted. Packed bed thermal energy storage technology is one of the valid methods to coordinate the balance of energy sources supply and demand and settle the matter of the time and space mismatching of renewable energy in the future. In this paper, the thermal energy storage characteristics of a packed bed thermal energy storage device (PBTESD) filled with spherical phase change capsules are analyzed. The PA/EG/CF composite phase change material (CPCM) was used as an encapsulation material, and water was used as heat transfer fluid (HTF). Based on Schumann’s model, a one-dimensional two-energy equation two-phase mathematical model of PBTESD was established. The heat transfer resistance between the spherical phase change capsules and HTF and the heat loss between the heat storage tank and the surrounding environment were considered in the model. MATLAB was used for numerical simulation calculation of the equation, and the results obtained were compared with the experimental results and literature results. The effects of Reynolds number, Stefan number, dimensionless diameter and effective thermal conductivity of phase change material (PCM) on the temperature evolution trend and thermal performance of PBTESD were investigated by single factor analysis. The results showed that the increase of Stefan number leaded to the increase of thermal energy storage density in the charging process. Increasing Reynolds number and Stefan number and decreasing dimensionless diameter increased the average energy storage rate and average exergy storage rate. The reduction of Stefan number and dimensionless diameter could improve exergy efficiency, while the effective thermal conductivity of PCM had little effect on the thermal characteristics of PBTESD. This paper elaborated on the transient thermal characteristics of PBTESD, which laid a foundation for subsequent research.

Loofah-derived eco-friendly SiC ceramics for high-performance sunlight capture, thermal transport, and energy storage

Emerging integrated solar thermal conversion and latent heat storage has a great potential in harvesting solar energy continuously and efficiently by avoiding redundant energy transfer processes. However, the energy harvesting performance is limited by weak solar absorption and low thermal conductivity of phase change materials (PCMs). Here, loofah-derived eco-friendly SiC ceramics is proposed for fast, efficient, and compact solar thermal energy storage beyond state-of-the-art. We design a facile way to fabricate eco-friendly porous SiC ceramics with robust structure and tunable porosity by impregnating flour paste into loofah followed by carbonization and molten silicon reaction processes. After impregnation with NaCl-NaF eutectics, broadband sunlight capture with average solar absorptance of 95.25%, rapid thermal transport with thermal conductivity of 20.7 W/mK, and compact latent heat storage with energy storage density of up to 424 kJ/kg are demonstrated simultaneously. Highly conductive light SiC materials, hierarchical continuous loofah skeleton structure, and high energy density eutectics are attributed to this superior performance. This work opens new routes for efficient harvesting solar thermal energy based on biomimetic eco-friendly ceramics.

Optimization of shell and tube thermal energy storage unit based on the effects of adding fins, nanoparticles and rotational mechanism

According to the high storage capacity of latent heat thermal energy storage (LHTES) systems, finding a suitable solution to compensate for the weakness of these systems is logical. The main weakness of these systems is the low thermal conductivity of phase change materials (PCMs) as the storage reservoir of thermal energy. Many methods have been proposed previously to overcome this limitation. Most of these methods can be divided into three types that including changes in the geometric configurations, improving thermophysical properties of PCMs and applying external conditions to improve the LHTES systems' performance. Nonetheless, limited studies have been conducted with combination approaches between these methods. In line with this, the present study investigates the effect of combining three different types of improvement methods in the applicable ranges simultaneously. These methods are selected based on utilizing three different ways to heat transfer rate enhancement. So that these ways include increasing heat transfer area (by adding fins), increasing natural convection effect (by adding rotational mechanism) and improving the thermal conductivity of PCM (by adding Cu nanoparticles). Results show that the combination of these methods has a significant effect on the improving performance of LHTES system during charge and discharge processes. So that increasing productivity of each method leads to decreasing melting and solidification times and following this heat transfer rate enhancement. Based on comparing results, rotational speed increment has the highest effect on increasing heat transfer rate in charge and discharge processes. Moreover, since storage and release capacities are important parameters in the LHTES systems, to shed further light on the impact of utilizing combination methods on reducing these capacities, an optimization process is conducted by the response surface methodology (RSM). Optimization results present an optimal case based on the highest heat transfer rate with the highest storage and release capacities in charge and discharge process. Comparing results between simple and optimal cases show that applying optimal conditions leads to enhancing heat transfer rate significantly based on decreasing melting and solidification time at about 74% and 70%. While based on this comparison, storage and release capacities are reduced by just 2.5% and 4.1%, respectively.

Role of copper foam on solidification performance of ice-cool storage sphere system

Due to the poor thermal conductivity of phase change material (PCM), the application of the ice-cool storage sphere system is hindered. In this paper, the solidification performance of heat transfer after adding copper foam to the ice-cool storage sphere system is numerically studied by Computational Fluid Dynamic (CFD). The enthalpy-porosity method is used to describe the PCM solidification. Local thermal equilibrium is numerically adopted for modeling the heat transfer between the PCM and the solid matrix in copper foam. The variations of temperature field, ice front evolutions, solidification fraction, total solidification time, and cold storage capacity are investigated with the consideration of natural convection. The influence of surface temperature is explored by Stefan (Ste) number. A new evaluation index is proposed that can evaluate the cold storage performance of the energy storage system in real-time. The results show the metal foam focuses on accelerating the upper heat transfer due to the influence of natural convection in the plain ice storage sphere. The total ice storage time can be reduced by at least 72.7% in copper foam ice storage sphere with the porosity of 0.97, at the cost of very little ice storage capacity reduction. A higher porosity of copper foam is recommended with a compromise on the total melting time. This paper provides a clear and comprehensive vision of the metal foam effects of different temperatures and porosity inside the ice-cool storage sphere systems.

Influence of Phase Change Material Physicochemical Properties on the Optimum Fin Structure in Charging Enhancement

Orthogonal fins made of a vertical and a horizontal fin shorten total charging time and enhance average charging rate of lowly conductive phase change materials (PCMs) such as paraffin wax. An optimum dimension of orthogonal fins exists during charging of paraffin wax under top heating. The optimum dimension is represented by the optimum relative distance. The relative distance d/lv is defined as the ratio of the distance between horizontal fin and bottom wall of enclosure to length of vertical fin. However, the physicochemical properties of PCMs are variant in practical. Their influences on this optimum relative distance of orthogonal fins are not conducted. In current investigation, the investigations on influence of PCMs’ physicochemical properties on the optimum relative distance of orthogonal fins are numerically carried out. Influences of PCMs’ physicochemical properties including thermal conductivity, thermal expansion coefficient and viscosity on the optimum relative distance of the orthogonal fins are analysed. Results demonstrate that these physicochemical properties significantly influence the optimum relative distances. The optimum relative distance decreases from ~0.1633 to ~0.1020 when thermal conductivity increases from 0.1 W·m-1·K-1 to 1.5 W·m-1·K-1. When thermal expansion coefficient of PCM increases from 0.0001 K-1 to 0.005 K-1, the corresponding optimum relative distance decreases from ~0.1877 to ~0.0816. When viscosity of the liquid PCMs increases from 0.2 mPa·s to 80 mPa·s, the optimum relative distance of orthogonal fins increases from ~0.1224 to ~0.2245. The results supply an effective guideline to design an optimum orthogonally structured fins to enhance the average charging rate of organic PCMs with random physicochemical properties.

Thermophysical properties analysis of graphene-added phase change materials and evaluation of enhanced heat transfer effect in underwater thermal vehicles

Underwater vehicles are one of the most important tools for ocean observation and exploration, whose duration and range of underwater vehicles can be significantly extended by harvesting and utilizing ocean thermal energy. Generally, most underwater vehicles use the thermal engine to harvest ocean thermal energy. The phase change material (PCM)is the most important component of the thermal engine, the heat transfer performance of which directly affects the performance of the underwater vehicle. Enhancing the thermal conductivity of phase change materials is an effective way to improve the heat transfer rate of underwater thermal vehicles. The heat transfer performance of thermal engine can be effectively improved by incorporating graphene into PCM. In this paper, the molecular dynamic simulations of PCM with different addition ratio of graphene were carried out. Then the models of temperature–pressure-density, temperature–pressure-thermal conductivity and pressure-heat capacity were established for different simulation systems. On this basis, the internal connection between the additive ratio of graphene and the heat transfer rate of the thermal engine was revealed by using the phase change heat transfer model considering pressure conditions. The simulation shows that the appropriate addition of graphene is beneficial to the heat transfer rate of thermal engine at 0.1 MPa. Under the pressure condition of 20 MPa, the thermal engine can achieve the highest the heat transfer rate when the addition ratio is 1.2%, which also shows the best performance under simulated ocean conditions. The melting time can be reduced by 11.97% compared with the thermal engine without added graphene.

Melting assessment on the angled fin design for a novel latent heat thermal energy storage tube

Latent heat thermal energy storage was widely used to solve the problem of the intermittency in time and space for solar energy systems. To improve the energy storage efficiency, metal fins were typically further added to the shell side to increase thermal conductivity of phase change materials (PCMs). However, the positive effect of metal fins on enhancing heat transfer has not been fully utilized. In this paper, a novel design on angled fins was proposed to improve the thermal transport for PCMs in a shell-and-tube thermal storage unit. A numerical model was built and verified by comparing with experimental observations on the melting front evolution and temperature history. Bending angles for fins ranging from 0° to 75° were designed upwardly and downwardly and quantified on the melting front shape and location, melting time, and temperature field. Results demonstrated that melting rates were improved for the angled-fin cases other than cases with large bending angles. The case with a 10° downward angle exhibited as much as 55.41% reduction in full melting time. Simultaneously, the temperature uniformity can be improved by 20.00%. The novel design strategy on fin angles engendered a promising solution to enhancing thermal storage for emerging engineering applications.

Performance optimization and experimental analysis of a novel low-temperature latent heat thermal energy storage device

Due to the continuous penetration of renewable energy in the building sector, its instability increases the importance of energy storage in balancing energy demand and supply. However, the low thermal conductivity of phase change materials limits its application. This paper proposes a shell-tube latent heat thermal energy storage device with fins to enhance heat transfer. The ANSYS software is used to establish a three-dimensional simulation model of the device, considering of the nature convection. Furthermore, for this study, an experimental platform is built, and the influence of factors on the device during the charging and discharging period is analyzed. Simulation results show that the melting effects of the device vary with the fin and tube pitch; their optimization results are 40 mm and 90 mm, respectively. Experimental results exhibit that the inlet temperature influences the storage effect of the device, but as long as the phase change material is completely melted, pursuing excessively high temperature is not necessary. The same pattern was observed with the flow rate when the heat exchange fluid reached a turbulent state. After optimization, the effective energy release efficiency of the device reaches 77%, and the corresponding inlet temperature, heat storage flow, and heat release flow are 60 °C, 0.144 m3/h, 0.288 m3/h, respectively.

Characteristic study of modified nano CuO powder-based paraffin composite and its experimental investigation of melting/solidification behavior for mobilized cold thermal storage systems

The low thermal conductivity of Phase Change Materials (PCM) reduces its performance and remains a challenging issue. In the present study, modified nano copper oxide powder (CuO) with various weight percentages is dispersed into paraffin wax to form Nano-PCM composites (NPCM). Transmission Electron Microscopy analysis showed the uniform dispersion of modified CuO and spherical in structure. Diffraction Scanning Calorimeter analysis (DSC) showed a trivial difference in the melting point of PCM and NPCM. The peak melting temperature of PCM was 18.56°C and for NPCM with 1% concentration was 17.14°C. The thermal conductivity of NPCM in solid and liquid states was high when compared to that of pure PCM. The thermal conductivity of NPCM with a 1% concentration is enhanced by 52% in a solid state and 20% in a liquid state. Solidification/Melting experiments conducted at different bath temperatures such as 15°C, 17°C, and 19°C for PCM and NPCM revealed that the solidification period and melting period reduced with an increase in concentrations of modified Nano CuO due to augmented heat transfer rates. The solidification time for NPCM with 1% concentration is reduced by 18.33% for discharging temperature 25°C, and melting time are reduced by 16.6% for charging temperature.

Effects evaluation of fin layouts on charging performance of shell-and-tube LTES under fluctuating heat sources

The previous studies focus on the heat storage process of shell-and-tube latent thermal energy storage (LTES) under steady heat sources, without considering the fluctuating and intermittent characteristics of the most available heat sources in real applications. The effect of different fin sizes and locations on the charging performance of shell-and-tube LTES still keeps unclear under fluctuating heat source, and it is critical to improve the heat storage rate and density due to the low thermal conductivity of phase change materials (PCM). Consequently, this study aims to investigate the charging performance of a shell-and-tube LTES considering different fin layouts. Firstly, the effects of different fin number and configurations on heat storage process are performed under fluctuating heat sources. The case with comprehensive performance of high melting rate and large heat storage capacity is obtained. Then the effects of critical parameters on the charging process, including the fin angle, fin thickness, fin height and deviation distance of tube under fluctuating heat sources are further analyzed based on this case, and the results are compared with that of steady heat source. Results indicate that the fin height is the dominant factor influencing the heat storage rate and density under both steady and fluctuating heat source conditions, while the total melting time is shorter and the heat storage capacity is smaller, and the heat storage capacity is less obvious with the variation of fin parameters under the fluctuating heat source. In addition, the effect of downward deviation distance of tube on heat storage capacity is much obvious under fluctuating heat source than that of steady heat source.

A novel compensating fins configuration for improving the thermal performance of latent heat thermal energy storage unit

The low thermal conductivity of phase change materials (PCMs) severely limits the performance and operational capability of latent heat thermal energy storage (LHTES) systems. In this study, the authors not only first revealed the contradiction of the optimization strategy of the fins in the melting and solidification processes but also proposed a novel compensating fins configuration based on LHTES units with double sources (heat and cold sources) for promoting the performance and flexibility of the LHTES units. A transient two-dimensional numerical model using the enthalpy-porosity method is used to study the characteristics of energy transfer during heat storage, heat release, and heat storage-release process in the LHTES unit. The five developed types of compensating fins are well compared. The results illustrated that the unequal-length compensating fins reduced the melting and solidification time by 64.2% and 82.1%, respectively. Moreover, the unequal-length compensating fins increased the heat transfer rate by 155%, and the steady-state time was shortened by 73.3% in the heat storage-release process. Compensating fins configurations effectively improved the thermal performance and flexibility of the LHTES unit.

A heat sink integrating fins within high thermal conductivity phase change material to cool high heat-flux heat sources

Removing heat from heat generating sources at a high heat flux is a serious challenge in many industries, e.g., high power electronics. Towards this end, this numerical study demonstrates the performance of a new heat sink design that integrates high conductivity fins within high thermal conductivity phase change materials (PCM) i.e., Gallium (Ga) metal. The bases of the fins are attached to the bottom heat sink base that receives heat directly from the hot source that requires cooling whereas the upper parts of the fin are exposed to the ambient. Two heat flux levels from the heat source are considered i.e., 3 and 10 W/cm2. A major novelty aspect of this work is rooted in the way fins are installed in the heatsink such that they facilitate creating temperature imbalance between different regions of the molten PCM hence inducing effective natural circulations that lead to clear enhancement in heat removal from the hot sink base. As such, our proposed fins are not merely a way to enhance thermal conductivity of used PCM. In addition to this, they have by far more reaching implications by forming a second heat escape path from the hot base to the outer surroundings, in addition to direct heat transfer from the hot sink base into molten PCM and subsequently to the solid PCM above it. The upper fins parts exposed to the cool ambient surroundings play a crucial role in respect to the above by sucking heat from bottom hotter fin parts. The aforementioned buoyancy-driven circulating motions augmented by induced temperature imbalance caused by the fins smooth out temperature gradients and alleviate peak temperatures at the sink base. The levels of temperatures attained in the presence of the fins were found to be much lower than cases with no fins. The effectiveness of buoyancy was quantified by performing simulations with and without buoyancy effects. The role played by the fins becomes so decisive in limiting peak temperatures especially under the higher heat flux levels.