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The venation-finned porous network has been demonstrated as a promising method to maximize the thermal transport access. To improve the heat storage efficiency, an innovative venation-finned porous network is employed here to enhance the melting performance of phase change materials (PCMs). The venation-finned porous network is quantitatively described by Murray's law and Voronoi method, and a modified thermal lattice Boltzmann model of PCM melting processes in a square cavity is developed and numerically analyzed to optimize the venation-finned porous network. The melting performance of composite PCMs with three configurations (venation fin, porous network and venation-finned porous network) are compared and analyzed. Moreover, the effects of branching angle and Murray coefficient on melting performance are comprehensively studied. It indicates that venation-finned porous network is favorable to melting performance improvement due to venation's inherent efficient heat transfer paths. Compared to venation fins and porous networks, the melting duration time of venation-finned porous networks is reduced by 78.4% and 21.4%, respectively. Furthermore, the branching angle of 45 ∘ and Murray coefficient of 3 are suggested for maximizing the melting efficiency. Importantly, the melting mechanism is conduction and convective conjugated heat transfer in composite PCMs with venation fins, however, it is dominated by heat conduction for those with porous networks or venation-finned porous networks. [ABSTRACT FROM AUTHOR]

Summary: The performance enhancement of latent heat storage (LHS) units is of great consequence for the development of sustainable energy. In this article, the transient models of phase‐change heat transfer processes in LHS units with consideration of natural convection are developed and numerically analyzed, in an effort to explore the role of the fractal tree‐shaped fin in the energy charging performance. The solid‐liquid interface evolution and dynamic temperature response in the tree‐shaped finned LHS unit are presented and compared with the wheel‐shaped one. Moreover, the influence of the fin number is investigated for maximizing the energy charging performance. The results indicate that the tree‐shaped fin has merits of effective layout optimization for the point‐to‐area heat transfer and the time‐coordination of energy charging and discharging process. Compared with the wheel‐shaped fin, the melting duration time is decreased only a little for the presence of tree‐shaped fin, however, the solidification process is decreased significantly. The presence of tree‐shaped fin leads to a lower energy charging rate during the early and middle stages of the charging process due to the natural convection suppression, however, the energy charging rate is faster during the later stage due to the thermal conduction dominated interior heat transfer. For maximizing the melting performance, the appropriate fin number in practical applications is 16. [ABSTRACT FROM AUTHOR]

The fractal geometry provides a new insight for the description for actual pore structure of metal foams. In this paper, the fractal grids are introduced to describe the pore structure of metal foams. A two-dimensional unsteady melting model of phase change material (PCM) in the cross-fractal metal foam is developed and numerically simulated. The transient temperature variation and melting front evolution during the charging process in the cross-fractal metal foam are analyzed. The effects of initial temperature difference, porosity and fractal dimension on the melting heat transfer in fractal metal foam are examined and analyzed. The results indicate that the temperature distribution is more uniform and the melting rate is faster in the cross-fractal metal foam compared with that in the corresponding cavity structure. Interestingly, the fractal metal foam with smaller fractal dimension provides a faster heat flow path and hence enhances the melting performance though the porosity is identical. The melting performance in fractal metal foam can be enhanced when the metal foams have a lower porosity, a smaller fractal dimension and a larger initial temperature difference. [ABSTRACT FROM AUTHOR]

• LHS is proposed to enhance thermal performance of AGHP under intermittent heating. • Thermal performance of AGHPs with three LHS modes are experimentally investigated. • Introduction of LHS unit into AGHP reduces the temperature of heat source by 27.4%. • The presence of LHS unit greatly enhances the thermostat performance of an AGHP. • Temperature homogenization of AGHP & LHS units becomes worse as heat load increases. Heat pipe coupled with phase change material (PCM) based latent heat storage (LHS) is a significant thermal management system that can efficiently control the intermittent high heat loads of electronic devices. Herein, an axially grooved heat pipe-LHS (AGHP&LHS) system has been proposed. The influence of LHS units and their location on dynamic temperature response of AGHP has been investigated both experimentally and theoretically. The effect of filling rates of phase change materials (PCMs) as well as cooling temperature on thermal response of the AGHP has been compared and analyzed. Results indicate that the LHS effectively stabilizes the heat source temperature under the intermittent heating process, enhances the thermostat performance and brings the temperature uniformity in AGHP. In addition, LHS units arranged at the evaporator section are optimal for AGHP under intermittent heat load conditions, reducing the heat source temperature by 27.4% and prolonging the melting time by 81.5%. As the heat load increases, the melting time of AGHP&LHS system becomes shorter, and the overall temperature uniformity is worsened. In particular, the melting time is prolonged by 34.8% for AGHP&LHS system with PCM filling rate of 89% than that of 44% filling rate. [ABSTRACT FROM AUTHOR]

The fractal Brownian motion is introduced to describe the pore distribution of porous metal foam. By the fractal description, a model of melting heat transfer for the phase change material (PCM) is developed and applied to investigate the melting behaviors in porous metal foam with a particular focus on the role of pore distribution. The dynamic response of temperature and the evolution of melting front are presented. The effects of porosity and fractal dimension on the melting heat transfer are all examined and investigated. In addition, an experiment of melting heat transfer is performed to verify the present model. The results indicate that the porous metal foam is of significance for the enhancement of melting heat transfer. When compared with PCM alone, the melting process in porous metal foam possesses the larger melting rate, the faster evolution of melting front and the higher liquid fraction. Unlike the PCM alone, the melting front is no longer continuous and many independent solid-liquid interfaces are formed inside pores owing to the interstitial heat transfer. Interestingly, the melting phase change is also affected by the fractal dimension even though the porosity is identical. A porous metal foam with smaller fractal dimension is beneficial for the melting heat transfer. [ABSTRACT FROM AUTHOR]

• Buoyancy-driven melting/solidification performance with different PCMs is studied. • Thermal expansion and contraction properties of PCMs affect the natural convection trend. • Downward and upward flow modes have opposite effects on PCM phase change performance. • Suitable non-uniform fin layout enhances melting but weakens solidification performance. The thermal expansion and contraction property of phase change materials (PCMs) is a significant factor in affecting the buoyancy-driven melting/solidification heat transfer performance in latent heat storage (LHS) units. To reveal the intrinsic mechanisms, a mathematical model of buoyancy-driven melting/solidification processes in finned LHS units is constructed. The phase-change behaviors, thermal transport properties of different PCMs, and roles of heat transfer fluid (HTF) direction and fin layout in melting/solidification performance are explored. The results indicated that when compared to conduction-dominated cases, the buoyancy-driven melting duration of gallium and n-octadecane increases by 1.8% and decreases by 32.6%, respectively, while the corresponding solidification times decrease by 8.4% and increase by 15.2%, respectively. The downward HTF enhances the melting rate of gallium with thermal-contraction properties and the solidification rate of n-octadecane with thermal-expansion properties. Conversely, the upward HTF enhances the melting rate of n-octadecane with thermal-expansion properties and the solidification rate of gallium with thermal-contraction properties. For finned LHS units with upward HTF, the ladder-type and reverse ladder-type fins facilitate the melting performance of n-octadecane and gallium, respectively. Moreover, the ladder fins with non-uniform layouts weaken the solidification performance of PCMs with different thermal characteristics. [ABSTRACT FROM AUTHOR]