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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]

• Pumped two-phase loop (PTL) integrated with thermal storage (LHS) is proposed. • Thermal response behaviors of PTL-LHS under step heat load are investigated. • Fast tracking and delay response is sequentially observed as heat load increases. • Thermal response behavior regime diagram is quantitatively recognized. • Variable flow rate optimization strategy is validated by comparative experiments. Pumped two-phase loop integrated with thermal storage is an emerging solution for the short-term high-heat-flux cooling. The transient microchannel boiling heat transfer of pumped two-phase loop (PTL) integrated with latent heat storage (LHS) under step heat load are experimentally investigated, with special focuses on dynamic thermal response of two-phase loop and latent heat storage unit. The transient thermal behaviors of PTL-LHS are determined based on the wide variations of heat load and flow rate. A thermal behavior regime diagram is proposed to quantitatively recognize the transient thermal response of PTL-LHS, depending on the heat load and flow rate. The results indicate that the fast tracking mode and the delay response mode are observed and sequentially experienced for PTL-LHS as the step heat load increases. With respect to delay response mode, thermal storage efficiency is high with short thermal storage duration but cooling performance is insufficient, while the transient thermal performances are contrary under the fast tracking mode. The increase of heat load accelerates the transformation of the heat transfer mechanism in LHS from sensitive-heat-dominated to latent-heat-dominated, while increasing flow rate is conducive for the enhancements of thermal capacity and thermal stability of PTL-LHS. Increasing heat load brings about a larger critical flow rate of the transient thermal behavior regime transition, and hence the range of flow rate tends to be larger for the delay response mode. Particularly, the proposed variable flow rate optimization strategy is validated by comparative experiments, showing better cooling performance (the average evaporator wall temperature decreases by 10 °C) and more remaining load of phase change material. [Display omitted] [ABSTRACT FROM AUTHOR]

The present research conducts an experimental study on the thermal performance of the finned metal foam (FMF) heat sinks with phase change material. The dynamic temperature response of an FMF heat sink is analyzed and compared with the corresponding finned heat sink. The effects of porosity and pore density on the thermal performance of FMF heat sinks are analyzed. Furthermore, the enhancement ratio and heat exchange capability are evaluated for the optimization of FMF heat sinks. The results indicate that the thermal conduction enhancement caused by the addition of metal foam exceeds the heat transfer loss arising from the suppression of natural convection. A decrease in porosity leads to an increase in heat exchange capability and contributes to a higher enhancement ratio. Considering the tradeoff between the low operating temperature and longer duration of reliability, the porosity of 0.9 is the best choice for FMF heat sinks. Though the porosity is identical, the thermal performance of an FMF heat sink is better with the increase of pore density. Considering the maximum energy charging capacities are identical, the FMF heat sink with larger pore density is recommended for practical engineering applications. [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]

Latent heat thermal storage (LHTS) using phase change materials (PCMs) faces a significant challenge of poor heat transport efficiency. Fortunately, nature has evolved numerous features and functions that can enhance material properties and heat transport efficiency. This paper provides a comprehensive review of bionic studies on LHTS technology, summarizes bionic strategies for improving LHTS performance, and explores in detail the research progress and challenges faced by bioinspired PCMs and LHTS configurations. The review demonstrates that natural morphology, structure, and function can improve heat charge/discharge efficiency. However, current research mainly focuses on simple configurations of morphological and structural bionics, so more attention is needed to develop high-level functional bionics to maximize LHTS performance. The paper also emphasizes the enhancement methods of heat transfer rate in bioinspired LHTS systems, such as synthesizing bionic hierarchical porous and three-dimensional networks, constructing biomimetic shells, extending the heat exchange area, enhancing the convective heat transfer, and optimizing the heat transport path in PCM regions. Importantly, future research should focus on micro/nano-scale bionics to construct bioinspired PCM and LHTS configurations with more advanced performance. Moreover, a complete enhancement mechanism of multiscale phase-change heat transport needs to be investigated for the development of multiscale biomimetic LHTS technology. • Bionic optimization is deemed to be a pathway for highly efficient heat storage. • Bionic strategies include morphology, structure, and functional bionics. • Bioinspired materials and configurations facilitate thermal storage efficiency. • Multiscale bionic on latent heat storage is the most promising development direction. [ABSTRACT FROM AUTHOR]

A model of vapor condensation on a solid surface is developed and numerically analyzed using the free-energy lattice Boltzmann method. Based on the model, the condensation phase change on hydrophobic, hydrophilic and gradient surfaces are simulated with a particular focus on the condensation on a gradient surface. The droplet nucleation, growth, deformation, coalescence and motion during the condensation on a gradient surface are investigated. The present simulation reproduces the self-propelled dropwise condensation on a gradient surface, the film condensation on a hydrophilic surface and the conventional dropwise condensation on a hydrophobic surface. The results indicate that the condensed droplets on a gradient surface can be swept in time to provide a favorable condition for the subsequent condensation. On a smooth gradient surface, owing to the unbalanced wetting force, the vapor condenses into a thin film firstly and then fractures into droplet nucleation as the condensation process goes on. The larger wettability gradient results in a larger amplitude oscillation of condensation rate and a slighter variation of surface coverage. [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 Sierpinski fractal is introduced to construct the porous metal foam. Based on this fractal description, an unsteady heat transfer model accompanied with solidification phase change in fractal porous metal foam embedded with phase change material (PCM) is developed and numerically analyzed. The heat transfer processes associated with solidification of PCM embedded in fractal structure is investigated and compared with that in single-pore structure. The results indicate that, for the solidification of phase change material in fractal porous metal foam, the PCM is dispersedly distributed in metal foam and the existence of porous metal matrix provides a fast heat flow channel both horizontally and vertically, which induces the enhancement of interstitial heat transfer between the solid matrix and PCM. The solidification performance of the PCM, which is represented by liquid fraction and solidification time, in fractal structure is superior to that in single-pore structure. [ABSTRACT FROM AUTHOR]

Abstract: Based on the enthalpy-porosity technique, a model of thermal conduction accompanied with solidification and melting processes is developed and numerically analyzed to investigate the thermal response of the brick wall filled with phase change materials (PCM). The thermal response, which is represented by indoor wall surface temperature response, of brick wall filled with PCM is evaluated and compared with that of solid brick wall. The effects of PCM filling and its filling amount on thermal response of brick wall are investigated and discussed. It is indicated that, compared to the common solid brick wall, the thermal storage of brick wall filled with PCM is elevated by the alternate process of melting and solidification under fluctuating outdoor temperatures. The use of PCM in the brick walls is beneficial for the thermal insulation, temperature hysteresis and thermal comfort for occupancy. In addition, with the increasing filling amount of PCM, the fluctuation of indoor wall surface temperature is significantly smoothed. Correspondingly, the hysteresis in response to the outdoor temperature fluctuation is enhanced. Moreover, the present model is verified by experimental data available in the literature. [Copyright &y& Elsevier]

• Ice storage process with natural convection is numerically studied and verified. • Natural convection is negatively related to the ice storage performance. • Buoyancy reversal induces the intensification of natural convection. • Optimization of shell-tube ice storage units is performed by Taguchi method. • Fin height is the dominated factor to the overall ice storage performance. The present paper reports on a numerical study of the ice storage process in finned shell-tube ice storage (STIS) units, with a focus on the special solidification behavior using water as the phase-change material (PCM). The proposed model is experimentally verified using an energy-discharging process in an ice storage unit. The effects of natural convection and buoyancy reversal on the solidification behavior are examined and investigated. Moreover, the Taguchi method is utilized to optimize the fin geometry of STIS units. The results indicate that the natural convection and buoyancy reversal are negatively correlated with the ice storage performance. An increase of the superheat factor leads to the enhancement of the buoyancy reversal intensity, which is not conducive to the acceleration of the solidification rate. In addition, the increases in fin height, fin width, and fin number are positively correlated with ice storage performance. It is demonstrated that the fin height is the dominant factor affecting the overall ice storage performance, and it is independent of the superheat factor. From the perspective of trade-off between ice storage rate and ice storage capacity, the optimal fin parameters for the STIS unit are fin height H = 40 mm, fin number N = 10, fin width Δ = 3 mm for engineering applications. [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]

• Gradient fins are introduced to enhance melting performance of LHS units. • Geometric structure of gradient fin are optimized by response surface method. • Coordination between natural convection and thermal conduction is achieved. • Optimal gradients of fin thickness and central angle are 1.846 mm and 14.96°. • Complete melting time of optimal latent heat storage unit is reduced by 30.5%. Latent heat storage (LHS) is critical for the large-scale utilization of sustainable energy. The present paper designs the gradient fins (i.e., fins with gradient thickness and gradient central-angle) to enhance the melting performance of a LHS unit. A two-dimensional model of the melting heat transfer process for phase change material with Paraffin wax RT58 in a finned LHS unit is developed and numerically solved to investigate the melting behaviors. The melting front evolution and the dynamic temperature distribution are analyzed, and the effects of natural convection, fin layout, and Stefan number are investigated as well. Moreover, the fin configuration is optimized by the response surface method (RSM) with the objective function of the complete melting time. The results indicate that the natural convection seriously affects the melting behaviors in LHS units, and the melting rate is improved by 180% as compared with the case without natural convection. The LHS unit with gradient fins has a faster melting rate and a more uniform temperature distribution due to the enhancement in heat transfer synergy between natural convection and thermal conduction. Moreover, the increase of Stefan number leads to a faster melting rate and a shorter complete melting time. The RSM optimization indicates that the optimal gradients of fin thickness and central angle in this paper are 2.846 mm and 14.96°, respectively, and the complete melting time is reduced by 30.5% for the optimized LHS unit as compared with the corresponding uniform fin. Therefore, the gradient fins are recommended to be configured in a LHS unit in the engineering applications, where the fins are distributed with gradient angle, and they are thinner at the upper part and thicker at the lower part. [ABSTRACT FROM AUTHOR]