• Energy Research

Abstract This paper reports on a novel phase change material macrocapsule for thermal energy storage, which can be dynamically and repeatably remodeled as needed to a complicated shape with large-scale deformation. In addition, it effectively eliminates the stress mismatch, induced by the volumetric expansion (or shrink) of the phase change material during melting (or solidification), through the self-adaptative deformation of the coated flexible shell. The shape-remodeled macrocapsule, consisting of octadecanol as the core and the silicone elastomer for encapsulation, was prepared through a cast molding method. The high-concentration microparticles of low-melting Bi-In-Sn eutectic alloys were embedded into elastic shell for significantly enhancing its latent heat storage and heat conductivity. The prepared macrocapsule has a high latent heat density of 210.1 MJ/m3, which of the contribution from the shell is about 20%. The thermal conductivity of the macrocapsule core reaches to 1.53 W/m·K with a 428% increase compared with pure octadecanol. The flexible shell attains a high thermal conductivity of 1.98 W/m·K with an 890% increase compared with pure silicone, which also remains a high stretchability with 432% strain. The performance of shape remodeling, energy storage capacity, and heat charging and discharging rates of the macrocapsule were demonstrated in detail. The applications of the prepared macrocapsule as thermal management for the flexible electronic devices and the thermal storage for thermoelectric energy harvesting were also investigated. The present study opens the way for further development of elastic phase change material capsule applications in energy storage systems and thermal control engineering.

Here we report an active method to enhance the thermal performance of phase change material (PCM) based on magnetically-stirring method. The magnetic bead with small size embedded in the container filled with octadecanol, is driven to rotate by rotating magnetic field, and induce the forced convective heat transfer of the liquid octadecanol. We investigate the impact of rotating magnetic velocity, magnetic bead size, the distance between magnetic bead and rotating permanent magnet on the surface temperature of the simulated heating plate. The experimental results indicated that magnetically stirring obviously improve the heat transfer from liquid phase to solid phase of octadecanol and make simulated heat source keep a lower and smoother temperature platform. We also find that the best condition point could be determined by matching the rotation velocity for the given size of magnetic bead. These results are expected to provide insights into the design and optimization of latent heat thermal energy storage systems. Keywords: Phase change material, Magnetically stirring, Heat transfer, Energy storage technology

Abstract For cooling system, liquid metal (LM) have attracted many attentions as an excellent coolant. In this study, we propose a superior liquid metal cooling blade dissipator with twin stage electromagnetic pumps (EMPs), whose thinnest dimension was only 4 mm. The coupling model is utilized to solve the distribution of Lorentz force and the field of velocity and temperature simultaneously in the COMSOL multi-physics software, and the validity of numerical model was verified by experimental data. It is demonstrated that the efficiency of twin stage EMPs was obviously higher than that of single stage of EMP at the same input power theoretically. The Nusselt number at the heater is calculated under the different driven current and heating power. It has been found that there was no obvious change for Nusselt number. Also it can be concluded that the superior property of suppressing thermal shock and high performance-cost ratio were presented.

Abstract In this paper, the low melting point metal phase change material (PCM) heat sink for coping with ultra-high thermal shock (10 2 W/cm 2 ) is developed and optimized theoretically and numerically. Gallium is selected as the best PCM candidate from the point of view of thermal performance based on an approximate theoretical analysis, and gallium based PCM heat sink with internal copper fin is configured. Different fin structures, namely plate fin, crossed fin and pin fin are investigated and compared; the effects of fin number, fin width and base thickness are parametrically studied; the influence of the structural material is briefly discussed. For arbitrarily given heating condition, the optimal geometric configuration of the heat sink is suggested and corresponding thermal performance is provided. The proposed low melting point metal PCM heat sink can cope with very large thermal shock like 100 W/cm 2 (1 s) with maximum device temperature of 46 °C, under the ambient temperature of 25 °C, which is extremely difficult to deal with otherwise by conventional PCMs. The conclusions drawn in this paper can serve as valuable reference for thermal design and analysis of PCM heat sink against ultra-high thermal shock.

AbstractPhase change materials have attracted significant attention due to their promising applications in many fields like solar energy and chip cooling. However, they suffer leakage during the phase transition process and have relatively low thermal conductivity. Here, through introducing hard magnetic particles, we synthesize a kind of magnetically tightened form-stable phase change materials. They achieve multifunctions such as leakage-proof, dynamic assembly, and morphological reconfiguration, presenting superior high thermal (increasing of 1400–1600%) and electrical (>104 S/m) conductivity, and prominent compressive strength, respectively. Furthermore, free-standing temperature control and high-performance thermal and electric conversion systems based on these materials are developed. This work suggests an efficient way toward exploiting a smart phase change material for thermal management of electronics and low-grade waste heat utilization.

Abstract In this paper, a finned heat pipe assisted passive heat sink based on a newly emerging high performance phase change material (PCM), the low melting point metal (LMPM), was developed for thermal buffering of high power electronics which works intermittently with heat generation rate up to 1000 W (10 W/cm2). Firstly, thermal performances of the PCM heat sink under different thermal shocks (from 200 W to 1000 W) were experimentally evaluated, in comparison with that of an organic PCM which has similar melting point. It was found that, the former one can prolong the working duration 1.4–2.4 times that of the latter one. Then, the performance of the heat sink was improved through reducing the contact thermal resistance and by increasing the fin number. Furtherly, an air cooling radiator was configured to accelerate the solidification process of the PCM module, which makes it capable of maintaining its highest temperature below 85 °C under 1000 W periodic thermal shock (10 min on and 15 min off). Moreover, energy dispersive spectrometer (EDS) analysis was conducted to verify the compatibility of the LMPM PCM and the structural materials. Finally, a simplified numerical model was developed and validated for the currently constructed finned heat pipe assisted LMPM PCM heat sink, which can be much helpful for future practical thermal design and optimization of this kind of thermal buffering module.