Summary For the sake of enhancing the heat storage tank performance, the thermal characteristics and structural improvement of a water tank equipped with phase change material (PCM) were explored in this paper. The influence of PCM on the performance of the tank under conditions was experimentally analyzed, and the optimal working condition is determined by comparing the difference in effective heat storage rate under different inlet flow rates and the temperature of the water. The concept of “heat transfer blind zone” is introduced and analyzed, and the temperature and velocity field in PCM tanks with different structures are numerically compared. The results show that the addition of PCM makes the discharging time and effective water supply increase by 12.0% and the charging time increase by 6.0%. As the inlet flow rate and temperature of water rise, the thermal storage capacity reduces, and the effective heat storage rate rises first and then drops. The PCM tank has the optimum performance at the inlet water temperature of 70°C and the inlet flow rate of 15 L/h. The inlet and outlet setting up and down has the best effect on eliminating the “heat transfer blind zone” in the water tank. The research results have a good reference value for the design and realistic operation of the phase change heat storage tank.

The topology optimization is considered to enhance the strength, stiffness, and specific energy absorption of a quasi-honeycomb sandwich structure since it can achieve the optimal distribution of materials. However, the existing material interpolation models do not make the topology structure have good clarity and stability. In the present study, a novel variable-density topology optimization based on an improved interpolation model is developed for the design of a quasi-honeycomb core. The combined cells are circularly spreading outward from the geometric center of the design domain, and the wall thickness function of the equivalent cell (i.e. a simplified model of the combined cell) is established on the basis of relative density. The SR material interpolation model is modified by adding the minimum elastic modulus term, fitting the weighting and penalty factors, and adopting the volume constraint of Bi-directional Evolutionary Structural Optimization (BESO). The optimization is conducted to minimize the compliance of the quasi-honeycomb core, in which the relative densities of equivalent cells are chosen as the design variables due to the mapping between topology elements and equivalent cells. The three-dimensional (3D) geometric models of original and optimized quasi-honeycomb cores, upper face sheets, and lower face sheets are built using SolidWorks and printed on a 3D printer. The deflection, strain, bending stiffness, and energy absorption under different material retention rates, restraint positions, and face sheet thicknesses are investigated by three-point bending tests. It is found that the improved SR material interpolation model is efficient for suppressing the grid dependence and checkerboard, and the mechanical properties of optimized quasi-honeycomb sandwich structures are significantly enhanced in comparison with original structures, confirming that the developed method provides important guidance for designing and optimizing the quasi-honeycomb sandwich structure.

There is a good application prospects in improving the performance for the heat storage system with Multiple phase change materials (PCMs). This article aims to evaluate the performance of multiple PCMs with reasonable PCM proportion from the perspective of entransy. A two-dimensional mathematical model of phase change heat storage unit is established, and verified experimentally. Two indicators, entransy dissipation rate and dissipation factor, are proposed with entransy theory to evaluate the heat storage performance. The influence of the PCM proportions, heat transfer flow (HTF) inlet temperature and flow rate on the performance are explored. Results indicate that the multiple PCMs with the PCM proportion of 2/3/4 is the most optimal. And with the increase of HTF inlet temperature and flow rate, the dissipation factor decreases at first and then increases. So there is also an optimal HTF inlet temperature and flow rate, which is 343 K and 0.0005 m/s respectively. The present research has guiding value for the performance improvement of the device using multiple PCMs.