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Kinetic characteristics of thermal energy storage (TES) using tetrabutylammonium acrylate (TBAAc) hydrate were experimentally evaluated for practical use as PCMs. Mechanical agitation or ultrasonic vibration was added to detach the hydrate adhesion on the heat exchanger, which could be a thermal resistance. The effect of the external forces also was evaluated by changing their rotation rate and frequency. When the agitation rate was 600 rpm, the system achieved TES density of 140 MJ/m3 in 2.9 hours. This value is comparable to the ideal performance of ice TES when its solid phase fraction is 45%. UA/V (U: thermal transfer coefficient, A: surface area of the heat exchange coil, V: volume of the TES medium) is known as an index of the ease of heat transfer in a heat exchanger. UA/V obtained in this study was comparable to that of other common heat exchangers, which means the equivalent performance would be available by setting the similar UA/V. In this study, we succeeded in obtaining practical data for heat storage by TBAAc hydrate. The data obtained in this study will be a great help for the practical application of hydrate heat storage in the future.

Microencapsulation of sodium nitrate (NaNO3) as phase change material for high temperature thermal energy storage aims to reduce costs related to metal corrosion in storage tanks. The goal of this work was to test in a prototype thermal energy storage tank (16.7 L internal volume) the thermal properties of NaNO3 microencapsulated in zinc oxide shells, and estimate the potential of NaNO3–ZnO microcapsules for thermal storage applications. A fast and scalable microencapsulation procedure was developed, a flow calorimetry method was adapted, and a template document created to perform tank thermal transfer simulation by the finite element method (FEM) was set in Microsoft Excel. Differential scanning calorimetry (DSC) and transient plane source (TPS) methods were used to measure, in small samples, the temperature dependency of melting/solidification heat, specific heat, and thermal conductivity of the NaNO3–ZnO microcapsules. Scanning electron microscopy (SEM) and chemical analysis demonstrated the stability of microcapsules over multiple tank charge–discharge cycles. The energy stored as latent heat is available for a temperature interval from 303 to 285 °C, corresponding to onset–offset for NaNO3 solidification. Charge–self-discharge experiments on the pilot tank showed that the amount of thermal energy stored in this interval largely corresponds to the NaNO3 content of the microcapsules, the high temperature energy density of microcapsules is estimated in the range from 145 to 179 MJ/m3. Comparison between real tank experiments and FEM simulations demonstrated that DSC and TPS laboratory measurements on microcapsule thermal properties may reliably be used to design applications for thermal energy storage.

Building envelopes are constantly subjected to temperature and moisture gradients. This loading induces a complex response, particularly for highly hygroscopic insulating materials. Latent effects can no longer be neglected for these materials in which heat and moisture transfers are strongly coupled. The purpose of this article is to analyze the behavior of a wood fiber insulation subjected to non-isothermal loading under a vapor concentration gradient. An experimental setup and a mathematical model of hygrothermal transfer were developed to analyze the behavior of the wall. The mathematical model describes the main physical phenomena involved, notably water vapor adsorption and the dependence of thermophysical properties in state variables. The experimental setup developed allows studying a wall under controlled conditions. The temperature and relative humidity profiles within the wall were measured. The evolution of the profiles with time suggests that the adsorption of the water vapor occurs together with the redistribution of liquid water within the envelope. The comparison of the experimental results with the numerical model shows good agreement although the prediction can be improved during the transient phase. The comparisons of these results with a purely diffusive thermal transfer model show the limits of the latter and permit quantifying the latent effects on the total heat transfer.

Energy storage pile foundations are being developed for storing renewable energy by utilizing compressed air energy storage technology. Previous studies on isolated piles indicate that compressed air can result in pressure and temperature fluctuations in the pile, which can further affect safety of the pile foundation. Meanwhile, the temperature changes and distributions for the pile and surrounding soil also are influenced by adjacent piles in typical group pile constructions. Therefore, dynamic thermal transfer simulations were conducted in this paper to investigate the temperature changes and distributions in the concrete pile and surrounding soil for group pile construction. The main parameter in this study is the spacing of the piles. The analysis results show that the group pile effect significantly increases the temperature up to more than 100 &deg, C depending on the location and changes its distribution in both concrete and soil due to the heat transferred from the adjacent piles. The final stabilized temperature can be as high as 120 &deg, C in the concrete pile and 110 &deg, C in the soil after numerous loading cycles, which is about 4 times higher than typical thermo-active energy pile applications. Thus, it is important to include the group pile effect for design and analysis of the energy storage pile foundation.

Over the years, solar collecting systems have gained interest in renewable energy. This study investigated improving the efficiency of the working fluid in thermal solar systems by using nanofluids with three concentrations of alumina, 0.1, 0.3, and 0.5 wt%. The UV-vis absorbance, electronic conductivity, and thermal transfer properties of the nanofluids were analyzed, and the thermal changes with exposure to solar radiation in an experimental collector system were measured by pyranometer. The electronic conductivity, thermal conductivity, and UV-vis absorbance increased with the alumina concentration. Moreover, the temperatures of the nanofluids increased more under solar irradiation than that of distilled water. This implies that the alumina nanofluids absorb solar energy more efficiently than water. The findings of this study suggest that the use of both alumina nanofluids and nanoparticles will improve the efficiency of thermal solar power systems.

Tunable mid-infrared lasers are widely used in laser spectroscopy, gas sensing and many other related areas. In order to solve heat dissipation problems and improve the environmental temperature adaptability of solid-state laser sources, a tunable all-fiber laser pumped optical parametric oscillator (OPO) was established, and a compact thermal control system based on thermoelectric coolers, an automatic temperature control circuit, cooling fins, fans and heat pipes was integrated and designed for the laser. This system is compact, light and air-cooling which satisfies the demand for miniaturization of lasers. A mathematical model and method was established to estimate the cooling capacity of this thermal control system under different ambient environments. A finite-element model was built and simulated to analyze the thermal transfer process. Experiments in room and high temperature environments were carried out and showed that the substrate temperature of a pump module could be maintained at a stable value with controlled precision to 0.2 degrees, while the output power stability of the laser was within ±1%. The experimental results indicate that this compact air-cooling thermal control system could effectively solve the heat dissipation problem of mid-infrared solid-state lasers with a one hundred watts level pump module in room and high temperature environments.