The effect of metal wool on the charging and discharging rate of the phase transition thermal storage material

Abstract

Thermal energy storage (TES) plays an important role in solar heat power systems. The use of phase change materials (PCM) and selecting additives to increase the rate of heat accumulation is a promising way to increase the efficiency and reliability of such systems. The objects of the study were pure paraffin wax (PW) and composite PCMs based on it (containing aluminum and copper wool of 30 and 45 μm in diameter, respectively). An experimental setup with a cylindrical measuring cell was created, which was also considered as a model of a capsule with a thermal storage material. The rate of temperature change in the pure PW sample and samples of composite PCMs was experimentally measured. Two modes of heating and cooling were investigated: from 48 to 59 °C (mode with a phase change) and from 30 to 40 °C (mode without phase changes). Heating time from 48 to 59 °C for the PW sample was 13 min., for the PW samples with the content of aluminum wool of 0.00588 and 0.01780 m3·m-3 − 11 and 10.5 min., for the PW samples with the content of copper wool of 0.00524 and 0.01380 m3·m-3 − 11 and 8 min., correspondingly. The minimum heating time from 30 to 40 °C was 6 min. for the sample of PW with 0.01380 m3·m-3 of copper wool in comparison with 9 min. for the sample of pure PW. The expediency of using copper wool as an additive to thermal storage materials of PW to increase the charging and discharging rate of TES devices without significantly raising their price was confirmed. The presence of metal wool in molten PW suppresses bottom-up convective currents, so the main mechanism of heat transfer is thermal conductivity. This fact will contribute to a faster equalization of the temperature field by the height of heat storage capsules

Experimental Investigation of the Effect of Expanded Graphite on the Thermophysical Properties and the Heating and Cooling Rates of Paraffin Wax in Capsule of Thermal-Energy Storage System

“…Experimental setup and measurements method for investigation the temperature-time curve for the capsule with the PCM sample during heating and cooling are described in detail in Ref. [20]. The experimental cell made from copper was considered as model of the capsule for the TES system (Fig.…”

“…The temperature-time dependence for the pure PW was considered in detail in Ref. [20] and then was used as a baseline characteristic to assess the influence of the EG on the composite PCM heating and cooling rates.…”

“…At the reaching the melting point in the centre of the sample, the liquid PW at the top of the cell had an overheated state relative to its melting point. Therefore, after melting the PW in the cell centre, the heat was supplied from the top of the cell to the centre with the currents of the molten PW [20] (Fig. 6).…”

Express Method of Experimental Investigation of the Effect of Carbon Nanostructures on the Caloric Properties of Paraffin Wax

“…However, the low thermal conductivity of PW restricts its thermal performance and limits its large-scale applications. Adding a suitable proportion of high thermal conductivity components into the PW can enhance the heat transfer rate, and thus, improve the thermal efficiency of the whole TES [2,3].…”