Study on Latent Heat Storage by Using Paraffin Wax-Water Emulsion

为了有效利用太阳能热能和低质量能源，需要一种储能手段。研究中的一种方法是利用固液相变的潜热来蓄热。众所周知，石蜡具有作为储热相变材料的理想特性。另一方面，石蜡也有一些不理想的性质，如：1)导热系数低；2)由于空气在液相中的高溶解度，相变时体积变化较大。两者都导致充放电过程中传热速率低。为了改善这一问题，有人建议使用金属填料、翅片和胶囊。然而，这些技术并不总是有效的。在本研究中，我们考虑使用石蜡-水乳液作为一种新的储热材料，它具有固相流动性和较高的导热系数和熔合热。采用壳管式蓄热器对两种乳化液和水进行了充放实验，并以水为参比。在不同的流动方向、质量流量和工质入口温度条件下，测量了储热材料和工质的温度随时间的变化。评估和比较了充电焓和放电焓。结果表明，乳化液是一种适合的有效的储热材料。明确了操作条件对充放电特性的影响。

In order to use solar thermal energy and low-quality energy effectively, a means of energy storage is required. One method under study involves heat storage in the latent heat of solid-liquid phase change. It is known that paraffin waxes exhibit desirable characteristics as a phase change material for heat storage. On the other hand, paraffin waxes have some undesirable proper-ties such as: 1) low thermal conductivity, 2) relatively large volume change in phase change due to the high solubility of air in the liquid phase. Both give rise to the low heat transfer rate in charging and discharging processes. To improve this problem, it has been proposed to utilize metallic fillers, fins, and capsules. However, these techniques are not always effective.In the present study, we considered to use paraffin wax-water emulsion as a new heat storage material, which has fluidity in solid phase and relatively high thermal conductivity and fusion heat. The experiments of charging and discharging for two kinds of emulsion and water as a reference were performed by using a shell-and tube type heat storager. Time-changes of temperature of heat storage material and working fluid were measured under varied conditions of flow direction, mass flow rate, and inlet temperature of working fluid. Enthalpies charged and discharged were evaluated and compared. As a result, it was found that emulsion is a suitable and effective heat storage material to enhance heat transfer. Effects of operation condition on characteristics of charging and discharging were made clear.