非饱和黏土地层中相变能源桩热性能测试

Measured thermal characteristics of a phase change energy pile in unsaturated clay

采用钢球封装相变材料替换混凝土中粗骨料能够增加能源桩桩体的能量密度、提高换热量,从而减小热交换所需的地下空间资源。该文通过模型试验对非饱和黏土地层中的普通混凝土和相变储能混凝土能源桩进行冷热加载,对比研究了其热响应特性和对桩周土体的影响。试验结果表明:在冷热加载的热交换过程中,相变桩体周围土体传热主要范围约为1.5倍桩径,相变桩的换热管进出口温度变化大于普通桩,说明相变桩热交换效率高于普通桩;相变桩与普通桩在制热阶段的温差小于制冷阶段的温差,说明制冷加载在相同循环工况下的换热效率大于制热加载;在制冷过程中相变材料的加入加大了桩内竖向和横截面温度分布的不均匀性,在温度荷载作用下正常固结非饱和黏土地基产生明显的固结排水,发生不可恢复的沉降变形。

The use of a phase change material(PCM) encapsulated in a steel ball in place of the coarse aggregate in concrete can improve the energy density and heat transfer in the energy pile which will reduce the underground space needed for the heat transfer. Cooling-heating loads are used in a traditional concrete energy pile and a PCM energy pile in a container containing unsaturated clay to experimentally study the thermal response of the piles and surrounding soil. The results show that the temperature influence range in the soil surrounding the phase change pile extends out to about 1.5 times the pile diameter during the cooling-heating processes with a larger temperature difference between the PCM energy pile inlet and outlet than with the traditional concrete energy pile, which indicates a larger heat transfer rate. The temperature differences in both the PCM pile and the traditional pile during heating are less than during cooling which shows that the heat transfer rates during cooling are larger than during heating for the same flow conditions. The results also show that the PCM increases the uneven temperature distribution during the cooling in the vertical and horizontal directions in the pile. In addition, irreversible settling of unsaturated clay is observed at the soil surface due to temperature induced soil consolidation and drainage.