制冷工况相变能源桩热交换规律

Heat exchange behavior of the phase change energy pile under cooling condition

相变材料是一种通过改变材料物态来吸收或放出潜热的物质。将其用于能源地下结构中可以增加结构体的能量密度、提高换热量,从而减小热交换所需的地下空间资源。该文搭建了缩尺模型实验系统,其中模型圆桩为相变储能混凝土能源桩,桩直径0.2 m,桩长1.5 m,将桩埋入装有饱和砂土的尺寸为2.45 m×2.45 m×2 m的模型箱中。实验中控制换热流体温度恒定为5.5℃,分别进行了0.15、 0.30和0.45 m^3/h 3组不同流量的制冷工况,每种工况包括"制冷-回温"3次循环。研究了饱和砂土中相变能源桩的温度热响应和换热量,分析了桩与周围土体的温度随时间变化规律;比较了换热流体流量对能源桩换热量的影响。研究结果表明:制冷工况下,相变能源桩在饱和砂土中的热传递主要沿径向,在热交换过程中对于桩周土体的温度影响范围约为2倍桩径。换热流体流量增大,进出口温差减小,而热量增大。

Phase change materials which absorb large amounts of heat can be used as backfill material around heat transfer piles to improve the heat transfer efficiency and reduce the underground space required by the heat transfer piles. This paper describes a scale model test of a 0.2 m diameter and 1.5 m long concrete phase-change energy storage pile. The pile was buried in saturated sand in a 2.45 m × 2.45 m× 2 m box. The heat transfer fluid temperature was kept constant by a temperature controller. The three tests used flow rates of 0.15, 0.30 and 0.45 m^3/h. Each case included three cooling-heating cycles. The tests measured the thermal response and the heat transfer rates to the phase change energy pile including the pile-soil temperature differences for various flow rates and the influence of the flow rate and the flow temperatures on the heat transfer capacity of the phase change concrete pile. The results are compared with the heat transfer capacity of an ordinary concrete pile. Cooling test results show that the heat transfer to the phase change energy pile in the saturated sand is mainly in the radial direction with the sand temperature influenced over an area about twice the pile diameter as the heat transfer approached steady state. The temperature difference between the system inlet and outlet decreased as the heat transfer capacity of the phase change pile increased with increasing flow rate.