套管式地埋管换热器热短路及换热性能

Thermal short-circuiting and heat transfer performance of coaxial borehole heat exchanger

套管式地埋管换热器是深层地源热泵系统常用的换热装置。基于流体流动换热方程,建立套管式地埋管换热器与周围岩体之间的传热模型。以第一个供暖季为例,分析内管导热系数和循环水流量对换热性能的影响,并引入换热器效能对热短路现象进行评估,研究结果显示:内管导热系数越大,热短路现象越显著;热短路使内外管中循环水温差降低,管内出现热堆积,导致换热器换热功率降低;套管式地埋管换热器的换热功率随循环水流量的增大逐渐增大;内外管之间存在热短路时,出口水温随循环水流量的增大先升高后降低,随着流量增大,换热器效能增大。研究成果可为深层地源热泵系统中地埋管换热器的设计提供借鉴。

The coaxial heat exchanger is a commonly used device for deep ground source heat pump systems.Based on the fluid flow heat transfer equation,the coupled heat transfer model of the coaxial heat exchanger and the surrounding rock mass is established.Taking the first heating period as an example,the influence of the inner tube thermal conductivity and circulating water flow on the heat transfer performance was analyzed,and the heat exchanger efficiency was introduced to evaluate the thermal short-circuiting phenomenon.The following conclusions were obtained:The phenomenon of thermal short circuit becomes obvious with the increase of the thermal conductivity of the inner tube.The thermal short-circuiting causes the temperature difference of the circulating water in the inner and outer tubes to decrease and the heat accumulation in the tube,resulting in a decrease in the power of the heat exchanger.The heat transfer power of the coaxial heat exchanger increases with the increase of circulating water flow.When there is a thermal short-circuiting between the inner and outer tubes,the outlet water temperature increases first and then decreases with the increase of the circulating water flow rate.As the flow rate increases,the heat exchanger efficiency increases.