地热井下换热器传热性能的实验模拟研究

AN EXPERIMENTAL SIMULATION ON HEAT TRANSFER CHARACTERISTICS OF A DOWNHOLE HEAT EXCHANGER

对基于井下换热器的模拟装置进行实验研究。井下换热器为U型铜管,采用装有35mm玻璃珠的方形箱体模拟渗透性含水层。通过改变U型管和井筒的几何参数实现不同尺寸的井、管配合,研究了U型管换热器入口水温、流量、含水层渗流速度等参数对井下换热器热输出的影响,得到了包括以上因素的井下换热器传热实验关联式。结果表明:与渗流速度相比,含水层热储与U管入口之间的温差是影响热输出的主要因素;热输出总量与该温差并非为线性关系,两支管外侧的平均对流换热系数在中等温差下达到最大值,而增加U型管内水流速可进一步提高外侧表面平均传热系数。

The heat transfer characteristics of a downhole heat exchanger （DHE） were studied experimentally in a laboratory scale. The permeable aquifer was simulated by using a rectangular tank filled with glass beads of diameter ranging from 3mm to 5mm. The downhole heat exchanger was modeled by a U-shaped copper tube. We have simulated various configurations of DHE by changing the geometrical parameters of U-tube and downhole, and different operating conditions at various inlet water temperatures, mass flow rates through the DHE. In addition, the experimental system was specially designed that capable of simulating an aquifer with flowing water. The results showed that the temperature difference be- tween the reservoir and the inlet water of U-tube is a dominant factor on heat extracted. However, the total amount does not necessarily follow a linear relation. The mean outside heat transfer coefficient of the two legs can achieve a maximum value at a moderate temperature difference.