中深层地热井换热性能模拟研究

Study on Performance Simulation of Heat Exchanger in Middle and Deep Geothermal Well

结合北方邯郸地区,通过Fluent软件建立中深层地热能井下同轴套管式换热器换热模型,模拟研究了岩土导热系数、内管导热系数、循环流体流量、循环流体入口温度变化对井下同轴套管式换热器换热性能的影响。结果表明:岩土的导热系数从1 W/(m·K)增加到9 W/(m·K),换热器换热量增长约324.53%;内管导热系数从0.5 W/(m·K)增加到4.5 W/(m·K),换热器换热量减少约40.37%;循环流体流量从10 m^(3)/h增加到50 m^(3)/h,换热器换热量增长约103.92%;循环流体入口温度从5℃增加到15℃,换热器换热量减少约23.14%。所以在实际工程中,应在岩土导热系数相对较大的地域开发中深层地热能,选择导热系数较小的内管以及循环流量较大的井下换热器,并保持外管循环流体入口温度较低。

Taking Handan area in northern China as an example,a downhole coaxial heat exchanger(DCHE) model was established by Fluent software for the mid-deep geothermal energy wells,and the effects of thermal conductivities of soil and inner pipes,the flow rate and inlet temperature of circulating fluid on the heat transfer performance of DCHE were simulated. The results show that as the thermal conductivity of soils and rocks increases from 1 W/(m·K) to 9 W/(m·K),the heat transfer volume of the heat exchanger increases about 324. 53%;as the thermal conductivity of inner pipes increases from 0. 5 W/(m·K) to 4. 5 W/(m·K),the heat transfer volume of the heat exchanger decreases about 40. 37%;as the circulating fluid flow increases from 10 m^(3)/h to 50 m^(3)/h,the heat transfer volume of the heat exchanger increases about 103. 92%;and as the circulating fluid inlet temperature increases from 5 ℃to 15 ℃,the heat transfer volume of the heat exchanger decreases about 23. 14%. Therefore,middle-deep geothermal energy should be developed in areas with relatively large geotechnical thermal conductivity,choosing inner pipe with small thermal conductivity and downhole heat exchangers with large circulating flow,and keeping the circulating fluid inlet temperature in outer pipes low.