回填空气间隙对水平埋管换热性能的影响

Influence of Backfill Air Gap on the Heat Transfer Performance of Heat Exchanger

建立了未夯实土壤初始温度数值计算模型,利用CFD软件求解,得到未夯实土壤初始温度数值计算结果,并将未夯实土壤初始温度数值计算结果与夯实情况下的理论计算值和实验测试数据进行比较,在该实验工况下,未夯实回填导致埋深2.2m处的土壤初始温度比夯实回填状况增大1℃左右.以未夯实土壤和夯实土壤的初始温度作为边界条件,建立埋深为2.2m的水平埋管耦合数值计算模型,利用CFD软件求解,得到土壤在未夯实和夯实情况下水平埋管换热器进出口温度及平均传热系数随时间的变化值,并与实验运行测试结果进行对比,在该实验条件下,土壤未夯实会使水平埋管进出口温度升高,系统效率降低,平均传热系数从2.71 W/(m·℃)下降到2.22 W/(m·℃).

Owing to the artificial backfill uncertainty, the air gap may emerge in the backfill process, which will influence the soil initial temperature distribution, and it will also influence the horizontal buried pipe heat transfer performance. The initial soil temperature numerical model with backfill air gap was set up. Using CFD software, the numerical calculation result was analyzed and compared with the theoretical calculation value without air gap and practical experimental test data. The soil initial temperature with backfill air gap in the deep of 2. 2 meters presents about one degree higher than that without backfill. Then, the horizontal buried pipe coupled numerical models with the deep of 2.2 meters were established on the boundary conditions of the initial soil temperature with air gap and that without air gap. Using CFD software, the horizontal buried pipeimport/export temperature and the average heat transfer coefficient changing along with time were analyzed and compared with experimental operating data. The result shows that the soil with air gap will lead the import/export temperature rise and reduce the heat transfer perform-ance, and the average heat transfer coefficient reduces from 2.71W/（m · ℃）to 2.22 W/（m · ℃）.