Reserch On The Heat Transfer Characteristics Of The Grout Materials And Diameter Of Ground Heat Exchanger

Ground source heat pump system which uses underground soil to do heat storage and heat release, has the characteristics of high efficient and steady operation. The performance of will directly grout material will affect the heat transfer characteristics of U-tube heat exchanger directly, which is the heat transfer medium between the U-tube heat exchanger and surrounding soil.In this paper, according to the engineering practice, a physical and mathematical heat transfer model has been established and uses CFD numerical simulation to analysis the influence of grout materials property parameters on the grout material coefficient of thermal conductivity and diameter size on the ground heat exchanger in short term heat transfer process based on reasonable simplification and assumption. Theoretical calculation has been carried on and the parameters, such as ground tube wall temperature and heat action radius, will be analyzed. The result showed that the grout materials coefficient of thermal conductivity plays a leading role in the process of heat exchanger comparison to the volume heat capacity and improving the coefficient of thermal conductivity of grout materials can greatly enhance heat exchanger features, but with the improvement of grout material coefficient of thermal conductivity, the improvement of the heat exchanger effect gradually reduced. K is the ratio of grout materials coefficient of thermal conductivity and the surrounding soil coefficient of thermal conductivity in the ground tube heat transfer system. It’s better to keep K around 1~1.1;when the K is in the interval of 1.1 to 2,it still can rise to enhance the effect of the heat exchanger, but the enhancement effect is only less than 1.1K range below 50%;For small coefficient of thermal conductivity of soil block, the relative coefficient of thermal conductivity K value can be increased to 1.2~1.3, so relatively speaking, the coefficient of thermal conductivity of backfill materials also need not too big, and can have better effect.When the grout materials coefficient of thermal conductivity is bigger than the surrounding soil coefficient of thermal conductivity, grout diameter increases from 100 mm to 200 mm and the ground tube wall temperature is decreased by 5.43% under this condition. That is to say. grout diameter can improve the buried tube heat transfer effect when increasing to a certain extent, but the enhancement effect is not obvious. Grout diameter increases from 100 mm to 140 mm, under the condition of buried pipe wall temperature dropped by 2.8%, from 160 mm to 200 mm increase, the ground tube wall temperature is decreased by 1.6%, but the former volume increased by 94%, while the latter is increased by 144%, the comprehensive practical consideration, suggest the single U-tube pipe grout diameter in 140~160 mm is more appropriate.On the basis of the theoretical model, this article in view of the grout materials coefficient of thermal conductivity and the grout diameter has carried out experimental study. First using TCI thermal conductivity meter to test with sand and cement grout material thermal physical property test, the component matching rules were explored. At the same time, the experimental platform, simulate heat exchanger set for grout materials coefficient of thermal conductivity and the grout diameter has carried on the experimental research, and according to the actual experimental model and parameters for the theoretical of the experimental verification. The results show that in the short term, heat exchanger, experiment results accord with the theoretical calculation conclusion, and the maximum error is less than 10%, shows in this paper, the theoretical analysis results are reliable, and it has a certain guiding significance to the grout materials and grout diameter for engineering design.