| The performance of the underground heat exchanger has a serious impact on the initial investment of the ground source heat pump system, therefore, the improvement of the heat transfer performance of the underground heat exchanger is an important goal of our pursuit. The energy-saving effect is the main advantage of the ground source heat pump system. But at the same time there are some problems such as; heat pump runs continuously evaporation or condensation temperatures due to fluctuations in temperature caused by the impact of changes. There are limitations to strengthening underground heat exchanger heat transfer. The underground pipe is divided into horizontal and vertical two parts. Vertical borehole is widely used due to its small cover. With the continuous development of technology, the pile foundation buried pipe emerged, which thereafter is widely used as it reduces the drilling cost taking full advantage of the structural pile foundation buried.For ground heat exchanger, there are many forms to choose from, of which different forms of ground heat exchanger have been put into use.The most widely seen and used forms are as:tube-in-tube, single U-shaped and double U-shaped. Some researchers have already conducted simulation studies on heat exchange of these ground buried heat exchanger, but the physical models of the most adopt equivalent tube method, which means the two branch pipes are simplified as one equivalent tube. In this article, we mainly conduct the analysis on influencing factor during heat exchange process of the U-type heat exchanger; the the Gambit software is used for building a geometric model of heat exchange between U-type pipe and the earth around; the large-scale commercial software, Fluent, is adopted for heat exchange numerical calculation. Building a physical model, which is consistent with the real heat exchanger shape, is more realistic than the equivalent tube method Calculate the three-dimensional heat transfer and flow on the basisi that the model is built similar to the real U-type pipe, then the effect of different factors(heat-conducting property of earth, water temperature in the inlet and the flow speed of the heat exchange, depth of the buried pile, pipe leg center distance, tube stock and so on) on the heat exchange is obtained as well as a optimal value, which takes a certain effect in the real engineering. Through the simulation tests conducted, the conclusion is obtained in this article as follows:(1) The double U-pipe buried pipe,the flow velocity is appropriate to be0.6m/s;(2)In summer, for the double U-pipe buried pipe, the inlet water temperature is appropriate to be36℃(3) In winter, for the double U-pipe buried pipe, the inlet water temperature is appropriate to be6℃;(4) When backfill earth conductivity equals to or exceeds the conductivity of the soil, increasing backfill conductivity has little effect on the heat exchange amount of the pile foundation buried pipe.Therefore,do not blindly choose the backfill earth of high conductivity, but in accordance with the actual earth condition.;(5) The conductivity of the pipe stock has minor effect on the heat exchange of the pipe foundation buried pipe, as a result, the pipes should be chosen according to the feasibility and the price; As the well depth has no obvious effect on the heat exchange, choose the appropriate well depth according to the local geologic condition, underground obstacle and so on.;(6) The heat exchange amount increases as the U-type pipe diameter increase. In the actual when we choice,we should also consider the pile diameter and other influence factors. |
