Study On The Numerical Simulation Of Ground Temperature Field And The Heat Transfer Of The Vertical U-tube Heat Exchanger

Ground-coupled heat pump system (GCHPS) is a form of renewable energy utilizing with the advantages of energy-saving, environmentally friendly, higher efficiency. So it is called the Green air-condition technology of 21st century. It plays more and more important role in the field of air conditioning and hot water systems in our country. Vertical U-tube ground heat exchangers have become the most popular form of pipe-burying because of many out-standing advantage such as:fewer area requirement, Wide range of applications, higher efficiency.A ground-coupled heat pump system (GCHPS) for hot water was established focusing on the climate and soil conditions of the Pearl River Delta in South China, and the experimental study on GCHP's performance characteristics was carried out on this platform. By measuring the inlet and outlet temperature of circulating fluid in U-tube ground heat exchangers and the ground temperature distribution around them, this paper studies the operating characteristic of the system and the performance of the heat transfer of U-tube under various operating conditions. And the vertical U-tube heat transfer model for three-dimensional unsteady heat transfer based on the platform was established through the GAMBIT and FLUENT, a software for constituting mathematical models and numerical computing. The major work and conclusions are as follows:Simulation of the temperature the outlet temperature of circulating fluid in U-tube ground heat exchangers, the heat exchange unit of borehole depth based on the platform under operating continuously for 48 hours conditions. The result shows that the maximum relative error between simulation and measured values is 13.3%(the deviation is 2.5℃). And the average relative error is only 4.82%, which was within the permitted. The comparison confirmed the validity of the model. At the same time, this paper analysis the simulation of the ground temperature distribution.Simulation of the temperature the outlet temperature of circulating fluid in U-tube ground heat exchangers, the heat exchange unit of borehole depth under the intermittent operation mode (the intermittent operation ratio 14:10). The result shows that the deviation between simulation and measured values of outlet temperature of circulating fluid is less as time goes on. And the accuracy of the model gradually increased as time goes on.Studies the influence of the ground temperature distribution and the performance of the heat transfer of U-tube at different parameters such as inlet flow velocity, inlet water temperature backfills, pipes. The conclusion is worthy to guide the operating characteristic of the system and the design of U-tube ground heat exchangers.