Numerical Simulation And Analysis On Heat Transferring Performance Of T-tube Ground Heat Exchanger In Winter

The ground-coupled heat pump (GCHP) is drawing more and more attentions due to its advantages like high efficiency, energy saving and environment protecting, and the significant one of the key technologies is to solve the heat transfer problems between the tube and the soil. Therefore, it is extremely significant to optimize the heat transfer model of the heat exchangers in GCHP in order to simulate the real heat transfer process more accurately. The GAMBIT is used to establish the mathematical model and the FLUENT to calculate the three-dimensional heat transfer and flow process based on the research item of YanTai university railroad LunDu GCHP in this paper. The model established agrees well to the real things in the geometrical figure, flow and heat transfer of the tubes, which has made a big improvement in geometrical and physical conditions compared with the former one that the two tube legs of the U-tube are equivalent to the columniation heat source.The temperature field of the soil around the U-tube, the heat flux of the U-tube and the factors influencing the heat flux and flowing pressure drop are analyzed in order to provide some advices to the engineering design of GCHP. Firstly, the heat transfer between the U-tube and the soil is simulated under the condition that the GCHP operates continuously for three months, gaining the characteristics of temperature field in the three dimension of the U-tube, the changing rate of heat flux with time, and the data & trend of the heat radius with time elapsing. Then, the condition that the GCHP operates intermittently for three days is simulated to gain the changing characteristics of the heat flux and temperature of the soil with the time going by.The heat flux is calculated at different parameters such as inlet flow velocity, inlet water temperature, tube deepness, radius and material of U-tube, backfill material, silo diameter and distance of U-tube leg center. Abundant data and rules useful for the engineering design of GCHP are gained, also some advices are given, such as, the heat flux will be improved when the flow velocity increases, and when the velocity increases persistently, the changing rate of the heat flux decreases while the pressure drop increases smartly, so it is suggested that the flow velocity should be set between 0.4m/s and 0.6m/s in winter.