Numerical Simulation On Soil Temperature Field Around Vertical U-tube Heat Exchange Used In Ground Source Heat Pump

Ground Source Heat Pump(GSHP) air conditioning systems utilize ground as a heat/cold source, achieve heat transfer between the ground and a working fluid circulating in a closed loop buried in the ground, and then provide the heat and cold energy by heat pump. Compared to other conventional air condition system, the GSHP system makes full use of renewable energy, and boasts the features of protecting the environment and reducing electric power consumption. It has arousing broad attention and extending application in China. However, researches on one of the GSHP core technology - the soil temperature field around the underground heat exchangers are far from adequate. This situation impedes its application.This thesis summarizes the existing researches of the vertical U-tube heat exchangers in GSHP system, in view of existing research results in the mainly concentrated in the U-tube heat and mass transfer model, the heat exchanger performance, enhanced heat transfer and the dynamic simulation of the heat pump systems, but the soil temperature field around the tube heat exchanger in GSHP system study less, and the soil temperature field around the tube heat exchanger can be more intuitive to reflect the thermal properties of soil and buried tube. Therefore this thesis using the soil temperature field around the tube heat exchanger as the major research content, using theoretics analysis, heat model foundation and numerical simulation, experimentation validation in the researches on the soil temperature field around vertical U-tube heat exchangers.This thesis utilizes founding soil temperature field model around the vertical U-tube heat exchangers, and using the engineering compute software MATLAB to make numerical simulation on soil temperature field. Through the numerical simulation of a detailed analysis of the two geological conditions, different bore backfilling materials, different running time of the heat pump systems, different size tube diameter and variable heat flux condition bring impact on the soil temperature field around the tube heat exchanger. and then gained the relationship between the thermal influencing radius and heat flux.The simulation results show that, in the short term (30 days) operating conditions, the soil thermal conductivity directly affect the size of thermal influencing radius, while the soil thermal conductivity are 2.035 W / m·℃and 3.49 W / m·℃the thermal influencing radius respective are 3.8 m and 4.2 m. The temperature of the soil near the tube wall only 42.3℃when using small river sand backfill material, however, when using cement mortar backfill, as high as 50.9℃, showing that the good thermal conductivity properties of backfilling materials to increase the temperature margin between the fluid and the surrounding soil thereby increasing the heat exchange. For the long-term thermal simulation analysis of three months operating the thermal influencing radius reach 4.5 m. The simulation results of the impact on soil temperature field while 505 W/m2, 550 W/m2 and 650 W/m2 three different heat flux density show that, when The greater the heat flux (650 W/m2), the greater the thermal influencing radius, but the temperature margin between the fluid and the surrounding soil is the largest ,too, so is adversed to heat exchange between the underground tube and soil. Finally, summarizing the advantageous heat exchanger tube spacing.Through the summer experiment tests of the Chongqing area, analysis the heat flux, the average heat transfer coefficient and soil temperature field of different flux. Then validating the simulation results through experiment.