Study On The Heat Transfer Performance Of Geothermal Heat Exchangers With Seepage

Nowadays, energy and environmental problems become increasingly deterioration; it can satisfy the urgent need of the world to save energy and find new energy. In china, it was put forward to improve the efficiency of energy development and utilization, and what’s more, to promote balanced and rapid development of a variety of new energy, during the 13 th Five-Year Plan period. As a result of the prominent environmental protection and energy saving effect, the soil source heat pump air conditioning system emerged gradually around our life that belongs to the ground source heat pump system; geothermal heat exchangers as an underground heat transfer part are included in the soil source heat pump air conditioning system, it’s thermal efficiency is closely related to the groundwater seepage. Therefore, it becomes one of the key to study on the heat transfer performance of geothermal heat exchangers with seepage.In this paper, temperature variation of medium sand was studied with and without groundwater seepage using a sand box(0.5m×0.5m×1m)that had been fabricated, which was based on heat transfer process and influence factor of geothermal heat exchangers. The results show that(1) the higher the heat load, the greater the temperatures, the ratio of temperature variation and heat load variation is approximate without seepage, it is 1.5、1.33、1.25、1.2 respectively.(2) When the heat source keep working, upstream temperature reduction and downstream temperature increment was reflected as the increase of seepage velocity, the heat accumulation phenomena exists in downstream area, the heat accumulation area skews to downstream, migration distance increases as the the increase of seepage velocity.The thermal seepage coupling heat transfer model was designed by COMSOL Multiphysics software, When the system is running 12 h, the temperature field of gravel sand, coarse sand, fine sand and silt were simulated with and without seepage respectively, the temperature distribution shows that(1) the thermal effect scope of gravel sand, coarse sand, fine sand and silt reduce without seepage orderly. The temperature distribution is symmetrical, and the heat source act as center of symmetry, the temperature gradient shows an inside-out decline trend.(2) When the seepage velocity increases from 7.5×10-7m/s to 7.5×10-6m/s, the thermal effect scope of gravel sand and coarse sand rise from 0.35 m to 0.65m;The thermal effect scope of other sand rise from 0.36 m to 0.66 m, the temperature field skews along seepage direction, the upstream thermal effect scope decrease, on the contrary, the downstream thermal effect scope increase.(3) Migration distance of sand temperature field and the sand thermal diffusion ability increases as the the increase of seepage velocity. The groundwater seepage is helpful to heat transfer of geothermal heat exchangers.(4) The capacity of thermal conductivity of gravel sand is the most strongest, and the silt is the most weakest, the gravel sand is the better choice as backfill material in the practical engineering with or without seepage.