Numerical Simulation Of Soil Temperature Field Of Double U-type Buried Tube Heat Exchanger In Cold Region

In recent years,with the rapid development of social economy,China's urbanization process has been accelerating,and the energy consumption of heating is also increasing year by year.In the northern part of the country,there will be serious environmental pollution problems during the heating period.To this end,the state issued the "Northern District Winter Clean Heating Plan(2017-2021)".In this environment,the use of ground source heat pump system heating is undoubtedly a clean heating method,while for the cold regions of the north,the heating load in winter is very large,the heating area in the whole winter is larger and the heating period is longer.In the non-heating period,the weather is relatively cool and basically no air conditioning is required.Therefore,in view of the special geographical environment and climatic conditions in the cold regions of the north,To study the change of soil temperature field after long-term operation of underground heat exchanger in cold regions of northern China,and to guide the operation of ground source heat pump system in cold regions.In this paper,the three-dimensional heat transfer model of double U-shaped buried tube heat exchanger is analyzed firstly to obtain the main factors affecting the heat transfer effect of the buried tube heat exchanger,including the drilling depth,the drilling radius and the thermal conductivity of the backfill material.When the drilling depth is less than 100 m,the thermal resistance changes little,and when the drilling depth exceeds 100 m,the thermal resistance changes drastically.As the depth of the borehole increases,the thermal resistance of the buried pipe becomes larger,which is in a direction that is not conducive to the heat conduction of the buried pipe.When the thermal conductivity of the backfill material is less than 1.4W/(m?K),the thermal resistance changes significantly.When the thermal conductivity is greater than 1.4W/(m?K),the thermal resistance changes slowly.The overall trend is that as the thermal conductivity of the backfill material becomes larger,the effect on the thermal resistance becomes larger first and then the thermal resistance.The effect is smaller.Secondly,the response surface method is used to analyze the heat transfer of the buried tube heat exchanger to optimize its buried pipe method.From the analysis of the influence law and the degree of influence of the influencing factors on the heat transfer of the buried pipe,the preconditions for the application of the response surface method are obtained(The experimental factors).And according to the BBD design test,the best way of burying is obtained.Compared with the engineering design,the heat transfer effect of the response surface method is increased by 40.69%.Finally,according to the response surface method,the best buried pipe arrangement is optimized for the buried pipe heat exchanger.The three-dimensional heat transfer model of the double U-shaped buried pipe heat exchanger is established,and the ground source heat pump system in the cold area is simulated.The distribution of soil temperature field around the buried heat exchanger during the year.At the same time,the temperature distribution of the soil around the double U-shaped buried heat exchanger in the cold area was analyzed comprehensively,and the distribution of the temperature field near the buried pipe in the cold area was obtained.The temperature drop rate of the surrounding soil was 0.31?/a.