Analysis Of Heat Preservation Of Rural Water Supply Line Under Freeze-Thaw Environment In Cold Area

In the cold regions of northern China,the soil will be frozen and thawed as the temperature changes due to the seasonal temperature changes.If the shallow buried pipeline directly in the surface soil,one hand in winter due to low temperature,water pipes will freeze,there may be pipeline split up;on the other hand,when the volume of frozen soil in winter will become large,therefore can be applied to the medium surrounding the frost heaving force,will destroy the pipeline.So in the north cold area of our country,usually the water supply pipeline buried under the frozen soil layer,this method can avoid the water supply pipeline in winter,frost heave and the surrounding soil and the damage of the pipeline.But for the rural areas with small population density,the distance of water supply is long,the water consumption is small,the construction cost is high.At the same time,the underground water level will change with the seasonal cycle.If the buried pipeline is immersed in the water for a long time,it will affect the safety of the water supply.In this paper,a physical model and a mathematical model of the shallow buried thermal insulation pipeline are established.Analysis of heat transfer mechanism of the shallow buried pipeline insulation,the numerical simulation of heat transfer pipeline,the pipeline in shallow design experiment,through experiments and simulations to verify the two aspects of shallow buried pipeline insulation in winter operation feasibility.The theoretical calculation of heat preservation and anti freezing of shallow buried water supply pipeline is made.It is very important for the safe operation of the shallow buried pipeline.Therefore,the thickness of the insulation layer is calculated in order to select the proper thickness of the insulation layer.The heat dissipation model of the shallow buried pipeline is established,and the radial heat loss and the heat loss of the pipeline are calculated respectively.The freezing and thawing cycle model of soil was established.The thermal effect of freezing and thawing condition and shallow buried pipeline is analyzed,and the mechanism of freezing and thawing is analyzed.The influencing factors of soil temperature field were analyzed.The results show that the change of soil temperature field is proportional to the change of surface temperature,and is inversely proportional to the change of water content.The influence factors of freezing thawing cycles were analyzed,and the diameter of freezing and thawing cycles was in inverse proportion to the thickness of insulation layer and the thermal conductivity of the soil,and it was directly proportional to the temperature of the outer surface of the thermal insulation layer.Finally,it analyzes the influence factors of the thickness of the insulation layer,and gives the recommended depth of the Daqing region as 1.5m,recommended insulation layer thickness of 5cm polyurethane insulation materials.Based on the basic theory of heat transfer,the shallow buried pipeline is modeled and calculated,and the temperature field around the pipe under different conditions is simulated.The results show that the temperature of the pipeline in different depth of field vary greatly,in the reasonable choice of the pipeline buried depth is very important.At the same time,the freezing and thawing condition of the surrounding soil directly affects the temperature field around the pipe.When the soil is melted,the thermal conductivity decreases and the heat dissipation around the pipe is reduced,which is conducive to the safe operation of the pipeline in winter.The temperature field in the intermittent water supply mode is analyzed,and it can be seen that the soil temperature around the pipeline has a certain thermal delay.Design experiment of heat insulation for shallow buried pipeline.Through the comparison of normal water supply and intermittent water supply,the temperature change around the pipeline under different operating conditions is obtained,which provides data support for the theoretical analysis and simulation analysis.The experimental results show that under normal water and intermittent water supply under the condition of shallow buried pipeline insulation can operate normally,no frost cracking phenomenon,can guarantee the safety of water supply in winter.