Study On Air-to-Earth Heat Transfer Characteristics Of Buried Pipelines

The energy issue is the primary problem facing the society at present,and it is also a major survival problem that human beings urgently need to solve.With the building energy consumption accounting for a higher proportion of the total energy consumption in society,the environmental damage caused by the burning of fossil energy is becoming more and more serious,so the use of clean renewable energy,improve the utilization rate of energy,energy conservation and emission reduction has become the top priority.Both air and shallow soil geothermal energy are inexhaustible renewable energy.The underground soil and the air in the buried pipe are used for heat exchange,and the air at the outlet of the buried pipe can be directly used for space heat treatment or used in combination with an air treatment unit.The utilization rate of energy can be effectively improved by using buried pipe earth-to-air heat exchanger in combination with air source heat pump.When considering the combination of the buried pipe earth-to-air heat exchanger and the air source heat pump,the first thing to be solved is the heat transfer characteristics between the air in the buried pipe and the surrounding soil.In order to explore the heat transfer characteristics between the air in the buried pipe and the surrounding soil,this paper theoretically analyzed and calculated the changes of soil thermophysical properties and soil temperature.By using the numerical simulation software Fluent,a three-dimensional unsteady numerical model of single and double buried heat exchange pipes is established to explore the influence of various structural parameters on the heat transfer performance and the changes of temperature field around the buried pipes under different heat exchange times.The effects of air velocity,pipe diameter and pipe length on the heat transfer performance in a single pipe during the hottest day continuous heat transfer in Beijing are simulated and calculated.And the variation law of soil temperature near the pipe with the axial and radial directions of the pipe is also analyzed.It is concluded that in the flow rate range of 5.0m/s and the pipe diameter of less than 400 mm,low flow rate,small pipediameter and long pipe are beneficial to improve the heat transfer performance of the buried pipelines earth-to-air heat exchanger at a certain depth.By simulating and calculating the operation of buried earth-to-air heat exchange pipelines in winter heating season,the influence of pipe spacing on heat exchange performance and soil temperature distribution and changes are studied.The smaller the pipe spacing,the greater the heat interference between buried heat exchange pipelines,the lower the heat exchange performance,and the smaller the soil temperature change.The soil temperature field of single pipe and double pipelines under the same working condition is compared and analyzed.When the two pipelines exchange heat,the fluctuation of soil temperature between the pipelines is smaller than that of the single pipe,and the temperature is symmetrically distributed on both horizontal sides at the midpoint of the central connecting line of the two pipelines.