Research On Earth-to-air Heat Exchanger Temperature Field In Saturated Soil Based On Fractal Theory

At present,with the increasingly serious problems of environmental pollution and energy crisis,energy-saving and emission reduction,development and utilization of renewable energy such as solar energy,nuclear energy and shallow soil energy have become the focus of sustainable and scientific development.In this context,the study of soil heat transfer around earth-to-air heat exchanger using shallow soil energy was carried.As for the application and development of earth-to-air heat exchange system,it is the key to understand the heat transfer of buried pipes and soil and the law of heat migration in soil.In this paper,the earth-to-air heat transfer system,which regulates the environment in the solar greenhouse,is taken as the background to analyze the effects of the complex structure of the soil on the heat migration,as well as the specific laws of the coupling of heat in the soil.The previous studies on the migration of soil Heat are mostly based on the traditional European geometric method.The soil is regarded as a homogeneous and stable virtual continuous medium on large scale,which describes the thermal properties of the soil macroscopically and studies the heat migration process.However,in fact,the homogeneous and stable porous medium is not existent.The thermal physical parameters and the heat migration process of the porous media such as soil are directly influenced by the internal microstructure.Based on the self similarity and scaling invariance of fractal theory,a random soil fractal model was established and the heat migration law was studied in this paper.For the concrete influence of the complex structure in the soil on the heat migration,the simplified porous medium model is firstly established.The soil thermal physical parameters are mainly influenced by its internal structure and are almost independent of the heat conduction process.The heat conduction process is simplified as the steady heat conduction,and the effective thermal conductivity of the soil thermal conductivity is calculated,and the effective thermal conductivity coefficient is analyzed.The influence of soil porosity,spatial distribution of pore channel,matrix rate,matrix channel size and space distribution in the direction of heat conduction,and the visualization of calculation results and simulation process by MATLAB are used to discuss and analyze the heat conduction process in the soil.The fractal model of stratified soil is established and simulated for the process of underground heat transfer in the operation of soil air heat exchanger.The results are compared with the experimental results and can be concluded as follows: The effect of soil-air heat exchanger to maintain the stability of air temperature in the greenhouse is obvious.The distribution of soil temperature is obviously changed under the action of soil air heat exchanger.The temperature gradient has a certain effect on the moisture transfer,and the humidity gradient will also affect the temperature distribution.The influence of earth-to-air heat exchanger on soil is mainly in the radial direction,that is,the obvious Humidity Stratification and temperature change are produced in the vertical direction,and the closer to the heat source,the greater the change span and the more obvious change trend.The heat action radius and heat transfer effect of the earth-to-air heat exchanger with different diameters will be distinctly different.The comprehensive analysis and comparison show that the pipe diameter of 110 mm is more scientific and reasonable than the 90 mm tube as the system pipe diameter,and the benefit is higher.