Heat And Mass Transfer Characteristics Of Cryogenic Nitrogen In Coal Porous Media

The heat and mass transfer problem of cryogenic nitrogen in coal porous media is a complicated local non-thermal equilibrium heat and mass transfer problem with fluid phase change.Since the heat and mass transfer process is extremely complicated,it is necessary to study it in theory and practice.In this thesis,the heat and mass transfer characteristics of cryogenic nitrogen in coal porous media was studied,and the numerical simulation of the heat and mass transfer processes based on the theory of the local non-thermal equilibrium was carried out.Main works include as follow:(1)A roadway model was used to explore the influence of gravity subsidence,internal heat source,roadway water,height and position of nitrogen injection on the heat and mass transfer characteristics of cryogenic nitrogen in coal porous media.The results show that gravity deposition plays a very important role in the heat and mass transfer process of low-temperature nitrogen in coal porous media.And internal heat source,roadway water,height and location of nitrogen injection also have significant influence on it.(2)The forward problem model and the inverse problem model of one dimensional unsteady heat transfer problem were established to explore the feasibility of calculating the heat transfer coefficient of coal by temperature distribution data.(3)The non-thermal equilibrium characteristics of cryogenic nitrogen in coal porous media was studied by using a multi-scale model,and the temperature distributions of fluid and coal porous media were obtained in this thesis.Besides,the effects of the equivalent diameter and mass flow rate on the heat transfer rate were revealed.(4)Considering the influence of Biot Number and the influence of the temperature difference between the fluid and the solid surface,we proposed the DBiot number for selecting the appropriate model in porous media with small heat conductivity,and discussed its influence on the complex local thermal non-equilibrium in porous media.