Fractal model of mass thermal dispersion coefficient for two-phase flow in porous media
The fractal theory was used to describe the microscopic pore throat structure of porous media,and the proportion of two-phase fluid in the pore space was studied.The local head loss caused by the secondary flow due to the change of flow state of the fluid passing through the pore throat struc-ture was taken into consideration,combining the difference in thermal storage capacity of the two-phase fluid along the way,the expression of the velocity dispersion effect and thermal dispersion coefficient of two-phase fluids in the pore space was derived.The research results indicate that when the saturation is less than 0.1 or greater than 0.9,the changes in velocity dispersion and thermal dispersion coefficient of non-wetting phase fluids are less affected by saturation and are only related to the microscopic pore throat structure.When the pore throat ratio is 1,the local head loss is 0,and there is no velocity dis-persion effect or thermal dispersion effect.When the pore throat ratio is between 1 and 200,the veloci-ty dispersion effect and thermal dispersion effect change with changes in saturation,pore throat ratio,and fluid physical parameters.When the pore to throat ratio is greater than 200,the change in velocity dispersion effect is not significant,and the influence on thermal dispersion coefficient is no longer sig-nificant,which is inconsistent with the conclusion that the velocity dispersion effect is no longer signifi-cant when the pore to throat ratio of saturated porous media is 150.When the wall temperature is con-stant and the pore to throat ratio is greater than 2,the stagnation of the secondary flow near the wall of the pore throat gap leads to an increase in the heating time.The fluid temperature between the pore throat structural gaps is approximately equal to the temperature of the hole wall.The velocity dispersion and thermal dispersion effects are not affected by temperature.
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