Influence Mechanism Of Moisture Content On Pore Characteristics Of Coal Under Microwave Irradiation

Microwave heating of water bearing coal and rock can promote the evaporation of water in the pores,fracture the pores under the action of steam pressure,and increase the permeability.In order to find out the change rule of temperature and permeability of coal and rock under microwave irradiation,a real-time NMR device was developed COMSOL is used to analyze the pore deformation characteristics of coal Multiphysics software established single hole numerical models under three different filling States,analyzed the stress evolution process of pores/fractures in coal and rock under the coupling effect of thermal stress and steam pressure;through the above physical and numerical experimental results,summarized and analyzed the mathematical relationship between microwave power,moisture content and internal temperature of coal and rock,formed the theoretical model of temperature rise and pressure rise of coal and rock under the effect of microwave Calculation formula.The main conclusions are as follows:It is found that microwave irradiation can promote the change of pore size to a higher level of pore.With the increase of water content of coal sample,the accumulated porosity of coal rock samples increased by 21.17%under microwave irradiation.The reduction of the pore size is about 21.18%,the overall variation of the volume of the middle hole is not very large,and the volume of the big hole increases by 74.49%.The permeability of coal rock samples has been greatly increased,with an increase of about 4.78 times.It was found that the temperature of the three groups was 60.0?,85.4?and 135.8?respectively when the microwave irradiation was 100 s under the conditions of different water content(0.1%,2.0%,6.0%),and the extreme value of the absolute vapor pressure in the pore inside the coal rock increased with the increase of water content.The temperature inside coal and the steam pressure in the pore are basically in accordance with the ideal gas state equation.The numerical model of porous medium coal rock mass with single fracture is established by COMSOL Multiphysics software.The deformation of pore inside coal rock is internal shrinkage deformation in vacuum state,and the maximum compressive stress is-0.12mpa,while saturated wet air and liquid water are expanded deformation,and the maximum tensile stress is+1.1mpa and+2.5MPa.At the same time,the mathematical model(?)is established.