Mechanism Of Thermal Transfer In Dense Gas-solid Two-phase Flow And Applied Research

Oil-based drilling fluid is used widely in oil and shale gas exploitation.Accordingly much oily cuttings are generated and 300 cubic meters are produced along with per well drilling.Thermal desorption is an effective oily cutting handling method where oil is recovered and mass fraction of cuttings is decreased to less than 1%.This work is based on thermal desorption used in oily cuttings cleaning,and numerical calculation and experimental method are combined.Computational fluid dynamics(CFD)is coupled with discrete element method(DEM)to study the particle flow,thermal transfer and energy conversion inside dense gas-solid two-phase flow based on Euler-Lagrange theory.The mechanism of energy conversion and thermal transfer inside oily cuttings flow,and the solid-liquid separation and energy consumption in oily cuttings thermal desorption are studied experimentally.Based on DEM the heat generated from particle deformation,sliding friction work and rolling friction work is calculated.And to calculate the heat convection between gas and the frictional contact surface in CFD-DEM simulations,a model parameter is brought about on account of Hertz elastic theory.By calculating the thermal conduction coefficient,the thermal distribution of friction heat between particle and blades is obtained as well as particle and barrel wall.Thus the energy conversion inside wet particle flow is modeled.What's more the Sun short-contact thermal transfer model is employed to calculate the contact thermal transfer.Based on the energy conversion model inside wet particle flow,the heat generated by liquid viscous force work is calculated and added to calculate the energy conversion of wet particle flow.The Sun short contact thermal transfer model is used to calculate the thermal transfer between wet particle and blades as well as wet particle and barrel wall.When it comes to the thermal transfer between wet particles,the thermal transfer between contacting solids is calculated based on Cheng long-contact model and the heat conduction between liquid of two wet particles is calculated on account of the thermal conduction coefficient.Thus the thermal conduction between wet particles is modeled which is suitable to this work.To calculate the thermal convection inside gas-solid flow,discrete element method is coupled with computational fluid dynamics to obtain the CFD-DEM simulation platform.In this work,the blades and barrel wall are set as aggregation of many cubes and the barrel wall is divided to two parts.The inner wall is employed in CFD-DEM simulations and the thermal transfer between inner wall and outer wall is simulated by CFD as well as the heat convection between outer wall and rounding gas.By gathering the energy models and thermal transfer models to the CFD-DEM simulation platform,the energy conversion and thermal transfer inside dense gas-solid two-phase flow is numerically studied.And the mass transfer between wet particles and gas is obtained experimentally and set as boundary conditions in CFD-DEM simulations.To validate the models and simulation method proposed in the paper,oily cuttings thermal desorption test rig is designed.The particle flow regularity and temperature increasing on barrel wall are studied experimentally and the simulation date is compared with experimental results of the temperature increasing and flow regularity.The heat-work conversion coefficient is corrected.The error between simulation date and experimental results is less than 3%,and the models and simulation method are reliable.Based on the CFD-DEM simulation platform,the influences of agitating speed,initial filling and liquid ratio of wet particles on temperature increasing on barrel wall are studied.On account of the particle flow regularity,the mechanism of energy conversion and thermal transfer are revealed.Heat is mainly generated from particle deformation and friction work,and friction heat is mainly generated closely to inner wall.The blade number and axial gap of blades is the key role in heat generating.The effect of agitating speed,initial filling,particle diameter and liquid ratio on the generation velocity of oil vaporation separated from oily particles.And on account of the temperature increasing on barrel wall,the influence of temperature increasing velocity of oily particle,agitating speed,particle diameter and liquid mass ratio on solid-liquid separation is studied.The agitating norque is obtained experimentally and the energy consumption of oily particle thermal desorption is studied.