Improving the absorbed gas to active desorption and seepage and delaying gas drainage attenuation are considered as key methods for increasing drainage efficiency and gas output.According to the solid mechanics theory...Improving the absorbed gas to active desorption and seepage and delaying gas drainage attenuation are considered as key methods for increasing drainage efficiency and gas output.According to the solid mechanics theory,the nonlinear Darcy seepage theory and thermodynamics,the heat-fluid-solid coupling model for gassy coal has been improved.The numerical model was founded from the improved multi-field coupling model by COMSOL Multiphysics and gas drainage by borehole down the coal seam enhanced by heat injection was modelled.The results show that the heatfluid-solid model with adsorption effects for gassy coal was well simulated by the improved multi-field model.The mechanism of coal seam gas desorption seepage under the combined action of temperature,stress and adsorption can be well described.Gas desorption and seepage can be enhanced by heat injection into coal seams.The gas drainage rate was directly proportional to the temperature of injected heat in the scope of 30-150 ℃ and increasing in the whole modelleddrainage process (0-1000 d).The increased level was maximum in the initial drainage time and decreasing gradually along with drainage time.The increasing ratio of drainage rate was maximum when the temperature raised from 30 to 60 ℃.Although the drainage rate would increase along with increasing temperature,when exceeding 60 ℃,the increasing ratio of drainage rate with rising temperature would decrease.Gas drainage promotion was more effective in coal seams with lower permeability than with higher permeability.The coal seam temperature in a 5 m distance surrounding the heat injection borehole would rise to around 60 ℃ in 3 months.That was much less than the time of gas drainage in the coal mines in sites with low permeability coal seams.Therefore,it is valuable and feasible to inject heat into coal seams to promote gas drainage,and this has strong feasibility for coal seams with low permeability which are widespread in China.展开更多
Aiming at the synergistic rock-breaking mechanism of supercritical carbon dioxide(SC-CO_(2))jet pressure and tem-perature difference,a heat-fluid-solid calculation model of rock-breaking stress was established and ver...Aiming at the synergistic rock-breaking mechanism of supercritical carbon dioxide(SC-CO_(2))jet pressure and tem-perature difference,a heat-fluid-solid calculation model of rock-breaking stress was established and verified to be effective,and the variations of jet flow field and rock stress with jet standoff distance of SC-CO_(2),water and nitrogen were studied.With the increase of jet standoff distance,the jet pressure of SC-CO_(2) decreases and the jet temperature difference increases.The SC-CO_(2) jet is higher in pressure than the nitrogen jet and differs little from the water jet.Temperature difference of SC-CO_(2) jet is 5 times that of water jet and more than 2.5 ti mes that of nitrogen jet when the jet standoff distance is larger than 10.The tem-perature stress is the main reason why SC-CO_(2) jet is superior to water and nitrogen jets in rock-breaking.The rock under the SC-CO_(2) jet has greater rock stress,effective rock-breaking jet standoff distance and rock-breaking area.The jet pressure plays a major role in rock-breaking when the jet standoff distance is small,while the jet temperature difference plays a major role in rock-breaking when the jet standoff distance is large.The SC-CO_(2) jet is an efficient volume rock-breaking method,which results in tensile and shear failure on the rock surface under short time jet and large area tensile failure inside the rock simultaneously under long time jet.展开更多
The double flapper-nozzle servo valve is widely used to launch and guide the equipment. Due to the large instantaneous flow rate of servo valve working under specific operating conditions, the temperature of servo val...The double flapper-nozzle servo valve is widely used to launch and guide the equipment. Due to the large instantaneous flow rate of servo valve working under specific operating conditions, the temperature of servo valve would reach 120℃ and the valve core and valve sleeve deform in a short amount of time. So the control precision of servo valve significantly decreases and the clamping stagnation phenomenon of valve core appears. In order to solve the problem of degraded control accuracy and clamping stagnation of servo valve under large temperature difference circumstance, the numerical simulation of heat-fluid-solid coupling by using finite element method is done. The simulation result shows that zero position leakage of servo valve is basically impacted by oil temperature and change of fit clearance. The clamping stagnation is caused by warpage-deformation and fit clearance reduction of the valve core and valve sleeve. The distribution roles of the temperature and thermal-deformation of shell, valve core and valve sleeve and the pressure, velocity and temperature field of flow channel are also analyzed. Zero position leakage and electromagnet＇s current when valve core moves in full-stroke are tested using Electro-hydraulic Servo-valve Characteristic Test-bed of an aerospace sciences and technology corporation. The experimental results show that the change law of experimental current at different oil temperatures is roughly identical to simulation current. The current curve of the electromagnet is smooth when oil temperature is below 80℃, but the amplitude of current significantly increases and the hairy appears when oil temperature is above 80℃. The current becomes smooth again after the warped valve core and valve sleeve are reground. It indicates that clamping stagnation is caused by warpage-deformation and fit clearance reduction of valve core and valve sleeve. This paper simulates and tests the heat-fluid-solid coupling of double flapper-nozzle servo valve, and the obtained results provide the refer展开更多
基金The authors acknowledge the financial support from the Natural Science Foundation of China(U1704131)Program for Science&Technology Innovation Talents in Universities of Henan Province(18HASTIT018)the Program for Changjiang Scholars and Innovative Research Team in University(IRT_16R22).
文摘Improving the absorbed gas to active desorption and seepage and delaying gas drainage attenuation are considered as key methods for increasing drainage efficiency and gas output.According to the solid mechanics theory,the nonlinear Darcy seepage theory and thermodynamics,the heat-fluid-solid coupling model for gassy coal has been improved.The numerical model was founded from the improved multi-field coupling model by COMSOL Multiphysics and gas drainage by borehole down the coal seam enhanced by heat injection was modelled.The results show that the heatfluid-solid model with adsorption effects for gassy coal was well simulated by the improved multi-field model.The mechanism of coal seam gas desorption seepage under the combined action of temperature,stress and adsorption can be well described.Gas desorption and seepage can be enhanced by heat injection into coal seams.The gas drainage rate was directly proportional to the temperature of injected heat in the scope of 30-150 ℃ and increasing in the whole modelleddrainage process (0-1000 d).The increased level was maximum in the initial drainage time and decreasing gradually along with drainage time.The increasing ratio of drainage rate was maximum when the temperature raised from 30 to 60 ℃.Although the drainage rate would increase along with increasing temperature,when exceeding 60 ℃,the increasing ratio of drainage rate with rising temperature would decrease.Gas drainage promotion was more effective in coal seams with lower permeability than with higher permeability.The coal seam temperature in a 5 m distance surrounding the heat injection borehole would rise to around 60 ℃ in 3 months.That was much less than the time of gas drainage in the coal mines in sites with low permeability coal seams.Therefore,it is valuable and feasible to inject heat into coal seams to promote gas drainage,and this has strong feasibility for coal seams with low permeability which are widespread in China.
基金Supported by the National Natural Science Foundation of China(51674158,51704324,51934004)。
文摘Aiming at the synergistic rock-breaking mechanism of supercritical carbon dioxide(SC-CO_(2))jet pressure and tem-perature difference,a heat-fluid-solid calculation model of rock-breaking stress was established and verified to be effective,and the variations of jet flow field and rock stress with jet standoff distance of SC-CO_(2),water and nitrogen were studied.With the increase of jet standoff distance,the jet pressure of SC-CO_(2) decreases and the jet temperature difference increases.The SC-CO_(2) jet is higher in pressure than the nitrogen jet and differs little from the water jet.Temperature difference of SC-CO_(2) jet is 5 times that of water jet and more than 2.5 ti mes that of nitrogen jet when the jet standoff distance is larger than 10.The tem-perature stress is the main reason why SC-CO_(2) jet is superior to water and nitrogen jets in rock-breaking.The rock under the SC-CO_(2) jet has greater rock stress,effective rock-breaking jet standoff distance and rock-breaking area.The jet pressure plays a major role in rock-breaking when the jet standoff distance is small,while the jet temperature difference plays a major role in rock-breaking when the jet standoff distance is large.The SC-CO_(2) jet is an efficient volume rock-breaking method,which results in tensile and shear failure on the rock surface under short time jet and large area tensile failure inside the rock simultaneously under long time jet.
基金Supposed by National Natural Science Foundation of China(Grant No.51075348)Hebei Provincial Natural Science Foundation of China(Grant No.E2011203151)Research Fund for Doctoral Program of Higher Education of China(Grant No.20101333110002)
文摘The double flapper-nozzle servo valve is widely used to launch and guide the equipment. Due to the large instantaneous flow rate of servo valve working under specific operating conditions, the temperature of servo valve would reach 120℃ and the valve core and valve sleeve deform in a short amount of time. So the control precision of servo valve significantly decreases and the clamping stagnation phenomenon of valve core appears. In order to solve the problem of degraded control accuracy and clamping stagnation of servo valve under large temperature difference circumstance, the numerical simulation of heat-fluid-solid coupling by using finite element method is done. The simulation result shows that zero position leakage of servo valve is basically impacted by oil temperature and change of fit clearance. The clamping stagnation is caused by warpage-deformation and fit clearance reduction of the valve core and valve sleeve. The distribution roles of the temperature and thermal-deformation of shell, valve core and valve sleeve and the pressure, velocity and temperature field of flow channel are also analyzed. Zero position leakage and electromagnet＇s current when valve core moves in full-stroke are tested using Electro-hydraulic Servo-valve Characteristic Test-bed of an aerospace sciences and technology corporation. The experimental results show that the change law of experimental current at different oil temperatures is roughly identical to simulation current. The current curve of the electromagnet is smooth when oil temperature is below 80℃, but the amplitude of current significantly increases and the hairy appears when oil temperature is above 80℃. The current becomes smooth again after the warped valve core and valve sleeve are reground. It indicates that clamping stagnation is caused by warpage-deformation and fit clearance reduction of valve core and valve sleeve. This paper simulates and tests the heat-fluid-solid coupling of double flapper-nozzle servo valve, and the obtained results provide the refer
