为解决固定式旋转喷头低压喷灌时,水射流向末端集中形成水量分布不均匀的问题,提出水气两相射流进行喷灌的方法。在摇臂喷头结构的基础上,增加掺气结构,形成掺气射流喷头,以相同工作水压力、射流仰角、喷嘴出口流量相同为约束,以及不考...为解决固定式旋转喷头低压喷灌时,水射流向末端集中形成水量分布不均匀的问题,提出水气两相射流进行喷灌的方法。在摇臂喷头结构的基础上,增加掺气结构,形成掺气射流喷头,以相同工作水压力、射流仰角、喷嘴出口流量相同为约束,以及不考虑副喷嘴对喷洒的影响,对比了掺气与不掺气2种情况下PY20喷头的射程、径向水量分布、1倍射程间距的正方形组合喷灌均匀系数,雨滴粒径等参数。试验结果表明:原不掺气摇臂喷头出口直径7 mm,安装内径2 mm的掺气管后出口直径改为8.3 mm,此时两者具有相同的出口流量,2种喷头在相同工作压力下具有近似相等的射程;在掺气喷头工作水压低至100 k Pa情况下,喷头仍具有76 mm水银柱高差的掺气负压能力;掺气摇臂喷头改善了径向水量分布线射程中段的水量,使水量分布线发生了中段略微增高、末端略下降的变化,从而使1倍间距的正方形组合喷灌均匀系数在低于国家标准工作压力的200 k Pa情况下,从62.8%提高到68.8%;采用激光雨滴谱仪测量射程中部和末端2个地方的水滴粒径表明:掺气状态下射程中部的水量累积百分比中位直径d50远大于不掺气状态,射流末端对比d50则小于不掺气状态,说明掺气改变了喷头的雨滴粒径分布。该文试验结果证明掺气摇臂喷头在农业喷灌中应用具有可行性。展开更多
This paper presented a method to create artificial fractures along the existing gas drainage borehole and increase the permeability of the coalbed using a high pressure waterjet cutting system.The field work conducted...This paper presented a method to create artificial fractures along the existing gas drainage borehole and increase the permeability of the coalbed using a high pressure waterjet cutting system.The field work conducted in Rujigou Colliery, Shenhua Ningxia Coal Group demonstrate that the coalbed permeability is increased, and accordingly, gas drainage efficiency is improved up to 3 to 6 times over the traditional methods using high pressure waterjet technique.Also, based on the monitoring data, the conceptual model for gas drainage process associated with different mining activities has been proposed, and few major advantages using waterjet assistance method have been identified.展开更多
The present study is concerned with the lifting of seabed materials by a BJT （bubble-jet-type） air-lift pump patented by Sadatomi. The targets are methane-hydrate rich muds on the bed about 200 m in depth around Jap...The present study is concerned with the lifting of seabed materials by a BJT （bubble-jet-type） air-lift pump patented by Sadatomi. The targets are methane-hydrate rich muds on the bed about 200 m in depth around Japan islands and rare-earth rich muds on the bed deeper than 4,000 m around Minami-Torishima islands in the Pacific Ocean. Feasibility studies were conducted using 50 mm I. D. （inner diameter） and 5.0 m long vertical pipe as the pump upriser, VC （vinyl chloride） particles and natural sands mixture in the methane-hydrate case, and ceramics particles with 3,761 kg/m^3 in density in the rare-earth case as the deposits. From the methane-hydrate simulation experiments, an efficient operation condition with high VC particles to sands lifting ratio has been clarified. In the rare-earth case, the air supplies from two different midways in the upriser pipe have been tested together with the bottom supply because the air supply from the upriser bottom is very hard in deep sea. The effects of the air supply position on the pump performance have been clarified by the experiments and the simulations with a revised model applicable to the midway air supply type.展开更多
We investigate the large-scale substorm current systems developed from its onset in an idealized substorm event simulated by global magnetohydrodynamic(MHD) models. Mainly three current systems(loops) are revealed:(1)...We investigate the large-scale substorm current systems developed from its onset in an idealized substorm event simulated by global magnetohydrodynamic(MHD) models. Mainly three current systems(loops) are revealed:(1) the classical substorm current wedge, which is composed by the disputed cross-tail current in the magnetotail, the nightside westward electrojet in the high-latitude ionosphere and a pair of region 1 field-aligned currents(FAC);(2) the partial-ring current system, which is braced by two region 2 FACs; and(3) the meridional current system, which is formed by an equatorial radial current(outward/inward in the morning/evening sector), and region 1 and region 2 FACs at its two ends. The region 2 FAC connects with region 1 FAC by a latitudinal horizontal current at each morning/evening ionosphere to complete Loops 2 and 3. A quantitative study shows the significant enhancement of these current systems during the substorm expansion phase, while Loop 1 dominates, which can reach a magnitude of ~1 MA. Empirical relations among the ionospheric currents and the related magnetotail currents are established based on the simulation results, implying that the substonn current systems are not evolved locally or separately, but must be viewed from a global perspective. This knowledge of large-scale substorm current system would deepen our understanding of the substorm development and could be validated by observations in the future.展开更多
Experimental results on the thermal characteristics of air-water spray impingement cooling of hot metallic surface are presented and discussed in this paper.The controlling input parameters investigated were the combi...Experimental results on the thermal characteristics of air-water spray impingement cooling of hot metallic surface are presented and discussed in this paper.The controlling input parameters investigated were the combined air and water pressures,plate thickness,water flow rate,nozzle height from the target surface and initial temperature of the hot surface.The effects of these input parameters on the important thermal characteristics such as heat transfer rate,heat transfer coefficient and wetting front movement were measured and examined.Hot flat plate samples of mild steel with dimension 120 mm in length,120 mm breadth and thickness of 4 mm,6 mm,and 8mm respectively were tested.The air assisted water spray was found to be an effective cooling media and method to achieve very high heat transfer rate from the surface.Higher heat transfer rate and heat transfer coefficients were obtained for the lesser i.e,4 mm thick plates.Increase in the nozzle height reduced the heat transfer efficiency of spray cooling.At an inlet water pressure of 4 bar and air pressure of 3 bar,maximum cooling rates670℃/s and average cooling rate of 305.23℃/s were achieved for a temperature of 850℃ of the steel plate.展开更多
文摘为解决固定式旋转喷头低压喷灌时,水射流向末端集中形成水量分布不均匀的问题,提出水气两相射流进行喷灌的方法。在摇臂喷头结构的基础上,增加掺气结构,形成掺气射流喷头,以相同工作水压力、射流仰角、喷嘴出口流量相同为约束,以及不考虑副喷嘴对喷洒的影响,对比了掺气与不掺气2种情况下PY20喷头的射程、径向水量分布、1倍射程间距的正方形组合喷灌均匀系数,雨滴粒径等参数。试验结果表明:原不掺气摇臂喷头出口直径7 mm,安装内径2 mm的掺气管后出口直径改为8.3 mm,此时两者具有相同的出口流量,2种喷头在相同工作压力下具有近似相等的射程;在掺气喷头工作水压低至100 k Pa情况下,喷头仍具有76 mm水银柱高差的掺气负压能力;掺气摇臂喷头改善了径向水量分布线射程中段的水量,使水量分布线发生了中段略微增高、末端略下降的变化,从而使1倍间距的正方形组合喷灌均匀系数在低于国家标准工作压力的200 k Pa情况下,从62.8%提高到68.8%;采用激光雨滴谱仪测量射程中部和末端2个地方的水滴粒径表明:掺气状态下射程中部的水量累积百分比中位直径d50远大于不掺气状态,射流末端对比d50则小于不掺气状态,说明掺气改变了喷头的雨滴粒径分布。该文试验结果证明掺气摇臂喷头在农业喷灌中应用具有可行性。
文摘This paper presented a method to create artificial fractures along the existing gas drainage borehole and increase the permeability of the coalbed using a high pressure waterjet cutting system.The field work conducted in Rujigou Colliery, Shenhua Ningxia Coal Group demonstrate that the coalbed permeability is increased, and accordingly, gas drainage efficiency is improved up to 3 to 6 times over the traditional methods using high pressure waterjet technique.Also, based on the monitoring data, the conceptual model for gas drainage process associated with different mining activities has been proposed, and few major advantages using waterjet assistance method have been identified.
文摘The present study is concerned with the lifting of seabed materials by a BJT （bubble-jet-type） air-lift pump patented by Sadatomi. The targets are methane-hydrate rich muds on the bed about 200 m in depth around Japan islands and rare-earth rich muds on the bed deeper than 4,000 m around Minami-Torishima islands in the Pacific Ocean. Feasibility studies were conducted using 50 mm I. D. （inner diameter） and 5.0 m long vertical pipe as the pump upriser, VC （vinyl chloride） particles and natural sands mixture in the methane-hydrate case, and ceramics particles with 3,761 kg/m^3 in density in the rare-earth case as the deposits. From the methane-hydrate simulation experiments, an efficient operation condition with high VC particles to sands lifting ratio has been clarified. In the rare-earth case, the air supplies from two different midways in the upriser pipe have been tested together with the bottom supply because the air supply from the upriser bottom is very hard in deep sea. The effects of the air supply position on the pump performance have been clarified by the experiments and the simulations with a revised model applicable to the midway air supply type.
基金supported by the National Natural Science Foundation of China(Grant Nos.41474145 and 41574159)the Specialized Research Fund for State Key Laboratories of China
文摘We investigate the large-scale substorm current systems developed from its onset in an idealized substorm event simulated by global magnetohydrodynamic(MHD) models. Mainly three current systems(loops) are revealed:(1) the classical substorm current wedge, which is composed by the disputed cross-tail current in the magnetotail, the nightside westward electrojet in the high-latitude ionosphere and a pair of region 1 field-aligned currents(FAC);(2) the partial-ring current system, which is braced by two region 2 FACs; and(3) the meridional current system, which is formed by an equatorial radial current(outward/inward in the morning/evening sector), and region 1 and region 2 FACs at its two ends. The region 2 FAC connects with region 1 FAC by a latitudinal horizontal current at each morning/evening ionosphere to complete Loops 2 and 3. A quantitative study shows the significant enhancement of these current systems during the substorm expansion phase, while Loop 1 dominates, which can reach a magnitude of ~1 MA. Empirical relations among the ionospheric currents and the related magnetotail currents are established based on the simulation results, implying that the substonn current systems are not evolved locally or separately, but must be viewed from a global perspective. This knowledge of large-scale substorm current system would deepen our understanding of the substorm development and could be validated by observations in the future.
文摘Experimental results on the thermal characteristics of air-water spray impingement cooling of hot metallic surface are presented and discussed in this paper.The controlling input parameters investigated were the combined air and water pressures,plate thickness,water flow rate,nozzle height from the target surface and initial temperature of the hot surface.The effects of these input parameters on the important thermal characteristics such as heat transfer rate,heat transfer coefficient and wetting front movement were measured and examined.Hot flat plate samples of mild steel with dimension 120 mm in length,120 mm breadth and thickness of 4 mm,6 mm,and 8mm respectively were tested.The air assisted water spray was found to be an effective cooling media and method to achieve very high heat transfer rate from the surface.Higher heat transfer rate and heat transfer coefficients were obtained for the lesser i.e,4 mm thick plates.Increase in the nozzle height reduced the heat transfer efficiency of spray cooling.At an inlet water pressure of 4 bar and air pressure of 3 bar,maximum cooling rates670℃/s and average cooling rate of 305.23℃/s were achieved for a temperature of 850℃ of the steel plate.
