Molten slag is broken up by supersonic air into droplets through the air quenching dry slag granulation technique.The breakup process of blast furnace slag directly determines the droplet diameter and the waste heat r...Molten slag is broken up by supersonic air into droplets through the air quenching dry slag granulation technique.The breakup process of blast furnace slag directly determines the droplet diameter and the waste heat recovery.In order to gain deep insight into the granulation mechanism and visualize the breakup process,three-dimensional unsteady numerical simulation based on the k-x based shear stress transport turbulence model was conducted to simulate the transient breakup process of molten slag(k is the turbulent kinetic energy,and x is the specific dissipation rate).The coupled level-set and volume-of-fluid method was utilized to capture the sharp air–liquid interface.The results show that a flat film is formed firstly under the effects of air impingement,recirculation zone and pressure gradients.Then,the axial wave and the spanwise wave appear simultaneously and the film is broken up into ligaments owing to the generation of vortex and hole structure at the intersection of axial trough and spanwise trough.Finally,the ligaments are broken up into droplets owing to Rayleigh–Taylor instability at the air–liquid interface.The droplets smaller than 3.00 mm account for 80%,with the average diameter of 1.95 mm.展开更多
为了研究液体横向射流在气膜作用下的破碎过程,采用背景光成像技术及VOF TO DPM方法进行了实验研究和仿真研究,模拟介质为水和空气.研究结果表明,液体射流在气膜作用下主要存在两种破碎过程:柱状破碎和表面破碎.Rayleigh-Taylor(R-T)不...为了研究液体横向射流在气膜作用下的破碎过程,采用背景光成像技术及VOF TO DPM方法进行了实验研究和仿真研究,模拟介质为水和空气.研究结果表明,液体射流在气膜作用下主要存在两种破碎过程:柱状破碎和表面破碎.Rayleigh-Taylor(R-T)不稳定性产生的表面波是液体射流发生柱状破碎的主要原因,气流穿透表面波的波谷导致射流柱破碎,破碎后的液丝沿流向逐渐发展呈带状分布.Kelvin-Helmholtz(K-H)不稳定性产生的表面波是液体射流发生表面破碎的主要原因,液丝和液滴从射流表面剥离.局部动量比对液体横向射流的破碎过程具有重要影响,当局部动量比较低时,液体射流的破碎由K-H不稳定性主导;随着局部动量比的增大液体射流的破碎逐渐由R-T不稳定性主导.液体射流的破碎长度及穿透深度均随局部动量比的增大而增大.展开更多
A visualized investigation was carried out on the effect of the diverging angle on the bubble motion and interfacial behavior in a Venturi-type bubble generator.It was found two or three large vortexes formed in the d...A visualized investigation was carried out on the effect of the diverging angle on the bubble motion and interfacial behavior in a Venturi-type bubble generator.It was found two or three large vortexes formed in the diverging section,resulting in strong reentrant jet flow in the front of the bubbles or slugs rushing out of the throat.The jet flow in return bumps into the ongoing bubbles or slugs,leading to strong interaction between the gas and liquid phases.The diverging angle has significant influence on the reentrant flow process and the performance of the bubble generator as well.Increasing the diverging angle results in the reentrant flow moving further forward to the upstream and intensifies the interaction between the two phases.As a consequence,the breakup or collapse of bubbles becomes more violent,whereby finer bubbles are generated.As such,the reentrant flow strongly links to the performance of the Venturi channel taken as a bubble generator,and that a moderate increase in the diverging angle can improve its performance without additional increase in flow resistance like that by increasing liquid flow rate.展开更多
为了更好地认识针栓式喷注器雾化场的结构,基于网格自适应加密技术以及VOF (volume of fraction)方法追踪气液的分界面,采用realizable k-ε湍流模型模拟整个流动过程,还原了不同时刻气/液撞击的初次破碎过程,数值模拟结果与高速摄影试...为了更好地认识针栓式喷注器雾化场的结构,基于网格自适应加密技术以及VOF (volume of fraction)方法追踪气液的分界面,采用realizable k-ε湍流模型模拟整个流动过程,还原了不同时刻气/液撞击的初次破碎过程,数值模拟结果与高速摄影试验结果定性定量对比均吻合较好,验证了数值方法的准确性。进一步对针栓式喷注器气/液撞击的初次破碎过程、内部流场涡结构、速度场进行分析,研究了初次破碎雾化的动力学过程和机理。研究结果表明:液桥的形成主要是由液洞的扩展和拉伸、合并而形成,而液滴主要是由中心液膜拉伸、液丝断裂以及液桥断裂而形成,液膜破碎阶段形成的涡结构是造成液膜断裂的主要原因。展开更多
基金This research was supported by the National Key Research and Development Project of China(2016YFB0601403).
文摘Molten slag is broken up by supersonic air into droplets through the air quenching dry slag granulation technique.The breakup process of blast furnace slag directly determines the droplet diameter and the waste heat recovery.In order to gain deep insight into the granulation mechanism and visualize the breakup process,three-dimensional unsteady numerical simulation based on the k-x based shear stress transport turbulence model was conducted to simulate the transient breakup process of molten slag(k is the turbulent kinetic energy,and x is the specific dissipation rate).The coupled level-set and volume-of-fluid method was utilized to capture the sharp air–liquid interface.The results show that a flat film is formed firstly under the effects of air impingement,recirculation zone and pressure gradients.Then,the axial wave and the spanwise wave appear simultaneously and the film is broken up into ligaments owing to the generation of vortex and hole structure at the intersection of axial trough and spanwise trough.Finally,the ligaments are broken up into droplets owing to Rayleigh–Taylor instability at the air–liquid interface.The droplets smaller than 3.00 mm account for 80%,with the average diameter of 1.95 mm.
文摘为了研究液体横向射流在气膜作用下的破碎过程,采用背景光成像技术及VOF TO DPM方法进行了实验研究和仿真研究,模拟介质为水和空气.研究结果表明,液体射流在气膜作用下主要存在两种破碎过程:柱状破碎和表面破碎.Rayleigh-Taylor(R-T)不稳定性产生的表面波是液体射流发生柱状破碎的主要原因,气流穿透表面波的波谷导致射流柱破碎,破碎后的液丝沿流向逐渐发展呈带状分布.Kelvin-Helmholtz(K-H)不稳定性产生的表面波是液体射流发生表面破碎的主要原因,液丝和液滴从射流表面剥离.局部动量比对液体横向射流的破碎过程具有重要影响,当局部动量比较低时,液体射流的破碎由K-H不稳定性主导;随着局部动量比的增大液体射流的破碎逐渐由R-T不稳定性主导.液体射流的破碎长度及穿透深度均随局部动量比的增大而增大.
基金supported by the National Natural Science Foundation of China (Grants 51709191, 51606130, and 51506099)
文摘A visualized investigation was carried out on the effect of the diverging angle on the bubble motion and interfacial behavior in a Venturi-type bubble generator.It was found two or three large vortexes formed in the diverging section,resulting in strong reentrant jet flow in the front of the bubbles or slugs rushing out of the throat.The jet flow in return bumps into the ongoing bubbles or slugs,leading to strong interaction between the gas and liquid phases.The diverging angle has significant influence on the reentrant flow process and the performance of the bubble generator as well.Increasing the diverging angle results in the reentrant flow moving further forward to the upstream and intensifies the interaction between the two phases.As a consequence,the breakup or collapse of bubbles becomes more violent,whereby finer bubbles are generated.As such,the reentrant flow strongly links to the performance of the Venturi channel taken as a bubble generator,and that a moderate increase in the diverging angle can improve its performance without additional increase in flow resistance like that by increasing liquid flow rate.
文摘为了更好地认识针栓式喷注器雾化场的结构,基于网格自适应加密技术以及VOF (volume of fraction)方法追踪气液的分界面,采用realizable k-ε湍流模型模拟整个流动过程,还原了不同时刻气/液撞击的初次破碎过程,数值模拟结果与高速摄影试验结果定性定量对比均吻合较好,验证了数值方法的准确性。进一步对针栓式喷注器气/液撞击的初次破碎过程、内部流场涡结构、速度场进行分析,研究了初次破碎雾化的动力学过程和机理。研究结果表明:液桥的形成主要是由液洞的扩展和拉伸、合并而形成,而液滴主要是由中心液膜拉伸、液丝断裂以及液桥断裂而形成,液膜破碎阶段形成的涡结构是造成液膜断裂的主要原因。
