高压水射流喷嘴效率解析

在高压水射流清洗机械中,整机重量约有2 000-3 000kg,可是它的主要工作机构喷嘴的直径和长度只有2-3cm,其重量也就100-200g。但是高压水射流却完全是从这里产生的,因此喷嘴的效率分析就显得非常重要。

JK90S可调喷嘴涡轮喷嘴冲角特性

为了使涡轮与发动机在较宽广的工况范围内保持良好的匹配,通过调节涡轮喷嘴环的转角,改变涡轮的流通面积,使涡轮的流量特性和效率特性发生变化.运用三维数值模拟技术,对JK90S可调喷嘴涡轮喷嘴冲角特性进行了数值计算和流场分析.结果表明,当仅改变喷嘴环的入口冲角,保持喷嘴入口的总温、总压和出口静压不变,喷嘴环的气流冲角小于某一值时,级效率对于喷嘴环入口来流的冲角不敏感;当冲角大于此值时,级效率将急剧降低,此时级效率主要受喷嘴环效率的影响.

冲击式水轮机效率优化措施

目前冲击式水轮机世界最高效率是91%,比反击式混流机同水头同用水量低3%左右,冲击式水轮机导水机构喷嘴口(固定内径)有2个缺陷,降低了水轮机总效率。解决的方法:固定内径时用混合型喷嘴口,由原单一内锥角,变为3个不同内角,将流经导水机构流通部件产生流态变化的急变流,在约束边界内转为缓变流再喷出,水机总效率大于93%;喷嘴口变径装置比用单个固定混合型喷嘴口每年发电量多4%。

微磨料浆体射流形成过程的能量传输

为了研究微磨料浆体射流形成的能量传输与转换,用碳化硅磨料对40CrMnMo7钢进行冲击,建立数学模型描述冲击力与射流压力、喷嘴效率、射流流量、水力功率等参数的相互影响,通过测量射冲击力、射流流量来预测射流系统的单位水力功率的出力状况。结果表明,该数学模型可以预测射流冲击力与水力功率之比,由系统压力模型计算的冲击力比实验结果小20%;在射流的滞止区内,压力与冲击力不呈线性关系,在相同压力下,磨料粒子具有更大的动能,微磨料浆体射流冲击力比纯水射流的大20%,单位水力功率提供的射流冲击力随着射流压力的增大而减小;射流冲击力随着喷嘴直径、射流压力的增大而增大,在靶距较小的情况下,冲击力随着靶距的增大而增大,当靶距达到一定值时,冲击力随着靶距的增大而减小。

Disintegration Process and Performance of a Coaxial Porous Injector

In order to understand the breakup performance of coaxial porous injectors,the sprays of coaxial porous injectors with two different porous material cylinder lengths were compared with those of conventional shear coaxial injectors.To allow comparison,the wall injection lengths were designed to be equivalent to the value of the recess depth.Cold flow sprays were visualized using back-lit photography methods and analyzed quantitatively with a laser diffraction apparatus,in order to study the effects of the momentum flux ratio and Weber number on the breakup for each type of injector.In case of the shear coaxial injector,the large liquid core was observed in low air mass flow rate condition.However,the destabilization of the liquid jet from the coaxial porous injector is almost complete within the inner region,near the injector face plate.Additionally,better breakup performance in low gas flow rate condition was obtained when the porous cylinder length decreased,while the shear coaxial injectors showed better breakup efficiency when the recess length increased.In conclusion,the different breakup process caused by the radial momentum in the inner region of the porous injector disintegrated the liquid core.