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水平螺旋槽管壁面升膜形成机理的研究 总被引:2,自引:1,他引:2
对驱动升膜形成的润湿力进行分析,建立单组分流体的数学模型,得出壁面液膜蒸发时的速度和厚度分布。基于此得到蒸发过程中水平螺旋槽管管外壁升膜的形成机理和流动特性,并给出液膜润湿整个管壁面的临界条件。 相似文献
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ANALYSIS OF THE MULTIPLE-SOLUTION RESPONSE OF A FLEXIBLE ROTOR SUPPORTED ON NON-LINEAR SQUEEZE FILM DAMPERS 总被引:3,自引:0,他引:3
The multiple-solution response of rotors supported on squeeze film dampers is a typical non-linear phenomenon. The behaviour of the multiple-solution response in a flexible rotor supported on two identical squeeze film dampers with centralizing springs is studied by three methods: synchronous circular centred-orbit motion solution, numerical integration method and slow acceleration method using the assumption of a short bearing and cavitated oil film; the differences of computational results obtained by the three different methods are compared in this paper. It is shown that there are three basic forms for the multiple-solution response in the flexible rotor system supported on the squeeze film dampers, which are the resonant, isolated bifurcation and swallowtail bifurcation multiple solutions. In the multiple-solution speed regions, the rotor motion may be subsynchronous, super-subsynchronous, almost-periodic and even chaotic, besides synchronous circular centred, even if the gravity effect is not considered. The assumption of synchronous circular centred-orbit motion for the journal and rotor around the static deflection line can be used only in some special cases; the steady state numerical integration method is very useful, but time consuming. Using the slow acceleration method, not only can the multiple-solution speed regions be detected, but also the non-synchronous response regions. 相似文献
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现有液膜反转方案都只利用一半的传热面积,本文介绍了一种双面液膜反转方案,用耙型导流器连接上下波纹板束.耙型导流器交叉地将上波纹对板两侧液膜引导到下波纹对板的对面,双面液膜反转后液膜的均匀性对于在下板束的波纹板上的传热传质效率十分关键.作者利用VOF法建立了液膜在耙型导流器单元上的动态气-液两相流CFD模型,并进行了模拟计算.导流器单元中的流场数值模拟结果显示溴化锂溶液液膜流过导流器时在重力和表面张力作用下从导流舌中间和沿圆弧缺口边分成三股流体流下并逐步扩展汇合,在较短时间内实现液膜分布均匀化,表明耙型导流器结构可以胜任双面液膜反转对液膜均匀性的要求. 相似文献
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水平管降膜蒸发器传热优化研究 总被引:1,自引:0,他引:1
基于分布参数方法,对大型制冷系统中的水平管外降膜蒸发进行了传热优化数值模拟计算.在计算中,分析了饱和的液态制冷剂R134a在水平的铜管束外流动蒸发的换热特性.模型考虑了不同的管子类型和2流程不同管程布置对蒸发器换热特性的影响,结果表明,蒸发器采用Turbo-EHP管的性能高于其它管;不同管程布置对蒸发器性能的影响比较大,其中,下进上出管程布置的换热性能优于其它管程布置.同时,本文考虑了传热管外"干斑"对换热的影响.本文结论对于大型制冷系统中的降膜蒸发器传热优化设计具有指导性意义. 相似文献
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冷面结霜初始形态的理论分析 总被引:14,自引:5,他引:14
从形核的概念出发,分析了水蒸气在冷面上的结霜并非单纯凝华的原因,对结霜前的微细观结露现象给予了理论解释:水蒸气在零度以下冷面上凝结生成液核的活化率远远大于凝华生成霜核的活化率,所以冷面上最先出现的是水珠。揭示了疏水面抑制结霜的原因,即增大接触角可以提高成核势垒,使新相变得难形成,从而降低新相的活化率。 相似文献