Non-equilibirum condensation effects on the flow field and the performance of a low pressure steam turbine

The influence of non-equilibrium condensation on the flow field and performance of a three stage low pressure model steam turbine is examined using modern three dimensional CFD techniques. An equilibrium steam model and a non-equilibrium steam model, which accounts for both subcooling and condensation effects, are used, and have been verified by comparison with test data in an earlier publication [1]. The differences in the calculated flow field and turbine performance with these models show that the latent heat released during condensation influences both the thermodynamic and the aerodynamic performance of the turbine, leading to a change in inlet flow angles of about 5°. The calculated three dimensional flowfield is used to investigate the magnitude and distribution of the additional thermo-dynamic wetness loss arising from steam condensation under non-equilibrium flow conditions. Three simple methods are described to calculate this, and all show that this amounts to around 6.5% of the total losses at the design condition. At other load conditions the wetness losses change in magnitude and axial distribution in the turbine. © 2010 by ASME.

A condensation particle counter insensitive to volatile particles

A High Temperature Condensation Particle Counter (HT-CPC) is described that operates at an elevated temperature of up to ca. 300. °C such that volatile particles from typical combustion sources are not counted. The HT-CPC is functionally identical to a conventional CPC, the main challenge being to find suitable non-hazardous working fluids, with good stability, and an appropriate vapour pressure. Some key design features are described, and results of modelling which predict the HT-CPC counting efficiency. Experimental results are presented for several candidate fluids when the HT-CPC was challenged with ambient, NaCl and diesel soot particles, and the results show good agreement with modelled predictions, and confirm that counting of particles of diameters down to at least 10. nm was achievable. Possible applications are presented, including measurement of particles from a diesel car engine and comparison with a near PMP system. © 2014 Elsevier Ltd.

Second-harmonic generation of Bogoliubov excitations in a two-component Bose-Einstein condensate

A second-harmonic generation (SHG) is predicted for the Bogoliubov excitations in a two-component Bose-Einstein condensate. It is shown that, because the linear dispersion curve of the excitations displays two branches, the phase-matching condition for the SHG can be fulfilled if the wave vectors and frequencies of fundamental and second-harmonic waves are selected suitably from different branches. The nonlinearly coupled envelope equations for the SHG are derived by using a method of multiple scales. The explicit solutions of these envelope equations are provided and the conversion efficiency of the SHG is also discussed.

The quantum tunnelling between two-component Bose-Einstein condensates in a double-well configuration

We examine in terms of exact solutions of the time-dependent Schrodinger equation, the quantum tunnelling process in Bose-Einstein condensates of two interacting species trapped in a double well configuration. Based on the two series of time-dependent SU(2) gauge transformations, we diagonalize the Hamilton operator and obtain analytic time-evolution formulas of the population imbalance and the berry phase. the particle population imbalance (a(L)(+)aL - a(R)(+)a(R)) of species A between the two wells is studied analytically.

The quantum tunneling between two-component Bose-Einstein condensates in a double-well configuration

In terms of exact solution of the time-dependent Schrodinger equation. we examine the quantum tunneling process in Bose condensates of two interacting species trapped in a double well configuration. We use the two series of time-dependent SU(2) gauge transformation to diagonalize the Hamilton operator obtain analytic time-evolution formulas of the population imbalance and the berry phase. The particle population imbalance (a(L)(+)a(L) - a(R)(+)a(R)) of species A between the two wells is studied analytically.

Multi-channel effect of condensation flow in a micro triple-channel condenser

Multi-channel effect is important to understand transport phenomenon in phase change systems with parallel channels. In this paper, visualization studies were performed to study the multi-channel effect in a silicon triple-channel condenser with an aspect ratio of 0.04. Saturated water vapor was pumped into the microcondenser, which was horizontally positioned. The condenser was cooled by the air natural convention heat transfer in the air environment. Flow patterns are either the annular flow at high inlet vapor pressures, or a quasi-stable elongated bubble at the microchannel upstream followed by a detaching or detached miniature bubble at smaller inlet vapor pressures. The downstream miniature bubble was detached from the elongated bubble tip induced by the maximum Weber number there. It is observed that either a single vapor thread or dual vapor threads are at the front of the elongated bubble. A miniature bubble is fully formed by breaking up the vapor thread or threads. The transient vapor thread formation and breakup process is exactly symmetry against the centerline of the center channel. In side channels, the Marangoni effect induced by the small temperature variation over the channel width direction causes the vapor thread formation and breakup process deviating from the side channel centerline and approaching the center channel. The Marangoni effect further forces the detached bubble to rotate and approach the center channel, because the center channel always has higher temperatures, indicating the multi-channel effect. 

Periodic bubble emission and appearance of an ordered bubble sequence (train) during condensation in a single microchannel

Condensation of steam in a single microchannel, silicon test section was investigated visually at low flow rates. The microchannel was rectangular in cross-section with a depth of 30 pm, a width of 800 mu m and a length of 5.0 mm, covered with a Pyrex glass to allow for visualization of the bubble formation process. By varying the cooling rate during condensation of the saturated water vapor, it was possible to control the shape, size and frequency of the bubbles formed. At low cooling rates using only natural air convection from the ambient environment, the flow pattern in the microchannel consisted of a nearly stable elongated bubble attached upstream (near the inlet) that pinched off into a train of elliptical bubbles downstream of the elongated bubble. It was observed that these elliptical bubbles were emitted periodically from the tip of the elongated bubble at a high frequency, with smaller size than the channel width. The shape of the emitted bubbles underwent modifications shortly after their generation until finally becoming a stable vertical ellipse, maintaining its shape and size as it flowed downstream at a constant speed. These periodically emitted elliptical bubbles thus formed an ordered bubble sequence (train). At higher cooling rates using chilled water in a copper heat sink attached to the test section, the bubble formation frequency increased significantly while the bubble size decreased, all the while forming a perfect bubble train flowing downstream of the microchannel. The emitted bubbles in this case immediately formed into a circular shape without any further modification after their separation from the elongated bubble upstream. The present study suggests that a method for controlling the size and generation frequency of microbubbles could be so developed, which may be of interest for microfluidic applications. The breakup of the elongated bubble is caused by the large Weber number at the tip of the elongated bubble induced by the maximum vapor velocity at the centerline of the microchannel inside the elongated bubble and the smaller surface tension force of water at the tip of the elongated bubble.

SU(2)规范场分解与Bose-Einstein凝聚体中的环流条件

利用SU(2)规范场的单位矢量场分解形式讨论了Bose-Einstein凝聚体中的环流条件.对于二分量Bose-Einstein凝聚,内部态的SU(2)对称性将导致一个拓扑环流条件,这是一个推广的Mer-min—Ho关系.