NUMERICAL SIMULATION OF WET STEAM CONDENSING FLOW WITH AN EULERIAN/EULERIAN MODEL

Wet steam condensing flow in low-pressure steam turbine leads to efficiencylosses and blade erosions. In order to investigate this problem by numerical approach, anEulerian/Eulerian model has been developed, in which the wet steam is regarded as mixture comprisingtwo coupled systems: the vapor phase and the liquid phase. These two systems are both described byconservation equations. High resolution TVD scheme is employed to capture condensing phenomena inwet steam flow. This model has been validated by numerical simulations of condensing flows in 1D and2D nozzles. Compared with experimental data, a good agreement is observed. This Eulerian/Eulerianmodel can be extended to 3D calculation of condensing flow.

Study of steady and unsteady wet steam condensing flows in a turbine stage

Objective To develop the numerical method for the steady and unsteady wet steam condensing flow in turbine stage. Methods An Eulerian/Eulerian numerical model is used to describe the spontaneous condensation flow in the steam turbine. For the steady condensing flow computations, the mixing plane model was used. For the unsteady condensing flow computations, the sliding mesh method was used to simulate the rotor-stator interactions. Results The numerical results showed the obvious differences between non-condensing and condensing flows. The results also showed the unsteadiness effect due to rotor-stator interactions had a deep influence on the formation and growth process of water droplets. Conclusion The numerical methods presented in this paper are valid for the condensing flow in the turbine stage.

Effect of carrier gas pressure on vapor condensation and mass flow-rate in sonic nozzle

Non-equilibrium vapor condensation of moist gas through a sonic nozzle is a very complicated phenomenon and is related to the measurement accuracy of sonic nozzle.A gas-liquid two-phase model for the moist gas condensation flow was built and validated by moist nitrogen experiment of homogeneous nucleation through a transonic nozzle.The effects of carrier gas pressure on position and status of condensation onset in sonic nozzle were investigated in detail.The results show that condensation process is not easy to occur at lower carrier pressure and throat diameter.The main factors influencing condensation onset are boundary layer thickness,heat capacity of carrier gas and expansion rate.All of results can be used to further analyze the effect of condensation on mass flow-rate of sonic nozzle.

Theoretical and Experimental Analysis of Heat Transfer and Condensation in Micro-Ribbed Tubes

The thermal transmission coefficient for a micro-ribbed tube has been determined using theoretical relationships and the outcomes of such calculations have been compared with experiments conducted using a R1234yf refrigerant undergoing condensation.In particular four theoretical single-phase flow and three multi-phase flow models have been used in this regard.The experimental results show that:the Oliver et al.criterion equation overestimates the experimental results as its accuracy is significantly affected by the specific conditions realized inside micro-fin tubes;the Miyara et al.criterion equation prediction error is less than 15%;the Cavallini et al.approach gives the highest prediction accuracy;the Goto et al.model overestimates the test data.Such results are critically discussed and some indications for the improvement of such models are provided.

Influence Factors on Particle Growth for On-line Aerosol Matrix-assisted Laser Desorption/Ionization Time-of-flight Mass Spectrometry

An evaporation/condensation flow cell was developed and interfaced with the matrix-assisted laser desorption/ionization （MALDI） time-of-flight mass spectrometer for on-line bioaerosol detection and characterization, which allows matrix addition by condensation onto the laboratory-generated bioaerosol particles. The final coated particle exiting from the con- denser is then introduced into the aerodynamic particle sizer spectrometer or home-built aerosol laser time-of-flight mass spectrometer, and its aerodynamic size directly effects on the matrix-to-analyte molar ratio, which is very important for MALDI technique. In order to observe the protonated analyte molecular ion, and then determine the classification of bi- ological aerosols, the matrix-to-analyte molar ratio must be appropriate. Four experimental parameters, including the temperature of the heated reservoir, the initial particle size, its number concentration, and the matrix material, were tested experimentally to analyze their influences on the final particle size. This technique represents an on-line system of detection that has the potential to provide rapid and reliable identification of airborne biological aerosols.

Research on Wet Steam Spontaneous Condensing Flows Considering Phase Transition and Slip

A new dual-fluid model considering phase ansition and velocity slip was proposed in this paper and the Cunningham correction was used in the droplet resistance calculation. This dual-fluid model was applied to the numerical simulations of wet steam flow in a 2D LAVAL nozzle and in the White cascade respectively. The results of two simulations demonstrate that the model is reliable. Meanwhile, the spontaneous condensing flow in White cascade was analyzed and it infers that the irreversible loss caused by condensation accounts for the largest share （about 8.78% of inlet total pressure） in total pressure loss while the loss caused by velocity slip takes the smallest share （nearly 0.42%）, and another part of total pressure loss caused by pneumatic factors contributes a less share than condensation, i.e. almost 3.95% of inlet total pressure.

Study on Characteristics of Steady Flow Condensation Heat Transfer in a Tube under Zero－Gravitation

In this paper, the annular flow. model for in tube completed condensation is employed to predict the steady flow condensation heat transfer characteristics in a tube under zero-gravitation. In this easel it is proposed that vapor condenses on the liquid film surface. Due to the effect of surface tension, the liquid exists in the form of liquid film ring contacting wall; when the velocity of vapor core decreases to zerol the condensation process ends. Putting forward the physical and mathematical models, the problem is solved and the multi-order equation of the thickness of liquid film is obtained, which includes terms of the pressure gradient along axial direction, the friction force between vapor and liquid on interface. By computational calculation, this model can be used not only to predict the thickness of liquid film, the condensation pressure gradient along the axial direction, but also to determine the Nusselt number, the condensation length and the total flow pressure drop of condensation etc. At the end, the calculation results of the necessary condensation length are compared approximately with those from the experiments, which are obtained on the test set-up placed horizontally in gravitation field, and the deviation is analyzed.

Condensation heat transfer characteristics of vapor flow in vertical small-diameter tube with variable wall temperature

To explore the condensation characteristics of vapor flow inside vertical small-diameter tubes, the classical Nusselt theory is revised and an analytical model with variable tube wall temperature is established by considering the effect of surface tension exerted by condensate film bending as well as the effect of shear stress on vapor-liquid interface. The effects of various factors including tube wall temperature and gravityon flow condensation in small-diameter tubes are analyzed theoretically to show the heat transfer characteristics. Comparison with the experimental data indicates that the proposed analytical model is fit to reveal the fundamental characteristics of flow condensation heat transfer in vertical small-diameter tube.

Effect of Nonequilibrium condensation of Moist Air on Transonic Flow Fields

When condensation occurs in a supersonic flow field, the flow is affected by the latent heat released. In the present study, a condensing flow was produced by an expansion of moist air in nozzle with circular bump models and shock waves occurred in the supersonic parts of the flow fields. The experimental investigations were carried out to show the effects of initial conditions in the reservoir and nozzle geometries on the shock wave characteristics and the turbulences in the flow fields. Furthermore, in order to clarify the effect of condensation on the flow fields with shock waves, Navier-Stokes equations were solved numerically using a 3rd-order MUSCL type TVD finitedifference scheme with a second order fractional step for time integration. As a result the effect of condensation on the aspect of flow field has been clarified.