Jian-Fu Zhao

Slug to annular flow transition of microgravity two-phase flow

A new model is developed for predicting the transition from the slug to annular flow of adiabatic two-phase gas/liquid flow in microgravity (mu g) environment. This model is based on the analyses of the effects of the surface tension and the gas inertia in a sense of more physical approach. The drift-flux model is applied to determine the gas void fraction near the transition region. The new model is compared with previous models and experimental data, and the results show the improvement in explanation of the experimental results.

Experimental studies on two-phase flow patterns aboard the Mir space station

A series of experiments on two-phase gas-liquid flow patterns in a test tube with a length of 356 mm and an inside diameter of 10 mm were performed aboard the Mir Space Station in August 1999. Carbogal and air were used as the liquid and the gas phase, respectively. In the present paper, the experimental results at the background microgravity environment of the Mir Space Station (no more than 10(-5)g) were reported. Five kinds of flow patterns, namely dispersed bubble flow, bubble flow, slug flow, slug-annular transitional flow, and annular flow, were observed in the space experiment. Due to the small length-to-diameter ratio of the test tube used in the present study, the observed flow patterns should be considered to be developing ones. The experimental results were compared with the model proposed previously which accounts for the entrance effects on the flow pattern transitions. A good agreement between the predictions and the experimental data was obtained. Some widely used models developed based on the analysis of fully developed two-phase flow at microgravity were also compared with the present data in order to make evaluations of these models and to have some insights on the flow evolution.

Pressure drop of bubbly two-phase flow in a square channel at reduced gravity

A new set of experimental pressure drop data, collected aboard the Russian IL-76MDK, is reported for bubbly airwater two-phase flow in a square channel with a cross-sectional area of 12x 12mm(2). The present data are compared to several frequently used empirical models, e.g. homogeneous model, Lockhart-Martinelli-Chisholm correlation and Friedels model. It is shown that the predictions of the models mentioned above are generally not satisfied. A new homogeneous model is developed based on the analysis of the characteristics of bubbly two-phase flow at reduced gravity. It is tested with the present data and other data collected by other researchers in circular pipes. Some questions related to the present model are also discussed

Statistical characteristics of evaporating-freezing process of water droplet during quick depressurization

This work investigates experimentally flashing evaporation process of water droplets released into vacuum, particularly on the quantitative characteristics of the process, in order to reveal the influences of the randomicity of the sub-process of nucleation and non-condensable air dissolved inside the liquid. It’s clearly shown that nucleation time is a random variable. That may be caused by the following facts that nucleation for ice in high-supercooled water exhibits a strong randomicity and that there exists strong perturbation during quick depressurization. Freezing temperature of liquid droplet is approximately constant after recalescence, which may be determined by the vapor partial pressure at the terminal state. Freezing time is independent of nucleation time, but exhibits an obvious dependence on terminal pressure and drop diameter. Supercooling corresponding to the nucleation is independent of terminal pressure. The averaged values of supercooling at three different terminal pressures of 450, 60...

Two-Phase Flow Patterns in A Square Mini-Channel

This paper presents a new set of experimental data of air-water flow patterns in a channel with a cross-section of 1×1 mm2. The ranges of the gas and liquid superficial velocities are 0.1–10 m/s and 0.2–7 m/s, respectively. Bubble, bubble-slug, slug, and frothy flows are observed. The present data are compared with other data in mini-channels reported in literature, and also compared with those in normal channel at microgravity, in which the Bond number has the same order of magnitude. The slug-frothy boundary is in consistent with each other, but for the bubble-slug transition, a much smaller value for the transition quality in the drift-flux model is obtained in the present study than those predicted by the empirical relations for the case of microgravity. It’s shown that the mini-scale modeling may not be an effective way to anticipate the bubble-slug transition of two-phase flow at microgravity.

Two-Side-Simultaneously-Observing Test System of Passive DMFC

In order to test passive direct methanol fuel cell and simultaneously observe anode and cathode of a fuel cell, we designed and built a test system. The test system consists of four units: temperature control unit, lighting unit, camera unit and test and data acquisition unit. With a two-floor placement design, we separated tested object and its close auxiliary components from other devices. The design is critical for changing inclination angle between outward normal of anode and gravity direction, which is important to the experiment. The control interface of the test system makes it suitable for a microgravity test system in NMLC (National Microgravity Laboratory Center). Considering the test system will be used for microgravity experiment besides routine normal gravity experiments, many specific issues have been taken into account.

Topological structure bifurcation of temperature field of deformable drop in Marangoni migration

The unsteady processes of the Marangoni migration of deformable liquid drops are simulated numerically in a wider range of Marangoni number (up to

Pool Boiling on Wire in Microgravity—What Have We Learned

Ma=500

TWO-PHASE FLOW AND POOL BOILING HEAT TRANSFER IN MICROGRAVITY

) in the present work. A steady terminal state can always be reached, and the scaled terminal velocity is a monotonic function decreasing with increasing Marangoni number, which is generally in agreement with corresponding experimental data. The topological structure of flow field in the steady terminal state does not change as the Marangoni number increases, while bifurcation of the topological structure of temperature field occurs twice at two corresponding critical Marangoni numbers. A third critical value of Marangoni number also exists, beyond which the coldest point jumps from the rear stagnation to inside the drop though the topological structure of the temperature field does not change. It is found that the inner and outer thermal boundary layers may exist along the interface both inside and outside the drop if

Investigation on mechanism of critical cavitating flow in liquid jet pumps under operating limits

Ma>70