The development of space is a great dream left to mankind. More than 30 years have passed since the world's first satellite was launched. Now, international telephone communication can be made via comsats and the image of clouds can be seen on television and in newspapers thanks to through a meterological satellites. As the power output of satellites and spacecraft increases, a thermal control system must be considerd for the recovery, transport, and disposal of waste heat. The change of phase of the working fluid results in lower electrical power requirements to operate pumps and gives a relatively isothermal sink temperature. Various system designs must be made to accomplish this two-phase thermal management capability. However, there is only little information available on two-phase flow pressure drop and heat transfer in reduced gravity environments. Here, the present status of investigation into two-phase flow in micro-gravity environments is introduced, with an emphasis especially on flow pattern.
Recently, many studies on annular mist flows have been reported. Most of them focus on a flow which has been fully developed or has reached its equilibrium state. On the flow in the non-equiliblium state, however, there are only a very few systematic studies. But two-phase flow phenemena in actual industrial devices are often in non-equilibrium. Therefore it is necessary to accumulate and analyze the fundamental data on the flow in non-equilibrium, in order to improve the efficiency of instruments connected with a two-phase flow, and to assure the generality and validity for the experimental data on two-phase flow. In the light of the above-mentioned facts, the author scrutinized some gas-liquid mixing methods in a two-component, annular mist flow closely related to the non-equilibrium length. The gas-liquid mixing devices involved can be classified into the following six classes: porous sinter, annular slot, center single jet, multi-jet, multi-hole and air-blast atomizer. Next, a variety of items relevant to the study of mixing methods, such as mixing devices, experimental conditions and measuremetns and details of some of those involved in this field of research, are set out in a table. Finally, some examples of flow behavior in the non-equilibrium region of an annular mist flow are looked at briefly.
In recent years, the two-fluid model has often been used in thermalhydraulic analyses. This model is considered to be theoretically more strict and to be more relevant in treating such two-phase flow phenomena as these that are affected by thermal or hydrodynamic non-equilibrium, because the model describes the conservation of mass, momentum and energy for both gas and liquid phases, separately. In order for the model to display its real worth, however, it is important that the constitutive equations be used properly. This review paper, therefore, presents the constitutive equations for flow-regime transitions, interfacial area concentration, behavior of liquid droplets, interfacial friction, interfacial heat transfer, wall friction and wall heat transfer that are actually used in computer codes for thermal-hydraulic analyses.
Multiphase flows are very popular in ironmaking and steelmaking processes and are characterized as follows:(1) The temperature of fluids in metallurgical reactors is higher than about 1500°C, hence measurements of transport phenomena (fluid motion, heat and mass transfer) are very difficult.(2) The flow in the reactors is highly turbulent (turbulence components are usually larger than mean flow values) and chemical reactions take place at the same time. Many “cold model” experiments have been carried out due to the difficulty in doing measurements under realistic conditions. Water, oil (silicone oil, pentane, liquid paraffin, etc.) and metals with low melting temperatures (mercury, Wood's metal, etc.) are Used as working fluids. Transport phenomena encountered in ironmaking and steelmaking processes (hot metal pretreatment, converter, second refining processes, etc.) are covered here and previous experimental and theoretical results on this subject are reviewed
Particle-Imaging Velocimetry (PIV) has advanced rapidly with the recent noticeable development of computers and image processors and the development and propagation of flow visualization techniques. The techique of PIV gives information on flow velocity, temperature and density through image analysis of visualized pictures and has been recognized as a strong new measuring tool in thermal and fluid engineering fields including multiphase flows. Its merits are: (1) simultaneous measurement of the whole flow field; (2) easy information processing of the other physical values from its measurement. Such merits are not shared by one point measurement methods such as the Pitot tube, hot wire anemometer and LDV. This article presents not only a general introduction of some methods of PIV but also some details of the fundamentals and applications of typical methods such as laser speckle technique, four consecutive time step particle tracking technique, the cross-correlation method using brigthness distribution patterns and the binary picture cross-correlation method using particle distribution patterns. Applications for these techniques are also suggested.
Experimental investigation was conducted into horizontal and near horizontal air-water annular two-phase flows. Following the previous papers, attention was paid in the present paper to the structure of the disturbance wave flow and the amount of liquid transported by disturbance waves. The effect of the angle of inclination of the test tube was also examined. The results are summarized as follows: (1) The angle of inclination is irrelevant to the passing frequency, distance and scale of disturbance waves when it is within 15 degrees of the horizontal. (2) Wave velocity, passing frequency and wave scale are correlated to within ±30% independent of the pipe inclination. (3) The amount of liquid climbed along the tube wall by the disturbance waves is not significantly affected by the tube inclination angle. It was also found that the increase in the rate at which liquid climbed along the tube wall, corresponding to an increase in superficial water velocity, is less than the increase in the amount of liquid transported by the disturbance waves.