Gas-liquid separation is a key task for various systems that are utilized onboard the International Space Station, such as active thermal control and waste management. In most of these system designs, performance is either significantly degraded or the equipment undergoes increased wear if two phase flow is not first separated.Unlike being under the influence of Earth gravity, where gas and liquid separate spontaneously due to buoyancy forces, gas bubbles remain suspended within the liquid under microgravity conditions. In the passive cyclonic separator studied in this research, the gas-liquid mixture is separated by the centrifugal force created by tangentially injecting the two phase fluid into a cylindrical housing. The inertia of the flow itself creates a swirling motion which generates the centrifugal acceleration. Due to the density differences between the two phases, the lower density gas phase moves towards the center of rotation creating a gas core surrounded by an annular liquid film.In such an operation, the separation efficiency is strongly influenced by the gas core behavior and the transport of bubbles within the turbulent liquid annulus. The main focus of the present study is to obtain physical insight into the gas core behavior as well as the bubble dynamics within the liquid film through experimentation and computational modeling.The experimental portion of this work entails the construction and operation of a specific cyclonic two phase separator operated across its useful parameter range under the influence of Earth gravity. The useful operating ranges and separation efficiencies are mapped. The numerical modeling work includes two hybrid-multiphase computational fluid dynamics techniques coupled with large eddy simulation turbulence modeling and are implemented by using the OpenFOAM library.Data analysis and comparison reveal that the injection nozzle design, swirl number, and volumetric gas quality all have a major influence on the gas core size. The control volume analysis reveals the importance of the skin friction coefficient. The trajectories of single gas bubbles are simulated numerically and graphed. It is found that fluid turbulence tends to disperse small gas bubbles in the liquid film resulting in a longer residence time.

The separation of two-phase flow is essential for many fluid systems in the microgravity environment. Unlike the situation on earth, gas and liquid cannot separate spontaneously due to the absence of buoyancy in space. Therefore, phase separators must be designed to complete this task. The passive cyclonic separator is a prominent technology for gas-liquid separation in microgravity for the reason that it is free of maintenance and power consumption. However, the complex flow physics within the separator presents significant challenges in designing the device and characterizing its performance. In the present study, numerical simulations and analytical modeling are combined to construct a system of control volume equations that can quantitatively describe the key features of the separator, as well as defining the parameters for design purposes. The numerical simulations are conducted utilizing an open-source computational fluid dynamics (CFD) software OpenFOAM. Both two dimensional (2D) axisymmetric modeling and three-dimensional (3D) modeling are performed. The CFD work in the current study focuses on pure-liquid injection cases in which gas cores would still form without small gas bubbles. Therefore, the volume of fluid (VOF) approach is used to capture the large scale gas-liquid interface. Since the swirling flow inside the separator is mostly turbulent, a Reynolds stress transport model (RSTM) is adopted for the simulations. The CFD technique provides enough amount of data to study the important parameters of the separator, which facilitate and complete the analytical modeling. The analytical modeling is developed based on control-volume approximations. This approach helps clarify the fluid physics by transforming the complicated physical phenomena into simple control-volume equations representing the mass and angular momentum conservations as well as pressure balance at the interface. With the aid of CFD results, the control-volume equations are closed. The predictions produced by solving the equations are reasonably accurate compared to the experimental results. Then, the equations are further improved to include gas-liquid two-phase injection situations. In addition, the surface tension effect is also investigated and included in the analysis.

The separation of multiphase flow constituents in a microgravity environment is of considerable interest as the functionality of many spacecraft systems is dependent on the proper sequestration of interpenetrating gas and liquid phases. Cyclonic separators provide the desired gas-liquid separatory action by swirling the multiphase flow {8211} causing the gas to accumulate along the axis of the vortex as the denser liquid is forced to the walls {8211} thereby allowing segregated extraction of the respective phases. Passive cyclonic separators utilize only the inertia of the incoming flow to accomplish this task. Knowledge gaps regarding their performance, however, preclude their use in operational systems. In the current work, combined experimental, numerical, and phenomenological modeling analyses have been performed to quantitatively describe the performance of these separators. First, a multifluid-VOF CFD technique was developed that could model the unique flow features in microgravity cyclonic separators. This multiscale approach could handle the disperse phase while also capturing the relevant capillarity features at gas core. The CFD techniques were then used to simulate the separator performance under the conditions of steady and unsteady injection of both single-phase and multiphase flow. The results were found to compare reasonably well with experiment. Next, a phenomenological control volume model was developed to capture the relevant physics of the flow in the separator. The approach was found to be a quick way to produce approximate results. Doing so helped to elucidate the fluid physics and allowed for the creation of operational maps that can be used as an aid for future design development. These techniques contributed to new design approaches to improve separator performance. Lastly, a reduced-gravity flight experiment was conducted confirming the performance of the separator design at flow rates impermissible in terrestrial conditions. The control volume model that was developed was compared to the results and good agreement was found. It is hoped that the resulting insight into phase separation, distribution, and control offered by this work will help to afford future designers the latitude to take greater advantage of the benefits offered by the use of multiphase systems in spacecraft applications.

The use of passive cyclonic separators in microgravity environment to perform phase separation requires taking into account the effect of capillary forces. The study utilizes control-volume approximation and VOF-based CFD simulation to investigate their effects on separator performance in microgravity.The configuration of liquid film and gas core rotating inside the separator involves the presence of a free surface (interface). In this situation the liquid film thickness becomes very critical because the increase of this film causes an increase in the capillary force at the interface, which may eventually cause a collapse of the liquid film. Therefore an investigation is performed by conducting a parametric study with respect to the dimensionless parameters that represent the separator geometry and the swirling flow hydrodynamics to determine the effects of all of these parameters on the liquid film thickness.The control-volume approximation in this study is developed using the conservation of mass and angular momentum as well as applying a pressure balance for the separator, taking into account the capillary force effect at the interface. The flow field is assumed to behave as a solid body rotation. The developed equations are solved to obtain the critical (minimum) Weber number at the interface before collapsing. The CFD approach utilizes 2-D axisymmetric meshing to discretize the governing equations. OpenFOAM, which is an open source software package, is used to generate the meshing and perform the simulation. The approach is used to develop a skin friction coefficient formula at a low volume flow rate injection which is needed in the control-volume approximation. The flow field is studied with decreasing Weber numbers until the liquid film collapses, which determines the critical Weber number. Also, the effect of contact angle on the liquid film stability is qualitatively investigated using this approach. Two-phase flow injection is also investigated using only the control-volume approximation. The investigation is carried out at several injection volumetric qualities with the assumption that the void fraction and injection volumetric quality are equal (homogeneous injection).

Cyclonic separation is a method of removing particulates from an air, gas or liquid stream, without the use of filters, through vortex separation. Rotational effects and gravity are used to separate mixtures of solids and fluids. A high speed rotating (air) flow is established within a cylindrical or conical container called a cyclone. Air flows in a helical pattern, beginning at the top (wide end) of the cyclone and ending at the bottom (narrow) end before exiting the cyclone in a straight stream through the center of the cyclone and out the top. Larger (denser) particles in the rotating stream have too much inertia to follow the tight curve of the stream, and strike the outside wall, then falling to the bottom of the cyclone where they can be removed. Cyclone separators have been used successfully in cement; agro; oil and various other industries. Its simple design and easy constructability make them very popular. This work is aimed for utilization by researchers, industrialists' and traditional businesses. Apart from this it will be especially relevant and useful for the students of Metallurgy, Mining, Mechanical engineering and Chemical engineering for carrying out research.

Cyclone separators have been described in detail and, although substantial research has been performed on solid / gas devices, the use of cyclones for gas / liquid separation has been comparatively ignored; this is particularly true for higher concentrations of liquid and for degassing applications. Consequently no generic models are available which will predict separation efficiency or pressure drop for all designs of cyclone. A novel design of axial flow cyclone called WELLSEP was examined for the purpose of degassing. This design was not believed to be optimal and no design criteria or performance prediction models were available for it. An experimental programme was therefore produced and executed to investigate changes in geometry and the affect of fluid dynamics. Changes to the length, vortex finder and swirl generator were examined first and then one design was selected and tested over a number of liquid flow rates, Gas Void Fractions (GVFs) and liquid extractions. Data was collected from the experiments which assisted in the development of semi-empirical models for the prediction of pressure drop and separation efficiency. These models could be used in the design of WELLSEP. Geometric and fluid dynamics changes have both been shown to influence the performance of the tested cyclone. The principal conclusions that have been drawn from this research are: " Of the tested designs, the design based upon a 30mm vortex finder diameter, settling chamber length of three times the diameter of the cyclone and a four start helix gave the optimum separation efficiency over the greatest range of conditions. 0 The separation efficiency is affected by the superficial liquid velocity and the liquid extraction but not the GVF." The dimensionless pressure drop coefficient (Euler number) is a function of liquid extraction and GVF. It may also be a function of the superficial liquid velocity but it is unproven by this research.

Problems associated with the use of compact cylindrical cyclone gas/liquid (CCGL) separators can be attributed to two physical phenomena: gas carry-under and liquid carryover(LCO). Inadequate understanding of the complex multiphase hydrodynamic flowpattern inside the cylindrical separator has inhibited complete confidence in its designand use, hence the need for more research. While many works have been done with a fixed inlet slot to predict the operational efficiency of the cyclone separator, very little is known about how separator performance can be influenced due to changes in fluid properties. During the operations of the CCGLseparator the complex flow situations arising from severe foaming within the separator has not been addressed. Also the effects of emulsion formation under three phase flow conditions on the properties of cyclone separators are yet to be studied. An understanding of liquid holdup and hydrodynamic nature of flow in a compact separator under zero net liquid flow (ZNLF) and zero net gas flow (ZNGF) conditions is necessary in many field applications, especially for the prediction of LCO and in the design of the CCGL separators. Also, ZNLF holdup is an important parameter inpredicting bottom-hole pressures in pumping oil wells. This research investigated the effects of fluid properties such as density, foam and emulsion formation on ZNLF, zero net gas flow ZNGF, and LCO in compact cyclone separators; this was achieved by replacing water, which is the conventional fluid used as the liquid medium in many previous research efforts with a foamy oil while maintaining air as the gas phase. Variable-inlet-slots that regulate the artificial gravity environment created by the separator were used to check for improved separator performance. Also experiments to check separator response to a range of water-cut in three-phase flow were performed. All experiments were carried out under low constant separator pressures. The ZNLF holdup is observed to decrease as the density of the fluid medium decreases. Varying the inlet slot configurations and recombination points does not haveany effect on the ZNLF holdup when changes in density of the liquid phase occur. Comparisons with previous work show that there exists a wide variation in the LCO operational envelope when severe foaming occurs in the CCGL separator. At high water cut (greater than 30%), the separator LCO performance was observed to be normal. However, at water-cut below 30%, LCO was initiated much earlier ; this is attributed to severe foaming in the CCGL separator.