The tangential velocity profile and momentum transfer within a microgravity, vortex separator

Liquid and gas do not separate naturally in microgravity, presenting a problem for twophase space systems. Increased integration of multiphase systems requires a separation method adaptable to a variety of systems. Researchers at Texas A&M University (TAMU) have developed a microgravity vortex separator (MVS) capable of handling both a wide range of inlet conditions and changes in these conditions. To optimize the MVS design, the effects of nozzle area, separator geometry, and inlet flow rate must be understood. Computational fluid dynamics (CFD), in the form of Adapco’s Star-CD, is used, along with laboratory testing, to accomplish this goal. Furthermore, as analysis aids for the laboratory data and CFD results, relationships for radial pressure, bubble transit time, and momentum transfer were developed. Ground testing data showed a linear relationship between rotational speed and inlet flow rate. The CFD results compared well with the ground data and indicated that the majority of the rotational flow travels at nearly the same rotational speed. Examination of the tangential velocity profile also showed that a reduction of nozzle outlet area resulted in increased tangential velocities. Using dimensional analysis, a relationship between separator radius, inlet momentum rate, fluid properties, and rotational speed was found. Applying this relationship to the ground data and CFD results showed a strong correlation between the two dimensionless groups. Linear regression provided an equation linking rotational speed to the separator parameters. This equation was tested against the ground data and shown to predict average rotational speed well for all separator models. These results were used to calculate the radial and axial transit times of gas bubbles within the separation volume. Radial transit time was found to decrease more rapidly than axial transit time as gas volume increased, indicating axial and radial transit times are closest in value for the all liquid case and increasing gas core diameter improves the operational characteristics of the separator. From a design standpoint, the all liquid case provides a minimum flow rate for successful phase separation. Maximum flow rate depends on the pressure resources of the system