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Description:
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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 . |