Cable Kurwitz

Development of a Unique, Passive, Microgravity Vortex Separator

In the microgravity environment experienced by space vehicles, liquid and gas do not naturally separate as on Earth. This behavior presents a problem for two-phase space systems, such as environment conditioning, waste water processing, and power systems. Furthermore, with recent renewed interest in space nuclear power systems, a microgravity Rankine cycle is attractive for thermal to electric energy conversion and would require a phase separation device. Responding to this need, researchers have conceived various methods of producing phase separation in low gravity environments. These separator types have included wicking, elbow, hydrophobic/hydrophilic, vortex, rotary fan separators, and combinations thereof. Each class of separator achieved acceptable performance for particular applications and most performed in some capacity for the space program. However, increased integration of multiphase systems requires a separator design adaptable to a variety of system operating conditions. To this end, researchers at Texas A&M University (TAMU) have developed a Microgravity Vortex Separator (MVS) capable of handling both a wide range of inlet conditions as well as changes in these conditions with a single, passive design. Currently, rotary separators are recognized as the most versatile microgravity separation technology. However, compared with passive designs, rotary separators suffer from higher power consumption, more complicated mechanical design, and higher maintenance requirements than passive separators. Furthermore, research completed over the past decade has shown the MVS more resistant to inlet flow variations and versatile in application. Most investigations were conducted as part of system integration experiments including, among others, propellant transfer, waste water processing, and fuel cell systems. Testing involved determination of hydrodynamic conditions relating to vortex stability, inlet quality effects, accumulation volume potential, and dynamic volume monitoring. In most cases, a 1.2 liter separator was found to accommodate system flow conditions. This size produced reliable phase separation for liquid flow rates from 1.8 to 9.8 liters per minute, for gas flow rates of 0.5 to 180 standard liters per minute, over the full range of quality, and with fluid inventory changes up to 0.35 liters. Moreover, an acoustic sensor, integrated into the wall of the separation chamber, allows liquid film thickness monitoring with an accuracy of 0.1 inches. Currently, application of the MVS is being extended to cabin air dehumidification and a Rankine power cycle system. Both of these projects will allow further development of the TAMU separator.Copyright

Experimental results of loop heat pipe startup in microgravity

An experimental package was constructed to operate a loop heat pipe (LHP) in microgravity aboard NASA’s KC-135 aircraft. Startup of the LHP was performed in flight and ground testing. Data revealed different temperature profiles for similar startups indicating different locations of the vapor and liquid inventories. A sharp increase in evaporator temperature of approximately 10 K followed by a small decrease was very comparable to startups in capillary pumped loops. In contrast, a steady linear rise in wall temperatures with time was used to indicate the absence of liquid in the vapor sections of the evaporator. Temperature transients in the liquid line during particular startups indicate movement of fluid out of the compensation chamber and into the liquid line. Experimental results match expected behavior and show a high degree of repeatability.

Equilibrium Interface Position During Operation of a Fixed Cylinder Vortex Separator

Microgravity separation is a critical need for the development of high performance thermal management and advanced life support systems. Texas AM Kurwitz and Best, 2000). Recent reduced gravity flight data has been analyzed to compare the interface position and shape as a function of liquid inventory and rotational speed. A comparison of the measured interface location with the interface shape predicted from irrotational flow resulted in a RMSD of 0.45 cm and the RMSD of the measured interface location to an interface determined assuming that the gas forms a right circular cylinder centrally located in the separator was 0.7015. The accuracy of the prediction method is better at higher rotational speeds corresponding to larger flow rates. The high degree of fidelity between the measured interface location with that predicted using a simple irrotational flow assumption indicates that secondary flows are small in mag...

A Statistical Comparison of Various Fluids for a Drift Flux Model in Reduced Gravity Two‐Phase Slug Flow

The desire to utilize enabling, two‐phase (gas‐liquid) systems for advanced life support and thermal management are driven by NASA’s exploration initiative and the early development of commercial space interests. Two‐phase flow heat transfer is highly advantageous over single‐phase systems. Two‐phase fluid loops provide significant thermal transport advantages over their single‐phase counterparts and are able to carry more energy per unit mass than single‐phase systems at reduced pumping power per unit mass. These advantages alone offer great reductions in both mass and volume, as well as power requirements; unfortunately, the ability to predict two‐phase phenomena such as flow regime transitions and void fraction at microgravity conditions is greatly limited and its development will facilitate the utilization of two‐phase systems. The drift flux model is a useful tool to predict the void fraction and thus, the pressure drop. Results of a statistical analysis indicate that for water/air and water‐Zonyl/ai...

New results in gravity dependent two-phase flow regime mapping

Accurate prediction of thermal-hydraulic parameters, such as the spatial gas/liquid orientation or flow regime, is required for implementation of two-phase systems. Although many flow regime transition models exist, accurate determination of both annular and slug regime boundaries is not well defined especially at lower flow rates. Furthermore, models typically indicate the regime as a sharp transition where data may indicate a transition space. Texas A&M has flown in excess of 35 flights aboard the NASA KC-135 aircraft with a unique two-phase package. These flights have produced a significant database of gravity dependent two-phase data including visual observations for flow regime identification. Two-phase flow tests conducted during recent zero-g flights have added to the flow regime database and are shown in this paper with comparisons to selected transition models.

Microgravity Phase Separation for the Rankine Cycle

Phase separation in reduced gravity continues to be an obstacle for the National Aeronautics and Space Administrations’ power programs. Phase separation would be necessary for the use of a Rankine power conversion cycle in microgravity. The vortex phase separator invented by Texas A&M University may be implemented in a microgravity Rankine cycle for successful phase separation. With the known characteristics of the separator/inventory control system, the Texas A&M University vortex phase separator can be operated successfully for a wide variety of uses in microgravity. The separator operating principle and envelope, test performance data, and inventory monitoring system are described.

Two-Phase Zero-Gravity Pressure-Drop Predictions from Single-Phase One-g Data

The purpose of this work was to use a single-component, R-12, two-phase flow test loop to produce and collect pressure-drop data from the corrugated tubes and quick-disconnect components and develop correlations and prediction methods for two-phase pressure drops in normal and reduced gravity. Results show it is possible to predict the zero-gravity pressure drops through the corrugated tubes using the homogeneous equilibrium model and single-phase, ground-based pressure-drop measurements. It was also found that prediction of pressure drop through the quick-disconnect attachment could be obtained using the homogeneous equilibrium model (with single-phase ground-based measurements) coupled with an orifice pressure drop model. The use of single-phase, ground-based experiments to predict two-phase, reduced gravity component performance could yield significant cost savings and increased reliability of reduced gravity fluid systems.

New Results in Two‐Phase Pressure Drop Calculations at Reduced Gravity Conditions

The mass, power, and volume energy savings of two‐phase systems for future spacecraft creates many advantages over current single‐phase systems. Current models of two‐phase phenomena such as pressure drop, void fraction, and flow regime prediction are still not well defined for space applications. Commercially available two‐phase modeling software has been developed for a large range of acceleration fields including reduced‐gravity conditions. Recently, a two‐phase experiment has been flown to expand the two‐phase database. A model of the experiment was created in the software to determine how well the software could predict the pressure drop observed in the experiment. Of the simulations conducted, the computer model shows good agreement of the pressure drop in the experiment to within 30%. However, the software does begin to over‐predict pressure drop in certain regions of a flow regime map indicating that some models used in the software package for reduced‐gravity modeling need improvement.

Zero‐Gravity Test Results For Ultrasonic Sensing of Air‐Liquid Interface in a Vortex Separator

An ultrasonic pulse‐echo method for detecting the location of the air‐liquid interface of a air‐liquid vortex in microgravity was tested. A vortex was established in near‐zero gravity conditions in hydraulically‐stirred phase separator. A single ultrasonic transducer located about mid‐plane of the vortex was used to sense the thickness of the layer of liquid inside the phase separator and local to the ultrasonic transducer. Comparison was made between the sensed liquid layer thickness and an ideal right circular liquid annulus calculated from the know liquid inventory in the phase separator. The absolute error between the sensed and ideal annulus thicknesses was found to be in the neighborhood of 0.1 inches for the full operational range of the separator.

Characterization of a Dual Chambered Two Phase Separator

Fuel cells have been used as a power source in the space shuttle for decades and are expected to be used in future higher power, larger systems. A new, passive gas/liquid phase separator for use in such large fuel cell space applications has been invented. It is a vortex separator designed to accommodate gas driven two phase flows. The work presented here is a first of a kind study of this newly invented separator examining the minimum inlet gas flow rate necessary for a stable vortex inside the separator as a function of separator size. A dimensional scaling analysis was done to predict this minimum inlet gas flow rate. Experiments were performed on the ground and in conjunction with the NASA microgravity simulating aircraft to validate modeling. The results of the experiments and scaling analysis are compared.Copyright