Bubble point data

Figure 3 shows the isothermal bubble point data for the aliphatic P-diketone/C02 systems at 35.0 C. This figure clearly shows that the type of alkyl substituent on the P-diketone moiety has little effect on the liquid phase behavior. Similar bubble point compositions were seen for all these systems at 30.0T as well. 

Appendix A presents a historical summary of previously attempted depot demonstration missions. Appendix B presents the full list of screens available for screen channel IADs as well as a summary of the data mining of all previously reported bubble point data. Appendices C and D present Langmuir isotherms for the data presented in Chapter 4 while Appendix E presents previously reported heated pressurant gas historical data relevant to Chapter 8. Appendix F presents the results of the literature review into previous solutions for porous channel flow. Appendix G presents LAD design logic and a summary of updated design tools. 

Rigorous and comprehensive survey of the literature was performed to gather all previously reported bubble point data for all possible screens. Detailed results are reserved for Chapter 10, where the full cryogenic bubble point pressure model is constructed. Appendbc B lists the 40 screens over which information is available in the literature. 24 of these 40 screens have actual historical bubble point data available pore diameter data for two new screens are added for the current work for a total of 26 screens. Figures 3.8a... 

But there is even more promise for improving LH2 screen channel LAD technology. Due to recent improved techniques in metallic wire cloth weaving, it is possible to fabricate an even finer mesh screen. During a recent comprehensive survey of particulate filtration techniques, a 510 x 3600 wire mesh was found in use in the filtration community. No bubble point data or information on the pore diameter yet exists in the literature. Given the expectation that this mesh screen should have a larger bubble point, this screen will be... 

Room temperature reseal pressure data was collected simultaneously with bubble point data. The same inverted bubble point test configuration used to measure the bubble point was used to measure reseal pressures. A bubble point test ceases once pressurant gas breaks through the wetted pore. To commence a reseal point test, the pressurant gas flow rate beneath the screen is slowly reduced in fixed quasi-static increments to slowly encroach upon the differential pressure across the screen at which the screen reseals. Eventually the screen rewets/reseals itself as evident in visualization of no more bubbles... 

Figure 4.4 illustrates this effect for a room temperature bubble point and reseal test where the corrected reseal pressure is superimposed on the raw DPT signal. As shown, the reseal pressure is always lower than the bubble point pressure. Unlike bubble point data reduction, the DPT across the screen carmot alone be used to determine screen reseal. Rather, time synchronization with the visualization system is required to determine the exact differential pressure across the screen at reseal. Sole reliance on visualization makes reseal point data inherently noisier than bubble point data. 

Room temperature reseal pressure data is shown in Figure 4.15 for a 325x2300, 450 X 2750, and a 510 x 3600 screen in IPA, methanol, acetone, and water. Also plotted in Figure 4.15 is a best fit line to the data. The exact same trends in bubble point pressure are seen in reseal pressures. Comparing Figures 4.6-4.15, all reseal pressures clearly lie below the corresponding bubble points. For all data collected here, reseal pressures are approximately 90% of the bubble point data. 

The second method to increase the low LH2 baseline bubble point is to simply operate at a colder liquid temperature. L/V surface tension is an inverse function of temperature, so at colder liquid temperatures L/V surface tension is larger, resulting in higher resistance to vapor ingestion. Thus, it was desired to obtain bubble point data over a range of liquid temperatures representative of the thermal environment for LH2 propellant tank. Finally, historical bubble point data shows that bubble point may be affected by the type of gas in contact with the screen experiments conducted in this chapter will quantify this effect. 

LH2 was filled offsite in portable 0.946 m (250 gallon) dewars and was cormected to the flow system through a flexible VJ line. LN2 was connected through the same VI line via a readable 1.89 m (500 gallon) dewar, and was used to perform all pre-test check outs and cold shocking of the hardware, and to collect bubble point data. GHe was available from a portable tuber trailer, while GN2 and GH2 were available via a high-pressure K-bottle. 

The discrepancy between saturated cryogenic bubble point data and room temperature model is attributed to two factors ... 

The actual interface temperature within the screen pores may be different from the measured liquid screen side temperature due to enhanced heating (vapor case) or cooling (helium case) at cryogenic temperatures. In Equation (3.16), surface tension is evaluated based on the liquid screen side temperature, but the helium data in Figure 5.10 imply that the interfacial temperature is cooler than the liquid screen side. In other words, unlike storable bubble point data, for cryogenic bubble points, it matters which pressurant gas is in contact with the screen. 

The second way to improve upon the 325x2300 reference bubble point value is to increase the surface tension of the liquid. Figure 5.12a and b plot LH2 and LN2 bubble point data using GHe to pressurize as a function of the liquid side screen temperature, SD1 for all three screens, respectively. Again, only bubble points taken in saturated or near saturated liquid states are plotted to permit direct comparison between screen meshes. As shown for all three meshes, higher bubble points are always achieved in colder liquid temperatures, since surface tension is an inverse function of temperature. Across the entire... 

The next parameter varied was the liquid pressure. Typically a mission designer will have control over the temperature and pressure and thus thermodynamic state of the liquid propellant prior to transfer, and so it was highly desirable to obtain bubble point data across a wide range of thermal conditions within a low-pressure propellant tank to bound screen channel LAD behavior. Figures 5.13a-c and 5.14a-c plot the LH2 and LN2 bubble... 

The fifth parameter varied in this study was the type of pressurant gas. This parameter has implications on both LAD and pressurization subsystems as mentioned previously in Chapter 3. To determine the effect of pressurant gas type on the LAD subsystem, bubble point tests were conducted for the three different meshes across the same set of thermodynamic states of the liquid using both non-condensable (GHe) and autogenous GH2/ LH2) pressurization schemes. Results are plotted in Figures 5.15a-c and 5.16a-c for the 325 X 2300,450 x 2750, and 510 x 3600 screens in LH2 and LN2, respectively. All the bubble point data collected in this experiment from Figures 5.8 and 5.9 is thus plotted for comparison. Solid lines are again model predictions based on room temperature predictions. Error bars are plotted but are barely discernible. 

Screen channel LAD performance in high-pressure propellant tanks may be affected by the degree of propellant subcooling and type of gas used during pressurization or liquid expulsion. Therefore it was ensured that bubble point data was collected over the widest possible range of thermal conditions inside a LOX propellant tank, consistent with the limitations of the test hardware. Therefore, the purpose of this chapter is to conduct an in-depth analysis on these high-pressure bubble point tests to understand parameters that affect LAD performance in an elevated pressure environment. 

Testing covered 8 weeks from February to April 2010. Numerous bubble point tests were conducted over the temperature range from 92 to 130 K and the pressure range from 0.138 to 1.79 MPa for both screens. Bubble point data was collected using GHe for the 200 x 1400 screen and GHe and GOX for the 325 x 2300 screen. 

The blue shaded region represents available thermodynamic conditions at the LAD screen over which the current bubble point tests were conducted. The same goal was to collect bubble breakthrough values over as wide a range as possible to give future mission designers direct bubble point data to characterize the LAD subsystem at any elevated... 

The availability of bubble point data using multiple pressurant gases over such a wide range of thermodynamic conditions warrants further thermal analysis. To compare between pressurization schemes, screen interfacial temperatures, screen Re numbers. 

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