Room temperature bubble point pressure

FIGURE 4.6 Room Temperature Bubble Point Pressure as a Function of Surface Tension of Pure Fluids for the (a) 325 X 2300, (b) 450 x 2750, and (c) 510 x 3600 Mesh Screen Samples. 

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. 

Figures 6.7a and b and 6.8a and b plot the experimentally obtained bubble point pressure as a function of the liquid screen side temperature and bulk liquid temperature, respectively for the 200 x 1400 and 325 x 2300 screens. The room temperature bubble point prediction curve is also plotted in these figures. The 200 x 1400 room temperature pore diameter is taken from Table 3.2. The results from Jurns and McQuillen (2008) are plotted in Figures 6.7b and 6.8b for comparison to the current data.

Third, for all liquid temperatures and for both pressurant gases, bubble point pressure does not scale with the mesh of the screen. This is the most complex trend of the original five parameters tested. The second finest 450 x 2750 mesh produced the highest bubble points, for both GHe and GH2. The 510 x 3600 mesh outperformed the 325 x 2300 mesh at LH2 temperatures, but the 325 x 2300 yielded higher pressures in room temperature liquids. The reason for this crossover in performance is due to the temperature dependence of the screen pore diameter and geometry of the actual L/V interface at breakdown, as mentioned previously. The 510 screen has the largest gain at LH2 temperatures over the room temperature bubble point. 

A few key points are noted from this comparison. First, the plots of APbp versus j lv are linear. But, the pore diameters based on experimental data show that bubble point pressure does not scale inversely with the mesh of the screen the highest bubble point pressures were obtained using the second finest 450 x 2750 mesh screen. Surprisingly, the coarser 325 X 2300 screen also outperforms the finest 510 x 3600 mesh at room temperature. 

Fourth, for all three screens and each room temperature liquid, the bubble point pressure is accurately linear with j lv cos 6c for each liquid. The effective pore ditimeter Dp, computed from Equation (3.20) was consistent with the effective diameter estimated from SEM images of the weaves for the two coarser screens. However, for the 510 x 3600 weave Dp, SEM = 9.95 0.05 im while Dp = 15.77 0.32 [im. It may be that the contribution of the pore structure of the weave to F(cos 9c, Dp) can be sharpened. 

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. 

Trends in room temperature reseal pressure data mirrors trends in bubble point pressure data. All reseal pressures collected here are about 90% of the corresponding bubble point values. Operationally, this implies that only a ->10% reduction in differential pressure across the screen is required to reseal the screen and prolong the point of total LAD failure to yield a higher overall expulsion efficiency. Wicking rate test results performed in IPA align nicely with historical trends as coarser meshes outperform finer meshes. 

HGURE 5.10 Bubble Point Pressure Dependence on Screen Mesh in (a) Liquid Hydrogen and (b) Liquid Nitrogen. Solid lines are computed from Equation (3.16) using pore diameters determined at room temperature. 

Figure 5.1 la-c plot the bubble point pressure dependence on the liquid type. The black line is the prediction curve based on room temperature pore diameters. Pure liquid test results from Chapter 4 are plotted along with NBP LH2 and LN2 data from the current work. Again, to isolate the liquid dependence, only cryogenic data collected using GHe to pressurize the screen is plotted. 

FIGURE 5.20 325 x 2300 Liquid Nitrogen Bubble Point Pressure as a Function of Liquid Temperature and Pressure Using (a) Gaseous Helium and (b) Gaseous Nitrogen as a Pressurant. The black line is the prediction curve based on the room temperature pore diameter. 

The current bubble point model, which is a simplification of the 3D YLE that was derived in Chapter 3, predicts bubble point pressures accurately for storable propellants and room temperature liquids. Effective pore diameters of a particular screen mesh must either be... 

To find the pore diameter at room temperature (295 K) Dp,29SK, bubble point pressure was plotted against contact angle corrected surface tension for each screen, and the pore diameter was back calculated using Equation (10.1) using only room temperature data. 

FIGURE 11.1 Ratio of Room Temperature Reseal Pressure to Bubble Point Pressure versus the Fineness of the Screen. 

The set of primary and secondary factors which influence LAD design were formulated, and a suite of physics-based models for the influential factors were developed and validated both in storable and cryogenic propellants. While the models agreed well with historical room temperature data, all LAD models validated by cryogenic data, including bubble point pressure, reseal pressure, FTS pressure drop, TVS cooling efficiency, and full-scale LAD channel pressure drop show strong temperature dependence and deviation from the room temperature behavior. The models derived here and validated both by the... 

---