Cryogenic bubble points

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... 

FIGURE 5.6 Test Matrix for the Low Pressure Cryogenic Bubble Point Tests. 

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. 

Based on cryogenic bubble point tests in LHz, LN2, LOX, and LCH4 from the current work, the bubble point equation correlates best with experimental data when surface tension is based on the liquid screen side temperature. Therefore, in cryogenic liquids. Equation (3.16) holds for saturated liquid states only. Ideally, the bubble point equation would be evaluated... 

The new model proposed here will therefore address the following three discrepancies that exist between cryogenic bubble point data and simplified room temperature model ... 

Table 10.2 Fitting Parameters for Computing Cryogenic Bubble Points in Normally Saturated Liquid States using the Non-condensable Pressurant...

FIGURE 10.5 Cryogenic Bubble Point Saturated State Fitting Parameter as a Function of the Fineness of the Screen. 

Figure 10.6a and h plot the model generated curves against data for normally saturated liquid states in LH2 and LN2, respectively. LH2 saturated state data is taken from Chapter 5, while the saturated LN2 data is taken from LN2 data collected edongside other cryogenic bubble point data. Error bars are plotted but are barely distinguishable. Excellent agreement is seen between LH2 data and new temperature dependent bubble point model. The model also matches LN2 data reasonably well, despite some scatter in the GN2/LN2 bubble point data taken in warmer liquid states. 

With the exception of warm pressurant gas bubble point tests conducted in Chapter 8, the majority of data in the literature was taken with the temperature of the pressurant gas approximately equal to the liquid temperature. This is due to the standard inverted testing configuration used for measuring cryogenic bubble point pressures which forces uniform,... 

If reseal diameter is known, the reseal pressure equation can theoretically be used to determine the reseal point of any fluid with a known surface tension. However, the same problem arises with cryogenic reseal data as with the cryogenic bubble point data. The room temperature prediction value matches neither the non-condensable or autogenous pressurant gas case. In addition, the room temperature model cannot be used to predict reseal pressures of subcooled cryogenic liquid states or elevated pressurant gases. Therefore, the new model must therefore address the following three discrepancies that exist between cryogenic reseal pressure data and simplified room temperature model. These are ... 

As mentioned in Section 3.9.2, there are only three previous studies where reseal data was reported. Reseal pressure data was collected alongside all bubble point test data from both room temperature as well as cryogenic bubble point tests for a 200 x 1400, 325 x 2300, 450x2750, and 510x3600 Dutch Twill LAD screen in IPA, methanol, acetone, water, LH2, LN2, LQX, and LCH4. A total of 4836 reseal pressure data points, of which 4815 were new points, were collected, processed, and analyzed to develop this model. 

The two primary parameters that are influential to LAD screen selection for a particular mission as outlined in Chapter 3 are the bubble point pressure, AP p, and the FTS pressure loss, APfts- The FTS pressure drop from Chapter 3 and the cryogenic bubble point model from Chapter 10 are used here. The FTS pressure drop can be rewritten in the following... 

Figure 13.1 plots the model predicted LH2 bubble point pressure values against the anticipated operating fuel depot liquid temperature range for several screen types using the new cryogenic bubble point model from Chapter 10. Figure 13.1a shows the bubble... 

As shown in Figure 14.5, the normalized interface velocity rapidly decays as the LAD is exposed to vapor. With an interface velocity profile, ullage bubble growth model, cryogenic bubble point model, and analytical flow model, the velocity and pressure fields inside the LAD can be determined in microgravity. The velocity can also be visualized as a function of time as the tank is drained. 

Low-pressure cryogenic bubble point tests in LH2 and LN2 revealed the functional dependencies of the cryogenic bubble point pressure, namely screen type, liquid type, contact angle, liquid temperature and pressure, and pressurant gas type and temperature. A significant increase in performance is achievable over the baseline LH2 historical value by using the finer 450 x 2750 mesh and pressurizing and subcooling the interface with... 

The huhble point model has been derived in a way to make it facile for a system designer to predict performance for any screen in any fluid at any thermodynamic state. From Chapter 10, the updated cryogenic bubble point equation is expressed as ... 

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