Pressurant Gas Type

Pressurizing gas type, temperature, and control. (2) Pressurizing gas distributor effectiveness. (3) Propellant slosh. (4) Vehicle acceleration (trajectory) and environment. (5) Tank configuration (cylinder, sphere, etc.). Without experimentally evaluated factors,... 

The final influential factor that governs LAD performance is the type of gas used to pressurize the propellant tank. This parameter has implications on both LAD and pressurization subsystems. Effects on LAD performance due to pressurant gas type have minimal effects in storable propulsion systems for cryogenic systems, the type of gas will affect heat and mass transfer during tank drain. 

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. 

FIGURE 7.10 Combined Liquid Temperature, Pressure, and Pressurant Gas Type Dependence on 325 x 2300 Liquid Methane Bubble Point Pressure using (a) Helium, (b) Nitrogen, and (c) Methane as Pressurants. Color indicates bubble point in units of [Pa],... 

The seven known parameters that affect the bubble point pressure include the surface tension (liquid type), contact angle, effective pore diameter (which takes into account screen style, mesh, and metal type), liquid temperature, degree of subcooling (pressure), and pressurant gas type and temperature. The model will be validated through data collected over the past half-decade, as well as with data from the current work, which spans the space of these seven parameters. Ultimately, to be of topmost relevance for all future cryogenic propulsion missions, the model will be formulated in such a way that typical mission parameters like screen mesh, liquid properties, and pressurant gas properties can be input into the equation to obtain bubble point pressure easily and quickly at any desired condition. 

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... 

Several authors also reported manufacture specified information, but not effective pore diameters, for certain screens (e.g. 325 x 1900). This is denoted by a blank row in Tables B.1-B.5. Although no discrimination is made in the tables, there is data available for certain meshes using different metals. For example, data is available for a 165 x 800 mesh constructed from Ti, Al, and SS. Next, the tables are organized by liquid type and then hy pressurant gas type. 

If gallery arms are the only solution that satisfies mission requirements, then updated models developed here can be used for cryogenic or storable propellants. An optimal screen can be chosen by trading the primary influential factors such as bubble point and FTS pressure drop, as well as secondary influential factors, such as wicking rate, screen compliance, material compatibility, and pressurant gas type. Once the optimal screen is chosen which meets all mission requirements, the LAD channel dimensions can be sized based on logic presented in Chapter 14. An optimal screen channel LAD is one that delivers the desired demand flow rate, against the specified adverse acceleration level, to the desired expulsion efficiency, using the least amount of LAD mass. 

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