Warm pressurant gas effects

Warm Pressurant Gas Effects on the Static Bubble Point Pressure for Cryogenic Liquid Acquisition Devices... 

This appendix presents historical warm pressurant gas LAD performance test results. A rigorous review of the literature revealed a total of 10 relevant studies of warm pressurant gas effects on LAD performance. IADs are primarily affected by the surface tension, and, thus temperature. Therefore, to make meaningful comparisons, historical results are organized by propellant type function of saturation temperature), and then by screen type. A brief overview of historical results is presented chronologically. Results are shown in Figures E.1-E.6. To compare between all the historical results across multiple LAD testing schemes, data is cast in a non-dimensional form using Equation 8.1. 

Screen channel LADS have flight heritage with storable propellants where heat transfer effects are not as severe as they are for cryogenic propellants. Before these IADs can be routinely used in cryogenic propulsion systems, the effects of undesirable heat on the LAD must be fully quantified. This environmental parasitic heat leak into the tank or heat input from warm pressurant gas may adversely affect LAD performance by vaporizing the liquid and drying out of the LAD screen. 

Ln addition, examination of Equation (3.16) shows that the current bubble point model does not account for variations in pressurant gas temperature, so warm gas data will be valuable for improving the prediction for cryogenic systems. Previous attempts were made to quantify the effect of warm gas on LAD degradation in the literature, but there were numerous reported inconsistencies in results as well as issues reported with the test apparatus. Historical attempts to quantify this effect are reserved for Appendix E. Clearly, carefully designed and controlled tests are required to accurately quantify the effect of warm pressurant gas on LAD performance. 

Warm pressurant gas bubble point tests from Chapter 8 were conducted in normally saturated liquid, essentially nulling out the subcooling effect. Examination of the heated gas data indicates that warm pressurant gas acts as a degradation factor on bubble point, and that the loss in performance is proportional to the difference between the liquid and... 

Differences in performance between the three different screens are due to the effect of screen thickness and porosity on the overall heat transfer across the screen. Differences in performance between pressurant gases are due to modification of the interfacial temperature due to added evaporation and/or condensation, as mentioned previously. Differences in performance between LH2 and LN2 are explained through differences in superheats required to initiate boiling on the liquid side of the LAD screen the LAD screen is more susceptible to drying out in LH2 with warm pressurant gas due to the lower superheat relative to the LN2 case. 

Cases (e), (g), and (h) are of interest in the cathodic protection of warm objects (e.g., district heating schemes [89] and high-pressure gas lines downstream from compressor stations [82]) because the media of concern can arise as products of cathodic polarization. The use of cathodic protection can be limited according to the temperature and the level of the mechanical stressing. The media in cases (a) and (f) are constituents of fertilizer salts in soil. Cathodic protection for group I is very effective [80]. 

Under high pressures, methane and ice form gas hydrates called clathrates. Methane hydrates can be considered as modified ice structures enclosing methane, melting at temperatures well above the melting point of pure ice. For instance, above a pressure of 3 MPa, methane hydrate is stable at temperatures above 0 C and under a pressure of 10 MPa it is stable at 15°C. From an environmental point of view methane exhibits a global warming potential 21 times the greenhouse gas effect of carbon dioxide. 

In the Heatric process, the warm wet pressurised gas from the inlet separator is pre-cooled in the PCHE and then throttled in a Joule-Thomson (JT) valve to a lower pressure. The drop in pressure produces a cooling effect and both hydrocarbon liquids and water condense out of the gas. The two-phase stream passes to a separator where the liquids are removed. The cold dry gas from the separator is returned to the exchanger to chill the incoming warm, wet gas (Figure 9.3). Refrigeration... 

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