Screen Compliance

Screen Type Weave Type Orientation Symons (1974) Wicking Effective Diameter, Dodge Fries et ai. (2000) (2007) (pm) Hastings etai. (2011) 

Plain Square and Twilled Square weaves do not wick. 

The orientation column signifies how the wicking front is oriented relative to the warp wire direction. 

Equation (3.2) due to expansion and distortion of the LAD screen pores. Therefore the rate at which a screen deflects or hends, known as screen compliance, is an important secondary factor affecting screen selection for LAD systems. 

---

VC patients prior experience with CRC Screening Compliance enhancer... 

Through experiments, the following relationship to quantify screen compliance for circular samples of fine mesh LAD screens has been established by Paynter (1973a) ... 

FIGURE 3.15 Ideal Experimental Setup fora Screen Compliance Experiment. 

A brief explanation of a potential screen compliance test is given here. A screen is clamped to the top of a liquid reservoir, as shown in Figure 3.15. The liquid reservoir is completely filled so that the screen is entirely wetted. A syringe is connected to the liquid reservoir so that it can draw liquid out of the reservoir. As liquid is removed, the screen deflects inward towards the reservoir. A screen deflection will not be directly measured, but the volume of liquid removed from the reservoir will be measured by tbe syringe. The higher the volume removed, the more the screen has deflected. The pressure difference across the screen that causes the screen deflection can be measured by a DPT. The liquid volume removed vs. pressure drop yields an acciuate measme of screen compliance. 

X 2300 SS, 200 x 1400 SS, and 200 x 1400 A1 from Paynter (1973a). The Ka values are listed in Table 3.6. For a given APd the maximum deflection occurred for the 200 X 1400 A1 screen, as expected, since it is made of a more elastic material than the other two screens. When comparing meshes of the same metal, the 200 x 1400 SS had a smaller. Kd value than the 325 x 2300 SS mesh. This supports the trend that finer meshes experience more deflection, or compliance, than coarser meshes for the same pressure difference and same metal. Since fine mesh screens are generally desirable for LH2 systems, additional screen compliance tests with these fine mesh Dutch Twill screens would help to verify this trend. 

Table 3.6 Screen Compliance Model Parameters for Three Different Screens...

Clearly the optimal mesh for a particular mission requires trading all of the aforementioned influential factors against one another. Space flight requirements which include mass flow rate, acceleration level and direction, and thermal environment dictate selection of the screen for a particular mission. The primary performance parameters governing screen channel LAD design are the bubble point (and reseal pressure) and FTS pressure drop, while secondary parameters are the wicking rate, screen compliance, and material compatibility. 

For screen compliance, implications for an LH2 system are as follows Recalling from Section 3.4, colder temperature LH2 will experience a higher pressure drop for the same mass flow rate. Therefore LH2 transfer systems operating at colder temperatures will see higher LAD screen deflections. Finer mesh screens are desirable to counter the low surface tension of LH2, but finer mesh screens are expected to have higher screen compliance. 

Second, the effect of screen compliance is compared between the two screens. Recall that screen compliance is the amount of deflection of the screen that can occur at the... 

Using the experimental apparatus outlined in Chapter 3, screen compliance tests need to be performed on coarse and fine mesh screens. 

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. 

---