Vapor Flow into a Capillary Propellant-Acquisition Device

An analytical model is described that specifies the conditions needed to cause a flow of vapor through the screens of a start basket. The analytical model is composed of several original submodels that interrelate the evaporation of the liquid in the basket, the bubble-point change of a screen in the presence of wicking, the drying out of a screen through a combination of evaporation and pressure difference, the vapor flow rate across a wet screen as a function of pressure difference, and the effect on wicking of a difference between the static pressure of the liquid reservoir and the vapor surrounding the screen. Most of the interrelations were verified by a series of separate-effe cts tests, which were also used to determine certain empirical constants. The equations of the model were solved numerically for typical start-basket designs. A simplified start basket was constructed and tested to verify these predictions, using both volatile and nonvolatile liquids. The test results verified the trends predicted by the model.