Technology Development for Cryogenic Fluid Management, 18-9250Printer Friendly Version
Inclusive Dates: 04/01/01 - Current
Background - The reusable launch vehicles planned for the nation's future space program will be powered by cryogenic propellants, such as liquid oxygen and hydrogen, because of their performance advantages. The advantages are offset, however, by the rudimentary state of the technologies needed to handle these fluids in a tank during low-gravity maneuvering. One of the critically needed technologies is a method to ensure a flow of liquid, free of vapor, to the engine for re-starts when the liquid is floating in the tank away from the outlet. Screened channels (a flow channel that has one or more walls made of a fine mesh screen) are commonly used for this purpose for space vehicles that employ nonvolatile propellants, such as kerosene. The screens allow liquid to enter the channel but block gas. With a cryogenic propellant, however, a screened channel is susceptible to the generation of vapor within the channel by heat transfer. When this formation occurs, further vapor can flow from the tank and into the channel.
Approach - This project will develop an innovative "tapered screened channel" designed to remove automatically and passively any vapor bubbles generated within the channel and thereby preserve the integrity of the screened seal. Laboratory experiments will be conducted on small tapered channels using a simulated cryogenic liquid. The channels will be horizontal and very shallow to eliminate the buoyancy effects of gravity on the bubble motion. The experiments will characterize the fluid mechanics of the vapor-bubble-clearing action of test channels as a function of the critical parameters, such as taper angle and fluid surface tension. In parallel with the experiments, analytical models will be developed, based on first principles and guided by the experiments, to predict the channel fluid dynamics. The models will be validated by comparing their predictions to the results of additional laboratory experiments for different sets of parameter values.
Accomplishments - A first-cut analytical model has been developed and used to guide the design of the experiments. A small tapered channel has been manufactured, with a five-degree taper. The screened wall of the channel is replaced by a glass wall to permit observations, since these tests do not have to duplicate the sealing characteristics of a screen. The channel is connected to a reservoir at its narrow end and has a small open area at the wide end to simulate the window screen where the bubble will vent from the channel. The first illustration below shows a plan view of the channel with a test in progress using ethanol as the test fluid and injected air as the bubble. The graph shows the location of the bubble as a function of time after it is inserted into the channel near the reservoir. These results prove that the concept of a tapered channel will passively clear out vapor bubbles generated within the channel by heat transfer to a cryogenic liquid.