Showing papers on "Ullage published in 1987"

Sensor and method for ullage level and flow detection

Abstract: A device is provided for detecting the ullage level and flow in a vessel by detecting the presence of a solid or liquid material in proximity to a microwave detector. The device may be mounted to the side of the vessel or suspended inside the vessel so as to bring the microwave sensor into proximity with the surface of the contents of the vessel. A microwave bridge circuit may be used to detect a change in either the amplitude or phase of a signal reflected by the material within the vessel compared to a reference signal tuned to either the presence or absence of the anticipated solid or liquid material. In one embodiment, the reflected material signal is compared to the signal from a sample chamber containing the material to be detected. The device can reliably detect the level of multiple interfaces for various materials having distinct electric or magnetic properties.

Passive propellant management system

Abstract: A passive propellant management system for a spacecraft liquid propellant tank (1) comprises several preferably V-shaped channels (2) which communicate liquid propellant from regions within the tank (1) to an outlet port (8), which expels liquid propellant but not pressurant gas. A liquid/bubble chamber assembly (9) couples the channels (2) with the outlet port (8). The channels (2) comprise relatively open portions (11) and relatively closed portions (10). In the relatively open portions (11), liquid is retained in a gap (12) between open ends of the V channels (2) and the inner wall of the tank (1). In the relatively closed portions (10), a screen, mesh or perforated plate (14) covers the open end of the V channels (2), intermediate the V channels (2) and the inner wall of the tank (1). The placement of the relatively open and closed portions (11, 10, respectively) is intentionally preselected based upon mission requirements. Where pressurant gas ullage is expected to be present, e.g., during periods of high g, relatively open portions (11) are used. Where liquid propellant is expected to be present, e.g., during periods of relatively low g, relatively closed portions (10) are used. The liquid/bubble chamber assembly (9) comprises a liquid trap (27) and bubble trap (28), which operate synergistically with each other and with the channels (2) to provide optimum liquid flow during all phases of the spacecraft mission.

Method of testing a package seal

Abstract: A method of testing the integrity of a package seal (14) provided between a container portion (11) and a lid portion (12), includes the steps of: initially reducing the pressure acting on the outer surface of the container portion to cause the lid portion to bow inwardly to a position of substantially maximum concavity while maintaining the ullage volume within the package substantially constant; further reducing the pressure acting on the outer surface of the container portion to distend the container portion for increasing the volume of the ullage space; and sensing for a change in position of the distended container wall.

Mixing-induced fluid destratification and ullage condensation

Abstract: In many applications, on-orbit storage and transfer of cryogens will require forced mixing to control tank pressure without direct venting to space. During a no-vent transfer or during operation of a thermodynamic vent system in a cryogen storage tank, pressure control is achieved by circulating cool liquid to the liquid-vapor interface to condense some of the ullage vapor. To measure the pressure and temperature response rates in mixing-induced condensation, an experiment has been developed using Freon 11 to simulate the two-phase behavior of a cryogen. A thin layer at the liquid surface is heated to raise the tank pressure, and then a jet mixer is turned on to circulate the liquid, cool the surface, and reduce the pressure. Many nozzle configurations and flow rates are used. Tank pressure and the temperature profiles in the ullage and the liquid are measured. Initial data from this ground test are shown correlated with normal-gravity and drop-tower dye-mixing data. Pressure collapse times are comparable to the dye-mixing times, whereas the times needed for complete thermal mixing are much longer than the dye-mixing times.

Liquid oxygen sloshing in Space Shuttle External Tank

Abstract: This paper describes a numerical simulation of the hydrodynamics within the liquid oxygen tank of the Space Shuttle External Tank during liftoff. Before liftoff, the tank is filled with liquid oxygen (LOX) to approximately 97 percent with the other 3 percent containing gaseous oxygen (GOX) and helium. During liftoff, LOX is drained from the bottom of the tank, and GOX is pumped into the tank's ullage volume. There is a delay of several seconds before the GOX reaches the tank which causes the ullage pressure to decrease for several seconds after liftoff; this pressure 'slump' is a common phenomenon in rocket propulsion. When four slosh baffles were removed from the tank, the ullage gas pressure dropped more rapidly than in all previous flights. The purpose of this analysis was to determine whether the removal of the baffles could have caused the increased pressure 'slump' by changing the LOX surface dynamics. The results show that the LOX surface undergoes very high vertical accelerations (up to 5 g) and, therefore, splashing almost certainly occurs. The number of baffles does not affect the surface if the structural motion is assumed; but, the number of baffles may affect the structural motion of the tank.

Development and Evaluation of an Airplane Fuel Tank Ullage Composition Model. Volume 2. Experimental Determination of Airplane Fuel Tank Ullage Compositions

Abstract: : The development and evaluation of a computer model designed to predict the composition of airplane fuel tank ullage spaces is documented in two volumes. Volume I - Airplane Fuel Tank Ullage Computer Model A detailed mathematical description of the model as it relates to the physical processes governing the ullage of an airplane fuel tank is included, along with user instructions and examples. Extensive comparisons of computer model predictions to experimental data are included. The model is interactive and can be used on a variety of computers including personal computers. Volume II - Experimental Determination of Airplane Fuel Tank Ullage Compositions Experimental work conducted using a fuel tank simulator to investigate the composition of airplane fuel tank ullage spaces is described. The investigations include ullage mixing by diffusion and convection, oxygen evolution during simulated climbs and refueling and complete mission simulations. Keywords: Fuel tank, Nitrogen- enriched air, Stratification, Ullage, Oxygen evolution, Mission simulation, Inerting, Diffusion.

Cryogenic Liquid Heat Transfer Analysis

Abstract: : The objective of the present study was to determine if there is a suitable cryogenic fluid which could serve to simulate the liquid hydrogen (LH2)-induced loads and stresses during structural strength testing of large space transportation systems Liquid helium (LHe) and liquid nitrogen (LN2) were identified early on as the only pure cryogenic fluids which needed to be considered Neon, while being a promising candidate based on its cryogenic properties, simply is not available in large enough quantities to warrant consideration The study showed that the primary factor to be considered in choosing a simulant was the magnitude of the heat leakage rate that could be expected to apply to the structure Analysis of several generic hydrogen fuel tank designs showed that heat leaks in the range of 100 to 500 Btu/hr-sq ft could be expected Expressed in alternate terms, this would roughly correspond to LH2 boil-off rates of 10 to 30 percent per day Based primarily on heat transfer considerations it was concluded that LHe essentially duplicates LH2 thermal effects providing the tank pressure of the test vehicle is less that 266 psia (0183 mPa) It was also found that liquid nitrogen duplicates LH2 effects providing the 57 deg K difference in boiling temperatures of these two cryogens is accounted for It was also determined that real difficulties can be expected in simulating LH2 effects in the ullage space of a fuel tank Based on heat transfer considerations, it is shown that helium as a simulant will over-cool the tank walls around the ullage space and the opposite is true for nitrogen