|
Propellant Management Device
A propellant management device (PMD) provides a way to expel propellant in a low-gravity environment. Devices can use surface tension as the primary expulsion device with a combination of baffles, fins, and vanes. The main goal of the PMD is to provide gas-free propellant to the rocket engine. Concept In the absence of gravity, buoyancy forces do not determine liquid and gas position in a vessel. The positions are primarily driven by surface tension Surface tension is the tendency of liquid surfaces at rest to shrink into the minimum surface area possible. Surface tension is what allows objects with a higher density than water such as razor blades and insects (e.g. water striders) to f .... The liquids tend to adhere to the walls and leave a gaseous bubble in the center of the vessel. Propellant management devices (PMDs) are required to provide gas-free operation of the engine. PMDs are typically unique and specially designed for each mission. Types There are two groups ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Surface Tension
Surface tension is the tendency of liquid surfaces at rest to shrink into the minimum surface area possible. Surface tension is what allows objects with a higher density than water such as razor blades and insects (e.g. water striders) to float on a water surface without becoming even partly submerged. At liquid–air interfaces, surface tension results from the greater attraction of liquid molecules to each other (due to cohesion) than to the molecules in the air (due to adhesion). There are two primary mechanisms in play. One is an inward force on the surface molecules causing the liquid to contract. Second is a tangential force parallel to the surface of the liquid. This ''tangential'' force is generally referred to as the surface tension. The net effect is the liquid behaves as if its surface were covered with a stretched elastic membrane. But this analogy must not be taken too far as the tension in an elastic membrane is dependent on the amount of deformation of the m ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
