Microgravity >> Fluid Physics

A fluid is any material that flows in response to an applied force; thus, both liquids and gases are fluids. Some arrangements of solids can also exhibit fluid-like behaviors; granular systems (such as soil) can respond to extraordinary forces, like those induced by earthquakes or floods, with a flow-like shift in the arrangement of solid particles and the air pockets or liquids that fill the spaces between them. Fluid physicists seek to better understand the physical principles governing fluids, including how fluids interact with solid boundaries; how fluids flow under the influence of energy, such as heat or electricity; how particles and gas bubbles suspended in a fluid interact with and change the properties of the fluid; and how fluids change phase, either from fluid to solid or from one fluid phase to another. Fluid phenomena studied range in scale from microscopic to the size of the atmosphere and include everything from the transport of cells in the human body to changes in the composition of the atmosphere. The universal nature of these phenomena makes their study fundamental to science and engineering.

Microgravity fluid physicists use microgravity environments to increase our knowledge of fluid behavior in order to advance science and technology. Understanding the fluid-like behavior of soils under stress will help civil engineers design safe buildings in earthquake-prone areas. Materials engineers can benefit from a better grasp of how the structure and properties of a solid metal are determined by fluid behavior during its formation. And knowledge of the flow characteristics of vapor-liquid mixtures is useful in designing power plants to ensure maximum stability and performance.

	When a liquid is heated from the bottom to the boiling point in Earth's gravity (a), small bubbles of heated gas form near the bottom of the container and are carried to the top of the liquid by gravity-driven convective flows.
	In the same setup in microgravity (b), the lack of convection and buoyancy allows the heated gas bubbles to grow larger and remain attached to the container's bottom for a significantly longer period.

The work of fluid physics researchers often applies to the work of other microgravity scientists. Materials science researchers rely on the knowledge of principles of fluid physics for materials processing. For example, impurities in materials such as glasses and alloys can be reduced by managing fluid behavior while the material is in a molten state. This is desirable because impurities may degrade sought-after properties of materials, such as corrosion resistance, mechanical toughness, and optical transmissivity. In addition, knowledge of fluid flow in microgravity can help combustion scientists improve fire safety and fuel efficiency.

Source: Hampton University/NASA