supercritical fluid

Examples of supercritical fluid in the following topics:

• Supercritical Fluids

  • In general terms, supercritical fluids have properties between those of a gas and a liquid.
  • Table 2 shows density, diffusivity, and viscosity for typical liquids, gases, and supercritical fluids.
  • One of the most important properties of supercritical fluids is their ability to act as solvents.
  • Solubility in a supercritical fluid tends to increase with the density of the fluid (at constant temperature).
  • Supercritical fluids have properties between those of a gas and a liquid.

• Three States of Matter

  • A liquid is a fluid that conforms to the shape of its container but that retains a nearly constant volume independent of pressure.
  • A supercritical fluid (SCF) is a gas whose temperature and pressure are greater than the critical temperature and critical pressure.
  • A supercritical fluid has the physical properties of a gas, but its high density lends it the properties of a solvent in some cases.
  • For example, supercritical carbon dioxide is used to extract caffeine in the manufacturing of decaffeinated coffee.

• Interpreting Phase Diagrams

  • At this point and beyond it, the substance being evaluated exists as a "supercritical fluid".

• The Structure and Properties of Water

  • Water also exists in a rare fourth state called supercritical fluid, which occurs only in extremely uninhabitable conditions.
  • When water achieves a specific critical temperature and a specific critical pressure (647 K and 22.064 MPa), the liquid and gas phases merge into one homogeneous fluid phase that shares properties of both gas and liquid.

• Flow through a Channel

  • Let's write out the Bernoulli equation (divided by $g$ as customary in hydraulics) for the fluid moving along the surface,
  • so if the fluid is subcritica} or streaming ("subsonic'') over the bump, the surface will dip, and if the fluid is supercritical or shooting ("supersonic'') the surface will bulge.
  • For the equation to make sense, if the flow becomes supercritical, it must do so at the top of the bump.
  • The second has a large deviation (supercritical flow).
  • For a particular set of initial conditions we can calculate the height of the bump where the fluid goes critical to be

• Hydraulic Jump

  • We neglect the vertical motion of the fluid and assume that all dimensions are large compared with the depth of the fluid --- this is the hydraulic approximation.
  • In practice the energy in the flow can be transferred to small scale motion of the fluid which is quickly dissipated.
  • Let us examine discontinuities in the fluid height and velocity by using the conditions of continuity on the particle and momentum flux.
  • Because the energy flux of the flow must decrease through the jump $h_2>h_1$ --- the height of the fluid must increase downstream of the jump.
  • The flow enters the jump supercritically and leaves the jump subcritically.

• Fluid Compartments

  • The major body fluid compartments include: intracellular fluid and extracellular fluid (plasma, interstitial fluid, and trancellular fluid).
  • The intracellular fluid of the cytosol or intracellular fluid (or cytoplasm) is the fluid found inside cells.
  • Extracellular fluid (ECF) or extracellular fluid volume (ECFV) usually denotes all body fluid outside of cells.
  • It is the intravascular fluid part of extracellular fluid (all body fluid outside of cells).
  • Examples of this fluid are cerebrospinal fluid, and ocular fluid, joint fluid, and the pleaural cavity which contain fluid that is only found in their respective epithelium-lined spaces.

• Nuclear Reactors

  • When the reactor's neutron production exceeds losses, characterized by increasing power level, it is considered "supercritical."
  • The mere fact that an assembly is supercritical does not guarantee that it contains any free neutrons at all.
  • At least one neutron is required to "strike" a chain reaction, and if the spontaneous fission rate is sufficiently low, it may take a long time before a chance neutron encounter starts a chain reaction—even if the reactor is supercritical.

• Flow Rate and Velocity

  • Flow velocity and volumetric flow rates are important quantities in fluid dynamics used to quantify motion of a fluid and are interrelated.
  • Fluid dynamics is the study of fluids in motion and corresponding phenomena.
  • Fluid velocity can be affected by the pressure of the fluid, the viscosity of the fluid, and the cross-sectional area of the container in which the fluid is travelling.
  • The magnitude of the fluid flow velocity is the fluid flow speed.
  • Fluid flow velocity effectively describes everything about the motion of a fluid.

• Poiseuille's Equation and Viscosity

  • Virtually all moving fluids exhibit viscosity, which is a measure of the resistance of a fluid to flow.
  • It describes a fluid's internal resistance to movement and can be thought of as a measure of fluid friction.
  • The greater the viscosity, the ‘thicker' the fluid and the more the fluid will resist movement.
  • Different fluids exhibit different viscous behavior yet, in this analysis, only Newtonian fluids (fluids with constant velocity independent of applied shear stress) will be considered.
  • In analyzing the properties of moving fluids, it is necessary to determine the nature of flow of the fluid.