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How to Determine Liquid Flux in Water Transfer

Water flux is the calculation of water flow across an area on a per unit basis. For example, water flux can be determined to figure out how many gallons of water are transferred by a stream down a bed of rocks or how many liters of water are passed through a hose. If you'd like to figure out the water flux of a given transfer scenario, learn how to use the water flux equation.

Instructions

- 1
  Use the Osmotic Pressure equation, pi=MRT, to determine the osmotic pressure of the water that will be transferred. "Pi" represents the osmotic pressure. Replace "M" with the 55.5 moles, the molarity of water. Substitute "R" with "8.3145 J/mol K," the Ideal Gas Constant, and substitute the water's temperature for "T."
- 2
  Determine water transfer's transmembrane pressure. The transmembrane pressure is deduced from the stopping force on one side of the filter and the pressure created as the water passes through the other side. Simply subtract the water's initial pressure from its post-filtration pressure.
- 3
  Subtract the water's hydrostatic pressure, "P = GPH," from the transmembrane pressure of any filter that your water transfer must pass through. Gravitational acceleration, depth and density determine a liquid's hydrostatic pressure. Replace "G" with 9800 newtons, the acceleration of gravity. Replace "H" and "P" with the depth and density of your transfer membrane -- these variables' values should be formatted in feet.
- 4
  Use Darcy's Law, "perm=(K/N)(Delta P/Delta L)(A)," to determine the permeability of your water transfer. Substitute the "K" in Darcy's Law with "M^2," the permeability coefficient. Substitute "N" with your water's viscosity. Replace "Delta L" with the difference in pressure between the start and end of your transfer. Replace "Delta L" with the length or thickness of your transfer medium. Replace "A" with the area of any cross section in your transfer.
- 5
  Multiply the subtotal of the water's hydrostatic and transmembrane pressures by the permeability of the water itself to determine the amount of liquid flux in your transfer.

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