Volume fraction
In chemistry and fluid mechanics, the volume fraction φ i is defined as the volume of a constituent Vi divided by the volume of all constituents of the mixture V prior to mixing:
  - φ i = V i ∑ j V j Being dimensionless, its unit is 1; it is expressed as a number, e.g., 0.18. It is the same concept as volume percent (vol%) except that the latter is expressed with a denominator of 100, e.g., 18%. The volume fraction coincides with the volume concentration in ideal solutions where the volumes of the constituents are additive. The sum of all volume fractions of a mixture is equal to 1:
  - ∑ i = 1 N V i = V ; ∑ i = 1 N φ i = 1 The volume fraction is one way of expressing the composition of a mixture with a dimensionless quantity; mass fraction and mole fraction are others.
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