Volume fraction

Proportion of the total volume of a constituent part

In chemistry and fluid mechanics, the volume fraction φ i {\displaystyle \varphi _{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 . {\displaystyle \varphi _{i}={\frac {V_{i}}{\sum _{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%.

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