Average linear velocity, definition

REYNOLDS NUMBER AND TRANSITION FROM LAMINAR TO TURBULENT PLOW. Reynolds studied the conditions under which one type of flow changes into the other and found that the critical velocity, at which laminar flow changes into turbulent flow, depends on four quantities the diameter of the tube and the viscosity, density, and average linear velocity the liquid. Furthermore, he found that these four factors can be combined into one group and that the change in kind of flow occurs at a definite value of the group. The grouping of variables so found was... 

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