Discharge coefficient rotameter

To size the rotameter, v nsx can be eliminated between these two equations and the expression simplifled so that the volumetric flow rate q is obtained as Eq. (24), where Q = l/ /C is a discharge coefficient with values between about 0.6 and 0.8 [9]. 

This meter may thus be considered as an orifice meter with a variable aperture, and the formulae already derived are therefore applicable with only minor changes. Both in the orifice-type meter and in the rotameter the pressure drop arises from the conversion of pressure energy to kinetic energy and from frictional losses which are accounted for in the coefficient of discharge. The pressure difference over the float —AP. is given by ... 

Coefficients of discharge for square-edged orifices with centered circular openings and for rotameters. (Subscript 0 indicates at orifice or at constriction and subscript 1 indicates at upstream... 

Values of Cd for various plummet shapes in rotameters are presented in Fig. 14-55. The Reynolds number applicable to the rotameter coefficient of discharge is based on the flow conditions through the annular opening between the plummet and the containing tube. The equivalent diameter for use in the Reynolds number consists of the difference between the diameter of the rotameter tube at the plummet location and the maximum diameter of the plummet. 

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