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How to calculate the flow coefficient of low Reynolds number liquid
Re is the dimensionless number indicating the flow state of the fluid in the pipe. The characteristics of fluid flow in a tube depend on a combination of four parameters (diameter, viscosity, density, and velocity). The Reynolds number can be used to determine whether the liquid flow is laminar or turbulent. The flow coefficient Kv is measured at the appropriate Reynolds number and turbulence conditions. As Re number increases, Kv value does not change much. However, when the Reynolds number decreases, the effective Kv value decreases. In extreme cases, the Reynolds number is very low. For example, for viscous fluid, the flow of liquid has become laminar flow state, and its flow rate is proportional to the valve pressure drop, but not proportional to the inverse of the square root value of the valve pressure drop. If Kv is calculated according to the above formula, the error must be large. Therefore, the Kv value of less than 104 fluid is calibrated. In the formula K 'v------, the revised flow coefficient K' v=Kv/FR (3-28); Kv-------- according to the above formula, namely the flow coefficient calculated according to the turbulence condition; FR---------- Re number correction coefficient, which can be obtained from FIG. 3-11 according to the size of Re number. Re number can be obtained from the following formula according to the valve structure, viscosity and other factors. With two parallel flow regulating valve, such as direct two-seater valve, butterfly valve, eccentric rotary valve, the Reynolds number for (3-29) for only a flow control valve, such as direct single seat valve, sleeve valve, ball valve, Angle valve, diaphragm valve, etc., the Reynolds number is (3-30) type v -- -- -- -- -- - liquid flowing temperature viscosity, was/s can be seen from the figure 3-11 curve, when the Reynolds number Re is more than 3500, correction is not big, so the Reynolds number is larger than 3500 generally do not need to correct the low Reynolds number.
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