I have a question regarding the parameters of orifice plate flow meters
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Dear experts~ While reviewing the calculation sheet for orifice plate flow meters today, I noticed that one parameter was left blank; its name is “Orifice diameter at 20°C”. . . What is this parameter for? I checked several different calculation software programs and reference books, and it seems that this value is also included in their calculations. How is this result obtained? What is its purpose? What is the calculation process? Generally, software stops its calculations once the β value is determined; once the β value is known, the orifice diameter can be calculated, so what’s the need to know the diameter at 20°C? Does this 20°C refer to the temperature of the orifice or the temperature of the medium? . . The medium temperature is a problem; many media change their state at 20°C. . . . I’m so confused~ Please help! :dizzy:
The last edit to this post was made by cqdfwy on 2017-5-27 at 11:58. “Orifice diameter at 20°C” refers to the orifice diameter under conditions of 20°C; what about the inner diameter of the pipe at 20°C? It is simply a matter of taking into account the thermal expansion and contraction of metal materials; under normal circumstances this has no significant impact. However, the requirements for the aperture size and pipe diameter in orifice metering are very strict (expressed in millimeters, with three decimal places usually required). The effect of thermal expansion and contraction on these dimensions is considerable, which is why it is necessary to specify the dimensions at a certain temperature (usually specified as “data at 20°C”). Dimension measurements and verifications are also carried out under these conditions ； For accurate orifice plate metering, the actual temperature of the fluid cannot always be 20°C (nor can the fluid be kept at a temperature of 20°C); the flow calculation formulas used in practice take this factor into account to make the necessary corrections.
The orifice plate specifications indicate the orifice diameter at 20°C; before installing the orifice plate, it is necessary to verify this diameter, which is measured at an ambient temperature of 20°C.
Hehe, what a strange question. If the aperture isn’t 20 degrees, do we still need to measure the temperature? That’s extremely difficult; a ruler isn’t enough – you also need to get a furnace.
I mean, since I’ve already given the β value and thus the aperture size is determined, what’s the need to specify the aperture size at 20°C separately? Isn’t the pore diameter simply obtained by multiplying the pipe diameter by β? Or is the pore diameter resulting from that calculation based on operating conditions rather than at 20°C?
What is the pipe diameter? It depends on the inner diameter of the pipe.
Okay, it’s the inner diameter, so what next? The problem still hasn’t been solved. What exactly is the aperture that results from multiplying my β value?
This post was last edited by hfrs on 2017-5-28 at 23:25. Hehe, whether direct multiplication is possible depends on the temperature; when the temperature is around 20 degrees, direct multiplication is fine, but otherwise the coefficient of thermal expansion needs to be taken into account.
Is my understanding correct then? This β value should represent the pore size ratio under operating conditions, and for processing, it’s necessary to consider the pore size at 20°C, is that right?
The β value is the ratio of the orifice diameter at 20°C to the inner diameter of the pipe at the same temperature. When the material of the orifice plate differs from that of the pipe, their coefficients of thermal expansion also differ; as a result, the β value calculated under the same temperature conditions becomes variable. However, the flow rate calculation formulas use only one fixed β value, which is the β value at 20°C.