Operating conditions and standard conditions in gas temperature and pressure compensation?

In general industry, gas flow rates are expressed in terms of standard conditions flow rate.

Listen to me: make sure to select the best answer. What you’re using here is the standard condition; if it’s under operating conditions, then you just need to swap the positions of P and T as well as P0 and T0. Additionally, your formula assumes that the molecular weight remains constant, but in reality, you need to take into account the difference in molecular weights between operating conditions and standard conditions

Are you sure? Is there any more detailed information? This formula comes from the DCS manufacturer; are there any technical documents that clearly indicate whether it refers to flow rate under standard conditions or under actual operating conditions? Is there any detailed derivation process?

The formula is incorrect; the correct formula is: Q = Q0 * ((273.15 + T0) × (P + 0.1) / (273.15 + T) / (P0 + 0.1)) * Z. Here, Q0 represents the flow rate under the given conditions, Q represents the flow rate under standard conditions, and Z is the compression factor (this parameter is applicable when the medium is compressible, and Z < 1)； If the medium is incompressible, this term is absent, or Z=1)

This post was last edited by seiluobin on 2016-5-19 09:35. I’m sure; otherwise I wouldn’t dare ask you for the best answer. Since you asked, I’ll write it down for you. Wait a moment. The formula used in the edit cannot be displayed, so send me a message via QQ and I’ll send it to you

This post was last edited by cqdfwy on 2016-5-19 at 16:58. 1. First, I would like to admit an error: my explanation of the compression factor in the formula I wrote was incorrect. The correct explanation is as follows: The compression factor is a factor that indicates the difference between an ideal gas and a real gas; for an ideal gas, the compression factor Z=1； For real gases, Z＜1. When the temperature and pressure of a real gas are not high, it can be treated as an ideal gas. It can be understood in this way: real gases cannot be compressed to infinite pressures; once the density becomes very high at a certain compression level, further compression is no longer possible. When trying to achieve the same degree of compression, high-pressure gases differ from low-pressure gases – more energy is required to compress high-pressure gases, and they cannot be compressed in the same way as low-pressure gases or ideal gases. That’s why the compression factor Z<1 is used to indicate the difficulty of such compression. 2. After researching and analyzing carefully, it was found that both the formula provided by the original poster and the one I wrote are correct; the only difference is the application scenario: the poster’s formula is used for measuring gas flow rate using orifice plates, and it serves as a formula for correcting the flow rate when the actual operating conditions differ from those designed ； The formula I have written is a conversion formula used to obtain the flow rate under standard conditions when the flow meter measures the flow rate under operating conditions; it is commonly used in the measurement of gas flow rates. There are many flowmeters other than throttling devices that can measure the flow rate under operating conditions; positive displacement flowmeters, velocity-type flowmeters, and so on all use this method to obtain the flow rate under standard conditions. They are usually referred to as thermobaric compensation formulas. 3. The formula used by the original poster is derived on the assumption that the discharge coefficient α in the orifice plate flow calculation formula remains constant; in reality, however, α changes with temperature and pressure. Therefore, while it can be used in DCS systems for general flow measurement purposes, it is not suitable for applications that require high accuracy.

In other words, do most flow meters have the capability to convert the flow rate under actual operating conditions to standard conditions before displaying it?