Orifice Calculations: Convert Pressure Difference to Mass Flow Rate

In summary, the conversation discusses using an orifice to measure pressure difference and mass flow rate of air in a 26 mm diameter pipe. The question is how to convert the pressure difference values into mass flow rate. The coefficient of discharge is needed for this conversion, which is typically 0.6 for a square or sharp-edged orifice. The reference provided gives a polynomial expression for calculating Cd based on beta ratio and Reynolds number. This can then be used to calculate the mass flow rate from the volumetric flow rate.
  • #1
almarzooq
6
0
Hi there,

I have used an orifice for my project to measure the pressure difference and hence the mass flow rate of air going through a pipe of 26 mm diameter. i kept changing the flow from max to min and ended up with values of pressure diference. The questions here is how to convert thses values ( in meters) into mass flow rate (kg/s) ?? I tried to find equations for this but they have the coefficient of discharge involved and i cannot find this value ! can anyone help me on this please ?

regards
 
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  • #2
If it is a square or sharp edged orifice, the starting point for Cd is 0.6.
 
  • #3
thanx a lote , can please post the equation to find the mass flow rate here and explain its parameters and variables ?
 
  • #4
http://www.pipeflowcalculations.com/orifice/theory.htm

This will give you volumetric flow rate, but I am assuming that you can calculate mass flow from there.

By the way, for anyone else interested, this reference gives the polynomial expression for calculating Cd based mostly on beta ratio and Re. This is referenced in the ASME spec on orifice calculations. I haven't found it stated anywhere else yet. It's a nice piece of information.
 
Last edited:

1. What is an orifice calculation?

An orifice calculation is a method used to convert the pressure difference across an orifice to a mass flow rate. This is important in industries where precise control of fluid flow is necessary, such as in chemical processing or HVAC systems.

2. Why is it important to convert pressure difference to mass flow rate?

Converting pressure difference to mass flow rate allows for more accurate measurement and control of fluid flow. It also allows for comparisons between different systems and ensures that equipment is operating within safe limits.

3. How do you perform an orifice calculation?

An orifice calculation involves using equations derived from Bernoulli's principle and understanding the properties of the fluid, such as density and viscosity. These calculations can be done manually, but there are also software programs and online calculators available to assist with the process.

4. What factors can affect the accuracy of an orifice calculation?

There are several factors that can affect the accuracy of an orifice calculation, including the type of fluid, the size and shape of the orifice, and the condition of the equipment. It is also important to consider the effects of temperature and pressure changes on the fluid.

5. Are there any limitations to orifice calculations?

While orifice calculations are a useful tool for measuring and controlling fluid flow, they do have limitations. These calculations may not be accurate for complex fluid systems or when there are significant changes in temperature and pressure. It is important to consider these limitations when using orifice calculations in practical applications.

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