Flow Measurement in Liquid and Gas 👍

💧 Liquid Flow Measurement

◾ Liquids are incompressible—their volume doesn’t change much with pressure.

◾ That’s why, even if there’s a pressure drop across a valve, the flow rate (in M³/hr) remains the same before and after the valve.

◾ In the image above, we see:

▪️ Inlet Pressure: 18 Kg/cm²

▪️ Outlet Pressure: 12 Kg/cm²

▪️ Flow Rate: 500 M³/hr → 500 M³/hr

✅ Conclusion: Volumetric flow remains constant for liquids, despite pressure drops.

💨 Gas Flow Measurement

◾ Gases are compressible—they expand as pressure drops.

◾ After passing through a control valve, gas expands, causing the volume to increase.

◾ In the image:

▪️ Inlet Pressure: 18 Kg/cm²

▪️ Outlet Pressure: 12 Kg/cm²

▪️ Flow Rate: 500 M³/hr → 750 M³/hr

⚠️ Important: Even though mass flow might be conserved, volumetric flow increases downstream due to expansion.

📏 Why It Matters

Flow meters must account for compressibility when measuring gas.

Engineers often use mass flow transmitters or corrected flow readings for gases, while volumetric transmitters work well for liquids.