What is the Difference Between Venturi and Orifice?

The main difference between a Venturi meter and an orifice meter lies in their design, working principle, and pressure loss. Both devices are used to measure the volumetric or mass flow rate of fluids by reducing the pressure of the flowing fluid. Here are the key differences between the two:

• Design: A Venturi meter consists of a converging section, throat, and diverging section, while an orifice meter has a thin plate with a bore on the plate, acting as a restriction.
• Working Principle: Venturi meters rely on fluid flow through a converging-diverging section called a Venturi tube, while orifice meters use a flat plate with a sharp-edged hole inserted into the fluid flow.
• Pressure Loss: Venturi meters introduce lower pressure drops (2-3% in a well-proportioned pipe), while orifice meters introduce higher pressure drops (60-70%).
• Coefficient of Discharge: Venturi meters have a higher coefficient of discharge (0.984 – 0.995), while orifice meters have a lower coefficient of discharge (~0.60).
• Turndown Ratio: Venturi meters have a higher turndown ratio (10:1), while orifice meters have a lower turndown ratio (3:1 to 5:1).
• Cost: Venturi meters are more expensive than orifice meters.
• Material: Both Venturi and orifice meters can be made from various materials such as stainless steel, cast iron, Monel metal, or polyester glass fiber.
• Operational Flexibility: Venturi meters can handle a larger range of flow rates, while orifice meters offer more flexibility in operation, allowing for easy removal and change of orifice plates.
• Clogging Problems: Clogging can occur in orifice meters when the working fluid contains solids, while Venturi meters are less prone to clogging issues.

In summary, Venturi meters are more suitable for applications requiring minimal pressure loss and accurate flow measurement, while orifice meters are simpler in design and more widely used in various industries.

Comparative Table: Venturi vs Orifice

Here is a table comparing the differences between Venturi and Orifice flow meters:

Both Venturi and Orifice meters apply Bernoulli's principle to measure flow, which can be difficult to directly measure especially in closed pipes. Venturi meters have a tapered structure, causing a gradual change in fluid velocity, while Orifice meters have a sudden change in fluid velocity due to the flat flanges. Venturi meters are more expensive and complex to fabricate but offer lower pressure loss, higher accuracy, and a wider measuring range. Orifice meters are cheaper, easier to install, and provide more operational flexibility but result in higher energy losses and lower accuracy.