Introduction

The Orificemeter and Pitot tube are both commonly used devices for measuring fluid flow rates. While both can provide accurate readings, there are certain factors that make the Orificemeter readings more accurate than Pitot tube readings. This answer will explain the factors that contribute to this accuracy difference.

Difference in Principle

The Orificemeter measures fluid flow rate based on the principle of pressure difference across a constriction in the flow path. It consists of a plate with a precisely machined orifice through which the fluid flows. The pressure difference across the orifice is measured and used to calculate the flow rate.

On the other hand, the Pitot tube measures fluid flow rate based on the principle of dynamic pressure. It consists of a small tube that is inserted into the fluid flow. The fluid enters the tube and comes to rest, creating a stagnation point where the dynamic pressure is maximum. This pressure is measured and used to calculate the flow rate.

Factors Contributing to Accuracy

1. Accuracy of Pressure Measurement: The accuracy of pressure measurement is crucial in determining the accuracy of flow rate calculation. Orificemeters typically have pressure taps located at precise positions, allowing for accurate pressure measurement. Pitot tubes, on the other hand, may be affected by factors such as misalignment, turbulence, and variations in fluid properties, which can introduce errors in pressure measurement.

2. Flow Profile: The flow profile in the pipe also affects the accuracy of the readings. Orificemeters are known to produce a more uniform flow profile downstream of the orifice, which helps in obtaining accurate measurements. Pitot tubes, however, can introduce disturbances in the flow profile, leading to inaccuracies in the readings.

3. Range of Measurement: Orificemeters have a wider range of measurement compared to Pitot tubes. They can accurately measure both high and low flow rates, while Pitot tubes may have limitations in accurately measuring very low or high flow rates.

4. Installation Requirements: Orificemeters have specific installation requirements, such as the need for a straight pipe section upstream and downstream of the orifice. If these requirements are met, the accuracy of the measurements can be ensured. Pitot tubes, on the other hand, may be more forgiving in terms of installation requirements, but this can also lead to less accurate readings.

Conclusion

While both the Orificemeter and Pitot tube can provide accurate readings, the Orificemeter readings are generally considered more accurate due to factors such as the accuracy of pressure measurement, flow profile, range of measurement, and installation requirements. It is important to carefully consider these factors when selecting a flow measurement device for a particular application.