Fluid Mechanics - Module 1 - Video 4 - Pressure, Pressure Measuring Devices; Manometers (S3 M & C)

Introduction

This tutorial covers the fundamental concepts of pressure in fluid mechanics, focusing on pressure measuring devices and manometers. Understanding these concepts is essential for students in mechanical and civil engineering, as it lays the groundwork for analyzing fluid behavior in various applications.

Step 1: Understanding Pressure

• Definition: Pressure is defined as the force exerted per unit area. It is a key concept in fluid mechanics necessary for analyzing fluid behavior.
• Formula: The mathematical formula for pressure (P) is: [ P = \frac{F}{A} ] where (F) is the force applied and (A) is the area over which the force is distributed.

Step 2: Types of Pressure

• Absolute Pressure: The total pressure exerted on a system, including atmospheric pressure.
• Gauge Pressure: The pressure relative to the atmospheric pressure. It’s what most pressure gauges measure.
• Differential Pressure: The difference in pressure between two points in a fluid system.

Step 3: Pressure Measuring Devices

• Manometers: Instruments used to measure pressure differences. They can be used for both absolute and gauge pressure measurements.
• Types of Manometers:
  • U-tube Manometer: A simple device consisting of a U-shaped tube filled with liquid. The difference in height of the liquid in the two arms indicates the pressure difference.
  • Inclined Manometer: Similar to a U-tube but inclined to allow for more precise measurements of small pressure differences.

Step 4: Using a U-tube Manometer

1. Setup: Connect one end of the manometer to the pressure source and leave the other open to the atmosphere.
2. Measure the Height: Observe the height difference (h) in the liquid columns.
3. Calculate Pressure: Use the height difference to calculate the pressure difference with the formula: [ P = \rho g h ] where (P) is the pressure, (\rho) is the density of the liquid in the manometer, (g) is the acceleration due to gravity, and (h) is the height difference.

Step 5: Practical Application of Manometers

• Use in Engineering: Manometers are widely used in HVAC systems, fluid transport, and process engineering to monitor and control fluid pressures.
• Common Pitfalls: Ensure the manometer is level and that the fluid is not vaporizing due to low pressure.

Conclusion

In this tutorial, we explored the concept of pressure in fluid mechanics, the types of pressures, and how to measure them using manometers. Understanding these principles is crucial for practical applications in engineering fields. For further study, consider diving deeper into fluid dynamics and the role of pressure in various engineering systems.