Fluid Pressure Design Equations Formulas Calculator Absolute

Fluid Mechanics Hydraulics Design Formulas

Solving for absolute pressure

Inputs:

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Conversions:

gauge pressure (P_gauge)

= 0

newton/meter^2

atmospheric pressure (P_atmospheric)

= 0

newton/meter^2

Solution:

absolute pressure (P_absolute)

= NOT CALCULATED

Other Units:

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References - Books

Tipler, Paul A.. 1995. Physics For Scientists and Engineers. Worth Publishers. 3rd ed.

Background

It is essential to understand the concepts of gauge pressure, atmospheric pressure, and absolute pressure. Gauge pressure is the pressure relative to atmospheric pressure. It is the reading most pressure gauges provide, showing the difference between the system's and ambient atmospheric pressure. Atmospheric pressure, on the other hand, is the pressure exerted by the atmosphere at a given point and varies with location and weather conditions. Absolute pressure is the total pressure measured relative to the absolute vacuum, which combines the effects of atmospheric and gauge pressures.

Equation

The relationship between absolute pressure (P_absolute), gauge pressure (P_gauge), and atmospheric pressure (P_atmospheric) is given by the equation:

P_absolute = P_gauge + P_atmospheric

How to Solve

To calculate absolute pressure, follow these simple steps:

Measure or obtain the gauge pressure (P_gauge).
Determine the atmospheric pressure (P_atmospheric) for your location at the time of measurement.
Use the equation P_absolute = P_gauge + P_atmospheric to calculate absolute pressure.

Example

Assume you have a gauge pressure reading of 50 psi from a compressor and the atmospheric pressure is 14.7 psi (average atmospheric pressure at sea level). To find the absolute pressure:

P_absolute = P_gauge + P_atmospheric = 50 psi + 14.7 psi = 64.7 psi

Hence, the absolute pressure in the compressor system is 64.7 psi.

Fields/Degrees

Mechanical Engineering: Used in designing and analyzing pressurized systems, including boilers and gas storage tanks.
Aerospace Engineering: Critical for calculating forces on aircraft and spacecraft bodies, especially at different altitudes.
Meteorology: Helps analyze atmospheric phenomena and predict weather conditions by studying pressure variations.
Oceanography: Essential in studying underwater phenomena calculating hydrostatic pressure at various depths.
Medicine: Used in hyperbaric medicine to determine the pressures necessary for hyperbaric chambers used in treatments.

Real-Life Applications

Tire Pressure Monitoring: Ensuring vehicle tires are inflated to the correct absolute pressure for safety and efficiency.
Weather Forecasting: Atmospheric pressure measurements assist in predicting weather changes.
Diving: Calculating the pressure experienced by divers and ensuring safe decompression upon ascent.
Food Processing: Pressure cooking and canning processes rely on understanding absolute pressure for safety and effectiveness.
Aviation: Aircraft cabin pressurization systems maintain a safe and comfortable absolute pressure environment for passengers and crew.

Common Mistakes

Confusing Gauge and Absolute Pressure: People often forget that gauge pressure excludes atmospheric pressure and must be corrected to find absolute pressure.
Ignoring Altitude Variations: Not adjusting atmospheric pressure for location altitude which can significantly affect calculations.
Measurement Errors: Using inaccurate gauge or atmospheric pressure values leads to incorrect absolute pressure.
Unit Conversion Mistakes: Failing to convert all measurements to the same units before calculation.
Neglecting Temperature Changes: Overlooking the impact of temperature on pressure measurements in some contexts.

Frequently Asked Questions

What happens to absolute pressure at sea level? At sea level, the atmospheric pressure is roughly 14.7 psi. To get absolute pressure, you add the gauge pressure to this value.
Can absolute pressure be negative? Absolute pressure cannot be negative because it is always positive and measured relative to a complete vacuum.
How does altitude affect atmospheric pressure? As altitude increases, atmospheric pressure decreases. This decrease must be considered when measuring absolute pressure at different elevations.
Why is absolute pressure important? Absolute pressure is crucial for understanding true pressures in a system and is necessary for safety, efficiency, and functionality in various applications.
Does temperature affect absolute pressure? Yes, the temperature can affect the volume, and, therefore, the pressure of a gas, but the equation for converting gauge to absolute pressure does not directly involve temperature. However, temperature variations can indirectly affect pressure readings, especially atmospheric pressure.

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