125 psig is equivalent to
A. 14.696 psia.
B. 135 psia.
C. 139.7 psia.
D. 147.7 psia.
The Correct Answer and Explanation is :
To convert pressure from pounds per square inch gauge (psig) to pounds per square inch absolute (psia), we need to understand the difference between these two units:
- Gauge Pressure (psig): This measures pressure relative to atmospheric pressure. It means that the reading excludes atmospheric pressure, which is approximately 14.7 psi at sea level.
- Absolute Pressure (psia): This includes atmospheric pressure, representing the total pressure exerted by a fluid, including the weight of the air above it.
The formula to convert from psig to psia is:
[
\text{psia} = \text{psig} + \text{atmospheric pressure}
]
Given:
- Atmospheric pressure (approximately) = 14.7 psi
- Pressure in question = 125 psig
Substituting the values into the formula:
[
\text{psia} = 125 \, \text{psig} + 14.7 \, \text{psi} = 139.7 \, \text{psia}
]
Thus, 125 psig is equivalent to 139.7 psia. The correct answer from the options provided is C. 139.7 psia.
Explanation of the Importance of Pressure Units
Understanding the difference between psig and psia is crucial in many fields, including engineering, meteorology, and fluid dynamics. Many systems operate under gauge pressure readings, as these are easier to measure and directly relate to the functioning of machines (e.g., tire pressure, boiler pressure). However, for calculations involving energy, work, or thermodynamic properties, absolute pressure is often needed.
For instance, in thermodynamic calculations, the properties of gases are typically defined with respect to absolute pressure. Using gauge pressure could lead to significant errors, especially in processes where low pressures are involved.
In summary, when dealing with pressures, it’s essential to clarify whether the values are gauge or absolute. This understanding allows engineers and scientists to make accurate calculations and ensure the safety and efficiency of their designs and operations.