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Daily Dose 006 | FLUID MECHANICS
How do you find the Absolute Pressure in tank?
Atmospheric, Gage, Absolute…what gives when it comes to talking Pressure – specifically, to find the absolute pressure in tank?
It’s not much of a problem type, typically easy money…but it trips students up for sure.
But this isn’t going to be your case, in this video, we jam on another FE Exam Practice Problem in the subject of FLUID MECHANICS, specifically revolving around the relationship of ATMOSPHERIC PRESSURE to GAGE PRESSURE.
Key Definition
What is the ATMOSPHERIC PRESSURE?
ATMOSPHERIC PRESSURE is defined as the force per unit area exerted against a surface by the weight of the air above that surface.
The STANDARD ATMOSPHERIC PRESSURE at sea level has a mean value of 101.3 pascals, which is roughly 14.7 psi.
There is a relationship between ATMOSPHERIC PRESSURE, GAGE PRESSURE and ABSOLUTE PRESSURE.
GAGE PRESSURE is the pressure relative to atmospheric pressure.
GAGE PRESSURE is positive for pressures above ATMOSPHERIC PRESSURE, and negative for pressures below it.
ABSOLUTE PRESSURE is the sum of GAGE PRESSURE and ATMOSPHERIC PRESSURE.
The Process
How to find the Absolute Pressure in Tank
Pressure is the force exerted per unit area – it’s like a crowd of tiny particles, each giving a little nudge against a surface.
When we talk about pressure in a tank or any closed system, we often deal with gage pressure, which is the pressure inside minus the atmospheric pressure.
The general formula can be expressed as:
- Absolute Pressure = Gauge Pressure + Atmospheric Pressure
With this formula, we can essentially take any data given to us in a problem statement and present it in any form that is required.
But in the case of defining the absolute pressure within a tank, this is the step-by-step process:
- Step 1: Identify the Gage Pressure
- Step 2: Know the Atmospheric Pressure
- Step 3: Calculate Absolute Pressure
This is the pressure reading from the tank, excluding the atmospheric pressure. Imagine it’s like weighing yourself while ignoring the weight of the shoes you’re wearing.
At sea level, it’s approximately 101,325 Pascal (or 14.7 psi). But, always confirm the atmospheric pressure for your specific location. It’s like adjusting a recipe based on your altitude. Higher up? Less pressure. Down in a valley? More pressure.
Using the general formula, plug in the data we have defined, rearrange, and solve for the absolute pressure.
This process is basic, but one that trips up many engineers for one reason or another.
Check out the video to see an FE Exam Fluid Mechanics Practice Problem that deals with finding the Absolute Pressure in a tank and how you can go about solving for it in the most efficient manner.
As always, we are here to help, Prepineer
