Pressure Measurement Flashcards
(22 cards)
What is the equation that relates absolute pressure, gage pressure, and atmospheric pressure?
Pabs = Pgage + Patm
pabs = Absolute pressure, pgage = Gage pressure, patm = Atmospheric pressure.
What does a positive gage pressure indicate? What does a negative gage pressure signify?
It is above atmospheric pressure. Negative shows it is below atmospheric pressure, sometimes called vacuum
Positive gage pressure is indicated in units of Pa(gage) or psig.
In what units is gage pressure indicated?
Pa(gage) or psig
Gage pressure can be expressed in either Pascals or pounds per square inch gauge.
In what units is absolute pressure indicated?
Pa(abs) or psia
Absolute pressure is expressed in Pascals or pounds per square inch absolute.
What is a barometer used for?
To indicate the value of local atmospheric pressure
Barometers can measure changes in atmospheric pressure, often used in weather forecasting.
Fill in the blank: A perfect vacuum is the _______.
lowest possible pressure
A perfect vacuum is defined as having no molecules present.
What is the typical atmospheric pressure assumed in this book?
101 kPa(abs) or 14.7 psia
This assumption is used unless specified otherwise.
What does the term elevation refer to?
The vertical distance from some reference level to a point of interest, called z.
A change in elevation between two points is called h.
What is the equation that relates pressure change to elevation change in a homogeneous liquid at rest?
Δp = yh.
Where Δp is the change in pressure, g is the specific weight of the liquid, and h is the change in elevation.
Under what conditions is the pressure measurement equation valid?
Only for a homogeneous liquid at rest.
This means that the liquid should not be moving and should have uniform properties.
What can be said about points on the same horizontal level regarding pressure?
They have the same pressure.
How does pressure change with specific weight of the liquid?
The change in pressure is directly proportional to the specific weight of the liquid.
What effect does a decrease in elevation have on pressure?
It causes an increase in pressure.
What effect does an increase in elevation have on pressure?
It causes a decrease in pressure.
What does the relationship p = yh indicate?
The change in pressure depends only on the change in elevation and the type of fluid.
What would happen to the pressure at the bottom of different containers?
All containers would have the same pressure at the bottom, despite containing different amounts of fluid.
How does pressure vary with elevation?
Pressure varies linearly with a change in elevation
What is Pascal’s Paradox?
The size of the volume of fluid does not affect the pressure result. ΔP depends only on the change in elevation and the type of fluid.
What is a manometer?
Device used for measuring pressure at a point in a fluid
Manometers utilize the relationship Δp = γ.h.
What are the common types of simple manometers?
- Piezometer
- U-tube manometer
- Single column manometer
These types are used to measure fluid pressure differences.
What are the two types of single column manometers?
- Well-type manometer
- Inclined well-type manometer
These are variations of single column manometers designed for different measurement applications.
What does a barometer measure?
Atmospheric pressure
The relationship used is patm = ρ.g.h.
