Ventilation Flashcards
What is standard air temperature for ventilation problems?
70F
What are the unit options for Q?
CFM or m3/s
What is standard pressure for ventilation problems?
14.7 PSI = 101,325 PA = 407 inches of H2O
It’s the same standard pressure we use on in other problems. It’s on the equation sheet.
Feet to miles conversion
5280 feet to 1 mile
cm to inches
2.54 cm to 1 inch
What is a density factor?
The ratio of density of air divided by the density of standard air
What is the formula for density factor?
Df = (530 R / T)*(P/14.7 PSI)
Df = (294K / T)*(P/101325 Pa)
What are the units in V = 4005 √VP/df
V = f/m
VP = in of H2O
What are the units in V = 1.29√VP/df
V = m/s
VP = Pa
Name two types of losses that can occur in a ventilation system
Static pressure losses and friction losses
How is an elbow loss factor expressed in an equation
Fₕ
Is a lower Fₕ better or worse?
Better
Name 3 kinds of enclosing hoods
- Laboratory hood
- Glove box
- Paint booth
Are hood energy losses directly proportional to velocity pressure?
Yes
What is hood static pressure?
The total energy associated with accelerating air into the system (SPₕ)
What is Cₑ?
Coefficient of entry
What is SPₕ?
Hood static pressure
What is the ideal Cₑ number?
The closer to 1, the better
What does a pitot tube measure?
Static pressure
What is the ideal pitot tube placement downstream of obstructions?
greater than or equal to 7 duct diameters
What is the ideal pitot tube placement upstream obstructions?
3 duct diameters
What is capture velocity?
The minimum hood induced air velocity necessary to capture and convey the contaminant into the hood
Coefficient of entry definition
A measure of how efficient the hood is at accelerating the air
Hood static pressure definition
The total energy associated with accelerating air into the system
Ideal pitot tube placement downstream
> or equal to 7 duct diameters
Ideal pitot tube placement upstream
> or equal to 3 duct diameters
Circumference of circle
2πr
