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Prevention And Control Of Airborne Hazards > Air Pressure (module 4) > Flashcards

Air Pressure (module 4) Flashcards

1
Q

What is pressure?

A
  • ratio of force to the area over which that force is distributed
  • force per unit area applied in a direction perpendicular to the surface of an object.
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2
Q

What is the symbol for pressure?

A

p or P

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3
Q

What is the equation for pressure?

A
  • force/unit area
  • P=F/A
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4
Q

what is the equation for energy?

A
  • force x distance moved
  • E= F x L
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5
Q

What is the equation for air pressure?

A
  • energy/volume
  • P= E/V
  • P= E/AL
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6
Q

How does air move?

A

From high to low pressure

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7
Q

What is absolute pressure?

A

Gauge pressure plus barometric or atmospheric pressure.

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8
Q

When is absolute pressure 0?

A

can be zero only in a perfect vacuum

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9
Q

What is atmospheric pressure?

A

the pressure due to the weight of the atmosphere (air and water vapor) on the earth’s surface.

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10
Q

What is the average atmospheric pressure at sea level on a column?

A

14.7 pounds per square inch (psia)= 1 atm

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11
Q

What is standard air?

A

14.7 psia at 70 °F
Density = 0.075 lbm/ft3 = 1.202 kg/m3

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12
Q

What is the baseline for absolute pressure?

A

407 in h2O absolute = 0 in h2O w.g.

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13
Q

What is 14.7 psia in gage pressure?

A

0 psig

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14
Q

What are the comparisons in gage pressure?

A
  • If p > 1 atm then pg > 0 (positive)
  • If p < 1 atm then pg < 0 (negative)
  • If p = 1 atm then pg = 0
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15
Q

What are the units for pressure?

A

PSI

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16
Q

Why do we use inches of water (water column) for ventilation systems?

A

More accurate and shows smaller differences and there’s low pressure in ventilation systems

17
Q

What level of pressure is there in ventilation?

A

Usually low

18
Q

Atmospheric pressure equation

A

407 h2o= 0 in h2o gage (w.g.)

19
Q

T or F: Thermal energy of molecular motion is kinetic (internally), but observed externally as potential

A

True

20
Q

What is potential energy?

A

Static pressure

21
Q

T or F: Static pressure (psig) can be +ve or -ve (above or below atmospheric pressure)

A

True

22
Q

What is static pressure?

A
  • associated with the potential energy
  • omnidirectional
  • atmospheric pressure at sea level static pressure
23
Q

what is the symbol for static pressure?

A

SP

24
Q

what is velocity pressure?

A
  • associated with the kinetic energy of the moving airstream and is exerted only in the direction of flow
  • ex: blowing on your hand
25
Q

What is the symbol for velocity pressure?

A

VP

26
Q

T or F: Velocity pressure can only be positive?

A

True

27
Q

What is total pressure?

A
  • reflects the combined static and velocity components
  • exerted in the direction of the flow
28
Q

What is the equation that connects TP, SP, and VP?

A

TP= SP + VP

29
Q

What is the abbreviation for total pressure?

A

TP

30
Q

What is an example of static pressure?

A
  • Put your finger over a small hole in your mouth and blow
  • Feel static pressure against your cheeks and finger
31
Q

How is pressure measured?

A
  • manometer
  • static pressure is higher inside the tire than in the atmosphere
32
Q

What is velocity pressure (dynamic pressure)?

A
  • pressure we feel from moving air
  • ex: Put your hand an inch in front of your mouth and blow. Feel pressure of moving air against your hand
  • air moves in one direction
33
Q

what happens if we pop a hole in a tire?

A
  • If we pop a little hole in the tire, the air will all exit because Ptire&raquo_space; Patm and Air naturally moves from high to low P
  • Sp goes down, Vp is high since the SP difference between the tire and atmosphere is large
  • Vp decreases until Vp=0 and Sp=SPatm
  • eventually balenced
34
Q

How do we measure velocity pressure?

A
  • manometer
  • put pressure tap facing stream of moving air
35
Q

What is the velocity equation?

A
  • V= 4005 X √VP
  • pressure units: inches of water in w.g
  • velocity units: ft/min
36
Q

What is the Velocity pressure equation? (VP)

A

VP = (1⁄2density) * (V^2)

37
Q

What are the 5 components of a Local exhaust ventialtion system? (LEV)

A
  • Hood
  • duct
  • filter
  • fan
  • stack

Prevention And Control Of Airborne Hazards (16 decks)

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