Ventilation Flashcards

1
Q

Purpose of ventilation

A

Control odors, temperature and humidity, contaminant concentration

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2
Q

Local exhaust ventilation

A

Capture contaminant at source and remove from work environment

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3
Q

Dilution ventilation

A

Dilute concentration by adding clean air

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4
Q

General ventilation

A

Climate control, comfort of building occupants

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5
Q

Dilution vs LEV

A

Dilution: moderate to low tox, disperse source, intermittent exposure

LEV: high tox, single source, direct exposure

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6
Q

What affects the density of air?

A

Temperature, elevation, humidity

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7
Q

Density correction factor

A

Accounts for non-standard conditions which affect air density

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8
Q

Major assumptions about movement of air

A
  1. Incompressible

2. Constant density

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9
Q

Flow profile difference between laminar and turbulent flows

A

Turbulent: flatter
Laminar: parabolic, center line has higher velocity than sides

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10
Q

How does air move through a duct?

A

Difference in pressure

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11
Q

Static Pressure

A

Pressure against the sides of a duct, acts equally in all directions, differences in SP cause air to move, is like potential energy

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12
Q

Velocity Pressure

A

Pressure of air motion, always positive and represents the pressure required to move air, is like kinetic energy

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13
Q

Total Pressure

A

SP + VP

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14
Q

Losses

A

SP in = SP out + losses

Losses are due to friciton and turbulence

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15
Q

Volume flow rate

A

Q = VA

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16
Q

3 types of hoods

A

Enclosing, capture, receiving

17
Q

Static hood pressure

A

SP[hood] = VP [duct] * (1 + K)

K values can be found in tables

18
Q

Coefficient of entry

A

Q[actual]/Q[ideal]

19
Q

Hood entry loss

A

he = F[h] x VP, where F[h] = loss factor (found in tables)

20
Q

How does SP losses occur in ducts?

A

Due to friction, affected by VP. Factors include smoothness of duct interior and presence of settled dust.

21
Q

Purpose of a fan?

A

To create SP

22
Q

Axial flow fans

A
  • Flow moves along axis of rotation
  • General/dilution ventilation
  • Not good for LEV, insufficient SP
23
Q

Centrifugal fans

A

Used for LEV, can run backwards with correct airflow direction and reduced efficiency

24
Q

Centrifugal radial fans

A

Blades look like paddle wheel, self cleaning, work horse

25
Centrifugal backward-curved fans
Wing shaped blades, higher performance, can't be used in dusty environments, noisy
26
Centrifugal forward-curved fans
Not good in dusty environments, moves large Q with little SP reqs, quiet
27
Fan static pressure
Fan[SP] = SP[out] - SP[in] - VP[in]
28
Six in three out
Allow 6D of duct into fan, allow 3D out of fan
29
Air hp
min power needed to move air
30
Brake hp
actual power needed to operate fan
31
Motor hp
Bhp plus power for drive losses
32
Fan Laws
Q ∝ RPM SP ∝ RPM^2 HP ∝ RPM^3
33
Volume of air needed to dilute
Q = (403 x 10^6 x SG x ER x k) __________________ (MW x C) ``` k = safety factor (0-10) SG = specific gravity ER = Evaporation rate MW = Molecular weight C = Concentration ```
34
What are non-equilibrium conditions?
Build up and decay