1. بنام خدا
با سلام

2. انتظار میرود دانشجو در پایان جلسه بتواند:
1- خواص هوای محیط کار را نام ببرد.
2- ترکیب طبيعی هوا را توضیح دهد.
3- دانسیته یا چگالی هوا را تعریف کند.

3. THE BEHAVIOR OF AIR

4. The Atmosphere Reaches 50 miles into space.
Pressure = 14.7 pounds per square inch.

5. Composition of Air

6. Pressure Measurement
Vacuum
Atmospheric Pressure
14.7 psia

7. Pressure Measurement 14.7 psia = 407in. Water 14.7 psia =
29.92 in. Mercury (Hg.)

8. How Do We Make Air Move ?

9. Pressure Differences in air pressure cause movement.
The pressure inside a ventilation duct is measured relative to the atmospheric pressure.

10. Pressure Differential Causes Movement
FLOW
LOW
HIGH
FAN
BURTON 3-6

11. Negative Pressure = Less Than Atmospheric

12. Positive Pressure = Greater Than Atmospheric

13. Pressure Relationships

14. Pressure Terms
Static Pressure
Velocity Pressure
Total Pressure

15. Static Pressure Flow SP Static pressure (SP) is
exerted in all directions.
The pressure inside a ventilation duct is measured relative to the atmospheric pressure.
It is measured perpendicular to air flow.

16. Velocity Pressure Flow SP VP Velocity Pressure (VP) is
kinetic (moving pressure) resulting from air flow.
It is measured parallel to the direction of the flow.

17. Total Pressure
Flow SP VP TP
Total pressure (TP) is the algebraic sum of the VP and SP.
It is measured parallel to the direction of the flow.

18. Pressure Upstream and Downstream of the Fan
TP SP VP
Up-stream
Down-stream
BURTON 3-8

19. What is use of the term “Velocity Pressure” ?
Determine the air flow.
To design the system.
V = 4005(VP)1/2

20. What is use of the term “Static Pressure” ?
Accelerate the air.
Overcome resistance to friction.
Friction losses are associated with hood entries, duct entries, dampers, air cleaners, and elbows.

21. Static Pressure and Velocity Pressure are Mutually Convertible
When air is accelerated, the static pressure is converted to velocity pressure. =
Think of static pressure as a “potential pressure”.
When air is decelerated, the velocity pressure can be transformed back into static pressure.

22. Industrial Ventilation Design Procedure
Find Q
Determine d
Calculate actual V
Calculate VP
Find VP loss coefficients
Calculate Fan SP
Calculate Fan TP
Choose Fan rpm from Fan Table