Pitot Traverse (module 6)

Question 1

Where do velocity profiles change in different parts of the LEV system?

Answer 1

• Vena Contracta
• Immediately downstream of a hood
• Further downstream of hood
• Immediately after an elbow
• Immediately after a fan

Question 2

what is the length of vena contracta?

Answer 2

Around 2D

Question 3

What is the maximum contraction for a vena contracta?

Answer 3

0.5D

Question 4

Why are the rules of thumb used for measurements?

Answer 4

• Field personnel may not have access to measurement equipment
• Impromptu assessments of a ventilation system may be necessary if the system malfunctions
• Designers may want to make first-pass estimates of changes to a ventilation system

Question 5

What is velocity on the centerline?

Answer 5

For a simple hood (plain duct or narrow flange)

Question 6

What is friction loss a function of?

Answer 6

VP

Question 7

T or F: Velocity/VP profile changes throughout the duct:

Answer 7

True

Question 8

Where is velocity the highest?

Answer 8

Centerline

Question 9

Where do you measure in a hood to eliminate elbow or hood effects?

Answer 9

traverse duct at least 6D downstream

Question 10

What do you measure TP and SP with?

Answer 10

pitot tube

Question 11

What do you measure velocity with>

Answer 11

A velometer (thermal or swinging vane)

Question 12

Where do we measure in ducts?

Answer 12

Across duct traverse

Question 13

How do you measure hood face velocity?

Answer 13

• Velocity over a hood face may not be uniform  Make sure differences are not too large
• Compute average velocity
• Break the hood face into small squares and measure the velocity in each