From ventilation Book

1. Effect of Airway Characteristics
on Power Consumption
By
Ibrahim Amin

2. • In air flow through mine openings, the
horsepower of the air Pa is dissipated in
overcoming energy losses.
• Eq. 5-27 indicates that Pa varies directly as
both H and Q.
• As H α Q2  Pa α Q3
• Hence only enough quantity should be
circulated to adequately air condition the
mine.
• When Q is constant, the only possible way is
to reduce HT

3. • Eq. 5-26 indicates that HT can be minimized by
reducing K, P, L or by increasing A.
• Based on this statement following airway
characteristics are discussed.
– Dimensions
– Surface Characteristics
– Shape
– Length
– Shock Loss
– Velocity Head

4. Dimensions
• The most important single variable affecting
head loss is the size of the airway.
• Both area and perimeter appear in the head-
loss equation;
• H α P/A3 α πD/(π/4 D2 )3 α 1/D5
• It shows that a slight increase in dimensions
can result in a sharp decrease in head loss.

5. Surface Characteristics
• The irregularity or the roughness of the
surface of an airway, reflected in friction
factor, may affect head loss in the range of 1-
10.
• Eq. 5-26 shows that head loss varies directly
with K.
• Hence for clean and smooth airways K is
reduced as shown in Table. 5-1.

6. Shape
• The effect of airway shape on head loss is
relatively slight compared to that of the
previous factors.
• Quantitative measure of the shape effect is
afforded by hydraulic radius; RH = A/P, then
HL α 1/RH

7. Length
• Length of airway required is fix for given
layout, impossible to reduce.
• However this is desirable to reduce since it is
directly proportional to head loss.

8. Shock Loss
• The various sources of shock loss should be
investigated when attempting to reduce
power consumption.
• The shock loss factor has great role in
magnitude of losses.
• Hence straightening airways, installing guide
vanes and making area changes are necessary.

9. Thank You
Questions?