Page 94 - Industrial Ventilation Design Guidebook

4,1 FLUID FLOW 59

If either p } or p 2 is known, simplification of the left side of Eq. (4.61) gives

where Ap l and Ap 2 are auxiliary quantities, which can be solved from Eqs.
(4,61) and (4.62). The real pressure loss can then be solved with the equations

and

These equations can be used when the Mach number is small, and the acceler-
ation effect is ignored.

Example 2
Calculate the final pressure of air flowing in a 200 rn long pipe, when the
1
initial pressure of air is 800 kPa and the mass flow is 2.5 kg s" . The pipe di-
ameter is 100 mm, the roughness is 0.03 mm, and the sum of the single resis-
tances is 6.5. The air temperature is 300 K, the molar mass 28.96 kg kmoH,
1
5
and the dynamic viscosity 1.85 x 10~ kg s^rrr .
First calculate

Determination of friction factor £:

and

Equation (4.61) gives