1. Definition
The pressure drop caused by piping valves, fittings and
other singularities is not the same in turbulent flow and in
laminar flow. Turbulent flow have been extensively studied,
thus the coefficient are available for many equipment but it
is less the case in laminar flow. This page is giving some
references from literature for laminar flow. Please
consult those references for more details.
2. Pressure drop calculation
K coefficient can reasonably be used until Re=500, below,
specific coefficients should be used.
2.1 Kittredge and Rowley
The data of Kittredge and Rowley are reported in many
books. They have tabulated the frictional loss coefficients
for different fittings and valves and different Reynolds. If
the flow is found to be laminar they should be used in
pressure calculation instead of the coefficients calculated
for turbulent flow
Table 1 : K coefficient for
calculation of pressure drop through valves and fittings
in laminar flow according to Kittredge and Rowley
2.2 Hooper
As an alternative, the method of Hopper can be used. As
most of the data obtained in laminar flow, results are
approximate.
The frictional loss coefficient can be calculated from the
value in turbulent flow and coefficients to account for
laminar flow :
Equation 1 : Hooper
approximation for calculation of pressure drop
coefficients of valves and fittings in laminar flow
With :
 K_{1} = pressure drop coefficient for Re=1
 K_{t} = coefficient in turbulent flow
If unknown, K_{t} can be calculated with the
following formula where K∞ is the coefficient in turbulent
flow for a very large diameter
Equation 2 : Calculation
of turbulent frictional loss coefficient for Hooper method
Coefficient K_{1} can be
calculated thanks to the following table.
Table 2 : K1 coefficient for
calculation of pressure drop through valves and fittings
in laminar flow with the approximation of Hooper
Source
Mecanique et Rheologie des
Fluides en Genie Chimique, Midoux, Tec et Docs, 1993,
pages 348
Perry's Chemical Engineers
Handbook, Perry, McGraw Hill, 2008, page 618
