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Valves and fittings pressure drop K coefficient (laminar)

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1. Introduction
2. Pressure drop calculation

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

Frictional loss coefficient K of valves and fittings in laminar flow - 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 :

Hooper formula for calculation of pressure drop coefficient for valves and fittings in laminar flow
Equation 1 : Hooper approximation for calculation of pressure drop coefficients of valves and fittings in laminar flow
With :
- K1 = pressure drop coefficient for Re=1
- Kt = coefficient in turbulent flow
If unknown, Kt can be calculated with the following formula where K∞ is the coefficient in turbulent flow for a very large diameter
Turbulent flow pressure drop calculation in Hooper method
Equation 2 : Calculation of turbulent frictional loss coefficient for Hooper method

Coefficient K1 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

K1 coefficient for Hooper method for calculation of pressure drop coefficients in laminar flow for valves and fittings


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 6-18