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Reynolds Number for Gas

 

Reynolds Number for Gas Formula

\( Re_g \;=\;  20,100 \cdot \dfrac{ SG_g \cdot Q }{ d \cdot \eta } \)     (Reynolds Number for Gas)

\( SG_g \;=\;  \dfrac{  Re_g \cdot d \cdot \eta  }{ 20,100 \cdot Q }\)

\( Q \;=\;  \dfrac{ Re_g \cdot d \cdot \eta  }{ 20,100 \cdot SG  }\)

\( d \;=\; \dfrac{ SG_g \cdot Q \cdot 20,100 }{ Re_g \cdot \eta  }\)

\( \eta \;=\;  \dfrac{ SG_g \cdot Q \cdot 20,100 }{ Re_g \cdot d }\)

Symbol English Metric
\( Re_g \) = Reynolds Number \( dimensionless \) \( dimensionless \)
\( SG_g \) = Gas Specific Gravity Relative to Water (water = 1) \( dimensionless \) \( dimensionless \) 
\( Q \) = Gas Flow Rate \(ft^3\;/\;sec\) \(m^3\;/\;s\)
\( d \) = Pipe Inside Diameter \( in\) \( mm \)
\( \eta \)  (Greek symbol eta)  = Gas Viscosity \(lbf - sec\;/\;ft^2\) \(Pa-s\)

The Reynolds number, a dimensionless number used in fluid dynamics, including when dealing with gases.  It essentially expresses the ratio of inertial forces to viscous forces within a fluid.   When applied to gases, this number helps predict the flow's behavior, determining whether it will be laminar (smooth) or turbulent (chaotic).   Factors influencing the Reynolds number for a gas include the gas's density, its velocity, a characteristic length (like the diameter of a pipe), and the gas's viscosity.  In ssence, a low Reynolds number indicates viscous forces dominate, leading to laminar flow, while a high Reynolds number signifies inertial forces prevail, resulting in turbulent flow.  This concept is vital in various applications, from designing pipelines to understanding aerodynamic forces on aircraft.

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