Mathematical model of Heat Transfer Coefficient through the annulus gap between concentric pipes filled with fluid:

U = \frac{\lambda_{ann}}{d_h} \, {\rm Nu}_{ann}

where

thermal conductivity of fluid in the annulus

annular hydraulic diameter

dimensionless Nusselt number (Nu)


The Nusselt number (Nu) correlations are:

Stagnant fluidNatural ConvectionForced Convection
OEIS sequence A282581
J. DIRKER & J. P. MEYER


{\rm Nu}=3.6568



{\rm Nu} = \frac{2 \cdot \epsilon({\rm Ra})}{\ln (r_{out}/r_{in})}



{\rm Nu}= c \cdot \mbox{Re}_D^p \cdot \mbox{Pr}^{0.4}\cdot \left( \frac{\mu}{\mu_w} \right)^{0.14}




wherewhere


 Reynolds number 

Natural Convection Heat Transfer Multiplier 

Prandtl number 

Rayleigh number 

kinematic viscosity



thermal diffusivity


inner radius of outer pipe


outer radius of inner pipe









See also

Physics / Thermodynamics / Heat Transfer /  Heat Transfer Coefficient (HTC) / Heat Transfer Coefficient (HTC) @model

[ Thermal conductivity ] [ Nusselt number (Nu) ]


Reference

J. DIRKER & J. P. MEYER (2005) Convective Heat Transfer Coefficients in Concentric Annuli, Heat Transfer Engineering, 26:2, 38-44, DOI: 10.1080/01457630590897097


DirkerandMeyer2005.pdf