# Homework Help: Hydraulic mean diameter

1. May 30, 2008

### jteixeira

a rectangular duct sides .2m x .1m conveys air at a velocity of 5m/s
detremine the surface convection coefficient, h if the following data apply

thermal conductivity, k of air .000025kw/mK
Dynamic viscosity of air .000018Pas
Density of air 1.2kg/m3
Specific heat capacity of air 1.03kJ/kgK

commoent on the reniolds number and the flow regime in the duct

Re=DxVxDensity/Viscosity
Nu=hD/k
Pr=Cp x Viscosity/k
Nu=.023 X Re ^.8 x Pr^.4

im stuck with finding the hydraulic mean diameter

could someone shed some light