Forced Convection:  The most common mode of heat transfer is forced convection.  A number of correlations have been developed for situations where fluid is flowing through pipes and annuli.  These correlations are functions of Reynolds number (Re), Prandtl number (Pr), and Graetz number (Gz) (see Tables 5.4 and 5.5).  During computation of these numbers, the properties of the fluid are taken at bulk temperatures.

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Module for calculation of heat transfer for forced convection through a pipe

d (Inside diameter of tube , in)
L (Tube length , ft)
visc (Viscosity, lb per ft per hr)
w (mass flow rate, lb per hr)
rho (Density, lb per ft3)
k (Thermal conductivity, BTU per hr per ft per deg F)
c (heat capacity, BTU per lb per deg F)
visc_w (Viscosity at wall temperature, lb per ft per hr)
phi (Viscosity correction factor)
tb (Tube side fluid bulk temperature, deg F)
t1 (Inlet temperature of cold fluid, deg F)
t2 (Outlet temperature of cold fluid, deg F)