5. “Heat flux is defined as the amount
of heat transferred per unit area per unit time
from or to a surface”.
In SI system its units are
W/ m2
or J/ m2s
Heat rate is a scalar quantity, while heat flux is
a vector quantity.
6. Ts = Surface temperature
Tm = Mean fluid temperature
hx = Local heat transfer coefficient
qs = Surface heat flux
7. This effect can be observed in several
situations like when a tube or a pipe is
subjected to:
1. Radiation
2. Electrical heating resistance
(Uniform from all directions)
13. From previous equations mean fluid
temperature at the exit of tube can be written
as
The surface temperature in case of constant
surface heat flux can also be calculated from
14. By re-arranging it can be written as
In fully developed region, the surface
temperature will also increase linearly in the
flow direction and h is constant so,