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Full text of "The Flow Of Gases In Furnaces"

222

APPENDIX VII

up heat to the stationary surface. For some reason or other
there seems to be an impression that the higher the velocity
of flow the better. Undoubtedly there is a certain velocity of
flow that will result in the maximum heat transfer per unit of
heating surface, and in the case of properly designed heat transfer
elements, be they regenerators, recuperators, steam boilers, etc.,
it is extremely probable that the natural convection currents will

10   20    30   40   50   60
Time., Minutes

70   80    90  100  110  120 130 140 150
Time, Minutes

FIG. 153.

Density.....p = l.8l

Specific heat, c=0.250
Conductivity in
cal/sec/cm2/! °cm =

0.00367
Diffusivity.. h* =0.00811

Rise in Temperature on
the Median Line of
Fireclay Brick in Per-
centage of Surface
Temperature. Both
faces exposed to heat.
Ordinates, percentages;
abscissae time in min-
utes.

assume this velocity themselves. Higher velocities, as well as
lower velocities, will reduce the rate of heat transfer. The
higher velocities may be obtained by forcing the gas or liquid past
the surface, when the velocity is too low, that is, when the heated
gases are not carried away from the chamber above the regenerator,
or the cooled gases cannot flow away from below the checkerwork,
recirculation will take place in the form of convection eddy
currents.