Determination of friction factors and heat transfer coefficients for flow past artifically roughened surfaces Page: 11 of 225
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Helium has advantages as a nuclear reactor coolant due to its chem-
ical inertness, absence of phase transition, and ve.y low cross section
for neutron interaction. The latter attribute is particularly desirable
in a breeder reactor where neutron economy is of primary importance.
However, because of its low density and thermal conductivity, helium is
not a good heat transfer medium. Therefore, its use as a coolant is
characterized by high reactor system pressure and large volumetric flow.
Since the maximum allowable fuel element cladding temperature is
limited, an increased surface heat transfer coefficient is important to
attainment of a high outlet coolant temperature with Its associated im-
proved cycle thermal efficiency and an adequately high reactor power
density. Because convective heat transfer is enhanced when surfaces are
roughened, much study has been given to the evaluation of artificial
roughening of the heat transfer surfaces of helium and other gas-cooled
There are a large number of possible artificial surface roughness
forms such as spiral or regularly spaced ribs of any shape at any angle
to the flow. Surface roughness promotes mixing by generating tx rbulent
eddies in the high thermal-resistance coolant sublayers adjacent to the
heat transfer surface. The increased transport of heat from the wall
into the fluid main stream is manifested as a higher Stanton number
(St), a dimensionless quanticy defined as
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Hodge, S.A.; Sanders, J.P. & Klein, D.E. Determination of friction factors and heat transfer coefficients for flow past artifically roughened surfaces, report, November 1, 1979; Tennessee. (https://digital.library.unt.edu/ark:/67531/metadc1092930/m1/11/?rotate=90: accessed June 16, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.