Abstract:
Jet impingement quenching shows promising potential of achieving high heat flux
today. Most recent studies investigated thermodynamic behaviors during quenching of
copper, brass and steel blocks by jet impingement and determined the effects of
dominating parameters on the maximum heat flux and wetting delay. Generalized
correlations for predicting maximum heat flux and wetting delay were also developed.
These correlations can predict the experimental data very well for both of copper and
brass blocks. Experimental data for steel block have different character and can not be
predicted by the above correlations. Therefore, the present study has been focused to
investigate separately to explore the characteristics of these two phenomena for the steel
block that has been experimented recently in Saga University, Japan. These two
phenomena have been analyzed under various test conditions which included the jet
velocities of 3-15 mis, jet subcoolings of 5-80K and initial block temperatures of 250-
600°C.
The surface temperature and surface heat flux was estimated by an inverse heat
conduction technique using the measured temperatures at two depths of 2.1mm and 5.0
mm from the surface. The surface temperature decreased very slowly with time just
after the jet impingement. After a certain time delay, the surface temperature decreased
at a faster rate. The digitized images of flow movement were also analyzed in the
present study. It was found that the liquid didn't wet the entire surface just after the jet
impingement. After a certain time period, the wetting front started to move in the radial
direction.
The effects of experimental parameters on the maximum heat flux and wetting
delay were also observed in the present study. The characteristics of maximum heat flux
and wetting delay are strongly influenced by the jet velocity and liquid jet subcooling.
The maximum heat flux increases with the jet velocity and also with liquid subcooling.
For higher jet velocity and higher jet sub cooling, the wetting delay is decreased. Both
the maximum heat flux and wetting delay are found to be almost independent of block
initial temperature. Finally, for the two regions of radial positions (lO-20mm and 20-
35mm) correlations of maximum heat flux together with the dominating parameters are
developed. The proposed correlations show the accuracy of maximum heat flux within
01025%and 01030%respectively for the block initial temperatures of 250-400°C.
