The cooling which occurs on the runout table (ROT) is a key processing step for hot
rolled steel strip. It determines the final microstructure and thus mechanical properties as
well as flatness of the hot band. The use of multiple jets during ROT cooling results in
interactions between neighboring water jets which can affect the overall heat transfer rate.
The heat transfer which takes place during cooling with multiple jets is fairly complex and
the available knowledge is limited. The research work described was done to obtain an
understanding of the effect of varying nozzle-to-nozzle distance, plate speed and flow rate
of the impinging water on the heat transfer taking place on the ROT.
Experiments were performed on the pilot scale runout table available at UBC, using
instrumented test samples of steel. Each sample was instrumented with twenty
thermocouples which measured the internal thermal history. This data was then used in
conjunction with an Inverse Heat Conduction (IHC) model to calculate surface heat fluxes
and temperatures. Some of the variables examined included: speed of movement of the test
plate (0.22 m/s and 1 m/s), nozzle spacing (114.3, 76.2 and 38.1 mm) and water flow rate
(15 1/min and 30 1/min). These experimental results provide important information for the
development of improved runout table cooling models.
The results indicated that, during multiple jet cooling, high heat extraction takes
place directly below the nozzles and adjacent to them due to direct impact of water. Lower
heat extraction occurs at the locations between the nozzles, i.e. the interaction region.
Visual observations of the tests-indicate that, when the water jets hit the strip, a small
darkened zone can be observed at the impingement point below each nozzle. In the interaction region, the water flowing from the two adjacent jets interacts with each other
and large splashing of the water is observed in this region. The dark zones below all three
nozzles expand with cooling of the strip, indicating that the water front is progressing
outwards from the stagnation line and more water solid contact is taking place. The boiling
curves below each nozzle are similar to each other and clearly show the different boiling
regimes while the boiling curve for the interaction region does not show these regimes as
clearly. In the interaction region, heat transfer remains relatively low until the water
completely wets the strip. The investigation of the effect of strip speed indicated that the
heat fluxes are higher for lower strip speeds as the strip spends a longer time under the
nozzle. This effect was seen both below the nozzle and in the interaction region. In general,
increase in water flow rate increases heat fluxes at all measuring locations due to higher
amount of water impinged on the strip surface. The nozzle configuration having two
adjacent nozzles at 38.1 mm apart has more cooling capacity than the other two
configurations indicating that, having two nozzles close to each other enhances heat
transfer.Applied Science, Faculty ofMaterials Engineering, Department ofGraduat
