THEORETICAL MODELING FOR IMPINGEMENT COOLING OF LARGE SCALE COILS OF ALUMINIUM

The use of a cylindrical array of air jets to cool a 4.1 tonne coil of Aluminium alloy is shown, theoretically, to improve the free convection cooling time over the 673K (752 degrees F) to 323K (122 degrees F) range from 49hrs to roughly 4hrs. The transient theory developed to model this process includes both radiation and convection heat loss in a numerical solution which is applicable to large coils of aluminium typically produced on a hot strip mill. In situations where liquid spray chambers are not chosen as an alternative cooling method, the results indicate that air impingement jets are a viable technique for cooling unscheduled coil batches which require rapid handling to meet market demands. When comparing the various combinations of surfaces of the coil that may be cooled, impingement cooling the entire surface area (cooling time 3.75hrs) offers little advantage over neglecting to cool the coil's hollow inner core (cooling time 4.28hrs). However, impingement cooling only the external and internal cylindrical areas (cooling time 5 hrs) represents possibly the easier method of cooling to apply in industry yet only extends the cooling time by 1.25hrs. Predictions for such coils of 6mm thick sheet over this 350K (662 degrees F) range, suggest that cooling times of roughly 6hrs may be possible in practice.