Heat Transfer and Observation of Droplet-Surface Interactions During Air-Mist Cooling at CSP Secondary System Temperatur
- PDF / 2,984,535 Bytes
- 18 Pages / 593.972 x 792 pts Page_size
- 20 Downloads / 179 Views
requirements on slab quality and productivity of continuous casters demands precise control of the heat extraction occurring in the mold and in the secondary cooling system. Although mold heat extraction is considered the most important component for its relation to initiation of solidification, cooling with sprays and air-mists plays a prominent role, since it is responsible for removing ~60 pct of the total thermal energy contained in CSP strands entering MARIO E. HUERTA L., Ph.D. Candidate, M. ESTHER MEJI´A G., M.Sc. Graduate, and A. HUMBERTO CASTILLEJOS E., Professor, are with the Laboratory of Process Metallurgy, Department of Metallurgical Engineering, Centro de Investigacio´n y de Estudios Avanzados, CINVESTAV Unidad Saltillo, Av. Industria Metalu´rgica 1062, Parque Industrial Saltillo-Ramos Arizpe, 25900 Ramos Arizpe, Coahuila, Me´xico. Contact e-mail: humberto.castillejos@cinvestav. edu.mx Manuscript submitted October 13, 2015. Article published online December 9, 2015. METALLURGICAL AND MATERIALS TRANSACTIONS B
the secondary cooling system. Secondary cooling is quite flexible, since it can be controlled through the selection of nozzle type, nozzle-operating conditions, nozzle setback distance from strand surface, and nozzle lateral position from strand edges.[1–4] The influence of these variables on heat extraction lies on their effect on the fluid dynamic characteristics of sprays and mists, i.e., on d, v, and w, which play an outstanding role in their interaction with the surface. The literature commonly mentions that the heat extracted is mainly controlled by W,[4] and this common belief is followed even in the case of pneumatic nozzles, which are regularly operated at constant pa.[4,5] However, in the case of pneumatic nozzles, it has been demonstrated that q can be substantially increased by controlling pa and A, in addition to W, to achieve high-casting speeds without experiencing quality problems.[6,7] Since the late 1970, investigations of air-mist heat extraction have been reported.[1–19] Mitsutsuka et al.[8,9] highlighted the broad range of cooling conditions, from soft to intense, and the small propensity to clogging as VOLUME 47B, APRIL 2016—1409
advantages of air-mist—pneumatic—nozzles in front of spray—hydraulic—nozzles. Furthermore, it was claimed that air-mist nozzles led to fewer longitudinal cracks than hydraulic nozzles by reducing variations in slab surface temperature.[9] For the same W, mist cooling was found to provide a larger heat transfer coefficient, h, than spray cooling,[9,10] which would be expected since mist cooling involves the application of an pa that modifies drop characteristics making mist cooling more intense. However, it has been reported that the heat extracted with both kinds of nozzles was alike if w’s were similar,[10] suggesting that d and v played a minor role. Prinz and Bamberger[11] indicated that the effect of increasing pa, in the range from 200 to 400 kPa, on heat extraction stems from its effect on droplet size and velocity, conjecturing that small droplets with
Data Loading...
