Three-Dimensional Numerical Study of Impinging Water Jets in Runout Table Cooling Processes
- PDF / 983,957 Bytes
- 10 Pages / 593.972 x 792 pts Page_size
- 113 Downloads / 158 Views
LED cooling from the impingement of water jets is used in many commercial processes to optimize the microstructure and properties of metal products. In the runout table (ROT) cooling process after hot rolling, steel producers have developed many new technologies[3–6] to lower production costs, to continuously improve product quality, and even to create new microstructures, in order to fulfill the increasing demands of customers. For example, to produce higher strength steel with less alloying elements, technology to increase the cooling rates is of growing interest. Several technologies[6–9] to increase the cooling rate in the ROT have been recently developed. Ultrafast cooling technology[6,7] increases the conventional cooling rate of 30 °C/s to 80 °C/s, depending on the final thickness, to 300 °C/s on 4-mm-thick hot strip. An acceleration cooling technology[8,9] having more than 200 °C/s on 3-mm thickness makes it possible to increase the strength of steel or to achieve the same level of strength with a low carbon equivalent design. [1,2]
MYUNG JONG CHO and PIL JONG LEE, Principal Researchers, are with the Technical Research Lab., POSCO, Pohang City, 790-785, Korea. BRIAN G. THOMAS, W. Grafton and Lillian B. Wilkins Professor, is with the Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801. Contact e-mail: [email protected] Manuscript submitted January 16, 2008. Article published online July 29, 2008. METALLURGICAL AND MATERIALS TRANSACTIONS B
These technologies use larger flow rates than conventional cooling methods (such as spray or water column cooling), basically. In the ultrafast cooling, total water flow is well known as 17,000 L/min m[6] of cooling length. This corresponds to 9200 L/min m2 assuming a 1.8-m width,[7] which is more than double the maximum flow rate for the conventional ROT cooling.[6] The tools to develop these technologies include models of transient heat conduction in the moving strip.[10] They rely on heat-transfer coefficients between the impinging water jets and the strip surface, which are generally obtained from plant measurements.[10,11] The design of better cooling header systems requires knowledge of these heat-transfer coefficients as a function of the flow conditions, which depend on header configuration, nozzle geometry, spacing, height, flow rate, and other parameters. This knowledge is generally obtained from lab-scale experiments that must be further verified with full-scale prototypes in expensive plant experiments. Thus, there is a strong need for fundamentallybased tools to predict surface heat transfer in the real process. There has been much previous work[12–16] on heat transfer from impinging jets (including free, confined, and submerged), based on experimental, analytical, and numerical studies. However, water impingement from multiple jets onto moving surfaces, and for the high flow rate conditions of real ROT cooling, has received much less attention. Specifically, these conditions involve the development of free gas-liquid
Data Loading...
