Experimental and Numerical Investigation of the Quenching Process on Rotary Hollow Cylinder by Multiple Impinging Jets
Sammanfattning: The worldwide competitive market on metal products with higher quality in industry has increased the need to implement more advanced and controllable quenching techniques in the hardening stage of the heat treatment process. Moreover, sustainability and energy efficiency are key factors to consider in the development of advanced quenching techniques. Among various cooling methods that are used in industry, a water impinging jet quenching system is one of the few that offers wide flexibility to adjust cooling rate based on the chemical composition and proper phase transformation in the continuous cooling transformation diagram (CCT) to achieve desired material properties. On an industrial scale, a large number of water impinging jets are placed in the cooling configuration introducing multiple array of jets in the quenching system. In the literature study by the author, there has been interest to study the quenching heat transfer by single water jet in various applications. Even so, little scientific attention has been paid to the multiple array of water impinging jets and the importance of various quenching parameters on the quenching heat transfer with multiple array of jets. This thesis deals with a study of quenching rotary hot hollow cylinder with multiple configurations of water impinging jets. The aim of this investigation is to obtain better understanding of boiling heat transfer phenomena in application of multiple array of water impinging jets and quenching parameters. An experimental test rig was designed to control most influential parameters in quenching experiments. The results of experimental study contained recorded temperature data beneath the quenching surface of a hollow cylinder. A heat conduction inverse solution based on the GMRES method was developed for application of quenching hollow cylinder. This model used the recorded temperature data of quenching experiments to predict surface temperature and heat flux. A thorough parametric study investigated the effect of various quenching parameters and multiple configuration of jets in terms of local and area-averaged heat transfer over surface as well as in the solid material.The local surface boiling curve captured clear effect of multiple array and cyclic variation of heat transfer caused by rotation of hollow cylinder. The delay in onset of wetting front flow growth over the surface, collision of adjacent wetting front flows and creation of upwash flow were captured on the surface heat flux contour plot. Higher heat flux was obtained around stagnation and upwash flow zones over the quenching surface. The relation between jet flow rate and multiple array configuration revealed a trade-off between these two parameters in terms of optimizing the water resource usage and desired cooling rate with this cooling technique.Comprehensive parametric study revealed effect of various quenching parameters in the local heat transfer in the boiling regimes. The results show improvement of heat flux in the film and nucleate boiling is more difficult than transition boiling regime. In the study of area-averaged heat transfer in 1-row array, higher subcooling and jet flow rate enhance the surface heat flux. In contrast, smaller rotation speed, jet-to-jet spacing and initial wall-superheat temperature increase the area-averaged surface heat flux of hollow cylinder. An extra row of nozzles in the array (2-row) also enhanced the area-averaged surface heat flux significantly. The results from comprehensive parametric study of 4-row in-line and staggered configurations have been used to propose correlation for surface area-averaged Nusselt number. In the local heat transfer, two correlations of average and maximum local heat flux at stagnation point of water impinging jet were proposed.The result of this study and the proposed correlations may provide a road map for engineers to design hollow cylinder quenching system with multiple array of water impinging jets based on cooling rate for proper phase transformation and optimized water resource and energy usage in the quenching process.
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