Heat transfer and uniformity enhancement in quenching process of multiple impinging jets with Newtonian and non-Newtonian quenchants

Abstract

Boiling jet impingements (normally water) are being widely used in various industries such as cooling power electronic components, due to the high heat transfer rate and low cost. Also, oils and molten salts are used in single-phase quenching processes. Many studies have been carried out into this field, but most of them were experimental. A quenching jet impingement process is simulated numerically in this research. For a comprehensive solution, a solver code based on the Volume of Fluid (VOF) method was modified to analyze the effects of conjugation and mass transfer. To validate the solution, an experimental quenching process of an impinging jet was simulated in 3D, and the results showed a good agreement. In addition to the temperature uniformity of the block, the cooling rate is also important during the process. Thus, Optimized Cooling Factor (OCF) was defined to involve both features simultaneously. Subsequently, the quenching of a hot steel cubic block by four simultaneous liquid jets was simulated in 3D. Studies were conducted on the effects of parameters such as the sinusoidal inlet velocity, jets width and spaces between the jets on the Standard Temperature Uniformity Index (STUI) and OCF, for water, molten salt and non-Newtonian molten salt quenchants. Some remarkable results are achieved by the proposed configurations. The results indicated that in all cases with pulsative jets, improvements in STUI and OCF relative to constant-velocity ones were observed and optimal STUI and OCF factors were accessible in lower values of the jet-flow frequency. Furthermore, by changing the quenchant from molten salt to non-Newtonian molten salt, the STUI and OCF plot averages enhanced from 0.1 to 0.085 and 4.8 to 6.5, respectively. Comparing the water and non-Newtonian molten salt from required input energy and pumping power points of view revealed that the input heat for non-Newtonian molten salt in all cases changes in the range of 2600–8200 J, while the input heat for water jet equals to zero, and the power needed to pump the water is almost 40–45% less than the needed pumping power of the non-Newtonian molten salt, on average.