> Problem statement: Jet impingement quenching has a very effective and large cooling potential and is a very effective means of cooling for many applications. It gives rise to heterogeneous and/or homogeneous nucleation of bubbles, which is yet to be explored. Approach: Analytically investigate the phenomenon that happened during a brief contact of a water jet impinging on a hot surface. In particular, explore the possibility of homogeneous bubble formation during jet impingement quenching. A simple semi-infinite conduction heat transfer model was considered in this case and the heat transfer analysis had been carried out for two heating cases of the impinging liquid, namely with (i) Prescribed Surface Temperature (PST-case) and (ii) Time-dependent Surface Temperature (TST-case). For each of above cases, explicit equations for temperature distribution within liquid, average liquid temperature, average internal energy and surface heat flux had been derived as a function of liquid depth and contact time. These equations were solved numerically and their outcomes were discussed. Furthermore, a critical contact time, t* at which the temperature on the opposite side of the liquid depth reached saturation temperature, Tsat was determined. The heat flux (qs) at time t* was also determined and compared with the thermodynamic limit of the maximum heat flux (qmax) which decided the validity of this analytical investigation. Results: During jet impingement quenching of hot surfaces near/above the thermodynamic limiting temperature, water stored enough energy for a contact period of 5-10 µs depending on the type of boundary conditions considered for triggering homogeneous bubble nucleation. A contact time of 4µs was required to trigger homogeneous bubble nucleation for the conditions where the impinging surface had a fixed temperature throughout the cooling process. A contact time of 6.5 µs was required to initiate homogeneous bubble nucleation for the conditions where the impinging surface temperature dropped at a rate depending on time. For both cases, the average internal energy of the liquid exceeded the minimum energy necessary for bubble formation. Moreover, the average heat flux, q never exceeded the thermodynamic limit of the maximum heat flux, qmax. Conclusion: When water was heated above the thermodynamic limit of superheat during jet impingement, there is always a chance of homogeneous bubble nucleation.
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机译： > 问题陈述：射流冲击淬火具有非常有效的冷却潜力，并且是许多应用中非常有效的冷却方法。它引起气泡的异质和/或均相成核，这有待探索。 方法：分析性地研究在热表面上喷水的短暂接触期间发生的现象。特别是，探索射流冲击淬火过程中均匀气泡形成的可能性。在这种情况下，我们考虑了一个简单的半无限传导热传递模型，并针对两种撞击液体的加热情况进行了热传递分析，即（i）规定的表面温度（PST-case）和（ii）时间依赖的表面温度（TST情况）。对于上述每种情况，已经得出了液体内部温度分布，平均液体温度，平均内部能量和表面热通量的显式方程，该方程是液体深度和接触时间的函数。对这些方程进行了数值求解，并讨论了其结果。此外，确定临界接触时间t * ，在该临界接触时间处，液深的另一侧的温度达到饱和温度T sat 。还确定了时间t * 处的热通量（q s ），并将其与最大热通量的热力学极限（q max ）进行比较。这决定了这种分析性调查的有效性。 结果：在热力学极限温度附近/之上对热表面进行射流冲击淬火期间，水存储的能量足以维持5-10 µs的接触时间，具体取决于触发均匀气泡成核的边界条件类型。在撞击表面在整个冷却过程中具有固定温度的条件下，需要4µs的接触时间来触发均匀气泡成核。在撞击表面温度随时间下降的条件下，需要6.5 µs的接触时间来引发均匀气泡成核。对于这两种情况，液体的平均内部能量超过了气泡形成所需的最小能量。此外，平均热通量q从未超过最大热通量q max 的热力学极限。 结论：当水在射流撞击过程中被加热到过热的热力学极限之上时，总会出现均匀气泡成核的机会。
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