ABSTRACT

In this paper, a numerical-experimental investigation was performed for estimation of the local convective heat transfer coefficients of a two-phase pulsating heated jet impinging a cold disk-shaped mass. By solving the energy equation, temperature history of thermocouples was obtained and then using the “temperatures measured” at locations of the sensors and the “temperatures calculated” from the numerical solution of heat equation and then minimizing the sum of squared errors by the conjugate gradient method (CGM), the convective heat transfer coefficients are estimated using the nonlinear inverse heat conduction procedure (IHCP). To compare the heat transfer characteristics of the pulsating, steady, bubbly, and liquid-only jets, the heat transfer coefficients were estimated with respect to the square pulse frequency produced by a solenoid valve in the range of $0.505\mathrm{H}\mathrm{z}\le fr\le 10\mathrm{H}\mathrm{z}$ and the gas volume fraction in the range of $0\le \beta \le 0.32$. In the case of single-phase jet, results show that flow pulsation increases Nusselt number up to $55\mathrm{\%}$ at the stagnation point and $7\mathrm{\%}$ for farther radial distances as compared to the steady jet. Also, for steady jet, increasing Reynolds number resulted in a $43\mathrm{\%}$ increase in the stagnation point Nusselt number and a $16\mathrm{\%}$ increase at farther radial distances.

摘要

在本文中，进行了数值实验研究，以估计两相脉动加热射流撞击冷盘状质量的局部对流传热系数。通过求解能量方程，获得热电偶的温度历史，然后使用传感器位置的“测量温度”和热方程数值解的“计算温度”，然后通过共轭梯度最小化误差平方和方法 ( CGM )，使用非线性逆热传导程序 ( IHCP )估计对流传热系数). 为了比较脉动、稳定、气泡和仅液体射流的传热特性，传热系数是根据电磁阀产生的方波脉冲频率在范围内估算的$0.505\mathrm{H}\mathrm{z}\le Fr\le 10\mathrm{H}\mathrm{z}$和范围内的气体体积分数$0\le \beta \le 0.32$. 在单相射流的情况下，结果表明流动脉动使努塞尔数增加到$55\mathrm{\%}$在驻点和$7\mathrm{\%}$与稳定射流相比，可获得更远的径向距离。此外，对于稳定射流，增加雷诺数会导致$43\mathrm{\%}$增加驻点努塞尔数和$16\mathrm{\%}$在更远的径向距离处增加。