In this paper, we demonstrate a heat transfer mechanism using ultrasonic standing waves. The basic idea behind the proposed heat transfer mechanism is the acoustic relocation phenomenon of inhomogeneous fluid due to acoustic body force. The acoustic body force depends upon the density gradient and the speed of the sound gradient of the inhomogeneous fluid. Heating a fluid creates an inhomogeneity in the physical properties of the fluid such as density, viscosity, and velocity of sound, etc. When this heated (inhomogeneous) fluid is subjected to ultrasonic standing waves, acoustic body force induces a fluid motion which is shown to be responsible for this heat transfer mechanism. Heat transfer enhancement is observed when a standing acoustic wave is passed perpendicular to the direction of heat transfer. Remarkably, it is found that acoustic forces can enhance heat transfer up to 2.5 times compared to natural convection and up to 11.2 times compared to pure conduction. Suppression of natural convection heat transfer is observed when the acoustic waves are passed parallel to the direction of heat transfer. In this case, acoustic forces could bring down the heat transfer by half or more than half from the natural convection. To characterize the heat transfer mechanism in the enhancement case, a modified Rayleigh number that can account for both acoustics and gravity effects is proposed. To this extent, we provide a clear understanding of how acoustic fields influence the fluid flow and heat transfer.

中文翻译：

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声场下声体力驱动的传热机理

在本文中，我们展示了使用超声波驻波的传热机制。所提出的传热机制背后的基本思想是由于声体力引起的不均匀流体的声重定位现象。声体力取决于不均匀流体的密度梯度和声梯度的速度。加热流体会导致流体的物理特性（例如密度、粘度和声速等）产生不均匀性。当这种加热（不均匀）的流体受到超声波驻波作用时，声学体力会引起流体运动，如图所示负责这种传热机制。当声驻波垂直于传热方向通过时，可以观察到传热增强。值得注意的是，研究发现，与自然对流相比，声学力可以将传热提高 2.5 倍，与纯传导相比提高 11.2 倍。当声波平行于传热方向通过时，观察到自然对流传热的抑制。在这种情况下，声学力可能会使自然对流的热传递降低一半或一半以上。为了表征增强情况下的传热机制，提出了一种可以同时考虑声学和重力效应的修正瑞利数。在这方面，我们清楚地了解声场如何影响流体流动和传热。当声波平行于传热方向通过时，观察到自然对流传热的抑制。在这种情况下，声学力可能会使自然对流的热传递降低一半或一半以上。为了表征增强情况下的传热机制，提出了一种可以同时考虑声学和重力效应的修正瑞利数。在这方面，我们清楚地了解声场如何影响流体流动和传热。当声波平行于传热方向通过时，观察到自然对流传热的抑制。在这种情况下，声学力可能会使自然对流的热传递降低一半或一半以上。为了表征增强情况下的传热机制，提出了一种可以同时考虑声学和重力效应的修正瑞利数。在这方面，我们清楚地了解声场如何影响流体流动和传热。提出了一个可以同时考虑声学和重力效应的修正瑞利数。在这方面，我们清楚地了解声场如何影响流体流动和传热。提出了一个可以同时考虑声学和重力效应的修正瑞利数。在这方面，我们清楚地了解声场如何影响流体流动和传热。