arXiv subjects

Kai-Xin Hu

Publications and source records attributed to Kai-Xin Hu.

6 recordsLinked to original sources

arXiv2026

The Impact of Turbulence on Hydroacoustic Waves

Traditional research suggests that when sound waves pass through a turbulent region, scattering occurs, causing the incident wave to attenuate and wave parameters to fluctuate. In contrast, our previous paper reported a new phenomenon in which turbulence causes changes in the amplitude of sound waves, a change that cannot be explained by scattering or resonance (HU, K.X, & HU, Y. J. 2025. Hydroacoustic Absorption and Amplification by Turbulence. arXiv:2512.07920). This work presents a more in-depth investigation into the impact of turbulence on hydroacoustic waves, including phase changes, amplification factors and the temporal evolution of the acoustic wave. Experiments indicate that turbulence simultaneously changes both the amplitude and phase of acoustic waves. The total phase shift along the entire pipe equals the sum of the phase shifts of the segments. Both the amplification factor and the phase shift due to turbulence vary periodically with frequency. In pipe flow, after the valve is closed, the temporal evolution of the acoustic waves during the subsequent turbulence decay process can be classified into six types. Acoustic waves with frequencies below and above specific thresholds are essentially unaffected by turbulence. In addition, vortices and unsteady flow in the laminar state do not cause changes in the amplitude and phase of sound waves, showing the essential difference between turbulent fluctuations and the two.

physics.flu-dyn↗

arXiv2026

Hydroacoustic Absorption and Amplification by Turbulence

Acoustic waves propagating through fluid media are significantly influenced by turbulence. This paper experimentally investigates the influence of underwater turbulence on the propagation characteristics of acoustic waves, revealing that acoustic waves can be absorbed or amplified at frequencies far exceeding the turbulent fluctuation frequency. The maximum observed attenuation or amplification of received signals exceeds 60%, with no spectral broadening. The amplification factor depends on the wave frequency rather than its amplitude. The study covers two flow conditions: pipe flow and free jet, driven by either a pump or hydraulic head difference. The frequency range generated by the hydroacoustic transducers covers 60 kHz to 4.4 MHz, while the wave propagation directions both parallel and perpendicular to the mean flow are considered. For each case, the amplitudes of all frequency components simultaneously decreases or increases under turbulence, with no new spectral components appearing. Turbulent fluctuations without mean motion can still alter the wave amplitude, while laminar flow has no effect on acoustic signals. Comparison with conventional theories and experiments indicates that mechanisms such as bubbles, resonance, scattering, or viscous dissipation cannot explain the observed phenomena. This indicates that there exists an incompletely understood new mechanism in the interaction between turbulence and acoustic waves.

physics.flu-dyn↗

arXiv2025

Fast directional transport of Leidenfrost droplets on spiked surfaces

The Leidenfrost effect enables droplets to levitate above a solid surface, significantly reducing the resistance to droplet motion. In this study, a spiked surface is utilized to achieve fast directional transport of Leidenfrost droplets, with a maximum average speed reaching 8.36 m per second over a 10 cm distance,far exceeding the previously reported maximum speeds for droplet transport. When a droplet falls onto a substrate heated above the Leidenfrost temperature, it becomes trapped between spikes and levitates. The sides and bottom surface of the droplet undergo vaporization, creating a gas film between the solid wall and the droplet. However, this gas film is unstable and prone to rupture at certain points, causing the droplet to come into contact with the solid surface. Therefore, the droplets undergo violent boiling, leading to intense compression and bursting into smaller daughter droplets, which are then propelled rapidly along the substrate. Additionally, the asymmetric geometry of the spikes ensures that droplets move unidirectionally along the longitudinal direction. This study proposes a novel droplet self-propulsion mechanism, pioneering new strategies for enhancing droplet transport speed..

physics.flu-dyn↗

arXiv2025

Experimental Study on Boiling of Nanofluids in Copper Foam

Nanofluids are suspensions of nanoscale particles (such as metals and their oxides) in base fluids (such as water, oil, or alcohol), which can significantly enhance the heat transfer performance of the base fluid. However, when nanofluids are applied to heat pipes, it is common for nanoparticles to accumulate within the heat pipe's capillary wick, clogging it and increasing thermal resistance. This paper investigates the phenomenon of boiling of water and nanofluids enhanced by copper foam through experimental methods. When the liquid is injected into copper foam placed on a heating plate, some of the liquid is squeezed out along the boundary of the heated surface of the copper foam during boiling. This phenomenon is independent of gravity but related to the hydrophilicity or hydrophobicity of the heating surface. Based on these properties, we design a device to guide the squeezed-out liquid to other locations, offering a promising solution to the problem of nanoparticle accumulation in the heat pipe's capillary wick.

physics.flu-dyn↗

arXiv2024

Efficient condensation on spiked surfaces with superhydrophobic and superhydrophilic coatings

Steam condensation on the surface of a solid is a widely observed mode of energy transfer in nature and various industrial applications. The condensation efficiency is closely related to the material properties and geometric morphology of the solid surface, as well as the method of liquid removal. Despite many surface modification strategies at the micro and nano levels having been employed to enhance steam condensation, understanding how to regulate steam condensation and liquid removal on complex surface morphologies remains incomplete. Here, we report a method that uses superhydrophilic and superhydrophobic coatings as well as spiked surfaces to achieve efficient steam condensation and rapid removal of the liquid. We reveal that on a copper plate with millimeter-scale spikes, hydrophobic spiked surfaces facilitate the dropwise condensation, while hydrophilic bottom grooves promote liquid spreading, and the suction in capillary gaps can promptly remove the condensate liquid. This method achieves a high condensation efficiency without relying on gravity. Additionally, we demonstrate that the condensation on spiked surfaces has a significant suction effect, as it continuously attracts the steam flow, thereby altering the flow direction. This finding provides a new approach for efficient steam condensation technology and opens up a promising pathway for providing circulation power and improving condensation efficiency in phase-change heat transfer devices such as heat pipes.

cond-mat.soft↗

arXiv2023

The Analogy between Electromagnetics and Hydrodynamics

The similarity between electromagnetics and hydrodynamics has been noticed for a long time. Maxwell developed an analogy, where the magnetic field and the vector potential in electromagnetics are compared to the vorticity and velocity in hydrodynamics, respectively. However, this theory cannot make a correspondence of energy between two subjects. In the present work, the electromagnetic fields in a conducting medium are compared to the flow fields of an incompressible Newtonian fluid. The result shows that the magnetic induction intensity, current density, Lorenz force, superconductor boundary, Ohm's law and Ampere force in electromagnetics are analogous to the velocity, vorticity, Lamb vector, solid boundary, Newton's law of viscosity and Kutta-Joukowski theorem of lift force in hydrodynamics, respectively. The Navier-Stokes equation is derived for the evolution of magnetic field in the medium by using the Maxwell equations, Lorenz force and Ohm's law. The work is useful for a deep understanding of electromagnetics and hydrodynamics.

physics.flu-dyn↗