Numerical investigation of electrohydrodynamically enhanced flow boiling inside minichannels: The seeding model

The evolution of turbulent liquid film on the corrugated plate is experimentally studied with the help of ultrasonic Doppler velocimetry and a high-speed camera, revealing the formation mechanism of rivulets and water columns necking rupture. The results show that the flow pattern of the liquid film on the corrugated plate is divided into three regions: stable region, fluctuating region, and oscillating region. In the fluctuating region, the connection between adjacent solitary waves leads to the generation of primary rivulets. In contrast, the formation of secondary rivulets mainly comes from the extinction of solitary waves. In the oscillating region, the collision between secondary rivulets promotes the formation of slender water columns. The necking diameter of the water column tended to decrease exponentially with time. The increase in Rel (liquid phase Reynolds number) promotes the necking rupture process of the water column due to the presence of corrugated structures. When Rel increased from 1.72 × 104 to 2.57 × 104, the characteristic time of necking rupture was shortened by about 25.7%.

Evolution of turbulent liquid films on the corrugated plate—rivulets and slender water columns necking rupture

Zeng,

Wang,

et al. 2023

Electrohydrodynamic effects on the bubble ascent in quiescent liquid using charge conservation approach

Patel,

Vengadesan

2023

The current study investigates bubble ascent under the influence of an applied electric field. To accomplish this, an electrohydrodynamic solver is developed and integrated with the open-source multiphase flow solver interFoam. The numerical model accurately calculates charge distribution and Coulomb force by solving the charge convection equation. This numerical model is utilized to study the effect of electric capillary number (CaE), electrical conductivity ratio (R), and permittivity ratio (S). The electrical force comprises dielectrophoretic force (DEF) and Coulomb force, which increases with higher values of CaE, R, and S. As the bubble begins to ascend in the presence of an electric field, the tangential component of the electrical force induces vortices in the vicinity of the bubble, which interact with the bubble's motion. These interactions result in various phenomena: the ascent of undeformed and deformed bubbles, the ascent of wall-attached bubbles, bubble ascent with path instability, and bubble breakup. The strength of the vortices increases with higher CaE and R/S values. The direction of the vortices depends on the R/S, with vortices flowing from the equator to the pole for R/S<1 and from the pole to the equator for R/S>1. The vortices become stronger as moving away from R/S=1. The vortices flowing from the pole to the equator cause horizontal deformation of the bubble, reducing rising velocity by providing resistance to the bubble's motion along with DEF. Conversely, vortices flowing from the equator to the pole cause vertical deformation of the bubble, increasing the rising velocity by facilitating the bubble's motion.

On interaction between a bubble with evaporation and heated pillar block in microchannel

Huang,

Yu,

Yan

et al. 2024

As demand for managing high heat flux in specialized applications grows, flow boiling in microchannels has received escalating attention for its high efficiency and cost-effectiveness. The complex interaction between an evaporating bubble and a heated pillar in a microchannel is governed by a confluence of transport mechanisms, including bubble morphology, fluid convection, heat transfer, and phase change phenomena. This study develops a three-dimensional mathematical model, employing the saturated-interface-volume approach to simulate the complex interaction process effectively. The results indicate that the liquid film thickness between the bubble and the heated surface is the primary factor affecting heat transfer. A reduction in the Reynolds number as well as an increase in the initial bubble diameter lead to a decrease in the liquid film thickness and an increase in the temperature gradient within the thin liquid film, which enhance both the evaporation rate and heat transfer efficiency. The temperature of the surrounding fluid is also decreased. The bubble passage disrupts the flow structure, particularly impacting the boundary layer and vortex structure. These perturbations in temperature and flow structure constitute a secondary factor influencing heat transfer. The efficiency of heat transfer varies significantly across different surfaces; surfaces with a larger thin liquid film region exhibit the most significant improvement, followed by the downstream surface where the flow and temperature fields are most affected. This study advances the fundamental comprehension of the complex interaction between an evaporating bubble and a heated pillar in a microchannel, integrating a detailed analysis of the relevant transport mechanisms.