To improve the operating performance of the large-capacity battery pack of electric vehicles during continuous charging and discharging and to avoid its thermal runaway, in this paper we propose a new hybrid thermal management system that couples the PCM with the liquid cooling plate with microchannels. The flow direction of the microchannel structure in the bottom plate is designed according to the characteristics of the large axial thermal conductivity of the battery, and the cooling performance of the whole system under continuous charge/discharge cycles is numerically simulated. The results show that the hybrid PCM/liquid cooling plate can maintain good cooling performance under the discharge process of a large-capacity battery pack. After each cycle the temperature of the battery pack can be reduced to less than 30°, and the maximum temperature change rate of multiple cycles is controlled within 0.8%. With the application of the hybrid PCM/liquid-cooled plate battery cooling system, a safe temperature range of the battery pack is ensured even under multiple cycles of charging and discharging. The present work can facilitate future optimizations of the thermal management system of the large-capacity battery pack of electric vehicles.

Fully resolved numerical simulations are used to examine the thermocapillary motion of a two- and three-dimensional fully deformable bubble in a channel with an obstruction. A front-tracking/finite volume method is used to solve the Navier-Stokes equations coupled with the energy conservation equation. The results show that, for a fixed obstruction and channel size, the influence coefficient α, defined as the ratio of arrival time in channels with and without an obstruction, increases with increasing Marangoni (Ma) number for both two- and three-dimensional flows, whereas an increase in the Reynolds (Re) number leads to an increase in the influence coefficient in two-dimensional flows but a decrease in three-dimensional flows. Moreover, a change in the Capillary (Ca) number does not have a visible effect on the thermocapillary motion if the width of the narrow part of the channel is larger than the bubble diameter. Results for both two- and three-dimensional flows show that the influence coefficient increases dramatically with an increase in the obstruction size W, and a larger obstruction makes the dependence of α on the fluid parameters more obvious.

The effect of electrostatic forces on the distribution of drops in turbulent channel flows is examined by direct numerical simulations. The droplets and suspending fluid are assumed to be leaky dielectric fluids. We set the electrical conductivity ratio (R = σ_i/σ_o) smaller than the dielectric permittivity ratio (S⁻¹ = ε_i/ε_o) to drive the flow from the drop poles to their equators. The results show that an applied external electric field has a significant effect on the microstructure and the flow properties. For flows without an electric field, where the Mason (Mn) number is infinity, the drops aggregated in the core of the channel and the liquid streamwise velocity are similar to those in single-phase flow. For Mn = 0.1, a low electric intensity, most of the drops are driven to the walls due to the unbalanced electric force on the drop interface. For Mn = 0.05, drops are more likely to stick together because of the stronger combination of electrohydrodynamic effect and dielectrophoretic force between drops. Therefore, the number of drops in the middle of the channel increases while still many drops are in the wall layer. For Mn = 0.007, the electric intensity is very strong and all the drops in the channel tend to line up and form columns spanning the channel width. These columns become unstable when the flow drives them close to each other. It is also found that an increase of the electric intensity can lead to an increase in the average wall shear stress. In addition, the liquid streamwise velocity will become more uniform, which means the effective viscosity of the system is increased, when Mn = 0.007.

Direct numerical simulations of two-way oscillating bubbly flows in a domain bounded by solid walls are presented. Ignoring gravity, the two- and three-dimensional flows of equal-sized bubbles are driven by periodically oscillating pressure gradients in the X and Z directions with the same amplitude and frequency but different phases. The results show that the oscillations will drive the bubbles together, promoting coalescence. The results depend on the amplitude and frequency, resulting in “crawling” flow, “revolving” flow, and “oscillating” flow. As the amplitude increases, the critical frequency separating these three flow regions increases. For each amplitude, there is an optimum frequency near the transition region between the crawling flow and the revolving flow that yields the fastest coalescence. A qualitative comparison between two- and three-dimensional flows shows that the dynamics observed for the two-dimensional flows is also found in three-dimensions.

The impact of fluid shear on the bubble distribution in channel flows with periodically oscillating pressure gradient is examined by direct numerical simulations. Equal-sized and nearly circular bubbles are placed randomly in the channel at the initial time. In the absence of shear, the bubbles form columns spanning the width of the channel, but a strong enough shear breaks up the columns, leading to a more random bubble distribution. The effect of the nondimensional shear rate on the flow can be divided into low shear rate, moderate shear rate, and high shear rate regimes. The flow dynamics is also influenced by the Reynolds and the Euler number, and when these numbers decrease, the low shear rate regime, with stable tilted columns of bubbles, becomes smaller. Comparison of results for two- and three-dimensional flows shows that the dynamics observed in two-dimensional flows is also found in three dimensions.