Due to their high porosity, high stiffness, light weight, large surface area-to-volume ratio, and excellent thermal properties, open-cell metal foams have been applied in a wide range of sectors and industries, including the energy, transportation, aviation, biomedical, and defense industries. Understanding the flow characteristics and pressure drop of the fluid flow in open-cell metal foams is critical for applying such materials in these scenarios. However, the state-of-the-art pressure drop correlations for open-cell foams show large deviations from experimental data. In this paper, the fundamental governing equations of fluid flow through open-cell metal foams and the determination of different foam geometry structures are first presented. A variety of published models for predicting the pressure drop through open-cell metal foams are then summarized and validated against experimental data. Finally, two empirical correlations of permeability are developed and recommended based on the model of Calmidi. Moreover, Calmidi’s model is proposed to calculate the Forchheimer coefficient. These three equations together allow calculating the pressure drop through open-cell metal foam as a function of porosity and pore diameter (or strut diameter) in a wide range of porosities ε = 85.7–97.8% and pore densities of 10–100 PPI. The findings of this study greatly advance our understanding of the flow characteristics through open-cell metal foam and provide important guidance for the design of open-cell metal foam materials for different engineering applications.

Liquid cooling strategies such as cold plates have been widely employed as an effective approach for battery thermal management systems (BTMS) due to their high cooling capacity and low power consumption. The structural design of the cold plates is the key factor that directly determines the thermal performance of the liquid cooling system. In this study, seven Z-type parallel channel cold plate and two novel cross-linked channel cold plate designs are proposed for the cooling of high-power lithium-ion batteries using two different cooling strategies. The average battery temperature, battery temperature uniformity and energy consumption of all designs are firstly analyzed holistically by three-dimensional conjugated simulation under the scheme of continuous cooling. Two selected designs that demonstrated superior performance (i.e., a Z-type parallel channel cold plate with 8-branches and an improved cross-linked channel design) are further analyzed to explore their integrative performance under different cooling schemes. The results show that within a battery temperature limit of 40 °C, employing the delayed cooling strategy can save 23% energy consumption compared to the continuous cooling strategy. Besides, the cold plate with an improved cross-linked channel configuration requires 13% less pumping power and provides a better temperature uniformity than the Z-type parallel channel cold plate with 8-branches. These results are of great significance to advance the cooling design of BTMS.

Capillary rise is ubiquitous in engineering applications and natural phenomena. In straight channels, the dynamics of capillary rise have been thoroughly investigated and are well understood. However, for nonuniform channels of varying radius, the dynamics remain largely unclear. In this study, the capillary rise in a sinusoidal wavy channel is investigated both analytically and numerically. Specifically, the capillary rate-of-rise of water in sinusoidal channels with different contraction frequencies and amplitudes is derived based on the principle of energy conservation. The change in capillary velocity and height over time is further validated by two-phase flow simulations based on the conservative level-set method. The results reveal a strong viscous dissipation in the interfacial region resulting from the wave-like wobbling motion of the liquid–air interface, constituting more than 50% of the total viscous dissipation when the channel profile changes rapidly. Failing to account for this interfacial effect will result in significant overestimations of the capillary velocity and erroneous predictions of the capillary rise curve, typically more than 4 times difference in the capillary velocity and more than 2.5 times difference in the time taken to arrive at the maximum height.

Metal foams have been widely used in heat pipes as wicking materials. The main issue with metal foams is the surface property capillary limit. In this paper, a chemical blackening process for creating a superhydrophilic surface on copper foams is studied with seven different NaOH and NaClO₂ solution concentrations (1.5~4.5 mol/L), in which the microscopic morphology of the treated copper foam surface is analyzed by scanning electron microscopy. The capillary experiments are carried out to quantify the wicking characteristics of the treated copper foams and the results are compared with theoretical models. A the microscope is used to detect the flow stratification characteristics of the capillary rise process. The results show that the best wicking ability is obtained for the oxidation of copper foam using 3.5 mol/L of NaOH and NaClO₂ solution. Gravity plays a major role in defining the permeability and effective pore radius, while the effect of evaporation can be ignored. The formation of a fluid stratified interface between the unsaturated and saturated zone results in capillary performance degradation. The current study is important for understanding the flow transport in porous materials.

The evaporative heat and mass transport characteristics from an array of continuously fed microdroplet on a heated substrate are investigated numerically by a Multiphysics model, which incorporates heat conduction, buoyant flow, Marangoni flow, Stefan flow, and vapor diffusion. The effects of droplet spacing, contact angle, and droplet size on the evaporation rate, heat flux, and convection strength were analyzed in detail with a fixed thermal and vapor concentration boundary condition. The results revealed the existence of extremely strong convection current in the ambient gas domain for evaporation from droplet array. This convection effect dominates the vapor transport process, overcomes the suppression effect from neighboring droplet, and causes the total evaporation rate to exceed the prediction from traditional diffusion-based model by up to ten times. The strength of the convective vapor transport is characterized by a dimensionless parameter, which increases first from 2.3 to 7 and then decrease to 4 with increasing contact angle from 30° to 150°, but remains invariant at 6.3 for hemispherical droplet irrespective of the change in droplet dimension. Finally, the numerical results demonstrate potential for microdroplet array evaporation to resolve the thermal management challenge of ultrahigh power electronics with heat flux up to 1 kW/cm2.