Despite the fact that engineered surface enabling remarkable phase change heat transfer have elicited increasing attention due to their ubiquitous applications in thermal management, the underlying mechanisms of intrinsic rough structures as well as the surface wettability on bubble dynamics remain to be explored. Therefore, a modified molecular dynamics simulation of nanoscale boiling was conducted in the present work to investigate bubble nucleation on rough nanostructured substrates with different liquid–solid interactions. Specifically, the initial stage of nucleate boiling was mainly investigated and the bubble dynamic behaviors were quantitively studied under different energy coefficients. Results shows that as the contact angle decreases, the nucleation rate increases, because liquid obtains more thermal energy there compared with that on less wetting surfaces. The rough profiles of the substrate can provide nanogrooves, which can enhance initial nucleate embryos, thereby improving thermal energy transfer efficiency. Moreover, atomic energies are calculated and adopted to explain how bubble nuclei are formed on various wetting substrates. The simulation results are expected to provide guidance towards surface design in state–of–the art thermal management systems, such as the surface wettability and the nanoscale surface patterns.

In this study, flow and heat transfer characteristics in novel non-closed 3/4 ring-shaped micro-pin-fin arrays with in-line and staggered layouts were investigated numerically. The flow distribution, wake structure, vorticity field and pressure drop were examined in detail, and convective heat transfer features were explored. Results show that vortex pairs appeared earlier in the ring-shaped micro-pin-fin array compared with the traditional circular devices. Pressure drop across the microchannel varied with layout of the fins, while little difference in pressure drop was observed between ring-shaped and circular fins of the same layouts, with the maximum difference being 1.43%. The staggered ring-shaped array was found to outperform the in-line array and the circular arrays in convective heat transfer. A maximum increase of 21.34% in heat transfer coefficient was observed in the ring-shaped micro-pin-fin array in comparison with the circular micro-pin-fin array. The overall thermal-hydraulic performance of the microstructure was evaluated, and the staggered ring-shaped array with a fin height of 0.5 mm exhibited the best performance among the configurations studied.

A gas cooler is one of the important parts of a carbon dioxide (CO₂) heat pump water heater, and it must meet the needs of not only pressurization but also heat transfer. It is important to study gas coolers. In this paper, a heat exchanger with a spiral channel is studied. ANSYS CFX software was used to analyze the flow and heat transfer characteristics of the heat exchanger (single-plate model). The influences of the cooling pressure of CO₂, the mass flux of CO₂, the mass flux of water and the channel radius of CO₂ are discussed. In this paper, the results show that the cooling pressure of CO₂, the mass flux of CO₂ and the channel radius of CO₂ all have a large influence on the local heat transfer coefficient: with an increase in the cooling pressure of CO₂, the peak value of the heat transfer coefficient of CO₂ decreases and the average heat transfer coefficient decreases; with an increase in the mass flux of CO₂, the peak value of the heat transfer coefficient of CO₂ increases and the average heat transfer coefficient increases; and with a decrease in the channel radius of CO₂, the peak value of the heat transfer coefficient of CO₂ increases. The water mass flux has only a slight effect on heat transfer, and the lower cooling pressure of CO₂ corresponds to a higher peak heat transfer coefficient, which can reach 27.5 kW∙m⁻²∙K⁻¹ at 9 MPa.

A novel experimental method for the lateral mixing of binary solids in bubbling fluidized beds was developed based on the capacitance probe technique. The evolutions of local mixing ratios in a fluidized bed which can be assumed as one mixing cell were analyzed in detail. The solids mixing within one mixing cell was resolved and the effect of convection and diffusion mechanism on lateral mixing was evaluated individually. The results show that at lower part of the fluidized bed, convection plays a more important role in the mixing process near the wall; meanwhile, diffusion is very important for the mixing around the center line. This is opposite with that at the higher part. A lateral micro dispersion coefficient was proposed to characterize the lateral mixing within the mixing cell and the value is generally between 0.005 and 0.025 m/s. A new mixing index was proposed to evaluate the lateral mixing quality of binary solids. It was found that at the lower part of the fluidized bed, the best mixing is acquired at the half radius, whereas mixing at the center line is the worst. At the higher part, solid mixing is better when increasing the distance from the wall. The influences of gas velocity and static bed on the lateral mixing were also discussed from a microscopic perspective.

This study systematically investigated flow boiling characteristics within a novel three-layer microchannel heat sink with 3/4 open-ring pin fin arrays, designed for high-heat-flux thermal management of low-carbon metallurgical reactors. Two-phase flow regimes, pressure drop, and wall temperature responses were analyzed. To evaluate the impact of functional surface material properties on thermo-hydraulic behavior, a hydrophilic nano-coating modification was applied to the inner copper channel walls for comparison. Increasing the flow rate triggered a transition from a vapor-dominated confined slug flow to a liquid-dominated dispersed bubble flow, which effectively improved the thermo-hydraulic stability. Hydrophilic surface modification resulted in an average pressure drop reduction of 33% and significantly diminished the sensitivity of flow resistance to velocity variations. Through hydrophilic treatment, the localized vapor film effect at high velocities was suppressed, and temperature field homogenization was promoted, yielding a maximum convective heat transfer coefficient of 7760 W/(m²·°C), i.e., 72.9% enhancement over the baseline heat sink. The underlying mechanism is attributed to the formation of a stable near-wall thin liquid film and the promotion of high-frequency nucleate boiling. These results will be of high relevance for developing efficient cooling solutions for power electronics, thereby supporting the advancement of low-carbon metallurgical reactors.

The demand for metallic nickel has been growing steadily. Laterite nickel ore, as an oxide mineral, contains a higher nickel content than sulfide ores, enabling more economical smelting in the nickel extraction process. However, an extremely thick slag layer generated during side-blown smelting of laterite nickel ore alters the bath circulation characteristic of conventional smelting processes. To address this, this study employs a validated Multi-Fluid VOF model to analyze the flow field characteristics of the side-blown furnace bath under varying slag layer thicknesses. Within the slag thickness range of 1.5–2.5 m, the ascending air plume shifts horizontally along the furnace wall with increasing slag thickness, entraining matte into the slag and promoting its diffusion toward the settling zone. Matte diffusion is governed by bath circulation: backflow from the settling zone dominates at lower slag thickness, while vertical kinetic energy from splashed melt reflux dominates at higher thickness. This reflux-induced circulation is blocked by the dense matte layer, causing no disturbance to the bottom matte and thus favoring slag–matte separation. Increasing slag thickness raises the near-wall circulation zone and plume entry point, reducing gas holdup near the tuyere and weakening oxygen–matte contact.