According to the Intergovernmental Panel on Climate Change, CO2 capture using liquid absorbents is a key strategy for mitigating climate change. However, the energy footprint of the technique is still high and novel solutions are needed to design better units. To that end, this study presents a novel and detailed diffuse-interface model for interfacial mass and heat transfer coupled with chemical reactions for CO2 capture. Two scalar transport equations describe the species evolution in each phase, coupled through a variable apparent Henry’s constant that captures non-ideal vapor–liquid equilibrium at the interface. Momentum and energy transport are modeled through single-scalar formulations, with interfacial velocity discontinuities arising from reactive phase change, handled via a Stefan condition. A conservative phase-field method closes the equations, with regularization applied to suppress numerical diffusion when tracking the interface. The model resolves key physical phenomena, including reaction kinetics, mass transfer resistance, H2O phase change, and interfacial velocity jumps during both absorption and desorption. A sensitivity analysis shows that increasing the solvent mole fraction enhances chemical reactivity but increases diffusive resistance, inducing complex nonlinear effects on the interfacial reactive transport. The coupled CO2 and H2O interphase transport are captured simultaneously, with water evaporation shown to have limited impact on CO2 uptake and on the interfacial reactive Stefan velocity for isolated droplets. Additionally, multi-droplet simulations demonstrate that the droplet number and an imposed gas-phase mean flow significantly affect absorption rates and spatial asymmetry through droplet-droplet interactions and convective transport. The findings offer critical insights into interfacial CO2 transport in reactive, two-phase systems and supports the need for advanced numerical studies like the present one, given the lack of droplet-scale data and the limited applicability of bulk-scale experiments to localized transient interfacial processes.

Enhancing heat transfer in turbulent convection has been a long-standing challenge in many energy and industrial processes. However, despite decades of efforts, conventional strategies have achieved only limited success, due to the intrinsic bounds of turbulent mixing. Inspired by thermal-chemical energy conversion, this work unlocks a fundamentally new route for intensified heat transfer by introducing a reversible chemical reaction (N2O4 ↔ 2NO2) into Rayleigh-Bénard convection. The resulting reactive convection achieves an unprecedented increase in heat transfer (over seven times) relative to conventional non-reactive fluids. The underlying mechanism is described by a simplified double-film model: heat is absorbed as chemical energy in an endothermic film near the heated wall, then transported by reaction-intensified turbulence, and finally releases in an exothermic film near the cold wall. Unsteady analysis further confirms the coupling between chemical reaction and turbulence, particularly the coherent structures. Beyond advancing thermal convection theory, the approach offers practical potential for low-temperature waste-heat recovery where reaction reversibility is maintained, and for the design of gaseous space thermal management system

While sweeping jets generated by fluidic oscillators have been regarded as an effective means of enhancing heat transfer, their unsteady flow and thermal behaviors remain insufficiently understood. The present study introduces an actively rotational sweeping jet and examines both time-averaged and unsteady behaviors under different frequencies (Str) and inclined angles (α). Through high-fidelity large eddy simulations, we elucidate the vortex formation, coherent structure evolution, and their contributions to heat transfer enhancement and uniformity. Results show that sweeping jets enhance surface-averaged Nusselt number (Nu) by up to 3.25% and reduce spatial non-uniformity by 52.41%, compared to the classical steady jet. Additionally, pressure loss is reduced by 14.51%, leading to a 7.74% improvement in overall thermal performance. Unsteady analysis reveals a spring-like spiral vortex structure forming in early jet development, whose profile could be influenced by sweeping frequency and angle. These vortices periodically transport the migration of high-Nu regions along the radial direction, which weakens the stagnation effect and promotes wall jet uniformity. Probability distribution analysis indicates that optimal sweeping parameters (e.g., α = 30°, Str = 0.33) can improve time-averaged efficiency while reducing temporal instability in heat transfer. Power spectral density analysis further confirms that jet sweeping disrupts the classical -5/3 energy cascade by both effects of vortex shedding and periodic forcing, leading to anisotropy and altered inertial sub-range development.

This work proposes novel double wall cooling designs for modern gas turbines, where the traditional pin-fins are substituted by triply periodic minimal surface (TPMS) structures. A series of numerical simulations have been carried out to study the flow, heat transfer and temperature gradient (thermal stress for mechanical implications) behaviors for these novel configurations, which are validated against experimental data by infrared thermal imaging in a hot-gas wind tunnel. Results show that compared to the traditional pin-fin double wall structure, the internal convective heat transfer rate can be enhanced up to 57.9% by the TPMS design, which leads to an over 10% enhancement for overall cooling effectiveness. Proper design of TPMS structure could also reduce pressure loss, e.g., the P-B-0.6 configuration demonstrates a 2.7% reduction in pressure loss at the discussed condition. These advantages are correlated with the enlarged heat transfer area and the smooth pore-size curvatures that could decrease the turbulent dissipation loss. Further analysis revealed that TPMS designs could improve the temperature uniformity in the target surface, decrease the temperature gradient within the solid domains, and thereby reduce the thermal stress. The effect of porosity, TPMS type and mass flow ratio are further discussed.

Through time-resolved experiment and large eddy simulation, we have studied the influence of separation wake caused by convex curvature on film cooling behaviors. Four different film-holes drilled in convex surface are selected as research objects, which are compared with their corresponding baseline models in flat plates. Results show that the coherent vortical structures of film cooling are influenced by the separation wake, which fundamentally alters time-averaged and unsteady film coverage performances. For the cylindrical and fan-shaped holes, negative counter-rotating vortex pairs (CRVP) is weakened, therefore a better time-averaged film behavior is exhibited on the convex surface; for the film-hole configurations with trench designs, the positive anti-counter rotating vortex pairs (ACRVP) is inhibited, thus complete opposite results are observed. Unsteady analyses of film coverage demonstrate that the separation wake is benefit to decrease the instability of film cooling for all kinds of film-holes, which is caused by the reduction of near-wall pulsation for vortex trajectory. These designs of fan-shaped/trenched film-holes could significantly improve time-averaged film performance. It should also be noted that the trenched fan-shaped hole could also lead to a 200 % higher unsteadiness level compared to the cylindrical hole.

This study investigates the effects of turbulent jet mixing, mainstream pulsation, and convex curvature on unsteady film cooling behaviors by high-fidelity large eddy simulation. Trenched film-holes are drilled on two convex surfaces with different curvatures, which are compared to a baseline flat model (FM). Under both mainstream steady and pulsed conditions, the time-averaged and transient thermal and flow behaviors are analyzed. Results indicate that coherent vortical structures and velocity fluctuations of flow field significantly influence the time-averaged and unsteady cooling performances: 1) Compared to baseline FM, favorable anti-counter-rotating vortex pair (ACRVP) of the low-curvature model (LM) is more closely attached to the cooled wall, thereby enhancing the time-averaged coverage performance. In contrast, for the high-curvature model (HM), the coverage scope of favorable ACRVP is decreased and the cooling-jet coverage degrades. 2) Unsteady analyses reveal that the high unsteady region shows a symmetrical distribution, which is caused by symmetrical vortical structures. In addition, the consistent fluctuation-trend and distribution-pattern between velocity and film effectiveness suggests a direct correlation between flow dynamics and cooling performance. Moreover, mainstream pulsation markedly increases overall instability, in comparison with steady condition, the overall instability of FM, LM, and HM is increased by 47.5%, 44.3%, and 27.4%, respectively.

In this work, the large eddy simulation (LES) method is used to study the instantaneous and time-averaged characteristics of flow and heat transfer in three internal structures i.e., swirl cooling (SC), impingement cooling (IC), double chamber cooling (DC) in the leading edge of a turbine blade at three Reynolds numbers (6.0 × 103, 9.0 × 103, 1.2 × 104). Comparison with RANS method, LES method can provide internal cooling designers with a more comprehensive understanding of flow and heat transfer. The numerical results reveal the following important conclusions: (1) At the view point of time-averaged, the tangential jet in SC and DC can significantly increase the heat transfer rate (Nu), and therefore their heat transfer rates (Nu) are higher than that of IC, but IC has the lowest friction resistance. (2) At the view point of unsteady analysis, the flow instability of SC along the flow direction increases with Re, while the flow instability of DC decreases. The heat transfer rate (Nu) instability of IC is the highest, at Re = 6.0 × 103, the Nu fluctuation amplitude of IC is increased by 34.9 % compared with SC.

In accordance with the United Nations Sustainable Development goal #7 – affordable and clean energy, the concept of reversible reactive flow (N2O4/NO2) inside ribbed channel is proposed for low-temperature waste heat recovery. Quasi direct numerical simulations are performed to reveal the relationship between flow, heat/mass transfer, and chemical characteristics with different rib inclined angles (90° and 45°). The analyses indicate that the reaction of N2O4 ⇌ 2NO2 has limited influence on flow patterns inside the ribbed channel, but intensifies the heat transfer considerably. For the 90° reactive case, the enhancement of Nusselt number reaches 112.7 % when Reynolds number is 2000. Although non-equilibrium thermal-chemical phenomenon is observed by instantaneous snapshots, time-averaged results show that the forward endothermic reaction is concentrated close to the heated wall. The flow structures transport fluid pocket consisting of “overheated” gas and triggers local backward exothermic reaction, which decreases the thickness of thermal boundary layer and thereby intensifies the overall heat transfer. For the 45° inclined reactive case, a flow circulation at local equilibrium between heat release and absorption is formed by the rib-induced large-scale vortices. The comprehensive thermal performance is further improved by 24.6 % compared to the 90° reactive case, which attributes to higher Nusselt number and lower friction loss.

In practice, film cooling on gas turbine blade inevitably works in an unsteady environment, which is introduced by periodical rotor/stator interaction and unsteady combustion. Previous studies have introduced two methods to simulate the realistic unsteady condition: 1) the pulsation of mainstream velocity; and 2) the pulsation of coolant injection. However, up to this point, the differences in instantaneous film cooling behaviors between these two methods remain unclear. This work presents a series of large eddy simulations to exhibit the unsteady flow and film cooling behaviors under steady and the two unsteady flow conditions. The numerical strategy is validated against our time-resolved experimental data. Time-averaged results show that the difference between the two pulsations is not significant if the averaged blowing ratio remains the same. However, the pulsation type plays a dominant role on the transient mode of film coverage. Under the steady condition, film coverage instability is induced by the unsteady trajectory of near-wall vortex structure; but with pulsed environments, the unsteadiness magnitude increases, and the area with high unsteadiness level enlarges. The pulsation of the mainstream velocity induces a more severe film coverage instability compared to the pulsation of the cooling air injection, because of the higher fluctuation energy of the mainstream bulk. Under mainstream pulsation, the probability distribution of instantaneous cooling effectiveness is the most scattered, and the corresponding fluctuation range is the largest.