Phase-change transpiration cooling is one of the most promising thermal protection technologies for next-generation hypersonic vehicles. However, heat transfer deterioration (HTD) under complex thermal environments may induce local overheating and thermal protection failure. To investigate the process of phase-change transpiration cooling and mechanism of heat transfer deterioration, experiments are conducted on a Φ26.5 mm porous media subjected to a large-area oxy-propane flame. Three porous samples with permeabilities ranging from 0.10 µm2 to 2.57 µm2 are tested to evaluate the effect of permeability on cooling performance and characteristics of heat transfer deterioration. The results show that phase-change transpiration cooling exhibits three flow regimes: all-liquid, partial phase-change, and partial dry-out. In the early stage of the partial phase-change regime, capillary force effectively sustains coolant transport to the local phase-change area. Capillary force effectively sustains coolant transport during the early stage of partial phase-change regime; whereas heat transfer deterioration occurs when the coolant supply can no longer balance the local phase-change rate, leading to vapor backflow and thermal instability. Permeability significantly affects the characteristics of phase-change transpiration cooling. As permeability decreases from 2.57 µm2 to 0.10 µm2, the critical flow rate for heat transfer deterioration decreases from 2.00 mL/min to 1.50 mL/min, accompanied by lower near-surf temperature and improved temperature uniformity. The results indicate that reducing the permeability of porous media can enhance the stability of phase-change transpiration cooling.
The layout of dilution holes plays a crucial role in improving combustor outlet temperature uniformity. However, few studies decouple hole arrangement effects from airflow distribution. This study systematically investigates the effects of dilution hole spatial arrangement, axial position, and length on outlet temperature profile under a constant 10
Natural gas (NG)/hydrogen(H2)-fueled micro gas turbines (MGTs), owing to their high operational flexibility and strong fuel adaptability, exhibit broad application prospects in distributed energy systems. However, existing studies still lack a data-driven analysis framework that can simultaneously account for thermodynamic mechanism constraints and rapid prediction under complex operating conditions. In this study, a physics-constrained hybrid data-driven modeling framework is developed, and signal to noise ratio and grey relational analysis are combined to achieve key parameter sensitivity identification and multi-objective optimization. Multi-layer perceptron, decision tree regression, and gradient boosting regression algorithms are further introduced to establish performance prediction models, thereby improving the efficiency of performance analysis and digitalized applications under complex operating conditions. The results indicate that rotational speed is identified as the dominant parameter affecting system performance, and the optimization results further determine the optimal operating parameter combinations that simultaneously achieve high efficiency and low compressor power consumption. In addition, the developed data-driven model demonstrates high prediction accuracy and enables rapid steady state performance prediction of MGTs under complex operating conditions. The proposed method effectively balances physical consistency and computational efficiency, providing a new research perspective for the intelligent operation and dynamic digital twin development of mixed-fuel MGT systems.
Non-condensable gases (NCGs) significantly degrade the efficiency of phase-change heat exchangers by creating additional transport resistance during surface condensation. As the first part (Part I) of a two-part review, this paper systematically evaluates the theoretical frameworks governing this process, spanning from microscale interfacial mechanisms to macroscale engineering predictions. It explores the physical foundations of existing models by analyzing filmwise and dropwise condensation, vapor diffusion within NCG-rich layers, and the specific impacts of suction, interfacial waves, fog formation, and tube bundle interactions. Furthermore, the review mainly compares various predictive approaches—including empirical correlations, heat and mass transfer analogies, resistance- and diffusion-layer models, data-driven techniques, and multiscale numerical simulations such as molecular dynamics, lattice Boltzmann, and computational fluid dynamics. By comparing their respective assumptions, accuracy, computational costs, and applicability, this theoretical assessment establishes the foundation for Part II, which provides complementary experimental validation, observed surface effects, and visualization evidence.
Based on the streamwise corrugation characteristics of dragonfly wing cross-sections, a non-smooth surface composed of streamwise-arranged grooves is proposed and applied to a compressor linear cascade. A numerical approach validated against experimental data is employed to investigate the influence of this surface on the suction-side boundary-layer transition characteristics and the underlying mechanisms. The results indicate that the location of the non-smooth surface has a significant effect on the development and evolution of the laminar separation bubble on the suction surface. When the non-smooth surface is placed within a specific upstream region of the laminar separation bubble, the wake loss can be effectively reduced, leading to a decrease of 6.11
To improve the low-load combustion stability of boilers firing low-grade coal, this study investigates the cold single-phase flow characteristics of the original Yingba burner and a newly designed stable-combustion burner developed from it. A 1:4 scale experimental test system is established, and ribbon-tracer visualization together with constant-temperature hot-wire anemometry is used to measure the outlet jet boundary, recirculation-zone structure, and three-dimensional velocity field. For the Yingba burner, the influence of the inner secondary-air ratio on the outlet flow field is first examined. The results show that no effective recirculation zone is formed outside the Yingba burner nozzle under inner secondary-air ratios of 0.2–0.8. Increasing the inner secondary-air ratio enhances the jet expansion angle and swirl number, with the expansion angle increasing from 16.7° to 21.8° and the swirl number increasing from 0.26 to 0.32. However, an excessively high inner secondary-air ratio accelerates the downstream decay of the mixed jet and weakens axial penetration. Considering both radial diffusion and axial momentum retention, the recommended inner secondary-air ratio is 0.4–0.6. For the newly designed stable-combustion burner, the effect of slit-air flow rate on flow-field organization and stability extension is further analysed. As the slit-air flow rate increases from 0 to 100
The ignition process is critical to the establishment of engine combustion, directly affecting flame development, combustion stability, and overall performance. Driven by carbon-neutrality goals, ammonia has attracted increasing interest as a carbon-free fuel; however, its poor ignitability under high-pressure engine conditions remains a critical challenge. Ignition characteristics of ammonia under high-pressure conditions are analyzed from a coupled physical-chemical perspective using a detailed ammonia/n-heptane mechanism in a Chemkin-II homogeneous reactor, covering initial temperatures of 500–1500 K, pressures of 6.0–24.0 MPa, equivalence ratios of 0.5–5, and varying ammonia-diesel blending ratios. Results show that initial temperature dominates ignition behavior, reducing ignition delay time (IDT) by 1–2 orders of magnitude in the range of 600–900 K, with a weakened effect above 1000 K. Elevated pressure further shortens IDT, while the influence of equivalence ratio is relatively limited. Increasing the diesel fraction from 5
Dry methane reforming (DMR) is a promising pathway for clean fuel production owing to its capability to convert CO2 into value-added carbon monoxide. However, its practical deployment is plagued by catalyst deactivation from carbon deposition and high activation energy barriers. Methane carbon cyclic reforming (MCCR) enables in situ removal of deposited carbon by coupling catalytic decomposition of methane (CDM) with the reverse Boudouard (RB) reaction, thereby generating H2 and CO with favorable selectivity. This makes MCCR a potential pathway for clean fuel synthesis. The development of numerical models has been hampered by the lack of understanding of the dynamics of MCCR, allowing key aspects such as kinetic response to remain in a state of confusion. In this study, a kinetic model for MCCR over commercial Ni/Al2O3 catalysts has been established. Apparent activation energies for CDM and RB are quantified under varying experimental conditions, and a numerical model is introduced to characterize the thermodynamic and kinetic properties of MCCR. Over 200 carbon deposition-removal cycles, the timely elimination of low-graphitized carbon enables a carbon removal efficiency of 99.73
Reliable experimental evidence is essential for evaluating vapor condensation when non-condensable gases (NCGs) accumulate near a cooled surface. This second part of a two-part review evaluates external, internal, and visualization experiments reported for NCG-containing condensation over the past decade, emphasizing the measurements used to determine heat-transfer performance and condensate behavior. Experimental results for flat plates, single tubes, tube bundles, channels, and modified surfaces are compared across key engineering parameters, including NCG species and concentrations, mixture pressure and velocity, wall geometry and wettability, and wall subcooling. The collected observations demonstrate that even a marginal NCG mass fraction (e.g., 0 to 0.1) triggers a steep initial deterioration in the heat transfer coefficient. Furthermore, the synthesis reveals how factors such as gas-side transport disruption, differences in molecular weight, condensate motion, and surface conditions jointly govern the measured thermal response. To provide a complete physical framework, the theoretical and computational formulations used to interpret these experimental data are reviewed separately in Part I.
This study used infrared thermal imaging to explore the multi-row discrete holes film cooling law under transonic mainstream conditions. The transonic mainstream conditions covered Ma=0.5–3.0, and the blowing ratios of the secondary flow were 0.5, 1.0, and 1.5. The cooling effectiveness of the different film-hole shapes under transonic conditions were compared. The effects of compressibility and the shockwave system on film cooling were also discussed. The multi-row superimposed film cooling effectiveness correlation formula was fitted for the cylindrical hole film experiments. The results showed that the strong compressibility of the near field increased the injection depth of the jet. As the mainstream transitioned from the subsonic to the supersonic state, the impact of shockwaves became more significant than that of compressibility. In the supersonic mainstream, the film cooling effectiveness appeared to be very low under near-sonic conditions, increasing with an increase in the mainstream Mach number. In the supersonic condition at Ma=2.0, the film cooling effectiveness along the path of the optimal hole, such as the fan-shaped and offset holes, was worse than that of the conventional cylindrical hole. The average error of the first four rows calculated by the fitted multi-row superimposed film cooling effectiveness correlation formula was 1.39
Operation strategy plays an important role in achieving the energy-saving, environmental protection, and superior economic performance of combined cooling, heating and power (CCHP) systems. This study proposes an active control operation strategy suitable for a novel CCHP system integrated with the solar-assisted sorption-enhanced chemical looping steam methane reforming (SE-CL-SMR) hydrogen production process. The load supply and demand balance of typical days are analyzed in detail. Compared with the traditional and novel CCHP systems following the electric load (FEL) operation strategy, an analysis is conducted on the exergy efficiency, primary energy consumption saving rate (PECSR), carbon dioxide emissions reduction rate (CDERR), net present value (NPV) and dynamic payback period (DPP) of the novel CCHP system using active control strategy. The results show that the novel CCHP system using active control strategy has the best performance, with exergy efficiencies of 48
To extend the lean ignition capability of a light turboshaft engine and address high-altitude ignition challenges, a cold-flow numerical study has been conducted on a full-annular evaporator tube combustor under simulated high-altitude conditions. The analysis focuses on the local flow field and fuel distribution near the ignition spark plugs. Through this analysis, the root causes of high-altitude ignition failure and the influence of fuel air ratio (FAR) on ignition characteristics are identified. Based on the simulation results, an igniter repositioning strategy is proposed, i.e., moving it forward from approximately 0.3L to 0.12L downstream of the combustor dome, and shifting its circumferential angle from θ=0° to θ=5°, relative to the evaporator tubes. Subsequently, flame propagation analysis is performed for the modified combustor. Following this, engine tests of both prototype and modified configurations are conducted, through which the lean ignition boundary and light-round boundary are obtained. These results confirm the validity of the igniter repositioning strategy, which extends the ignition boundary by approximately 50
Recovering waste heat from marine main-engine exhaust gas using supercritical CO2 (S-CO2) power cycles is an effective approach to improve onboard energy utilization. Under high-temperature, high-pressure, and high-speed operating conditions, unavoidable CO2 leakage through turbomachinery seals into turbine-alternator-compressor (TAC) assemblies can significantly influence cycle performance. This study develops a coupled numerical framework by integrating an improved thermodynamic model of a dual turbine-alternator-compressor recompression S-CO2 cycle (DTAC-PSRC) with a labyrinth seal leakage model to quantify leakage behavior and its influence on thermal efficiency. Off-design characteristics are investigated by comparing no-leakage and leakage-included cases, focusing on the effects of key operating parameters on leakage mass flow rate and thermal efficiency. Results indicate that turbomachinery leakage consistently reduces thermal efficiency and shifts optimal operating parameters toward lower values. For a representative off-design condition, the maximum thermal efficiency of 26.22
As data center power consumption continues to rise, improving the airflow and cooling design of conventional air-cooled servers is essential. Optimized airflow paths and thermal structures can enhance cooling performance and reduce energy use. A coupled flow and heat transfer simulation have been developed based on a detailed model of an air-cooled server, aiming to investigate how server geometric structures affect their thermal performance. The results show that the fan speed is proportional to the 1.8 power of the chip’s heat dissipation amount per unit temperature rise, while the chip’s equivalent convective heat transfer coefficient is proportional to the 0.43 power of the average inlet velocity. Moreover, the proposed air duct structure in this work effectively directs airflow through critical heat-generating components, significantly enhancing cooling efficiency and achieving up to a 22.4
To overcome the bottlenecks of liquid leakage, interfacial instability and oxidative corrosion of metal-based phase change materials (PCMs) in high-temperature thermal storage, core-shell structured microencapsulated phase change materials (MEPCMs) based on Al-Zn alloy were innovatively developed. Guided by the Al-Zn binary phase diagram, the Al-Zn alloy MEPCMs were prepared by a three-step method of Zn replacement reaction, static melt alloying and thermal oxidation. The phase change temperatures of Al-Zn MEPCMs were systematically regulated from 618.5°C to 655.5°C. The XRD, SEM, and DSC characterization results indicated that the obtained core-shell structure effectively mitigates the cracking problem caused by volume expansion of the PCMs through interfacial voids and a self-repairing oxide shell design. The MEPCMs exhibit a high thermal storage density (134 J·g−1) and a relatively high specific heat capacity (>0.7 J·g−1·K−1), along with a broad endothermic temperature range (540°C–660°C) and fast heat release capability. After 50 thermal cycles, the phase-change temperature and latent heat show negligible change. Compared with existing high-temperature phase change materials, Al-Zn@Al2O3 MEPCMs combine a widely tunable phase change temperature, a broad endothermic temperature window, and excellent thermal stability, providing tailor-made solutions for high-temperature thermal storage scenarios such as solar photothermal utilization and industrial waste heat recovery.
The maximum temperature characteristics are studied in detail, especially in longitudinally ventilated tunnel fires. However, the maximum temperature for longitudinally ventilated tunnels with bifurcated shaft exhaust is still unknown. To probe into this problem, the maximum temperature characteristic in longitudinal ventilation tunnels with bifurcated shaft exhaust is experimentally studied. Effects of ventilation and fire location are concerned. The results demonstrate that when fire is 1 m away from bifurcated shaft, increasing longitudinal and exhaust velocity has minimal impact on maximum temperature and flame shape. The presence of bifurcated shaft exhaust reduces the maximum temperature by about 40
Pumped storage hydropower (PSH) is a mature technology with over a century of application. However, for the past decades, a new challenge has emerged: the large-scale integration of intermittent renewable energy in the 21st century has significantly changed its operating requirements. While its traditional role is primarily limited to stable, long-cycle peak shaving, modern PSH plants are increasingly used for high-frequency grid balancing. Consequently, pump-turbines are now forced to undergo frequent start-stop cycles and operate for extended periods under severe off-design conditions. Although conventional hydraulic design can effectively mitigate static cavitation, these highly dynamic operations induce complex transient flow instabilities and intense pressure fluctuations. This significantly increases the risk of severe transient cavitation. The phenomenon can lead to reduced output power and lower energy conversion efficiency of pump-turbines in pumped storage power stations. Meanwhile, cavitation may cause vibration and noise of the unit, thereby shortening pump-turbines’ service life and undermining the reliability of energy storage operations. Conducting systematic research on the cavitation mechanism, evolution law, and suppression strategies of pump-turbines is necessary since it could provide significant engineering guidance. Thus, this paper systematically reviews the relevant research on cavitation in pump-turbines, including research methods and analysis of cavitation phenomenon, factors influencing cavitation in pumped storage power stations, and cavitation suppression measures. In addition, the paper emphasizes cavitation monitoring methods combined with machine learning, and further highlights that transfer learning can be used to address the current issue of insufficient data for high-head pump-turbines.
High penetration of photovoltaic (PV) generation requires coal-fired power plants (CFPPs) to operate under frequent deep peaking conditions, where conventional ultra-low-load operation can cause efficiency loss and higher fuel consumption. This study proposes and evaluates a start-stop deep peaking strategy for CFPPs and systematically compares it with conventional low-load continuous operation. Using actual operational data from a 2×660 MW supercritical CFPP, the technical feasibility, operational characteristics, and economic performance of the strategy are analyzed. The results show that short-term hot start-stop operation with 5–10 h shutdowns is technically feasible and already widely applied, with 81 events recorded within one year. During an 8-h deep peaking period, shutting down one unit while operating the other at 40
As aeroengines increasingly develop towards high efficiency and high load, the efficiency of low-pressure turbines (LPTs) has reached a high level, and further improving their efficiency has become increasingly challenging. The clocking effect has emerged as a promising approach to enhance LPT performance. Based on the Unsteady Reynolds-Averaged Navier-Stokes (URANS) method, combined with the Shear Stress Transport (SST) turbulence model and gamma-theta transition model, this study conducts numerical simulations on four clocking positions (CLK1, CLK2, CLK3, CLK4) of the stator blades in a two-stage high-load LPT, focusing on analyzing the influence mechanism of the clocking effect on wake transport, boundary layer separation-transition, and flow losses. The results indicate that the clocking position determines the disturbance mode of the downstream stator by altering the transport trajectory of the upstream wake: the wake can directly impinge on the suction surface (CLK1/CLK4), pressure surface (CLK2), or be transported to the mid-chord of the passage (CLK3). This difference in disturbance modes directly regulates the separation and transition processes of the boundary layer on the downstream suction surface. The clocking position that most effectively suppresses boundary layer separation (CLK2, with a separation bubble length 30
This study presents a comprehensive experimental investigation into the flow boiling heat transfer characteristics of R134a and its environmentally sustainable alternative, R513A, within horizontal micro-fin tubes. The primary objective is to develop a robust semi-empirical correlation for predicting the Nusselt number under a wide range of operating conditions. Experiments were conducted across mass fluxes ranging from 50 to 300 kg·m−2·s−1, heat fluxes between 12 and 36 kW·m−2, and saturation temperatures from 17°C to 27°C. The correlation was formulated based on critical dimensionless numbers, including the dimensionless vapor mass flux (Jg), Weber number (Wel), Jacob number (Ja), and Boiling number (Bo). The developed model was validated with experimental data, yielding a mean absolute error of less than 15
