Applied Thermal Engineering最新文献

Thermal management is critical to developing proton exchange membrane fuel cell systems, impacting their output performance, safety, and lifetime. Currently, studies on thermal management use single zone cooling technique to control the cell temperature, which leads to the non-uniform distribution of water inside the cell and reduces the cell’s output performance and life span. In this paper, a novel multizone cooling system is developed to optimise the thermal management of the cell, and the effect of multizone cooling technology on the cell is investigated under different operating parameters. The experimental results demonstrate that cell voltage and current density uniformity improved when the cell bottom temperature was high and the inlet temperature was low. The performance enhancement was significant as the back pressure and outlet temperature increased. Notably, the cell with multizone temperature control showed significantly reduced reverse current generation and improved current density uniformity. Compared to cells using single zone cooling technique at 60 °C, the voltage increased by 9.98 %, 12.07 %, and 15.98 % at current densities of 400, 800, and 1200 mA cm⁻², respectively. Multizone cooling technology notably enhances current density uniformity, achieving a 40.93 % improvement at 400 mA cm⁻².

The balance between water discharge and mass transfer within metal foam flow field is vital for elevating the performance of proton exchange membrane fuel cell (PEMFC). To obtain an improved balance, this work designs a novel bilayer structure with two types of PPI (pore per inch) for metal foam flow field. Experimental and numerical results confirmed that arranging a metal foam featuring a smaller PPI in the layer 1 near the membrane electrode assembly (MEA) and a larger PPI in the layer 2 away from the MEA is beneficial to enhance the output performance. The excellent PPI combination for balancing mass transfer and water discharge involves utilizing a 50 PPI metal foam for the layer 1 and 110 PPI metal foam for the layer 2. Compared to conventional metal foam with 50 PPI, metal foam flow field with excellent PPI combination showcases a 11.2 % increase in water discharge and a 13.2 % boost in mass transfer, leading to a notable 23.5 % performance enhancement. Similarly, compared to conventional metal foam with 110 PPI, there is a 7.3 % decrease in mass transfer but a significant 29.5 % increases in water discharge, leading to a 15.2 % performance improvement.

Condition based maintenance plays a crucial role in ensuring the safety and reliability of gas turbine engine. Specifically, fault detection and isolation (FDI) can improve efficiency and reduce costs during maintenance. The traditional FDI methods, which developed only using physical engine data, lack a comprehensive consideration of high accuracy and strong applicability across different engine individuals. In this paper, an enhanced digital twin-driven FDI method is proposed, which combines a digital engine, sensor series imaging mechanism and a convolutional neural network. The digital engine is constructed to mirror the operational status of the physical engine. The output residuals between the physical and digital engines are transformed into multi-channel images to train a convolutional neural network for FDI of the physical engine. The network is then fine-tuned using fault-free data from the target engine to further strengthen diagnostic performance across different engine individuals. The effectiveness of the digital engine is verified using actual ground test data, and the performance of the proposed method is demonstrated through comparative simulations. The network, trained on operational data from Engine A and fine-tuned with fault-free data from other engines, exhibits the highest diagnostic accuracy and fault isolation rate. Compared with the physical engine data-based method, the accuracy is increased from 68.25% to 97.95%, the fault isolation rate is improved from 85.91% to 99.26%, and the false alarm rate is decreased from 4.41% to 0.34%. The results show that the proposed method has better FDI capabilities across different engine individuals.

The investigation is motivated to analyze the influence of Phase change material (PCM), nano PCMs, and hybrid Nano PCM in sustainable hydrogen production systems. An emerging and highly effective method for hydrogen production involves the use of proton exchange membrane (PEM) technology, which separates water into its constituent parts through electrolysis. Its susceptibility to performance deterioration over time, however, demands routine maintenance and component replacement, which negatively impacts operational effectiveness and cost-effectiveness. In this study, the PEM system for electricity and water heating was integrated with the evacuated tube collector and photovoltaic panel to produce hydrogen. Additionally, hybrid Al₂O₃ and SiO₂ nanoparticles with a combined concentration of 0.1 % in equal shares improved the thermal characteristics of PCM in heat exchangers. The research result shows that the heat exchanger of the ETSC circuit with the hybrid nanoparticles enhanced PCM demonstrated improved thermal performance as well as increased hydrogen production. With hybrid nanoparticles enhanced PCM in the heat exchanger, the maximum energy and electrical energy were observed as 246.5 kWh and 44.7 kWh, respectively. The ETSC efficiency, electrical efficiency, and PEM electrolyser efficiency reached their highest points at 93.1 %, 15.5 %, and 39.2 %, respectively. Furthermore, hybrid nanoparticle-enhanced PCM produces an average of 25.9 g of hydrogen.

Zigzag-channel printed circuit heat exchangers (PCHEs) are widely used in nuclear energy, solar energy, and aerospace due to their good heat transfer performance. However, the high flow resistance of zigzag channels leads to large pumping power consumption and thus limits the overall performance. Although previous modified channels could reduce the flow resistance of PCHEs, they also bring a decrease in the heat transfer efficiency. Inspired by river islands, this study proposes a novel nature-inspired channel. The nature-inspired channel heat exchanger, along with a traditional zigzag-channel heat exchanger, were manufactured by 3D printing. The high-temperature air-air flow and heat transfer experiments show that the nature-inspired channel heat exchanger increases the average heat transfer rate by 1.5% and significantly reduces the pressure drop by 34.85%. The addition of airfoil fins at the corners effectively alleviates the flow resistance caused by flow separation, reattachment, and collision, leading to a higher Nusselt number and a lower Fanning friction factor. The Nusselt number of nature-inspired channel is 59% higher than that of the zigzag channel with a 15° inclined angle. This work demonstrates that the nature-inspired channel could significantly reduce the flow resistance while maintaining high heat transfer efficiency compared with the traditional zigzag channel.

Solid state transformers (SSTs) are at the forefront of emerging technologies, enhancing distribution and transmission networks. These transformers facilitate the development of highly controllable and robust smart grids, seamlessly integrating renewable energy sources and accommodating connections for both alternating current and direct current components/lines at medium or low voltage levels. This research paper introduces an innovative SST incorporating the inductive power transfer (IPT) technology, currently under development within SSTAR, a Horizon Europe project. This novel device operates at a frequency of 50 kHz and provides with an output power of 50 kW. The IPT system is submerged in an ester-based, biodegradable dielectric fluid, providing effective cooling and insulation characteristics. The primary focus of this research is to highlight the guidelines for the optimal design of the forced liquid cooling system of the SST module. The analysis employs a multi-faceted simulation strategy to calculate the cooling aspects of the transformer, utilizing the commercial software ANSYS. This involves 3D coupled Electromagnetic (EMAG) - Computational Fluid Dynamics (CFD) simulations, as well as stand-alone CFD and thermal FEA simulations, ensuring robust cross-verification of the obtained results. This novel SST exhibits improved thermal performance, achieving a hot-spot temperature of 58 °C, the lowest value found in similar research studies. The findings underscore the efficiency and robustness of the proposed design, marking a significant step towards the realization of active and environmentally-friendly electrical networks.

With the increasing environmental impacts of human activities and the demand for new air cooling alternatives, indirect evaporative cooling (IEC) emerges as a sustainable alternative. However, there is a gap in the literature regarding examining cyclone configurations in this context. Despite being good separator devices, cyclones can be used as heat exchangers, enhancing convective heat transfer through turbulence. This opens the possibility of developing improved and economically accessible geometries of IEC systems, especially beneficial for hot and arid regions, and communities with limited resources. This study aimed to investigate the performance of 25 geometric configurations of cyclones used as indirect evaporative heat exchangers. The researchers employed an experimental approach by subjecting cyclones covered with a wet cotton fabric to IEC tests under various geometric and operating conditions, followed by statistical analyses to identify relationships between the variables. The results showed significant thermal variation in the cyclones, with a considerable impact on all variables, particularly the cyclone’s total length, relative humidity, air temperature, and flow rate. The thermal efficiency of the cyclones varied widely, with total length and flow rate being the most significant factors. Additionally, an analysis of the Euler values revealed the importance of the cyclone geometry in selecting the one that reduces energy costs. Among the cyclones tested, the configuration with the optimal geometric design (Cyclone 8) achieved the highest thermal performance and lowest Euler number. The findings of this study could help developing more efficient and sustainable IEC systems, helping to reduce energy consumption and environmental impacts.

Plasma melting furnaces, as an innovative application of thermal plasma, have seen extremely limited numerical studies of their internal plasma arcs, remaining largely in the nascent stages. Due to the complexity of the material composition, the ultra-high currents and temperatures pose great challenges to the numerical calculation of the plasma arc, especially for plasma melting furnaces with an industrial-scale production capacity of 30 t/d. Therefore, this study uses computational fluid dynamics to deeply investigate the fluid flow and heat transfer of the plasma arc in a single-electrode plasma melting furnace operating at a current of 8000 A and a voltage of 170 V. Special attention is given to the impact of the plasma arc on the bath surface, with additional discussions on the effects of electrode gap and cathode bottom shape. The conclusions show that the plasma arc column exhibits a typical bell-shaped profile, and the reduced radial Lorentz force induces an outward expansion of the relevant parameters. The plasma arc achieves a maximum velocity of 2116 m/s and attains the peak temperatures of 19991 K. The heat transfer efficiency from the plasma arc to the bath surface is about 28 %. An innovative evaluation metric for the effective melting region on the bath surface is proposed, and it is currently circular with a radius of 0.525 m. The electrode gap has a minimal effect on the plasma arc. Enlarging the electrode gap can expand the effective melting region, while also bringing about numerous adverse effects. The graphite cathode with the planar bottom exhibits the optimal performance overall, followed by the cambered surface, with the conical surface showing the worst.

The accident of the steam generator tube rupture in the lead-bismuth-cooled fast reactor or the core meltdown in the light water reactor may cause violent heat and mass transfer between the melt and the coolant, potentially further damaging the reactor. Therefore, it is essential to study the corresponding mechanisms. In this study, numerical simulations are utilized to investigate the dynamic interactions between Wood’s metal and subcooled water in the coolant injection (CI) mode, focusing on jet behavior and critical cavity parameter changes. By analyzing these factors, this research aims to clarify the interfacial evolution and interaction mechanisms between the melt, water, and air, thereby tackling the problem of inadequate observation in experiments. A user-defined function (UDF) was employed to simulate the flow characteristics of the melt during the solidification process. This approach effectively addressed the limitation of Fluent’s inherent solidification model, where the fluid no longer participates in turbulent velocity calculations after solidification. In addition, an equivalence method was proposed according to the characteristics of two-dimensional simulations in Fluent. Comparisons with Cheng’s experimental results show that the equivalent model can accurately predict jet penetration characteristics while significantly reducing the demand for computational resources. According to this equivalence method, this research developed a new correlation for predicting the maximum jet penetration depth in the CI mode. The above results provide new perspectives for understanding the dynamic interactions between metals and coolants, which is significant for the application and optimization of technologies in the nuclear field.

The pre-swirl system of an aero engine provides cooling air with suitable temperature and pressure for turbine blades, rarely contributing to thrust. However, the traditional pre-swirl system with a fixed geometry leads to significant wastage of cooling air during part-load conditions, such as subsonic cruising, resulting in a decrease in engine performance. Unlike the existing approach, which uses valves to close a part of the pipeline, a novel modulated pre-swirl system based on the adjustment of the vane-shaped nozzle is proposed to overcome the flow nonuniformity in the circumferential air supply. The effects of the number of pre-swirl nozzles and receiver hole parameters (number, length, and structure) on the system performance are discussed in design and subsonic cruising conditions. The results demonstrate that increasing the number of pre-swirl nozzles significantly improved the flow adjustment efficiency and performance of the modulated pre-swirl system. A larger number and shorter length of receiver holes resulted in a higher system temperature drop in both design and subsonic cruising conditions. With regard to the configurations of the receiver holes, the vane-shaped receiver hole exhibited optimal aerodynamic performance. Compared to the baseline case, the system with N_p = 60, N_Rec = 60, l_Rec = 3 mm, and vane-shaped receiver hole showed a 27.6 % and 26.7 % improvement in the temperature drop efficiency in the design and subsonic cruising conditions, respectively.