Search Results (32)

Efficient ortho–para hydrogen conversion is essential to suppress spontaneous heat release and boil-off losses during cryogenic liquid hydrogen storage and pre-liquefaction processes. In this study, a novel catalyst-filled wavy plate-fin heat exchanger (CFHE) is proposed to simultaneously enhance heat transfer and ortho–para hydrogen conversion under cryogenic conditions. Compared with conventional straight-fin configurations, the wavy-fin structure introduces controlled flow perturbations and increased specific surface area, thereby intensifying transport processes. Three-dimensional computational fluid dynamics (CFD) simulations, using the SST k–ω turbulence model, coupled with an ortho–para hydrogen conversion kinetic model were performed to quantitatively investigate the effects of key geometric parameters and catalyst loading on hydrogen conversion, heat transfer, and pressure drop within a Reynolds number range of 941–1577 and a temperature range of 35–20 K. Within the same CFHE configuration, the para-hydrogen fraction remains nearly unchanged without catalyst but increases significantly with catalyst loading. However, the catalyst reduces the global average Colburn j-factor by about 25%. Despite higher friction losses, the outlet–inlet temperature difference decreases to about 0.866 times that of the non-catalyst case, indicating improved temperature uniformity. A comprehensive performance index e, integrating heat transfer enhancement, flow resistance, and conversion efficiency, was introduced and optimized using a genetic algorithm. The optimized CFHE achieves an outlet para-hydrogen fraction exceeding 95% of the thermodynamic equilibrium value while maintaining hydrogen entirely in the gaseous phase to avoid catalyst deactivation. Overall, the catalyst-packed wavy channel configuration demonstrates superior conversion efficiency, enhanced thermal uniformity, and improved overall performance compared with straight-fin structures, providing quantitative design guidance for high-performance heat exchangers in cryogenic hydrogen liquefaction systems. Full article

The demand for efficient dehumidification in evaporators has become one of the key technical challenges restricting the high-quality development of the refrigerated air dryer industry. To investigate the effects of fin structure on the air-side heat transfer and dehumidification performance of finned-tube evaporators applied in refrigerated air dryers under the operating conditions of 50 °C, RH = 85%, numerical heat and mass transfer models for the air side of evaporators with plain fins and wavy fins were established based on the Ansys Fluent software 2022R1. The study found that wavy fins possess superior heat transfer and moisture removal capabilities. Key performance indicators, including the air-side heat transfer rate (Q), moisture removal amount (Δm), friction factor (f), and the nusselt number (Nu), were all higher for wavy fins compared to plain fins. Building upon this, three types of vortex generators (VGs) were introduced to further optimize the performance of the wavy fins, aiming to balance heat transfer enhancement and flow resistance control. At an attack angle of 30°, the comprehensive performance factor (JF) showed the highest improvement, reaching 43% with the Delta Winglet vortex generators. The 15° configuration also showed improvement, while 45° led to the worst performance due to increased flow resistance. The results indicate that for typical high-temperature and high-humidity environments, the wavy fin is recommended as the preferred choice due to its superior overall performance and simple structure. For applications requiring higher dehumidification capacity, wavy fins equipped with vortex generators can be selected to achieve the most efficient dehumidification. This study provides valuable insights for the design and application of finned-tube evaporators in dehumidification systems under high-temperature, high-humidity conditions for refrigerated air dryers. Full article

Studies on autonomous underwater vehicles (AUVs) have gained momentum in recent years, and a special type of AUV, the robotic fish, has become a significant topic, with a superior maneuverability to traditional AUVs. In this paper, a prediction strategy for the hydrodynamic performance of a robotic fish to analyze undulatory swimming behaviors is proposed. The two-dimensional robotic fish model for computational fluid dynamics (CFD) simulations is constructed, and a dynamic network method is applied to orient the generated network based on the wavy motion. For the thrust force of the fin, a body traveling wave is derived. In the simulations, the effects of kinematic parameters such as flapping frequency and speed on swimming efficiency and drag are analyzed, and thrust force production, power expenditure, and overall efficiency of swimming are examined. Later, a deep learning-based prediction model is designed from the obtained parameters, and force predictions are performed. Long short-term memory (LSTM)-, convolutional neural network (CNN)-, and gated recurrent network (GRU)-based time series prediction models are used, and their variations are compared. In these experiments, while the CNN-GRU achieves the higher prediction performance for the root mean square error, with 0.0228, other approaches give a lower performance, between 0.0233 and 0.0359. The proposed method demonstrates a superior performance in CNN and LSTM models and exhibits lower prediction errors. Full article

Ensuring efficient heat transfer to maintain optimal system performance is crucial in modern electronics owing to the rise of artificial intelligence. In the last few decades, scholars have explored various strategies for enhancing electronic device thermal management, focusing on the effects of fin shape, dimension, and spacing on heat transfer efficiency. Recent advancements in additive manufacturing have enabled fabrication of complex geometries, such as triply periodic minimal surfaces (TPMSs), which represent promising alternatives to conventional designs. This study presents a comparative analysis of the thermal performance and fluid flow characteristics of two foam TPMS-based (gyroid and primitive) heat sinks with wavy fins made using aluminum foam. COMSOL Multiphysics version 5.1, employed along with the implemented finite element method, was used to simulate convective heat transfer, pressure drop, the Nusselt number, and thermal performance at different fluid velocities along the length of a channel. The foam structure was heated by a copper plate, and the Nusselt number was evaluated over porosity levels from 0.1 to 0.9. A porosity between 0.5 and 0.7 offers the best balance of cooling performance and pumping power. Foam TPMS heat sinks, particularly those with a gyroid structure, provide enhanced thermal dissipation owing to their high surface area-to-volume ratio and interconnected geometry. Our findings confirm that TPMS heat sinks have promising potential for use as alternatives to conventional wavy designs for advanced thermal management applications. Full article

This study explores the optimization of wavy-slit fins in the indoor units of air conditioners that use low-global-warming-potential refrigerants, with a focus on the interactions between slit length, width, and height. A response surface method was employed to analyze the trade-offs between thermal performance and pressure loss, and numerical optimization was performed using two objective functions: pumping power and volume goodness factor (Gv). The results demonstrated that optimizing the slits’ geometry significantly enhanced overall performance. For pumping power, a minimum point was observed near the design boundaries, which underscores the critical role of geometric interactions. The flow and temperature field analysis under fixed heat-duty conditions revealed substantial flow separation caused by the slits, enhanced mixing between the upper and lower surfaces, and a reduction of up to 2.05% in pumping power. In contrast, the Gv optimization model exhibited a more uniform flow, reducing flow separation beyond the pipe and improving the Gv by 1.85%, although it led to an increase in pumping power. These findings highlight the potential that tailored slit fin designs have to achieve a balanced enhancement in heat transfer and aerodynamic performance, offering valuable insights for the development of efficient, low-environmental-impact air conditioning systems. Full article

Aluminium plate-fin heat exchangers are widely used in automotive, aerospace, and other industrial applications. Extensive research has been conducted on these coolers, yet accurate predictive tools for their thermo-hydraulic performance are still lacking, due to the wide variety of geometric parameters and working fluids involved. This work proposes an original approach based purely on physical principles and established models, combining detailed numerical models for the extended surfaces and manifolds, with global models aimed at accurately evaluating overall head losses and heat transfer rates in plate-fin heat exchangers. Extended surfaces are studied by means of computational models of unitary fin modules under fully developed flow conditions. Entrance effects are analysed through dedicated numerical models. Numerical results on extended surfaces are extended to whole heat exchangers by global models for heat transfer and head losses, based on the $\epsilon -\mathrm{NTU}$ method and the Darcy–Weisbach equation, respectively. The proposed approach is presented and validated through the analysis of a case study comprising several heat exchangers featuring different geometries and working fluids. Numerically derived heat transfer rates and head losses are compared with experimental data showing maximum deviations of ±20% for most of the tested configurations, highlighting the strength of the proposed modelling methodology. Full article

Evolutionary algorithms are a large class of optimization techniques inspired by the ideas of natural selection, and can be employed to address challenging problems. These algorithms iteratively evolve populations using crossover, which combines genetic information from two parent solutions, and mutation, which adds random changes. This iterative process tends to produce effective solutions. Inspired by this, the current study presents the results of thermal variation on the surface of a wetted wavy fin using a genetic algorithm in the context of parameter estimation for artificial neural network models. The physical features of convective and radiative heat transfer during wet surface conditions are also considered to develop the model. The highly nonlinear governing ordinary differential equation of the proposed fin problem is transmuted into a dimensionless equation. The graphical outcomes of the aspects of the thermal profile are demonstrated for specific non-dimensional variables. The primary observation of the current study is a decrease in temperature profile with a rise in wet parameters and convective-conductive parameters. The implemented genetic algorithm offers a powerful optimization technique that can effectively tune the parameters of the artificial neural network, leading to an enhanced predictive accuracy and convergence with the numerically obtained solution. Full article

Energy storage technology provides a new direction for the utilization of renewable and sustainability energy. The objective of this study is to introduce a novel, wavy, longitudinal fin design, which aims to improve heat transfer in the melting process of a Latent Heat Thermal Energy Storage (LHTES) unit. The main goal is to mitigate the negative effects caused by the refractory zone at the end of the melting phase. A two-dimensional numerical model of LHTES unit is established by using the enthalpy porosity method and verified by experimental data. Through the quantitative comparison between the traditional rectangular fin and the innovative wave fin, the influence of wave fin on the heat transfer mechanism in the heat storage process is revealed. The results show that the average heat storage rate of five and six wave fins is 3.70% and 12.98% higher than that of conventional rectangular fins, respectively, and the average temperature response of six wave fins is 17.78% higher than that of conventional rectangular fins. The addition of the wave fin weakens the negative effect of the refractory zone, but prolongs the heating time of the initial melting point. Full article

The impact of convection and radiation on the thermal distribution of the wavy porous fin is examined in the present study. A hybrid model that combines the differential evolution (DE) algorithm with an artificial neural network (ANN) is proposed for predicting the heat transfer of the wavy porous fin. The equation representing the thermal variation in the wavy porous fin is reduced to its dimensionless arrangement and is numerically solved using Rung, e-Kutta-Fehlberg’s fourth-fifth order method (RKF-45). The study demonstrates the effectiveness of this hybrid model, and the results indicate that the proposed approach outperforms the ANN model with parameters obtained through grid search (GS), showcasing the superiority of the hybrid DE-ANN model in terms of accuracy and performance. This research highlights the potential of utilizing DE with ANN for improved predictive modeling in the heat transfer sector. The originality of this study is that it addresses the heat transfer problem by optimizing the selection of parameters for the ANN model using the DE algorithm. Full article

The microchannel heat sink has been recognized as an excellent solution in high-density heat flux devices for its high efficiency in heat removal with limited spaces; however, the most effective structure of microchannels for heat dissipation is still unknown. In this study, the fluid flow and heat transfer in high-temperature wavy microchannels with various shaped fins, including the bare wavy channel, and the wavy channel with circular, square, and diamond-shaped fins, are numerically investigated. The liquid metal-cooled characteristics of the proposed microchannels are compared with that of the smooth straight channel, with respect to the pressure drop, average Nusselt number, and overall performance factor. The results indicate that the wavy structure and fin shape have a significant effect on the heat sink performance. Heat transfer augmentation is observed in the wavy channels, especially coupled with different shaped fins; however, a large penalty of pressure drops is also found in these channels. The diamond-shaped fins yield the best heat transfer augmentation but the worst pumping performance, followed by the square-, and circular-shaped fins. When the Re number increases from 117 to 410, the Nu number increases by 61.7% for the diamond fins, while the ∆p increases as much as 7.5 times. Full article

The present research examines the steady, one-dimensional thermal distribution and heat transfer of a wavy fin. This heat transfer analysis considers convective effects as well as temperature-dependent thermal conductivity. Furthermore, a novel implementation of a neural network with backpropagated Levenberg–Marquardt algorithm (NN-BLMA)-based machine learning intelligent strategies is provided to interpret the heat transfer analysis of a convective wavy fin. The non-linear ordinary differential equation (ODE) of the study problem is converted into its non-dimensional form using the similarity transformation technique. The dimensionless equation obtained is then numerically explored via the Runge–Kutta–Fehlberg scheme. A data set for varying the pertinent parameters is generated, and an artificial neural network model is designed to estimate the heat transfer behavior of the wavy fin. The effectiveness of the proposed NN-BLMA is subsequently endorsed by analyses using a regression model, mean square error, and histograms. The findings of comprehensive computational parametric studies illustrate that the presented technique, NN-BLMA is an effective convergent stochastic numerical solver employed for the heat transfer model of the convective wavy fin. The wavy fin’s temperature dispersion optimizes as the thermal conductivity parameter rises. Heat transfer rate is higher in wavy fin compared to rectangular fin. Full article

As a promising new power source, the proton exchange membrane fuel cell (PEMFC) has attracted extensive attention. The PEMFC engine produces a large amount of waste heat during operation. The excessive temperature will reduce the efficiency and lifespan of PEMFC engine and even cause irreversible damage if not taken away in time. The thermal management system of the PEMFC plays a critical role in efficiency optimization, longevity and operational safety. To solve the problem of high heat production in the operation of the PEMFC, two approaches are proposed to improve the heat dissipation performance of the radiators in thermal management systems. Three kinds of nanofluids with excellent electrical and thermal conductivity–Al₂O₃, SiO₂ and ZnO– are employed as the cooling medium. The radiator parameters are optimized to improve the heat transfer capability. A typical 1D thermal management system and an isotropic 3D porous medium model replacing the wavy fin are constructed to reveal the effects of the nanofluid and the parameters of the radiator performance and the thermal management system. The results show that all three kinds of nanofluids can effectively improve the heat transfer capacity of the coolant, among which the comprehensive performance of the Al₂O₃ nanofluid is best. When the mass flow rate is 0.04 kg/s and the concentration is 0.5 vol%, the amount of heat transfer of the Al₂O₃ nanofluid increases by 12.7% when compared with pure water. Under the same conditions, it can reduce the frontal area of the radiator by 12%. For the radiator, appropriate reduction of the fin pitch and wavy length and increase of wave amplitude can effectively improve the spread of heat. The use of fin parameters with higher heat dissipation power results in lower coolant temperatures at the inlet and outlet of the stack. The performance of the radiator is predicted by the two model-based approaches described above which provide a reliable theoretical basis for the optimization of the thermal management system and the matching of the components. Full article

Based on the bionic design of the humpback whale fin, a passive flow control method is proposed to obtain greater flapping lift by applying the wavy leading edge structure to the straight symmetrical flapping wing. The leading edge of the conventional flapping wing is replaced by the wavy shape represented by regular trigonometric function to form a special passive flow control configuration imitating the leading edge of the humpback whale fin. The dynamic aerodynamic performance and flow field characteristics of straight wing and wavy leading edge flapping wing with different parameters are compared and analyzed by CFD numerical simulation. The simulation results show that the wavy leading edge structure changes the flow field of the baseline flapping wing and reduces the pressure on the upper surface of the flapping wing during the process of downward flapping, thereby increasing the pressure difference between the upper and lower surfaces of the flapping wing and increasing the lift. The sensitivity analysis of the design parameters shows that in order to obtain the maximum lift coefficient while losing the least thrust, the smaller amplitude should be selected on the premise of selecting the smaller wavelength. Among the configurations of different design parameters calculated in this paper, the optimal wavy leading edge flapping wing configuration increases the time average lift coefficient by 32.86% and decreases the time average thrust coefficient by 14.28%. Compared with the straight wing, it has better low-speed flight and can withstand greater take-off weight. Full article

Increases in power density and thermal efficiency of a highly efficient gas turbine engine motivate an ever-mounting turbine entry temperature. The combined metallurgical and cooling advancements ensure the structural integrity of a gas turbine rotor blade that spins at high rotor speeds in a gas stream with temperatures above the melting point of the blade material. The cooling performances promoted by a variety of heat transfer enhancement methods typical of the coolant channels of the leading edge, the mid-chord region, and the trailing edge of a gas turbine rotor blade are reviewed. The manifested rotational effects on the aerothermal performances of impinging jets and swirl chambers for leading-edge cooling, multi-pass ribbed, dimpled, and/or wavy channels over the mid-chord region, as well as pin fin and latticework narrow ducts in the trailing edge of a gas turbine rotor blade, are summarized and cross-examined. Research orientations for future cooling studies aimed at preventing the development of hot spots in a gas turbine rotor blade are recommended. Full article

In the paper, experimental analyses of the free convection heating transfer in a flat wavy-fin heat exchanger with the dimensions of 500 × 500 mm were investigated. The experimental reserch mainly included determining the average heat flux and heat-transfer coefficient for two selected types of finned heat exchangers. First, tests were conducted for exchangers without considering the so-called ’chimney’ effect; these tests will be treated as reference studies. Then, experiments for specially designed ’chimneys’ over the exchanger with heights of 350, 850, and 1350 mm, respectively, were carried out again. The analyses were performed for an average temperature difference between the heat-exchange surface and the environment in the range of 18 to 55 K. The experimental results demonstrated that, compared to the exchanger without a chimney, the addition of a chimney significantly affects the improvement in the thermal performance of the heat exchanger under natural convection conditions. Regarding the variant without a chimney, when a chimney is used with the highest height of 1350 mm and a maximum temperature difference of 55 K, the average heat flux increases by approximately 450% and the average heat-transfer coefficient is approximately 10 times higher. The heat exchanger characterised by lower airflow resistance showed higher values of average heat flux of 5 to 45% in the Rayleigh number range of 25 to 180. Studies have indicated that in some cases, a simple modification of the geometry of the heat exchanger leads to significant improvements in thermal performance and, in extreme cases, to the elimination of supporting equipment such as fans. Full article