International Journal of Thermofluids最新文献

This study examines the heat transfer enhancement and pressure drop of Al₂O₃ nanofluid in deep dimpled tubes in both longitudinal and circumferential directions. It explores mechanisms that improve the thermal performance of this novel tube geometry. Experiments were conducted using plain and deep dimpled tubes under laminar flow with Reynolds numbers from 500 to 2250, a constant heat flux of 10,000 W/m², and nanofluid concentrations from 0.1 wt% to 1 wt%. The findings indicate that local velocity enhancement, vortex generation, and flow rotation and mixing are the three main mechanisms that improve the thermal performance of deep dimpled tubes. The results demonstrate that a deep dimpled tube with 1 wt% nanofluid can increase the convective heat transfer coefficient by up to 3.42 times compared to a smooth tube at Re = 2250. At this Reynolds number, the Nusselt number reaches a maximum of 41.80, and the friction factor ratio increases by only 1.82. Additionally, circumferential analysis reveals how dimple-induced vortices enhance heat transfer. The results also indicate that the tube geometry modification changes the flow regime zones, allowing turbulent flow at lower Reynolds numbers near Re = 2000, as identified by Nusselt number and friction factor plots. The deep dimpled tube has a low improvement penalty, with the highest friction factor of 0.38 at Re = 500 and high thermal enhancement, resulting in a performance evaluation criterion (PEC) of up to 2.80 in the studied region. However, the deep dimpled tube is unsuitable for Reynolds numbers below 1000. For higher velocities, replacing simple tubes with deep dimpled tubes in traditional heat exchangers is highly recommended.

In the current work, flow of 2-D MHD Walters'B viscoelastic fluid is discussed in the existence of elastic deformation, Cattaneo–Christov Heat Flux Model (CCHFM), heat source, Newtonian heating, viscous dissipation and porous medium. Dimensionless equations that are in charge of the problem's analysis are produced by using the suitable similarity transformation, and Optimal Auxiliary Functions Method (OAFM) is employed to solve them. In the ongoing investigation, the main results are decreasing behavior of temperature profile for the thermal relaxation parameter and elastic deformation parameter, while the reverse effect is noticed while increasing the Weissenberg number and porosity parameter. Our findings reveal significant insights into the fluid dynamics and heat transfer characteristics. Integrating the Cattaneo–Christov heat flux model and elastic deformation analysis in Walters'B viscoelastic fluid flow having its importance in polymer processing, aerospace engineering and waste treatment systems.

This description focuses on how the magnetic field affects mass and heat transfer in a hybrid nanofluid (Hnf) between two parallel, rotating plates. By dispersing aluminum oxide (Al₂O₃) and molybdenum disulfide (MoS₂) nanoparticles (NPs) in ethylene glycol (EG), a hybrid nanofluid (Hnf) is created. This research aims to analyze the heat and mass transfer characteristics in the flow of a hybrid nanofluid (MoS₂-Al₂O₃/EG) between two rotating parallel plates under the influence of a magnetic field. Furthermore, the statistical technique of response surface methodology (RSM) has been employed to optimize the parameters of velocity, temperature, and concentration of the nanofluid within the flow region bounded by the rotating plates. Dimensionless differential equations have been calculated and checked using the Homotopy perturbation method. This study introduces a novel approach by utilizing the RSM method to identify optimal points for velocity and temperature parameters of nanofluids between two stretching plates for the first time. Additionally, the article innovatively applies the exact HPM method to validate dimensionless linear and non-linear coupling equations. As the Reynolds number and the suction/injection coefficient of nanofluids flowing between two plates under tension increase, the results indicate a decrease in the velocity field. This decrease in velocity field can be attributed to the reduction in fluid diffusion as viscous forces diminish with varying Reynolds numbers. The ideal temperature distribution for nanofluids flowing between two parallel plates occurs when they are uniformly dispersed at the midpoint between them. As the distance from the initial point of nanofluid entry to the end of the plates increases, along with the vertical distance from the bottom plate, the temperature gradient diminishes, reducing the thickness of the thermal boundary layer. The velocity gradient and the rate of heat flux transfer between the nanofluid and plate rise by 34 % when the volume percentage is raised from 1 % to 5 %.

Present study explores mixed convection characteristics in a long horizontal channel subjected to multiple periodically distributed flow modulators. The flow modulators are represented by oscillating blades placed along a centerline of the channel whose lower and upper walls are kept at constant high and low temperatures respectively. In replicating the blade oscillation, moving mesh approach has been adopted within Arbitrary Lagrangian–Eulerian (ALE) framework for a representative periodical unit. The corresponding non-dimensional governing mass, momentum and energy conservation equations have been solved through Galerkin finite element solver for a wide variations of modulator's dynamic condition (oscillating frequency and maximum angular displacement) for different fluids represented by Prandtl number. Heat transfer performance of the system has been demonstrated in terms of spatially-averaged transient as well as time-averaged Nusselt number while qualitative analysis of fluid flow and thermal field has been presented as streamline and isotherm plots. Present study indicates that the time averaged Nusselt number undergoes significant variation with blade oscillating frequency and maximum angular displacement depending on both the Prandtl number and Reynolds Number. Power spectrum analysis obtained through Fast Fourier Transformation (FFT) of the imposed blade frequency and induced thermal frequency reveals different correlation depending on the blade frequency. Blade friction power requirement has been found to increase at higher blade frequency as well as maximum angular displacement. However, contrary to power consumption, increase in frequency does not result in a significant rise in heat transfer. Consequently, specific heat transfer decreases at higher blade oscillating frequency and maximum angular displacement.

The need for desalination is expected to evolve, and interests in novel techniques to enhance thermal desalination are developing. Research studies on ultrasonic atomization for desalination application has been observed in the last few years. Hence, this study aims to examine humidification process enhancement using ultrasonic atomization and interaction of atomized droplets with hot air in the humidifier. In the Humidification and Dehumidification (HDH) desalination system examined, the humidifier is equipped with a single ultrasonic atomizer unit which operates continuously with preheated hot air entering the humidifier chamber. The system is investigated for different air flowrates (40 – 100 LPM) and hot air temperatures (40, 50, and 60 °C). The average relative humidity at the humidifier outlet was maximum reaching 94 % for the highest flowrate. The results indicate that increasing hot air temperatures have significant improvement in droplet evaporation which causes higher relative humidity at the outlet, and increasing hot air flowrates have significant impact on the faster response of the humidification process to reach equilibrium.

Waste heat recovery involves capturing and reusing heat from a system that would typically be discarded. In industries like manufacturing and power generation, this method is gaining importance due to its potential to reduce greenhouse gas emissions and fuel consumption. This paper discusses a novel heat exchanger system that utilizes gravity to extract heat from exhaust gas, providing an alternative solution to the difficulties encountered by the conventional heat recovery techniques. Moreover, by adding both the ORC (Organic Rankine Cycle) and LNG (Liquefied Natural Gas) cycle to this system, excess heat can be used more efficiently, allowing for better energy recovery. The gravity-pipe heat exchanger and two cycles are used in the combined energy recovery system to extract useful heat from a low-grade waste stream. Energy performance is measured by using heat transfer analysis, energy efficiency testing, and exergy analysis followed by a comprehensive parametric analysis. To identify the optimal operating parameters for maximizing energy recovery and minimizing energy losses including economic analysis of GPHE with conventional HE, mathematical optimization models are developed. The heat exchanger demonstrates good effectiveness, close to 52.3 %, at an optimum temperature of approximately 275 °C to 280 °C for a 35 kg/s air flow rate. The ORC cycle is most efficient with optimum operating condition when pentane's mass flow rate is 3.3 kg/s. The maximum work output is obtained at a condenser pressure of 0.21 MPa, reaching 280 kW. When using pentane, the cycle's maximum efficiency is 36.8 %. However, the system's exergy efficiency drops by 4.94 % when the pinch temperature goes up by 7 °C. The output of ORC turbine increases from 220 kW to 240 kW, and the output of LNG turbine increases from 25 kW to 40 kW, as the condenser pressure rises. From economic analysis it's attain that the designed GPHE is economically viable for waste heat recovery from dirty exhaust gas. This paper develops a theoretical model to evaluate several cycles for extracting energy from waste heat, which could reduce fuel use and greenhouse gas emissions in industries.

Electricity transmission line is the most significant way of power transmission. Regular detection of it can find and eliminate its defects and hidden dangers in time and prevent major accidents, which is of great significance to the power system. In order to find the problems in the electricity transmission line in time, this paper applied the data mining algorithm to the intelligent detection method of electricity transmission line equipment defects. An electricity transmission line equipment defect intelligent detection and monitoring system was constructed, and the differences between clustering analysis image recognition technology in data mining algorithms and the XGBoost algorithm were analyzed. The results showed that compared with using XGBoost algorithms, the highest accuracy rate of the intelligent detection method of electricity transmission line equipment defects using data mining algorithm in the detection results was 98 %, which was generally higher than that of XGBoost algorithms, and could reduce the consumption of time. From the perspective of replication rate, the overall average value of XGBoost algorithms was 52.38 % and the overall average value of data mining algorithms was 7.63 %. The replica rate of data mining algorithm was much lower than that of XGBoost algorithm and the performance of fault signal detection was better. Therefore, the application of data mining algorithm to the intelligent detection method of electricity transmission line equipment defects can be more suitable, thus significantly improving the efficiency of all aspects. At the same time, the method has the advantages of simple operation, fast, reliable and not affected by region.

This study investigates Williamson fluid with stratification aspects through an inclined medium with radiative effects and with consideration of transversally applied magnetic field. Additionally, the study involves novel contribution of thermal generating source and chemically reactive species. Modelling is conceded by incorporating conservation laws in view of ordinary differential setup after employing similar variables. Afterwards, numerical simulations through shooting and Rk-4 procedures are executed to inspect the behavior of flow and thermosolutal distributions versus variation in key parameters. Subsequently, the collected data is evaluated by utilizing a multilayer perceptron-based ANN model. The input data for the heat flux, corresponding to different fluid model parameters, is trained by employing Levenberg-Marquardt paradigm and validated against numerical experiment results. The precision of the predicted data is assessed by calculating the mean squared error, determination coefficient and error rating scale. The magnitude of heat flux coefficient elevates up to 15 % in the existence of radiation effect, while depreciates up to 6 % in the presence of stratification effect. The implementation of ANN model depicts a mean square error value 1.36×10⁻³ when no heat source, which rises to 1.41×10⁻² when a heat source is present. From small values of mean squared error for testing, training and validation estimated for Nusselt number ensures the performance of developed ANN network.

Water heating with heat pumps can contribute to reduce carbon dioxide emissions and meet sustainability goals due to its high thermal efficiency, versatility in terms of alternative energy sources and thermal energy storage capability. In this study, the heat transfer of the condenser subsystem of an accumulation heat-pump water heater is analyzed by means of 2D CFD simulations. After validating the simulation methodology with benchmark natural convection problems, the influence of different geometric parameters of the condenser coil on the heat transfer is studied, which include the distance between turns and the distance from the tank wall. For each case, Nusselt number correlations in terms of Rayleigh number are found via power-law fitting. According to the CFD results, a greater coil pitch improves the average heat transfer. Moreover, a shorter distance from the tank wall generates a velocity field that laterally diverts the plume that forms around each turn. Hence, the heat transfer is enhanced because the preheating effect from downstream turns is mitigated, while the velocity gradients are strengthened. Additionally, a condenser design is proposed with geometric parameters that promote effective heat transfer, and the performance is compared against a reference design with geometric parameters that limit the heat transfer but are common in commercial solutions. The proposed geometry has a 43% increase in the Nusselt number, with respect to the reference geometry. Also, based on a dynamic simulation model of heat pump performance, it is determined that, for the same operating conditions, the proposed geometry improves the overall coefficient of performance (COP) of the system by up to 7%. These results highlight the importance of the geometric design of the condenser in heat-pump water heating systems, since they can contribute to a better overall performance and a more efficient thermal storage.

The rise in airport and airline operations has increased compelling interest in aircraft noise. The aerodynamic noise initiated by the high-lifting devices is now comparable to the aircraft engine's noise. The gurney flap, a simple and easy-to-manufactured high-lifting device is suitable to study the trailing vortex shedding and its effects on generating aerodynamic noise. In the current study, the effect of adding a gurney flap on vortex shedding around the airfoil, its effect on the airfoil's aerodynamic parameters, and its effect on the generation of aerodynamic noise were observed. A numerical simulation was carried out using ANSYS Fluent for various angles of attack at Re=300 K around an Asymmetrical Airfoil, namely NACA 66₂–015 by varying the gurney height from 1 % to 3 % of the chord of the airfoil with 0.5 % incremen steps. For aerodynamic parameters alone 2.5% h/c gurney height was found to be the optimum gurney height when the airfoil was simulated from α=-20° to α=20° with 2° increments. For NACA 66₂–015, the irregular vortex pattern is perceived at a 20° angle of attack for Re=300 K. Upon simulating the airfoil for α=20° to α=28° with 2° increments, it was observed that for all the angles of attack with increasing gurney heights increases the strength of shedding, the mean values as well as amplitudes of the aerodynamic parameters. From the Strouhal number based on the Power Spectral Density amplitude of the Fast Fourier Transform (FFT) of the immediate lift coefficient, it was presented that the highest value of the Strouhal number value and Power Spectral Density amplitude was found at α=24° for all gurney heights and larger angles Strouhal number values were found to be smaller. With the help of a logarithmic scale called Sound Pressure Level (SPL), it was found that on a clean airfoil vortex, shedding emits little to no aerodynamic noise as compared to that with the gurney. While adding the gurney flap to the airfoil, the optimum gurney height, i.e., 2.5% h/c gurney height, yielded the highest (C_L/C_D) _Max and highest aerodynamic noise. It was also found that for larger angles of attack aerodynamic noise possesses a significant far-field effect. Observing the results of the study suggests that for Micro Air Vehicles where aerodynamic noise plays a significant role smaller height of the gurney should be considered as most effective. Meanwhile, for larger Air Vehicles where aerodynamic parameters play a more important role 2.5% h/c gurney height should be considered the most effective.