International Journal of Thermofluids最新文献

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.

This study analyses the properties of ternary and tetra hybrid nanofluids using the Blasius Rayleigh–Stokes time dependent variable model. The aim is to provide a model for solar aeronautical engineering. The study focuses on the behavior of the hybrid nanofluids under various conditions and the effects of variable viscosity and variable thermal conductivity on their performance. Copper (Cu), Zirconium dioxide (ZrO₂), Aluminium Oxide (Al₂O₃) and Iron Oxide (Fe₃O₄) are the four nanoparticles examined in this study with the mixture of ethylene glycol (EG) as the base fluid. The governing Partial Differential Equations (PDEs) were reduced to a non-dimensional equation with the aid of the Blasius Rayleigh–Stokes variable resulting into a set of coupled nonlinear Ordinary Differential Equations (ODEs). The resulting non-linear ODEs together with their boundary conditions (BCs) were solved numerically using Homotopy Analysis Methods (HAM). The results showed that the tetra hybrid nanofluid flow has enhanced velocity when compared to the ternary nanofluid as a result of the presence of magnetite in the fluid. The magnetite nanoparticles are found to be highly soluble in Ethylene glycol due to steric and electrostatic interaction between the particles arising by the surface adsorbed molecules and associated positive charges. The use of ternary and tetra hybrid nanofluids also showed improved thermal conductivity and stability. These findings have significant implications for the design and development of more efficient and sustainable solar aeronautics. Overall, this study provides a comprehensive analysis of the potential of hybrid nanofluids in solar aeronautical engineering and highlights the importance of considering variable properties in their design and implementation. The unique aspects of this work include the creation of a model for the installation of parabolic trough solar collector (PTSC) on solar-powered aircraft and the numerical analysis of hybrid nanofluid flow using a time-dependent variable model under the effect of variable characteristics, thermal radiation, and magnetohydrodynamics (MHD).

The objective of this article is to investigate on the natural convective MHD flow of viscous fluid with assessment of mass and heat transfer effects. The flow is confined by two parallel plates. The walls of plates are assumed to be porous. The thermal radiation effects and inclined magnetic field applications are endorsed. One plate maintains the adiabatic phenomenon. The simplified form of problem is achieved with help of dimensionless variables. The analytical outcomes for given formulated problem are obtained with help of perturbation technique. Effects of various flow parameters involving to the problem are graphically impacted. It is claimed that velocity profile enhances due to modified Grashof number. An enhancement in heat transfer is subject to increasing the radiation parameter. Moreover, concentration profile reduces due to Reynolds number.

This study delves into exploring and comparing various cooling technologies for PV panels, with a special focus on revealing the harmful effect of excessive heat absorption on solar energy efficiency. Effective temperature management and dissipation of excess heat are essential to protect the integrity of PV panels and improve power generation. With a strong emphasis on the importance of experimental setups, this comprehensive research examines the methodologies and cooling methods used across a wide range of experimental studies, illustrating the complexities of data collection and analysis. Supported by schematic illustrations depicting various experimental setups, this study demystifies the complexities inherent in distinct PV cooling methods. Furthermore, the research extends beyond experimentation to include a comprehensive examination of the energy and economic aspects associated with various cooling technologies, including the calculation and presentation of energy efficiency ratios. It is worth noting that the results confirm the superiority of passive cooling techniques, including heat sinks (43 %), PCM (25), evaporation techniques (36 %), and spray cooling systems (54 %), in contrast to active cooling methods, as indicated by their net energy efficiency ratios. Passive cooling is advantageous for its low maintenance and cost-effectiveness, whereas active cooling, though effective in hot climates and enhancing PV efficiency, incurs higher initial costs and maintenance requirements. The novelty of this research lies in its detailed classification of cooling techniques and the specific materials used for each method, coupled with a thorough examination of the measuring tools employed. Furthermore, this study includes a comprehensive comparative analysis based on energy and economic aspects, alongside the advantages and disadvantages of each cooling technique. These invaluable insights hold the potential to revolutionize the development of efficient and dependable cooling strategies for PV systems, thereby elevating the feasibility and sustainability of solar energy as a pivotal cornerstone in our future energy landscape.

This study presents numerical simulations of dropwise condensation on inclined chemically heterogeneous substrates in pure vapor atmosphere. To capture the dynamics of this process, a one-sided condensation model with a disjoining pressure is employed that incorporates the effects of gravity and chemical heterogeneities. We consider surfaces decorated with an array of square patches which are more hydrophilic compared to the rest of the surface, which act as nucleation, inception regions over which droplets form and grow and ultimately depin once their size becomes sufficiently large. The impact of the size and of the inception regions and the angle of inclination on the dynamics is considered, revealing significant qualitative and quantitative differences between the cases. For cases with purely structured substrates, it is observed that, as the number of inception regions increases, the condensation process transitions from steady to unsteady, with the critical number of inception regions increasing with the inclination angle increases. Further insight is provided by analyzing the snapshots of the liquid phase on the substrate, revealing the formation of liquid streaks or films, which influence both the dynamics of the flow and the total liquid volume on the substrate. The inclusion of random impurities on the structured substrate dramatically impacts the condensation dynamics, which is found to hinder the formation of liquid film, leading to a decrease in the total liquid volume generated on the substrate.

The development of electronic devices is accompanied by the generation of significant heat. A novel plate-fins design with various orientation angles of 30°, 35°, 37.5°, 40° and 45° was studied. The plate-fins design aims to boost the performance by increasing the surface area and redirecting airflow towards the heat sink plate. The experimental results obtained by this work were employed to validate the numerical results for pin-fins heat sink. A three-dimensional computational domain was investigated using ANSYS Fluent 19.1. The air flow was turbulent and modelled using k-ω turbulent flow. The plate-fins with an orientation angle of 37.5ᴼ exhibit the optimum hydrothermal performance among other configurations. Equally, several optimisation parameters including the number of rows, the diameter and thickness of the pins and the width of the plate-fins were investigated. It was observed that the heat sink with two rows of plate-fins outperformed other designs. This configuration resulted in a significant reduction of 2 % in hot spot temperature and a notable reduction of 60.8 % in pressure drop.