Heat Transfer最新文献

The present work focuses on the influence of continuous and interrupted fins on laminar natural convection above a heat sink with different fins' arrangements. The hydraulic and thermal performances of a three-dimensional model of the heat sink were simulated using ANSYS Fluent software based on the finite volume method. The dimensions of the heat sink were 305 mm in length and 100 mm in width, while the fin height was 17 mm, and the fin spacing was 9.5 mm. Various power supplies were applied to the heat sink (20, 40, 60, 80, 100, and 120 W) to investigate the effect of different ranges of heat sink performance. Different fins' configurations were tested, including straight-fin, interrupted with different angle inclinations (30°, 45°, and 60°), and staggered arrangements with an angle of inclination of 60°. The results showed that the increase in the interruption length leads to an increase in the heat transfer (HT) rate. Moreover, five interruptions with a length of 30 mm lead to an HT rate of 22.3% as compared with continuous fins. The inclination of 60° gave the optimum HT rate. Furthermore, there will be a weight reduction of 47% for the optimum HT rate. An empirical correlation was developed to relate the Nusselt number to the Rayleigh number and inclination angle for interrupted rectangular fins at angles of 90°, 60°, and 45°, providing a robust predictive tool for assessing thermal performance. Furthermore, the current numerical and experimental results demonstrated an 89.5% concordance in the average temperature difference, with a divergence of less than 4.68% from existing literature.

A fine-tuned pattern net artificial neural network (PNANN) is explored for design of porous ceramic matrix (PCM) based burner by using classification model. The PNANN is attempted to fine-tune by comparing two different performance functions: mean squared error and sum absolute error. Three different numbers of hidden neurons are also tested while using scaled conjugate gradient as training algorithm. The data for the classification model is obtained by simultaneously solving the governing equations of two phases for the porous ceramic matrix (PCM) based burner. Different values of two critical parameters are used in the numerical model. The critical parameters considered for influencing the performance of the PCM based burner are: convective coupling and extinction coefficient. Radiative heat flux is also incorporated in the numerical model by solving radiative transfer equation by discrete transfer method. Based on the difference between the temperature profiles of the two phases (solid and gas), binary array are constructed and used in the classification model. Ten different classes of data signify ten different regime of operation, each having a unique range of values for the critical parameters. All PNANNs with performance function mse are able to give correct identification above 41.3% and upto 81.1%.

This study presents an in-depth analysis of mixed convection flow through a porous medium incorporating the effects of internal heat generation and heat absorption. The novelty of this study lies in the combined evaluation of localized heat sources, chemical reactivity, and magnetohydrodynamic (MHD) influences within a single porous configuration—an approach rarely addressed collectively in prior work. The governing equations, expressed as nonlinear, dimensionless ordinary differential forms, are solved using the regular perturbation method. The results reveal the combined influence of these factors on velocity, temperature, and concentration profiles, offering insights applicable to engineering applications such as advanced cooling systems, filtration processes, fuel cell design, and biomedical devices like blood purification units.

This study investigates the thermal performance of a thermosyphon through experiments, focusing on optimizing operational parameters and understanding transient behavior. A two-phase thermosyphon finds wide applications across various engineering domains, with its internal vapor–liquid phase change and flow dynamics being crucial factors influencing heat transfer efficiency. A thorough analysis of the heat transfer mechanism in thermosyphons (2 m in length) designed for cooling nuclear fuel storage, particularly under different operating conditions, is essential for optimizing their thermal design and performance. In this study, heat loads (300–600 W), filling-ratio (40%–100%), operating pressure, and inclination angle (60°−90°) of the thermosyphon are varied to analyze its performance of heat transfer in terms of transient temperature variation and thermal resistance. The results indicate that among the tested filling-ratios, a 60% filling-ratio is optimal for efficient thermosyphon operation. Furthermore, the thermal resistance decreased with higher heat loads applied to the evaporator, demonstrating an enhanced heat transfer. The presence of non-condensable gases (NCGs) is found to increase the evaporator-to-condenser temperature difference, impeding performance; however, their removal improves startup behavior and overall heat transfer efficiency. This parametric and methodological analysis provides comprehensive insights into the role of operational conditions in thermosyphon performance. The findings can be applied to optimize passive cooling systems in electronics, energy storage, and nuclear safety applications.

This study focuses on understanding the system's response to gravity modulation with two frequency components, characterized by both sinusoidal (sine wave) and non-sinusoidal (square, triangular, and sawtooth) waveforms, on three-component convection, considering a viscoelastic fluid modelled using an Oldroyd-B fluid. We apply the Venezian approach to evaluate the Rayleigh number, its corrected form, and the wave number by deriving a five-mode Lorenz model to investigate the onset of convection. A nonlinear analysis is conducted to investigate the dynamics of heat and mass transfer by solving an extended eight-mode Lorenz model, capturing higher order interactions. The onset of convection and the transport properties were observed to be influenced by combinations of sinusoidal and non-sinusoidal waveforms. This study optimizes convection-driven systems subjected to external periodic forcing by offering a more comprehensive understanding of convective instabilities in viscoelastic fluids.

A numerical study is carried out to investigate the flow and heat transfer of a viscoelastic fluid impinging obliquely over a circular stretching cylinder. Using the continuity, momentum, and energy equations, the problem is expressed as a set of partial differential equations with the proper boundary conditions. Normalized variables and similarity transformations reduced the governing equations into a system of transformed nonlinear ordinary differential equations, which is simulated numerically by employing a second-order accurate implicit finite difference scheme. The numerical method is validated by comparing the results with previously published results. A comparative analysis of the cylinder and sheet is presented graphically to show the impact of various involved parameters on the different aspects of fluid motion and heat transfer against the similarity variable. Deborah number improves the axial velocity up to $��\; �0.78�\; �\%�$, while the time-retardation parameter reduces the tangential velocity up to $��\; �18�\; �\%�$. The nonlinear radiative heat flux enhances the temperature distribution up to $��\; �0.91�\; �\%�$. Axial and tangential velocities are large in magnitude over a stretching cylinder as compared with a stretching sheet. Furthermore, nonlinear radiative heat transfer is observed over the cylinder instead of the sheet.

The investigation of the unified approach of the dynamic and static slips with the Caputo–Fabrizio (CF) and Atangana–Baleanu in Caputo (ABC) fractional time-derivative models through the Isothermal heating process has been done on the incompressible and viscous fluid of the transient natural convection flow in a vertical channel. The CF and ABC Laplace transform approaches are adopted in transforming the governing equations from the time purview to the Laplace purview. The transformed governing equations are solved, and semi-analytical solutions are obtained through the inversion of the solutions from the Laplace domain to the time domain with a numerical Riemann sum approximation. The analysis of the governing parameters is presented with a graphical representation and in tabular form. Specifically, it is found that the CF and ABC temperature and velocity increase with the increment in time and relaxation time parameters. Vividly, it is perceived that the increment in the value of fractional order parameters led to the drop of heat and slowed down the flow of the fluid. It is confirmed that the position of the fluid raised pointedly near the hot and cold plates with the increment in static slips, while the fluid motion decreases with the increase in the value of the dynamic slip. It is noticeable that the values of the temperature, velocity, skin friction, and mass flux are higher in the case of the CF model than in the ABC model. Also, it is observed that the pooled impacts of the dynamic and static slips on the skin friction are higher near the hot plate than the cold plate. Similarly, it is observed that the mass flux is higher with the increment of time and Prandtl number in the case of static slips than the dynamic slip, and the collective of static and dynamic slips. Another significant observation is that the effects of the static slips on velocities are opposite to each other.

Nuclear fuel reprocessing focuses on recovering valuable materials from spent fuel and plays a crucial role in managing the closed nuclear fuel cycle. A significant by-product of this process is high-level liquid waste (HLLW), known for its intense radioactivity and potential environmental risks. Effective treatment, conditioning, and disposal of HLLW are essential. Notable equipment in this field is a Joule-heated ceramic melter (JHCM), which utilizes high-temperature ceramic melters to vitrify radioactive waste, converting it into a stable glass matrix suitable for long-term storage. Developing a numerical model for a JHCM offers valuable insights into its design, operation, and performance evaluation. This paper proposes developing a numerical model, incorporating various physical phenomena within a JHCM such as Joule heating, conduction, convection, and fluid flow along with the geometrical arrangement of the insulation and refractory layers of a JHCM and validating it using benchmark JHCM data and also with JHCM temperature data from a waste vitrification plant. Using electrical current, temperature, and velocity distributions, the melter's performance and operation are studied in preheating and heating phases. The melter's performance parameters are defined and evaluated using a numerical model. Further, the model includes suitable time-dependent property variations of different JHCM materials to evaluate the performance variation for a period of 5 years of operation. This model can be utilized for optimizing the design, operation, and performance of JHCMs meant for nuclear waste management.