Heat Transfer最新文献

Numerous applications, such as heat sinks, gas turbine blades, and various electronic components, use spine fins for heat transmission, as they transfer substantially more energy than straight fins for the same surface area. This study looks at the thermal properties of porous spine fins in totally wet condition, with an emphasis on the repercussion of temperature-sensitive thermal conductivity and a nonlinear internal heat source. A correlative analysis of cylindrical, conical, and convex parabolic spines is initiated by altering the radius along the length of the fin. Also, several conventional methods often face difficulties in providing precise solutions when addressing highly nonlinear problems. The study tackles this issue by leveraging the Hermite wavelet collocation technique. The primary factors affecting the energy field and efficiency of the fin are visually examined and physically interpreted. The findings highlight that an increase in generation number, thermal conductivity parameter, and Peclet number enhances the thermal dispersion of the fin. Conversely, an increase in the wet porous parameter, convection, and radiation parameter reduces the thermal efficiency of the fin. Among the fin structures considered, the conical fin achieves the highest efficiency. This study is particularly beneficial in the field of microelectronics, especially in the development of various micro-pin-fin designs.

The present work investigates the effects of zinc and manganese co-doped bismuth ferrite nanoparticles (BZnFMO) on the combustion behavior of a diesel engine running on a 20% blend of Terminalia bellirica biodiesel (B20). To overcome the challenges associated with biodiesel combustion efficiency and dispersion uniformity, BZnFMO nanoparticles were incorporated at concentrations of 50 ppm and 75 ppm. CTAB was used as a surfactant and TWEEN 80 as a dispersant to promote a stable and homogeneous distribution of the nanoparticles in the fuel matrix. The stability of the nanoparticle dispersion was evaluated by UV-visible spectral analysis over a period of 3 weeks, with the formulation containing 75 ppm BZnFMO and 75 ppm TWEEN 80 showing higher stability. The combustion characteristics of these nanofuels were experimentally evaluated in a single-cylinder diesel engine at three injection timings: 21°, 23°, and 25° bTDC. The addition of BZnFMO nanoparticles optimized combustion performance by increasing cylinder pressure (CP), net heat release rate (NHRR) and mean gas temperature (MGT), driven by superior catalytic activity and refined fuel atomization. At an advanced injection timing of 25°bTDC, the B20 fuel formulation containing 75 ppm BZnFMO and 75 ppm TWEEN 80 achieved superior combustion metrics, including a maximal CP (71.14 bar), highest NHRR (56.18 J/°CA), and peak MGT (1645.66°C). This study presents an innovative strategy that combines surface-modified, encoded nanoparticles with optimized injection timing to significantly improve the combustion of biodiesel in engines. This represents a significant advance over previous studies on biodiesel-based nanofuels.

The technology of thermal energy storage is an efficient method to reserve thermal energy for further use. This review paper mainly focuses on the heat transfer (HT) enhancement in phase change materials (PCMs) and evaluates the impact of fin geometry on the thermal performance of PCMs used in latent heat thermal energy storage systems (LHTESs). Fins of longitudinal, annular, spiral, and letter shapes (e.g., Y, T, and L) were categorized and evaluated according to their thermal performance and efficacy in improving the charging and discharging processes in LHTESs. Low thermal conductivity (TC) of PCMs is one of the most significant challenges facing PCMs, as it adversely affects HT efficiency during the melting and solidification processes. Advanced fin designs have shown efficacy in overcoming this issue. Letter-shaped fins significantly decrease melting duration, while spiral fins expedite the phase change process relative to traditional fins. To achieve the best thermal efficiency at the lowest possible cost, several design factors must be considered when selecting fins, such as material type, size, thickness, and distribution. The study results demonstrated the significant role that innovative fin designs play in improving TC, making them promising solutions in many applications, particularly in regulating building temperatures, cooling electronic devices, and storing solar energy.

The impact of flash evaporation on the thermal performance of a wickless heat pipe utilized in desalination applications is examined experimentally and numerically in this study. Injecting water through a jet nozzle into a wickless heat pipe at high temperatures (between 373 and 393 K) causes it to become superheated. Using a jet nozzle with a small diameter (0.4 mm), the rapid evaporation process was started. The study looks at the main factors that affect how effective quick evaporation is, such as the cooling water flow rate, the input temperature, and the feeding water's mass flow rate. A constant liquid mass flow rate of 0.00138 kg/s was used for the experiments. The two-phase flow and related heat transfer processes, such as evaporation, condensation, and phase change events, inside the straight heat pipe were modeled using computational fluid dynamics simulations. To more accurately reflect these intricate interactions, a nonhomogeneous multistage model was employed. The findings demonstrate that raising the liquid's inlet temperature increases the production of steam by excessive evaporation, which raises the condensate flow rate. It was found that the condenser's maximum output happened at 388 K. Higher condensate flow rates and inlet temperatures also increased the evaporation efficiency, which peaked at 86% at 393 K. The effectiveness of the thermal system and the validity of the numerical model were confirmed by the good connection between the experimental data and the temperature models predicted by computational thermodynamics.

This study explores the improvement of the performance of refrigeration systems by adding aluminum oxide (Al₂O₃) and zinc oxide (ZnO) nanoparticles to compressor oil and studying their impact through Response Surface Methodology. The nanoparticles increase the thermophysical characteristics of the refrigerant–lubricant mixture, which results in better cooling performance and energy efficiency. The study examines how shifting Al₂O₃ and ZnO concentrations and capillary tube lengths affect crucial performance metrics, such as net refrigeration effect, mass flow rate, work of compression, and Coefficient of Performance (COP). Experimental results, supported by mathematical models and three-dimensional response surface plots, show that the ideal nanoparticle concentrations and capillary tube lengths considerably improve system performance. A concentration of 0.15% Al₂O₃ and a capillary length of 9 mm gives the highest COP, while excessive concentrations led to agglomeration and reduced efficiency. ZnO nanoparticles improved heat absorption and dissipation, with optimal performance observed at a concentration of 0.05%. This study illustrates the capability of hybrid nanolubricants to attain maximum thermal performance and energy efficiency in refrigeration systems. The results are significant contributions to the design of next-generation refrigeration systems that reimburse contemporary energy and environmental conditions, highlighting the significance of nanoparticle concentration as well as capillary tube optimization.

A partial least squares discriminant analysis (PLS-DA) classification model is first developed for the decision support system in a porous ceramic matrix (PCM) based burner. The PCM-based burner is numerically solved for the generation of 121 pairs of gas and solid temperature profiles. The data are divided into four different classes, signifying four distinct regimes of operation of the PCM-based burner, based on the values of the extinction coefficient and convective coupling. The data are then used for the development of the classification model. The developed classification model is then used to correctly classify the operation regime of the PCM-based burner for 11 new samples. Very high values of sensitivity (1.00), specificity (0.98), and precision (0.96) were obtained for class 3, under the no noise case. The classification model is also explored for two different assignment criteria (Bayes and max) and noisy cases (2% and 5%). Very high values of the classification parameter were obtained for 2% noise case. For 5% noise case, even though the parameters of the classification model were poor, the plots can help identify the corresponding class easily for new samples.

The Falkner–Skan model is widely used to describe boundary layer flows in various engineering systems. Incorporating magnetic fields, slip conditions, and chemical reactions is critical for understanding real-world applications involving non-Newtonian fluids in porous media. This study aims to examine the combined effects of magnetohydrodynamics, radiative heat transfer, internal heat generation/absorption, dual slip (momentum and thermal), and homogeneous–heterogeneous chemical reactions on non-Newtonian fluid flow over a permeable wedge. The governing partial differential equations are transformed into a system of coupled nonlinear ordinary differential equations using similarity transformations. These equations are then solved numerically using the Runge–Kutta–Fehlberg method along with the shooting technique, implemented in Maple software. The results show that increasing the Hartmann number, slip parameters, and reaction rates suppress fluid velocity and enhance thermal gradients, while reducing the thickness of the concentration boundary layer. The Prandtl number and the radiation parameter significantly affect the thermal distribution and heat transfer rate. Surface quantities such as skin friction and Nusselt number vary meaningfully with changes in magnetic intensity and chemical activity, and the results exhibit good agreement with existing literature.

Heat and mass transport in electrically conducting fluids under magnetic fields can be better understood by examining Magneto-Oberbeck convection in a rectangular enclosure with homogeneous mass and heat fluxes along the vertical sides. It may be used in technical domains, like, geophysics, metallurgy, and electronic device cooling. Transport phenomena, flow patterns, and stability are all impacted by the interaction between buoyancy-driven stream and magnetic forces. The study's conclusions aid in the optimization of thermal management and magnetohydrodynamics-related industrial operations. The natural convection that results from the combined effects of concentration and temperature buoyancy within a rectangular cavity with uniform mass and heat flow along the vertical sides with a magnetic field is investigated analytically in this paper. Magnetic fields are used in many sectors, such as everyday technology, engineering, and medicine. Convection affects the mass and heat transport rates in the boundary layer domain, where the analytical approach is accurate. An Oseen-linearized solution is reported foe tall spaces filled with mixtures characterized by $��\; ��\mathrm{Le}�\; �=�\; �1��$, and arbitrary buoyancy ratios. The impact of changing the Lewis number is shown by a similarity solution that works for $��\; ��L�\; �e�\; �>�\; �l��$ in flows driven by heat transfer and for $��\; ��\mathrm{Le}�\; �<�\; �1��$ in flows driven by mass transport. Graphical analyses of the solutions are performed for varying Rayleigh numbers, buoyancy ratios, and Chandrasekhar numbers.

The present study intends to examine how the viscoplasticity of the liquid affects heat transfer characteristics in a wavy channel that contains metallic porous blocks, taking into account the effect of conductive heat flow within the finite wall thickness. Additionally, the second aim of this initiative is to establish an Artificial Neural Network (ANN) framework capable of forecasting the thermohydraulic performance factor and average Nusselt number based on different combinations of thermal and rheological parameters. To examine the flow field, conductive heat flux field, conductive heat lines, average Nusselt number, and performance factor, parameters such as the Darcy number, Bingham number, and thermal conductivity of the solid wall are varied within a justified range. It turns out that the flow field is significantly influenced by its fluid's viscoplastic characteristics, which allow the vortex to disappear at larger Bingham numbers. The average Nusselt number and performance factor show a monotonic increase with increasing Bingham numbers at higher Darcy numbers. The same exhibits a nonmonotonic tendency for lower Darcy numbers. Interestingly, the performance has been shown to have a value larger than unity, indicating that the current design has promising potential for use in applications involving thermal management of heat. The current ANN model predicts the average Nusselt number and performance factor with great precision. This endeavor represents the first exploration of how the viscoplastic properties of the liquid affect heat transfer characteristics within a wavy channel with metallic porous blocks, as well as the impact of conductive heat flow in solid walls.