Heat Transfer最新文献

This study introduces a novel Y-shaped twisted insert with trapezoidal perforations, a numerical study was performed to investigate the thermal-hydraulic performance of circular pipes equipped with Y-shaped inserts, for heat transfer enhancement in circular heat exchanger pipes. employing computational fluid dynamics (CFD) with Ansys 2022-R2 (finite volume method, k–ε turbulence model). Five geometric configurations cases (A, B, C, D, and E) variations included twisted Y-strips (twist ratios 2 or 7), and trapezoidal perforations were analyzed under constant heat flux (1000 W/m²) with air as the working fluid across Reynolds numbers (Re) range (3000–21,000). Results demonstrated significant heat transfer enhancement, with case E (twisted Y-strip, twist ratio 7, 30 trapezoidal holes) achieving a peak Nusselt number (Nu = 197.673 at Re = 21,000), a 258% increase over the plain pipe (Nu = 55.23). Thermal Performance Factor (TPF) peaked at 3.863 (Re = 3000, case E), indicating superior efficiency at lower Re. Flow resistance reduction was observed, with case E exhibiting the lowest friction coefficient (f = 0.016 at Re = 21,000). The synergistic effects of twisted geometries and perforations enhanced turbulence, fluid velocity, and heat dissipation. These findings underscore the efficacy of Y-shaped inserts with optimized twist ratios and perforations in augmenting passive thermal performance while mitigating hydraulic losses, positioning case E as a promising configuration for energy-efficient heat exchange systems. The results showed remarkable agreement with previous research on Y-shaped inserts, reinforcing the credibility of the findings, which reflect scientific consensus in the field of heat transfer.

This piece of work provides an in-depth analysis of magnetohydrodynamics (MHD) fluid flow and heat transport near a continuously moving vertical plate in the presence of nonlinear thermal radiation with convective boundary condition. A nonlinear dependence of thermal radiation on temperature enhances thermal transport, while convective boundary conditions govern heat transfer at the plate surface. The governing partial differential equations (PDEs) are transformed into ordinary differential equations (ODEs) through the application of a similarity transformation. To numerically solve these ODEs, we have used bvp4c method in MATLAB. The influences of dimensionless parameters on heat transfer and fluid flow are presented using tables and graphs. The key novelty of this study lies in analyzing the impact of nonlinear thermal radiation on MHD flow over a constantly moving vertical plate using the bvp4c method. When the fluid flows in the positive x-direction and the plate moves in the opposite direction, the coefficient of skin friction decreases. Moreover, when the direction of the fluid and the plate is the same, both the velocity and the temperature profiles increase with greater nonlinear thermal radiation. Near the wall, the temperature gradient decreases as nonlinear thermal radiation intensifies, while it increases in the free stream. The thickness of the thermal boundary layer decreases, while the thickness of the velocity boundary layer increases with increasing magnetic parameter. Similarly, when the Grashof number increases, the velocity boundary layer becomes thicker, while the thermal boundary layer tends to become thinner. However, when the Prandtl number increases, the thermal boundary layer becomes thicker, whereas the velocity boundary layer tends to become thinner. Practically, these findings aid in optimizing heat transfer in engineering applications such as cooling systems, heat exchangers, aerospace thermal protection, and biomedical devices.

Researchers are driven to explore alternative and environmentally friendly energy sources due to the significant impacts of environmental degradation. Thermal energy storage utilizing phase change materials (PCMs) has developed as a novel option for mitigating environmental pollution. This study numerically proposes an approach to enhance the energy storing and heat transmission rates of PCMs in a triangular space. Within the space, there is a rotating cylinder that maintains a consistent speed, resulting in the production of forced heat transfer. Natural convection occurs due to the thermal gradient between the space's partially hot left wall and the remaining cold walls. To achieve optimal outcomes, an investigation was performed to assess the impact of various elements on mixed convection in the given region. The elements that need to be considered are the Reynolds number Re (10–100), which represents the speed of the inner cylinder, the Darcy number represents the permeability Da (10⁻⁵–10⁻²), the Hartmann number Ha (0–100), which represents the intensity of the magnetic field, and the volumetric percentage of the nanoparticles ɸ (0–0.08). The obtained findings demonstrated a notable augmentation in heat transfer rates when the Da value increased and the position of the heated section on the left wall was altered. Conversely, the heat transmission rates decreased with a rise in Ha and ɸ. The study found that increasing the values of Ha and ɸ to their maximum levels resulted in a reduction of 20% and 15% in Nu_avg, respectively. By raising Da and shifting the heated area of the left wall lower, Nu_avg experienced a significant rise of 320% and 162.5%, respectively.

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.