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Theoretical research has been done on the hydromagnetic three-dimensional nanofluid flow across an inclined stretching sheet in the presence of Brownian motion and thermophoresis. It is taken into account that there are two different kinds of water-based nanofluids that contain copper and alumina. Three-dimensional nonlinear-type similarity transformations are used to convert the governing boundary-layer equations into a collection of similarity equations, which are then numerically solved by MATLAB. Further, results obtained in some limiting cases are compared to some results that have already been published, and it is found that there is good agreement. The problem is controlled by a number of physical factors, and the impact of these factors on different flow distributions is thoroughly examined with the help of graphs and tables. It has been observed that the nanofluid has better heat transfer conductivity than the ordinary base fluid. [ABSTRACT FROM AUTHOR]

The advances in the field of nanotechnology tends to improve the rate of heat extraction and transmission from foreseeable causes and has fascinated researchers and scientists. Furthermore, nanofluids are having a useful impact on various fields such as nuclear industries, powered lasers, chilling of microelectronic devices, solar energy capture, transformers oil cooling, and in cancer diagnosis. Hence, magnetohydrodynamic (MHD) three-dimensional bioconvective flow of nanofluid accommodating gyrotactic microorganisms over a wedge surface with zero nanoparticles mass flux boundary conditions is studied, using large Reynolds number approximation. The additional novelty of the study is the implementation of the revised Buongiorno model, which deliberates the effects of thermo-migration and Brownian diffusion of nanoparticles, together with passive control of nanoparticles fraction on the wedge surface. The self-similar form of conservation equations of energy, nanoparticle fraction, gyrotactic microorganisms, and momentum are handled numerically. T The results of the Blasius and the Hiemenz flows are retrieved as special cases of the model. It was found that the temperature of the nanofluid increases considerably when considering the nonlinear thermal radiation compared to the linear radiant heat. Increasing the strength of the Brownian diffusion increases the heat transport but reduces the mass transport. [ABSTRACT FROM AUTHOR]

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AbstractThe boundary layer fluid flow past a wedge surface occurs in various industrial processes, including wire drawing, metal foaming, polymer extraction, fiber processing, and in determining the dynamic properties (shear stress, drag) of working fluids. Theoretically, the boundary layer three-dimensional flow of a magnetized hybrid nanoliquid over a wedge surface is studied with viscous dissipation and radiation effects. The flow is due to moving wedge surface and power-law free-stream velocities. The current study unifies three different classical flow problems, namely, the Blasius flow, the Hiemenz flow, and the Falkner-Skan flow. Single-phase description of hybrid nanofluid is considered, and the problem is kept realistic by considering the experimental thermophysical properties of the nanomaterial. The governing system consists of conservation of mass, momentum, and the energy equations for hybrid nanofluids. Prandtl’s boundary layer approximations are applied to study the viscous dominant fluid regimes. The entropy equation and the Bejan number are also derived. Numerical computations of self-similar equations are obtained to explore the rheological and the heat transport features against the physical parameters. The Nusselt number and the drag on the wedge surface are computed and analyzed. Of the three classical flow problems, the maximum thickness of the momentum layer occurs for the Blasius flow problem. A minimum drag force on the wedge surface occurs for lower Hartmann number values. Furthermore, an increase in the volume fraction of the hybrid nanoparticles leads to an enhanced heat transport. The use of carbon nanotubes which has exceptional characteristics are taken into consideration in this study. This study also demonstrates the comparison on three-different classical flow problems (Blasius flow, Hiemenz flow, and Falkner-Skan flow). [ABSTRACT FROM AUTHOR]

This study presents the formulation and validation of a three-dimensional Flow Lattice Model (FLM) with application to the Hygro-Thermo-Chemical (HTC) model for analysis of moisture transport and heat transfer in cementitious materials. The FLM is a discrete transport model formulated in association with meso-mechanical models, such as the Lattice Discrete Particle Model. This enables the simulation of transport phenomena at the length scale at which the material exhibits intrinsic heterogeneity. The HTC theoretical formulation is based on mass and energy conservation laws, written using humidity and temperature as primary variables, and considering explicitly various chemical reactions, for example, cement hydration and silica fume reaction, as internal variables. In this work, the HTC formulation was extended to include the effect of temperature on the sorption isotherm. The FLM solutions were compared with those of a continuum finite element implementation of the HTC model and experimental data available from the literature; the overall agreement demonstrates the reliability of the proposed approach in reproducing phenomena such as cement hydration, self-desiccation and temperature-dependent moisture drying. [ABSTRACT FROM AUTHOR]

Due to the large bending of turbine blades, there is strong three-dimensional flow in cascade channel, the three-dimensional flow at the endwall of blades generates extremely complex heat transfer characteristics. The design concept of high heat load turbine blades, particularly comprehensive optimization of flow and heat transfer at the endwall, has gained increasing attention. In this paper, we have developed a three-dimensional endwall parameterized modeling platform based on Body-Fitting Coordinates and introduced a novel approach for streamwise direction and normal direction concerning endwall profile construction. The endwall modeling was optimized using Genetic Algorithm to obtain a modified one with low heat transfer level on the premise that the aerodynamic loss is not increased. The analysis indicates that the reduction of aerodynamic loss with the modified endwall is relatively marginal, whereas the heat transfer intensity on the endwall surface experiences a significant decrease. Additionally, employing an endwall model can effectively mitigate the lateral pressure gradient in the cascade channel, which exerts a pronounced influence on suppressing secondary vortex development in the cascade. [ABSTRACT FROM AUTHOR]

In order to study the infrared radiation characteristics of an air-breathing hypersonic vehicle powered by a scramjet, it is necessary to solve the internal and external flow field of the air-breathing hypersonic vehicle. Owing to the complexity and difficulty of solving the three-dimensional flow and heat-transfer process in a scramjet combustor, a quasi-one-dimensional calculation method was established. Utilizing zooming technology, a combination of quasi-one-dimensional simulation within the combustion chamber and three-dimensional numerical simulation elsewhere on the vehicle was employed to obtain the flow field. The accuracy of the zooming method in determining flow, heat transfer, and infrared radiation was verified through comparison with experimental data. The results show that under the flight condition of Ma = 6, the gas temperature and wall heat flux in the scramjet combustor first increased and then decreased along the flow direction. The Mach number of the plume was smaller than that of the free flow, while the velocity of the plume was slightly larger. In the wavelength range of 3–5 μm, as the azimuth angle increased, the integrated radiation intensity of the air-breathing hypersonic vehicle demonstrated a characteristic pear-shaped distribution. [ABSTRACT FROM AUTHOR]

The flow field structure of the bipolar plates is a key factor in determining the heat and mass transfer performance of proton exchange membrane fuel cells (PEMFC). To improve its performance and obtain an optimized design and fabrication method, this paper proposes a novel baffled flow field bipolar plate and successfully realizes its preparation using 3D printing technology. A PEMFC computational fluid dynamics model was established for numerical simulation, and polarization tests were also performed to verify the simulation results. The results show that the incorporation of 30°, 60°, and 90° sub-baffles helped to increase the maximum power density of the PEMFC by 3.5%, 8.4%, and 14.7%, respectively, compared to no sub-baffles. The oxygen mass transfer efficiency of the flow field with a 90° sub-baffle increased by 9.4% and 22.1% compared to the 60° and 30° sub-baffles, respectively. However, the increase in inclination angle also causes more water and heat in the flow channel to enter the membrane electrode, which hinders the further improvement of PEMFC performance. This study will provide new ideas and solutions for the flow field structure design and preparation of bipolar plates. [Display omitted] • A novel flow field structure with main and sub-baffle was designed. • Forming of metal bipolar plates with complex flow field structure by 3D printing. • The mass and heat transfer characteristics in different flow field structures were studied. • Oxygen transfer efficiency increases with increasing inclination of the sub-baffle. [ABSTRACT FROM AUTHOR]

The escalating demand for heat dissipation has prompted considerable interest in the manifold micro-pin–fin heat sink (MMPFHS) as a promising solution for high heat flux cooling applications. The two-dimensional topology of this multi-layered heat sink plays a pivotal role in organizing the three-dimensional spatial flow, consequently influencing both hydraulic and thermal performance. This study proposes and comparatively analyzes the only three rhombus-based tiling topologies applicable to MMPFHS, specifically the rhombus topology (RT), triangle hexies topology (THT), and firecracker topology (FT), all of which adhere to the principles of gapless, non-overlapping, and spatially expandable tiling topology. The relations of topological geometry and the hydraulic and thermal performances are explored and compared. And figure of merit (FOM) is also introduced to assess their overall performance. The results indicate that the overall performance of THT is predominant. When DPF = 100 μm, a = 200 μm, Din = 50, Re = 64.87, the temperature non-uniformity on the heating surface of THT is only 0.022 K, the thermal resistance is 9.4 × 10–6 km2 W−1, and the FOM of THT is about 1.14 times of that of RT. RT and FT have a similar performance, and the maximum deviation of FOM for both of them within the conditions studied in this paper is only 0.04. The paper provides a reference for selecting topologies in MMPFHS design. [ABSTRACT FROM AUTHOR]

Three-dimensional subcooled flow boiling of R134a in a threaded tube was numerically simulated at the conditions of 200~400 kW/m2 heat flux, 3~20 K inlet subcooling, and 0.2~0.6 m/s inlet velocity. The bubble behavior in the horizontal threaded tube with 0.581 mm thread tooth height was observed. The effect of heat flux, inlet subcooling, and inlet velocity on bubble departure diameter and heat transfer coefficient were explored. The results presented the whole growth process of five kinds of bubbles. It was found that the bubbles either collapsed in cold liquid after leaving the heating wall or grew along the axial direction and contacted the heating wall. And there was no bubble sliding during the growth. In addition, the most important and special characteristic of bubble behavior in threaded tubes was the phenomenon of the bubble passing through the cavity. The coalescence and breakup behavior occurred after the bubble passed through the cavity. According to the discussions of the departure diameter and heat transfer coefficient, it was inferred that the bubble departure diameter increased with the increase of heat flux from 200~400 kW/m2 and subcooling from 3~20 K while decreasing with the increase of inlet velocity from 0.2~0.6 m/s. And due to the influence of the threaded tube structure, there are special points in the change of bubble departure diameter. The heat transfer coefficient of the bubbles in the threaded tube was higher than the smooth tube, which was increased by 1.5~12.5%. The heat transfer coefficient increased with the increase of heat flux and subcooling and is closely related to the bubble departure diameter. [ABSTRACT FROM AUTHOR]

Mold structure and cooling parameters are significant factors that affect the heat transfer capacity of high-speed continuous casting molds of billets. Therefore, a three-dimensional fluid flow and heat transfer model of a 160 mm × 160 mm billet mold was established, and its accuracy was verified. Thereby, the characteristics of heat transfer and influences of mold structure and cooling parameters on heat transfer in the high-speed continuous casting billet mold region were revealed. It was found that extending the effective length of a mold is the most valuable method to improve its heat transfer capability and achieve high-speed continuous casting. The total heat and the shell thickness at a mold outlet increased by 19% and 9.21% on average with every 100 mm extension. Enlarging the fillet radius could enhance the uniformity of heat transfer in the mold. Considering the loss of material, the optimal fillet radius of the mold was determined to be R = 10 mm. [ABSTRACT FROM AUTHOR]

The importance of non-Newtonian fluid (Casson fluid) in industry is increasingly appreciated. However, little is known about the flow rheology of Casson fluid flowing over a Riga plate. Thus, the purpose of this investigation is to examine the nature of entropy generation (EG) and heat transfer (HT) on Casson hybrid nanofluid flow past a Riga plate by considering the influences of magnetic field and thermal radiation. The Hamilton–Crosser (Model 1) and Xue model (Model 2) of thermal conductivity are incorporated for Casson hybrid nanofluid. The governing equations are solved by numerical methods i.e., bvp4c and shooting techniques. In the current framework, the comparative patterns for both models of temperature, velocities, EG and Bejan number are depicted due to the existing parameters. The domain of the pertinent parameters is taken as thermal radiation, 4 ≤ R a ≤ 7 ; stretching parameter, 0. 6 ≤ λ ≤ 1 ; Casson factor, 0. 5 ≤ δ ≤ 2 ; rotation parameter, 1 ≤ ℜ t ≤ 4 and Hartmann number, 2 ≤ H a ≤ 1 1. The outcomes show that the rise in volume fraction and thermal conductivity profile of Xue model (Model 2) is better than Hamilton–Crosser model (Model 1). Moreover, EG profiles are escalated with augmentation in values of Hartmann number and stretching parameter for both models. The results of the study are useful for predicting the rheology of right fluid, while it also assists in safeguarding the boundary layer (BL) separation, along with establishing a parallel force to the surface in assisting the domain of science and technology. Mathematical model addressing the three-dimensional flow of Casson hybrid nanofluid over a Riga plate subject to viscous dissipation and linear thermal radiation was investigated. The solution to the governing equations are obtained through two numerical schemes, (i) shooting method and (ii) bvp4c. Effect of the active parameters on entropy generation is discussed through graphs and it was observed that for increasing value of both Hartmann number and stretching parameter the profiles of entropy generation increases. [ABSTRACT FROM AUTHOR]

The present study investigates the steady three-dimensional flow of a Sisko fluid over a bidirectional stretching sheet under the influence of Lorentz force. Heat transfer effects have been carried out for constant heat flux and Newtonian heating systems. The transformed governing equations of the flow model are solved by using the spectral relaxation method (SRM), taking into account similarity transformations. The effects of controlling parameters on flow and derived quantities have been presented in the form of graphs and tables. Numerical benchmarks are used to characterise the effects of skin friction and heat transfer rates. It is noticed that in the case of Newtonian heating, the rate of heat transfer is higher than that in the constant heat flux case. As the stretching parameter increases, the fluid temperature decreases in both Newtonian heating and constant heat flux. It was discovered that successive over (under) relaxation (SOR) approaches will considerably boost the convergence speed and stability of the SRM system. The current findings strongly agree with earlier studies in the case of Newtonian fluid when the magnetic field is absent. [ABSTRACT FROM AUTHOR]

A numerical study estimated the mixed convection around a sinusoidal cylinder inside a rectangular cavity. The key parameters for sinusoidal circular cylinders were the wavelength and Reynolds number (Re = 100, 500, and 1000) with a fixed Prandtl number of 0.7. The flow regimes were greatly affected by these parameters. The unsteadiness of the flow pattern was also affected by λ and Re. The results were analyzed by the thermal structure, vortical structure, and Nusselt number. Furthermore, the orthogonal enstrophy was used to quantify the three-dimensional flow characteristics, and the frequency of the surface-averaged Nusselt number for the heated bottom wall was used to analyze the unsteady characteristics. The heat transfer performance was enhanced by 6.6% at Re = 100 for λ = 3 compared to the circular cylinder. In addition, the heat transfer performance was enhanced by 6.6% and 2.6% at Re = 500 for λ = 2 and Re = 1000 for λ = 1, respectively, compared to the circular cylinder. [ABSTRACT FROM AUTHOR]

This work examines the non-Newtonian Cassonnanofluid's three-dimensional flow and heat and mass transmission properties over a Riga plate. The Buongiorno nanofluid model, which is included in the present model, includes thermo-migration and random movement of nanoparticles. It also took into account the Cattaneo–Christov double flux processes in the mass and heat equations. The non-Newtonian Casson fluid model and the boundary layer approximation are included in the modeling of nonlinear partial differential systems. The homotopy technique was used to analytically solve the system's governing equations. To examine the impact of dimensionless parameters on velocities, concentrations, temperatures, local Nusselt number, skin friction, and local Sherwood number, a parametric analysis was carried out. The velocity profile is augmented in this study as the size of the modified Hartmann number increases. The greater thermal radiative enhances the heat transport rate. When the mass relaxation parameter is used, the mass flux values start to decrease. [ABSTRACT FROM AUTHOR]

• Achieved anisotropic control of complex three-dimensional structures. • Minimized hot spot area by regulating fluid distribution. • Enhanced coolant utilization by Turing pattern-induced 3-D mixing effect. Heat dissipation is a critical issue for various engineering applications such as electronic devices, turbine blades and batteries. Existing heat sink structures contained inherent shortages in geometric flexibility which prevented further development of heat dissipation technologies. This study proposed a self-organized design method for heat sinks inspired by Turing Patterns (TP) in nature morphogenesis. The biomimetic structures were parametrically controlled with the aid of reaction-diffusion equations in terms of feature size, feature density, structural morphology and structural orientation. The metallic selective laser melting (SLM) technology was adopted to fabricate the three-dimensional (3-D) heat sinks. Experimental and numerical evaluations were conducted to compare TP structures with traditional pin-fin (PF) arrays baselines. Results showed substantial advantages of the TP structures in regulating flow field and enhancing height-wise fluid mixing. The thermal performance factor (TPF) of TP structures is approximately 45 % higher than traditional PF structures with similar feature sizes. The globally averaged magnitude of height-wise velocities of TP structure is around 2.4 times larger than that of PF structures due to the existence of the threshold-like and bridge-like structures. With the aid of three-dimensional structures, full utilization of the coolant was achieved to further increase the heat transfer intensity, while a high synergic level was formed within the flow field and temperature field to reduce the pressure drop. The design method proposed in this study demonstrated strong capability in tuning three-dimensional flow field and is expected to provide new insights to the heat transfer area that faces nonuniform thermal conditions and inhomogeneous flow conditions. [ABSTRACT FROM AUTHOR]

Three-dimensional flow via swirling porous disks and an annular sector is carried out using fully developed hybrid nanofluids. Here, a single-phase simulation based on thermophysical characteristics using various nanoparticle sizes and shapes is taken into account. A regression function connected with the permeable Reynolds number for injection and suction was created. We used the well-known and accurate "shooting approach" to apply to the governing, nonlinear, ordinary differential equation systems to obtain numerical results. Additionally, parametric research was employed to control the impact of embedded flow factors on concentration, velocity, and temperature. While the physical features of the bottom and upper disks, such as the skin friction coefficient and Nusselt number, are provided in a table, their characterization of the flow of several regulatory flow parameters, such as fluid velocity and temperature, is depicted graphically. The experimental range of nanoparticle fractions of 1% to 4% is considered with the Nusselt number having notable effects at φ = 4%. Both walls demonstrate the effects of an increase in injection factor, shear stress, and tensile stress. As the Eckert number rises at the lower wall, the rate of heat transfer dramatically increases, and the opposite is true for the upper wall. The rate of heat transmission is significantly impacted by the addition of different base fluids containing various kinds of nanoparticles. The aforementioned research created a solid foundation for the development of electronic computers with an emphasis on nanotechnology and biomedical devices. [ABSTRACT FROM AUTHOR]

The flow of viscoelastic fluid owing to stretching surfaces (SSs) has become well-known among the demanding study fields of fluid mechanics due to its numerous practical applications. As a result, the major goal of this work is to scrutinize the three-dimensional (3D) unsteady flow of second-grade nanofluid. A magnetic field influences the fluid when an indefinitely long, straight wire delivers an electric current. Thermal radiation is taken into consideration while studying heat transmission characteristics. The effective thermal conductivity of nanofluid flow is scrutinized by adopting Koo–Kleinstreuer–Li (KKL) nanofluid model. Through suitable transformations, relevant flow expressions are converted to ordinary differential equations (ODEs). The numerical approach Runge–Kutta–fourth–fifth Fehlberg's order method (RKF-45) with shooting technique is used to solve the generated ODEs. Further, it was noted that the CPU time to estimate the solutions of flow fields was less than (2.23 s). The outcome reveals that the rise in values of the time-dependent parameter positively impacts both velocity and thermal profiles. The improved heat transport is seen for augmented values of radiation and ferromagnetic interaction parameters. [ABSTRACT FROM AUTHOR]

Under the influence of an alternating magnetic field, flow and heat transfer of a ferrofluid flow over a flexible revolving disc are examined. The flow is hampered by the external magnetic field, which is dependent on the alternating magnetic field's frequency. The current work examines the heat transfer and three-dimensional flow of fluid with high viscosity on a spinning disc that is stretched in a radial direction. The governing equations' symmetries are computed using Lie group theory. In the problem, there is a resemblance that can accomplish with radially stretching velocities divided into two categories, specifically, linear and power-law, by imposing limits from the boundary conditions. The literature has already covered linear stretching, but this is the first discussion of power-law stretching. The governing partial differential is turned into an ordinary differential equations system using additional similarity transformations, which are then numerically handled. The results are presented for hybrid alumina–copper/ethylene glycol ( Al 2 O 3 - Cu / EG ) nanofluid. The calculated findings are novel, and it has been seen that they accord quite well with those of the earlier extended literature. It has been found that hybrid nanofluid flow outperforms nanofluid flow in terms of Nusselt number or heat transfer rate. The heat transmission in the fluid is reduced as the Prandtl number is increased. The heat transfer increases as dimensionless magnetic field intensity ξ increases. Also, axial velocity and radial velocity decrease as magnetic field intensity increases. As the ferromagnetic interaction parameter is raised, the efficiency of heat transmission decreased. For non-linear stretching with stretching parameter 0 < m < 1, the velocity decreases with the increase in m. [ABSTRACT FROM AUTHOR]

The heat transport analysis in the three-dimensional unsteady flow of non-Newtonian nanofluid is studied in this research communication. Comparison of water-based ternary hybrid nanofluid conveying three various shaped nanoparticles (titanium spherical-carbon nanotube (CNT) cylindrical-graphene platelet) and Zinc Oxide-Society of Automotive Engineers 50 nanolubricant (ZnO-SAE50Nanolubricant) is emphasized with two different models. Also, this paper is mainly focused on an electrically non-conducting and incompressible magnetic liquid with moderate saturation magnetization and low Curie temperature. An infinitely long, straight wire delivering an electric current generates a magnetic field that affects the fluid. To study heat transfer characteristics thermal radiation is taken into account. Pertinent flow expressions are reduced into ordinary differential equations (ODEs) through appropriate transformations. The obtained ODEs are solved by means of the numerical method Runge–Kutta–Fehlberg's fourth-fifth order method (RKF-45) with shooting technique. Results reveals that the ZnO-SAE50Nanolubricant flow shows maximum heat transport followed by titanium spherical-CNT cylindrical-graphene platelet-water hybrid nanofluid flow for increased values of radiation parameter. Further in this scenario, it is found that the heat transfer rate in ternary hybrid nanofluid increases about 2–5% whereas in Nanolubricant it is about 3–8% for the gradual increasing values of the ferromagnetic interaction parameter. [ABSTRACT FROM AUTHOR]

With the rapid development of UHV power transmission and transformation project in our country, the gradually increasing electromagnetic capacity and electromagnetic loads of power transformers causes serious heating of the transformers. Therefore, it is particularly important to accurately calculate its temperature rise. Based on field-circuit coupling method, this paper took a 240000 KVA, 330 KV power transformer as the research object to calculate the whole temperature rise and heat transfer characteristics. Firstly, the average velocity of fluid was gotten by three-dimensional flow field of transformer which is calculated by establishing thermal network model of the transformer, phase winding and related structures. And then substitute it into thermal network model. The whole average temperature and temperature rise was gotten by using first law of thermodinamics and after the iteration. And according to the temperature rise test, this paper comprised and analyzed the computed results of thermal network and numerical analysis. Results showed that the error of the thermal network model was within the scope of the permit, and it was simple and quick. The method can provide basis for the future heat transfer research and temperature rise prediction of transformer. [ABSTRACT FROM AUTHOR]

This article is an editorial that discusses the thermal-hydraulics in once-through steam generators (OTSG) for nuclear reactors. The OTSG is a key component in nuclear power plants, but its flow and heat transfer characteristics differ from conventional steam generators. The article highlights four research papers that focus on experimental and numerical studies of thermal hydraulic problems in OTSG. These papers cover topics such as friction pressure drop, heat transfer characteristics, flow characteristics under different ocean conditions, and the development of a coupled flow and heat transfer model. The article concludes by inviting further research on this topic. [Extracted from the article]

We explore the geometric effects on the thermocapillary flow instabilities in large Prandtl number (Pr = 1.4) liquid bridges between two coaxial disks with different radii under microgravity, focusing on the impacts of radius ratio Γr and aspect ratio Γ. The static deformation of the free surface is concerned by the solution of the Young–Laplace equation, and the linear stability analysis based on spectral element method is conducted for accurate identification of the instability characteristic. We observe that the flow stability is generally improved with the decrease in radius ratio Γr or aspect ratio Γ, especially for the liquid bridge heated from the upper disk. The critical oscillation frequency experiences an abrupt drop around Γr = 0.56 as Γr decreases for the liquid bridge with the bottom disk heated. Moreover, three transitions between two-dimensional axisymmetric steady flow and three-dimensional oscillatory flow are observed within the interval 0.87 < Γ ≤ 0.91 at Γr = 0.50 when the liquid bridge is heated from the upper disk. The energy analysis indicates that the instabilities for all cases are predominantly caused by the hydrothermal wave instability and the phenomenon of three transitions results from the variation of thermal energy transfer efficiency with the growth of the Marangoni number. [ABSTRACT FROM AUTHOR]

Natural convection heat transfer in cavities commonly occurs in various engineering problems. Specifically, the problem of a differentially heated cavity with oscillatory boundary conditions arises in the design of energy-saving strategies or energy evaluations within the building sector. This work addressed numerically and experimentally the natural convection in a full-scale room subjected to diurnal heating and nocturnal cooling. The experiment was instrumented with temperature sensors and an air velocity sensor, inspired by works reported in the literature. The numerical model involved solving the equations governing natural convection, considering turbulent bi-dimensional and three-dimensional flow in a transient state. This research allowed the selection of an appropriate turbulence model and evaluated the performance of the two-dimensional and three-dimensional approaches in simulations. Results showed that the k-omega SST model performed best in predicting velocity, while the standard k-omega model performed best in predicting temperature for the two-dimensional simulation, and the RNG k-epsilon model performed best for the three-dimensional simulation. Additionally, the three-dimensional simulation more accurately reproduced the chaotic fluctuations observed in experimental velocity data, demonstrating up to 30 % better estimation during periods of high velocities. The study identified the reversal of convective cells in the cavity, with an approximate duration of 2 h and 40 min in a real case. This study contributes to improving the understanding of turbulent natural convection in a differentially heated cavity with oscillatory boundary conditions. These findings have significant implications for various environmental and engineering applications, including the design of thermally comfortable buildings. [ABSTRACT FROM AUTHOR]

The injection mode of oxidizer gas significantly affects the flow and heat transfer characteristics of rocket motors with separated oxidizer and fuel propellants. In the present study, the effect of the multi-hole injector on flow and heat transfer of a novel combined rocket motor is studied with a three-dimensional numerical model. The results show that as the number of injection holes increases from one to five, muti-jet interference effect could occur. The original single coupled combustion zone is split into multiple coupled combustion zones. Multi-peak distributions of temperature and velocity are thus observed. As the combustion heat release is gradually advanced towards the injector, the multiple injection flows form three high-flow velocity zones. The three-dimensional distribution of heat transfer coefficient is highly consistent with that of flow velocity. The average heat transfer coefficient first increases and then decreases with the increase in the number of injection holes. The 4-hole injector renders the largest average heat transfer coefficient. Due to the multi-peak distribution of flow velocity and heat transfer, a multi-peak distribution of regression rate for solid propellant is thus observed. The average regression rate increases greatly and reaches the maximum value for the 4-hole injector. The results also show that the regression rate is controlled by the combustion reaction kinetics in the proximal injector region but is controlled by heat transfer in the region far away from injector. The present study contributes to a better insight into the flow and heat transfer effects on combustion performance of the combined solid rocket motor with multi-hole injector. • Obtained three-dimensional distribution of heat transfer coefficient of the motor. • Revealed multi-jet interference effect on mixing and heat transfer properties. • Observed multi-peak distributions of temperature and flow velocity. • Identified effects of flow and heat transfer on regression rate distribution. [ABSTRACT FROM AUTHOR]

To reduce the heat exchanger's costs in a highly competitive industry, thermal performance enhancement of the heat exchangers has successfully gained attention in the last few decades. Among different engineering approaches, the application of the enhanced pipes provides a key solution to improve heat performance. In this paper, the investigation develops a numerical study based on the commercially available computational fluid dynamics codes on the turbulent flow in three‐dimensional tubular pipes. Various concavity (dimple) diameters with corrugation and twisted tape configurations are investigated. The study has shown that perforated geometrical parameters lead to a high fluid mixing and flow perturbation between the pipe core region and the walls, hence better thermal efficiency. Moreover, a model of concavity (dimple) with a 4 mm diameter allows the highest heat transfer enhancement among other designs. In addition, the study shows that due to the disturbance between the pipe core region and the pipe wall, the transverse vortices and swirl flow generated are forceful, which leads to better heat transfer enhancement compared with the conventional (smooth) pipes. As the Reynolds number (Re) rises, the mixing flow, secondary, and separation flow extend to become higher than the values in a smooth pipe, allowing a higher value of performance evaluation factor to be achieved for a dimple diameter of 1mm at the low Re values. This study, therefore, shows the promising potential of the enhanced pipes in the heat transfer enhancement of heat exchangers that is crucial in industrial applications to save more energy. [ABSTRACT FROM AUTHOR]

The objective of the present research is to obtain enhanced heat and reduce skin friction rates. Different nanofluids are employed over an exponentially stretching surface to analyze the heat transfer coefficients. The mathematical model for the problem has been derived with the help of the Rivilin–Erickson tensor and an appropriate boundary layer approximation theory. The current problem has been tackled with the help of the boundary value problem algorithm in Matlab. The convergence criterion, or tolerance for this particular problem, is set at 10−6. The outcomes are obtained to demonstrate the characteristics of different parameters, such as the temperature exponent, volume fraction, and stretching ratio parameter graphically. Silver-water nanofluid proved to have a high-temperature transfer rate when compared with zinc-water and copper-water nanofluid. Moreover, the outcomes of the study are validated by providing a comparison with already published work. The results of this study were found to be in complete agreement with those of Magyari and Keller and also with Lui for heat transfer. The novelty of this work is the comparative inspection of enhanced heat transfer rates and reduced drag and lift coefficients, particularly for three nanofluids, namely, zinc-water, copper-water, and silver-water, over an exponentially stretching. In general, this study suggests more frequent exploitation of all the examined nanofluids, especially Ag -water nanofluid. Moreover, specifically under the obtained outcomes in this research, the examined nanofluid, Ag-water, has great potential to be used in flat plate solar collectors. Ag-water can also be tested in natural convective flat plate solar collector systems under real solar effects. [ABSTRACT FROM AUTHOR]

The advanced thermal characteristics of nanomaterials allow better heat transfer efficiency in engineering, industrial and technological processes. In this report, the outcome of a comparative analysis between the dynamics of blood carrying Cu nanoparticles and blood carrying single-walled carbon nanotubes (SWCNTs) due to the stretching and rotation of two disks at various levels of rotation, stretching, power-law index and heat source/sink is presented. By using appropriate similarity variables, the leading partial differential equations (PDEs) are altered into one-dimensional equations (ODEs). The resulting ODEs are handled using the shooting method. The impact of governing parameters on the boundary layer profiles is analysed graphically. Fluid velocity gets enhanced in three dimensions during the rotation of the disk, but they predict different behaviours for the stretching parameters of the upper and lower disks. The temperature decays for power-law index, rotation and stretching parameters. Also, the rates of heat transfer are more extensive for shear-thinning. Finally, the effects of the Cu–blood(blood) nanofluid are dominant over the base fluid (blood) and SWCNTs–blood nanofluid. [ABSTRACT FROM AUTHOR]

In the present study, the silent characteristics of magnetized mixed convection flow in porous medium suspended with both microorganisms and nanoparticles induced by two expanded or contracted disks are investigated. The Buongiorno's model, in which the Brownian diffusion and thermophoresis are taken as dominant factors, is introduced to describe behaviors of the nanofluid. Multiple slip boundary conditions are also included into this problem. The nonlinear system is converted into five fully coupled nonlinear ordinary differential equations via suitable scaling transformations. The homotopy-based algorithm BVPh2.0 is employed to give their solutions. Physical interpretation is made through analyzing the graphs of different constraints for profiles of velocity, temperature, nanoparticle volume concentration and density of motile organism. Furthermore, we extend this model to seek the physical behaviors of heat transfer and the wall motile microorganism fluxes. Significant findings are presented, including that the wall expansion ratio and the magnetic parameter impose contrary effects on microorganism profiles, the Prandtl number and the radiation parameter play opposite roles on heat transfer rate, and the Brownian motion and the thermophoresis exhibit totally different influence on microorganism flux rate. It is expected that this study is helpful to understand heat transfer mechanism in multiple physical fields. [ABSTRACT FROM AUTHOR]

An analytical solution, based on the asymptotic series expansion method, for the problem of a fully developed chemically reactive laminar three‐dimensional flow through a porous vertical infinite plate in a porous medium with sinusoidal permeability as suction in the existence of appreciable radiation is presented. The effects of the physical parameters entering into the problem on the flow and transport characteristics are studied and demonstrated through graphs. The flow is three‐dimensional due to sinusoidal suction as well as porosity. It is found that concentration of the fluid rises due to thermal diffusion (Soret) effect. Furthermore, it is seen that fluid velocity is increased for increasing thermal diffusion effect. Also, viscous drag at the plate is increased under the Soret effect. [ABSTRACT FROM AUTHOR]

This paper presents the findings from a research study using computational fluid dynamics (CFD) on the impact of different diameter Ball Tabulators Inserts (BTI) on the three-dimensional flow pattern and heat transfer characteristics within a circular tube. This analysis was carried under uniform heat flux conditions with different BTI diameters (1, 2, 3, 4, 5, 6, 7, and 8 mm). Fluid flow, pressure drop, dynamic pressure, velocity components, thermo-hydraulic, turbulent kinetic energy, and turbulent viscosity were analysed qualitatively and quantitatively. The performance evaluation results revealed that the characteristics of flow behaviour and the velocity field contours variations are closely associated with the BTI configurations. Also, the computational results indicated that the change in fluid flow velocity near the pipe wall and around the BTI is important parameters for the heat transfer enhancement as compared to that obtained without BTI under the same conditions. Moreover, using BTI presented a distinguished influence on the rate of heat transfer. Additionally, vortex flow through means of this kind of BTI is an important parameter in the enhancement of heat transfer. The use of BTI can enhance the rate of heat transfer performance by more than 46%. Furthermore, the maximum value for the PEF is found to be more than 1.03. [ABSTRACT FROM AUTHOR]

The flow and heat transfer models of hot dry rock are mainly based on the assumption of two-dimensional model, which cannot fully reflect the physical process of three-dimensional flow and heat transfer in artificial fractures. The three-dimensional flow heat transfer numerical model of a single fracture was established by ANSYS Fluent, and the relevant numerical simulation calculation was carried out. The influence of different factors on the fluid temperature in the fracture of hot dry rock was analyzed, and the heat transfer rules of the fluid in the fracture under different conditions were obtained. Numerical simulation results show that the main factors affecting the heat transfer of hot dry rock fractures include: the injection rate of working fluid, fracture width, fracture length and initial fluid temperature. Under the conditions of a given fracture length and inflow velocity, the smaller the width of the artificial fracture, the higher the temperature of the fluid flowing out of the outlet, the longer the length of the fracture which the fluid flows through, and the greater the temperature increase. With the same fracture width and length, the smaller the flow rate, the higher the temperature at the fluid outlet, the slower the flow rate, the longer the heat exchange time, and the more heat is transferred. For different frac ture widths and different inflow speeds, after the fracture length reaches a certain level, the water temperature can be increased to be consistent with the bedrock. [ABSTRACT FROM AUTHOR]

In this study, heat transfer and airfield around a parabolic trough solar collector are simulated. The effect of the pitch angle, two-axis tracking system, and wind speed on the collector thermal performance is evaluated. Three-dimensional and turbulent flow equations are used. Simulations are performed at noon, for the 45th day of summer, for the geographical location of Isfahan. The effects of wind velocities from V = 1 to 3 m/s are studied. The results of this study are investigated for a single-axis tracking system at pitch angles 0°, 15°, 30°, and 45°, and for a two-axis tracking system for the angles of 45°–35°, 45°–25°, and 45°–15°, respectively. The results indicate that factors such as the change in the heat transfer coefficient, collector pitch angles, and amount of flow deviation between the upper and lower dome of the collector resulting in a distinction between the absorption of maximum radiation fluxes or the maximum heat transfer (heat loss) rate. Moreover, the higher the pitch angle, the higher the amount of received sunlight, but on the other hand, it causes the wind to affect all the collector surfaces (more heat loss). The drag force applied to the two-axis collector is lower than the one-axis collector. Therefore, using a two-axis system not only does not increase the structure size but also can decrease it, too. [ABSTRACT FROM AUTHOR]

Supercritical pressure fluids are widely used in heat transfer and energy systems. The benefit of high heat transfer performance and the successful avoidance of phase change from the use of supercritical pressure fluids are well-known, but the complex behaviours of such fluids owing to dramatic thermal property variations pose strong challenges to the design of heat transfer applications. In this paper, the turbulent flow and heat transfer of supercritical pressure $\textrm {CO}_2$ in a small vertical tube influenced by coupled effects of buoyancy and thermal acceleration are numerically investigated using direct numerical simulation. Both upward and downward flows with an inlet Reynolds number of 3540 and pressure of 7.75 MPa have been simulated and the results are compared with corresponding experimental data. The flow and heat transfer results reveal that under buoyancy and thermal acceleration, the turbulent flow and heat transfer exhibit four developing periods in which buoyancy and thermal acceleration alternately dominate. The results suggest a way to distinguish the dominant factor of heat transfer in different periods and a criterion for heat transfer degradation under the complex coupling of buoyancy and thermal acceleration. An analysis of the orthogonal decomposition and the generative mechanism of turbulent structures indicates that the flow acceleration induces a stretch-to-disrupt mechanism of coherent turbulent structures. The significant flow acceleration can destroy the three-dimensional flow structure and stretch the vortices resulting in dissipation. [ABSTRACT FROM AUTHOR]

Numerical investigation of the three-dimensional flow and heat transfer of 36 nm Al 2 O 3 –H 2 O nanoliquid over a wedge surface is carried out by utilizing the modified Buongiorno model (MBM). The boundary layer approximation is assumed to be valid. The thermophysical properties of Al 2 O 3 –H 2 O nanoliquid are deliberated in the study by modeling them through the use of correlations based on experimental data. The thermal boundary layer equation comprises the Brownian motion and thermo-migration effects caused by nanoparticles. Zero mass flux boundary condition is also accounted. Optimization of the heat transfer rate of nanoliquid is made using the Response surface methodology (RSM). Two stream functions are used to derive the similarity transformations and they are employed to arrive nonlinear ordinary differential system from the governing partial differential system, and then the subsequent nonlinear problem is treated numerically using the Finite Element Method (FEM). The heat flow features are scrutinized using two-dimensional, surface, and streamline plots. The results of flow due to a moving wedge in the same direction of free stream velocity are compared with those of a moving wedge in the opposite direction of free stream velocity. The thermal layer and nanoparticles volume fraction layers are enlarged due to the chaotic movement of nanoparticles. The thermophoresis mechanism improves the thermal layer at the wedge surface. The high level of pressure gradient factor, high level of shear-to-strain rate and low level of Lewis number, were found to be the optimal operating condition that would maximize the heat transfer rate. [ABSTRACT FROM AUTHOR]

Three-dimensional invisible finned-tube is a kind of high-efficiency enhanced tube which is widely used at present. In order to study and analyze advantages and disadvantages of heat transfer and flow performance of the three-dimensional invisible finned-tube, other enhanced tube heat exchangers are introduced and compared through experiments. After analysis and research, it is found that the total heat transfer coefficient K is not the only indexes for evaluating the performance of the heat exchanger, and the resistance is also one of the indexes. According to the evaluation standard of the comprehensive performance of the heat exchanger, the comprehensive performance factor η of the tube side and shell side of the three-dimensional invisible finned-tube heat exchanger is better than that of the other enhanced tube heat exchanger, and the enhanced tube standard is reached under certain conditions, which shows that the three-dimensional invisible finned-tube heat exchanger has excellent performance. The analysis results in this paper have certain guiding significance for engineering design and application of three-dimensional invisible finned-tube heat exchanger. [ABSTRACT FROM AUTHOR]

Enhancement of heat transfer in plate-fin heat exchangers can be obtained using vortex generators (VG). The three-dimensional laminar flow of water/Al2O3 nanofluid with different nanoparticle volume fractions in a channel with longitudinal vortex generators is numerically simulated. Two novel forms of modified delta winglet VG pairs (MDWP1, MDWP2) are introduced by adding and subtracting a part of the quadrant profile to the delta winglet VG profile. Simulation is carried out for the classic delta winglet pair (DWP) and MDWPs. Performance of heat transfer and pressure drop is compared as well as the overall performance analysis of channel is conducted for all three forms of VGs and two flow arrangement types, common flow up (CFU) and common flow down (CFD). Analytical expressions from the literature are used to check the validity of the model. Governing equations of laminar fluid flow and heat transfer are solved based on the finite-element method. The range of Reynolds number is from 100 to 500. Results show that in the range of the present study, using nanofluid increases about 20% of the heat transfer coefficient and 18% of pressure drop compared to pure water. As results confirm in all of the cases, the heat transfer coefficient increases using VG. The MDWP2 leads to the highest pressure drop and heat transfer between the three VGs types. It can produce up to 9% higher heat transfer coefficient in Re = 100 and 20% of higher pressure drop for CFD flow arrangement. The overall performance of the CFD arrangement is higher than CFU for the studied cases relatively. And the values of performance in a channel with DWP are greater than MDWP1 and MDWP2, which is due to the lower pressure drop of DWP. [ABSTRACT FROM AUTHOR]

The non-axisymmetric three-dimensional flow and heat transfer in the stagnation-point region of a planar jet impingement boiling on a flat surface has been investigated by using similarity solution approach, considering additional diffusivity terms in momentum and energy equations as a result of bubble-induced mixing in flow. The free jet stream along z direction impinges on the surface and produces a flow with different velocity components. This situation may happen if the flow pattern on the plate is bounded from both sides in one of the directions, because of any physical limitation or due to conditions of the surface such as moving plates or stretching sheets with different values of stretching velocities in the x and y directions. The governing equations have been transformed into ordinary differential equations by introducing appropriate similarity variables, and an exact solution has been obtained for three-dimensional boiling problem for the first time. The similarity variables have been presented based on non-axisymmetric three-dimensional and additional diffusivity effects. The bubble-induced diffusion due to bubble formation, growth, departure and collapse causes an enhancement in heat transfer rate from the surface to the bulk flow. The total heat flux transferred from the surface to the flow has been estimated as summation of the single-phase heat transfer due to forced convection and the nucleate boiling heat flux due to bubble-induced diffusion. The effects of the velocity components ratio and the ratio between the maximum total diffusivity to the molecular diffusivity on the flow field and heat transfer characteristics have been obtained and discussed and illustrated graphically. A comparison of the predicted heat flux has been made with previously published experimental data. As expected, the average deviation values show relatively more accurate results for the three-dimensional simulation than the two-dimensional one because of being closer to the experimental conditions. [ABSTRACT FROM AUTHOR]

In this study, three-dimensional Bödewadt hybrid nanofluid flow has been investigated. Base fluids are water and hexanol which contain Fe 3 O 4 and MoS 2 . The governing nonlinear PDEs are converted into nonlinear ODEs and the nonlinear equations are solved by the homotopy perturbation method (HPM). The effects of nanoparticle volume fraction, Eckert number, base fluid and shape factor on entropy generation, Nusselt number, skin friction coefficient and Bejan number have been studied. Entropy generation is increased with an increment in Eckert number; while, it is decreased by growth in nanoparticle volume fraction and shape factor. In a similar situation, hexanol has higher rate of irreversibility, higher Bejan number and higher Nusselt number than water. The skin friction coefficient is not a function of the Eckert number and shape factor, but it is an increasing function of nanoparticle volume fraction. In this paper, by averaging the differences of Nusselt number and skin friction coefficient between water and hexanol, it can be observed that the Nusselt number and skin friction coefficient for hexanol are 11% and 5% more than water, respectively. Indeed, in a fixed situation, hexanol-based fluid flows have higher heat transfer and drag than water-based fluid flows. [ABSTRACT FROM AUTHOR]

This study presents a two and three-dimensional numerical simulations of a flow-through a sudden expansion and contraction microchannels. The finite element method was used to discretize the equations governing the physical model. By carrying out the numerical simulations, results indicate the apparition of a separate vortex, situated in the corner after the sudden expansion of the microchannel for low Reynolds numbers. For high values of Reynolds number and expansion ratios, the vortex separation length increases. Also, the three-dimensional character of the flow is more pronounced for higher Reynolds numbers. [ABSTRACT FROM AUTHOR]

The heat and mass transfer characteristics of a micropolar nanofluid-filled cubic cavity are investigated with different types of nanoparticles (Al2O3, TiO2, Cu and Ag). Pure water is assumed as the base fluid. The governing equations are simplified by means of vorticity-vector potential formulation and subsequently solved numerically using the finite volume method. The influences of relevant parameters on heat and mass transfer characteristics are well explored and the results show that for the micropolar nanofluid model both heat and mass transfer rates and the three-dimensional character of the flow are smaller compared with that of a pure nanofluid model. It is also found that the rate of heat and mass transfer decreases with an increase in vortex viscosity parameters as well as volume fractions. The enhancement in the volume fraction of nanoparticles weakens both flow strength and three-dimensional nature of the flow, which are more prominent in the thermal buoyancy dominated flow. The average Nusselt and Sherwood numbers decrease with the increase in the volume fraction of nanoparticles resulting in a significant enhancement in thermal properties of nanofluids with elevated heat and mass transport features. The effects of type of nanoparticles on the rate of heat and mass transfer and flow structure are analyzed. [ABSTRACT FROM AUTHOR]

Through this paper, three-dimensional fluid flow and heat transfer of Al2O3 nanofluid within ventilated enclosures was taken into consideration. Crossed by the nanofluid, the ventilation system is assured by two equivalent openings located at the vertical walls. So, the cold nanofluid gets enter using the opening located at the top of the left side and leaving by the second one, which is located at the bottom of the right side. Except the adiabatic rear and front sides, all parts of the cubic space are maintained at a constant temperature, higher than that of the entrance nanofluid. To make clear the impact of main parameters such as Reynolds number, the Richardson number and nanoparticles volume fraction as well as the 2D extension, the convection phenomenon was reported by means of streamlines and isotherm plots, side by side with the velocity profiles. The main results obtained show that when the Reynolds number increases, the heat exchange rate is an increasing function and the pressure drop is a decreasing function. In addition, in a conductive dominant regime for low Reynolds numbers, the two-dimensional (2D) is valid and can predict the studied phenomena in three-dimensional (3D). Finally, a correlation for the pressure drop is obtained in polynomial form. [ABSTRACT FROM AUTHOR]

According to the heat transfer and flow resistance characteristics of the tube belt radiator, the three-dimensional flow and heat transfer model of shutter fin in belt-type radiator was established, and the effects of steering area number and length of the louver fin on the flow and heat transfer performance of radiator were investigated. The results show that when the head wind speed is constant, the heat transfer factor and friction factor of radiator under the arrangement of single-row pipe and three-row pipes are decreased with the increasing of the product of steering area length and number. When the products of steering area length and number are equal, the heat transfer factor and friction factor are increased with the increasing of steering area number. With the single-row pipe layout arranged, the comprehensive performance of radiator is the best when the steering area length and number are respective 1. 5 mm and 3. With three-row of pipes arranged, the comprehensive performance of radiator is the best when the steering area length and number are respective 3. 0 mm and 3. The optimal matching of steering area length and number can effectively improve the comprehensive performance of multi-row pipe layout and narrow the gap with that of single-row pipe layout. [ABSTRACT FROM AUTHOR]

The objective of the present research is to obtain enhanced heat and reduce skin friction rates. Different nanofluids are employed over an exponentially stretching surface to analyze the heat transfer coefficients. The mathematical model for the problem has been derived with the help of the Rivilin–Erickson tensor and an appropriate boundary layer approximation theory. The current problem has been tackled with the help of the boundary value problem algorithm in Matlab. The convergence criterion, or tolerance for this particular problem, is set at 10−6. The outcomes are obtained to demonstrate the characteristics of different parameters, such as the temperature exponent, volume fraction, and stretching ratio parameter graphically. Silver-water nanofluid proved to have a high-temperature transfer rate when compared with zinc-water and copper-water nanofluid. Moreover, the outcomes of the study are validated by providing a comparison with already published work. The results of this study were found to be in complete agreement with those of Magyari and Keller and also with Lui for heat transfer. The novelty of this work is the comparative inspection of enhanced heat transfer rates and reduced drag and lift coefficients, particularly for three nanofluids, namely, zinc-water, copper-water, and silver-water, over an exponentially stretching. In general, this study suggests more frequent exploitation of all the examined nanofluids, especially Ag-water nanofluid. Moreover, specifically under the obtained outcomes in this research, the examined nanofluid, Ag-water, has great potential to be used in flat plate solar collectors. Ag-water can also be tested in natural convective flat plate solar collector systems under real solar effects.