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Numerical predictions are made for Laminar Forced convection heat transfer with and without buoyancy effects for Supercritical Nitrogen flowing over an isothermal horizontal flat plate with a heated surface facing downwards. Computations are performed by varying the value of from 5 to 30 K and ratio from 1.1 to 1.5. Variation of all the thermophysical properties of supercritical Nitrogen is considered. The wall temperatures are chosen in such a way that two values of T are less than is the temperature at which the fluid has a maximum value of C for the given pressure), one value equal to and two values greater than. Three different values of are used to obtain range of to for forced convection without buoyancy effects and range of 0.011 to 3.107 for the case where buoyancy effects are predominant. Six different forms of correlations are proposed based on numerical predictions and are compared with actual numerical predictions. It has been found that in all six forms of correlations, the maximum deviations are found to occur in those cases where the pseudocritical temperature TT lies between the wall temperature and bulk fluid temperature. [ABSTRACT FROM AUTHOR]

The characteristics of forced convection heat transfer across a row of heated square cylinders kept in side‐by‐side arrangement are numerically investigated to examine the combined effects of Reynolds number and cylinder spacing for Ri = 0, 60 ≤ Re ≤ 160, Pr =.71, and s/d = 1.0–8.0, where the space between cylinder surfaces is s and the cylinder size is d. A numerical study was carried out using the thermal lattice Boltzmann method. The goal of this work is to explore the transitions in heat transfer phenomenon that occurs behind the cylinder and to report the corresponding regimes for heat transfer namely synchronous, quasiperiodic, and chaotic. The proposed regime of heat flow is a function of Reynolds number and spacing. The synchronous heat regime is obtained for s/d ≥ 5.0 and quasiperiodic, chaotic regimes are observed for 3.0 ≤ s/d < 5.0, s/d < 3.0, respectively at Re = 100. The instantaneous isotherms, the power spectra of the corresponding Nusselt number signals, and the significance of cylinder Nusselt number frequency are used to examine these heat flow regimes. The heat transfer regimes for a row of heated cylinders and flow regimes for a row of unheated cylinders both have comparable appearances except for the fact that the heat transfer regime is synchronous at s/d ≥ 5.0 and flow is synchronous at s/d ≥ 4.0. The chaotic or quasiperiodic heat transfer regimes occur due to merging and strong interactions between thermal blobs shed from the cylinders. Heat transfer is synchronous at a higher spacing and characterized by independent thermal blobs shedded from the cylinders. It is reported that as spacing reduces and Reynolds number increases, the mean value of the Nusselt number experienced by all cylinders increases. The important outcome of the present numerical work is that for understanding heat transfer from bluff body, the transitions that occur in heat transfer are useful. [ABSTRACT FROM AUTHOR]

Weaire-Phelan (thereafter W-P) structures, as a foam-liked structures, were widely used in the field of flow and heat transfer. The effect of various methods for removing connecting struts on the flow and heat transfer characteristics of W-P structures was investigated, while maintaining constant porosity for all structures. Furthermore, the influence of porosity on the optimal strut removal scheme for W-P structures was examined. Computational fluid dynamics (CFD) was employed to analyse the flow and heat transfer characteristics of these structures. Additionally, four representative structures were created through 3D printing technology to experimentally validate the results. The effects of geometric structure parameters on the flow resistance and heat transfer characteristics of different structures were also analysed in depth. The findings indicate that all the proposed methods for removing connecting struts result in a reduction in pressure drop of up to 20.2 %. However, the most overall heat transfer performance (OHTP) was achieved when only the symmetry direction connecting struts were removed. Furthermore, as porosity decreases, the improvement in OHTP with the strut removal scheme becomes more significant compared to the original W-P. This study provides ideas for the optimisation of complex strut structures. [ABSTRACT FROM AUTHOR]

The heat transfer of fluids in pipelines under conditions with variable thermophysical parameters is ubiquitous in engineering applications, but effective methods to predict the heat transfer parameters are scarce. To address this issue, an experimental method was proposed to measure the heat transfer parameters in a circular tube by considering the effect of the insufficient development of turbulence in the inlet region and a Robin boundary on the wall. The variation of the Nusselt number of the inner wall was calculated by measuring the temperature distribution of the outer wall, and a temperature-related Gnielinski correlation was developed for conditions under which the thermophysical parameters vary with the fluid temperature. The results demonstrated that the deviations between the experimental Nusselt numbers and the values predicted using the traditional Gnielinski correlation became larger and larger as the flow distance increased. The temperature-related correlation generally improved the prediction accuracy by more than 25%, and the accuracy was better with increasing inlet temperature and decreasing airflow velocity. This study provides an important empirical reference for the prediction of the convective heat transfer parameters in pipelines and related engineering applications under strong heating or cooling conditions.

It is aimed to enhance the temperature by increasing the heat transfer with the hot air jet impinging on the moist objects. In the non-angle position of the objects, the air jet has the least contact with the object's surface in all three positions, causing the temperature contour change around the object to be less. However, increasing the angle of the objects relative to the impinging jet increases the gradient in the temperature contour distribution. Especially in cases of 90°, the temperature of the air jet around the objects is highest, which specifies that the heat transfer to the moist object is less than in other angled situations. Besides, as the distance (H) of the object to the jet (H / D = 3.33) decreases, the temperature near the object also increases. At 30° angle object positions and basing on the distance to the jet flow, the temperature of the fluid around the objects is much lower than in other angle situations, which proves that the heat of the hot air jet can be better transferred to the moist object. Thus, as the drying process becomes more effective, more moist objects can be dried in the same period in industrial applications. [Display omitted] • For Re = 500 and H / D = 3.33, increasing the placement angle (θ) of the object relative to the impinging jet from θ = 0° to 30° causes the Nu a number to increase by 17.98 %. Therefore, it is important to optimally select the angle and position of the moist object relative to the hot air jet to ensure optimal drying conditions. • By reducing H / D from 5 to 3.33 in the angle position of 90° of the moist object at Re = 300, a 6.95 % increase in the Nu a number is achieved. • The lowest moisture rates are reached at θ = 45° − H / D = 3.33, while the highest rates are seen at θ = 0° − H / D = 5. • The effect of raising the angle on increasing both Nu number and moisture transfer (M) is greater than increasing the distance (H / D) for the same Re number. Drying is used as a preservation method for berries and greenstuffs. Thanks to the drying process, most of the water in the food is removed, creating an unsuitable environment for the activities of microorganisms. In this study, the heat and mass transfer characteristics of semi-circular moist objects placed at different angles (θ) of 0°, 30°, 45°, 60°, and 90°, and at different distances (H / D) of 5, 4, and 3.33 parallel to the impinging hot air jet flow were numerically investigated. Numerical calculations were carried out by solving the forced convection heat and mass transfer equations for two-dimensional, steady, laminar, and incompressible flow using the Ansys-Fluent program. For drying, moisture transfer equations were also resolved by typing a User-Defined Function (UDF) code in Ansys-Fluent. While the temperature of the jet flow (T jet) is 323 K, the moist object surface temperature (T s) is 298 K. Calculations were conducted for different values of Re numbers: 300, 400, and 500. The effects of the placement angles and positions of the moist object on the average Nu number (Nu a) were examined for different Re numbers. Additionally, temperature and moisture variations at the midpoint length of the object along the x -axis-(X) were evaluated in detail. However, streamline distributions around moist objects, and temperature and moisture isotherms inside the moist objects were visualized at distinct H / D distances and Re numbers for θ = 0°, 45°, and 90°. Velocity and temperature contour distributions were displayed for all θ angles and H / D distances for the Re number of 500. The consequences of this work were matched with the computational and empirical consequences of the studies conducted in the literature, and it was noticed that the outcomes were in good agreement with each other. For Re = 500 and H / D = 3.33, an increase in the θ from 0° to 30° resulted in a 17.98 % increase in the Nu a. Furthermore, the lowest moisture rates were reached at θ = 45° − H / D = 3.33, while the highest rates were observed at θ = 0° − H / D = 5. [ABSTRACT FROM AUTHOR]

• The thermodynamic analyses for CoFe 2 O 4 /H 2 O nanofluid flow under laminar regime. • Impact on thermo-hydraulic performance of wavy tape insert in tube has been observed. • The irreversibility analysis for different wavy rate has been carried out. • Thermal and hydraulic basic variable contours is compared under different cases. The primary objective of this investigation is to assess the impact of vortex generator geometry and nanofluid on thermohydraulic and irreversibility characteristics within a laminar flow regime. The study introduces an original CoFe 2 O 4/ H 2 O (1 % vol.) nanofluid and employs a wave tape insert to induce forced convection in a tube, accompanied by first and second-law thermodynamic analysis. The novelty of this research lies in the numerical exploration of heat transfer and flow profiles for a nanofluid in a tube, varying the wave rate (y = 4-5-6). The investigation considers the laminar model and single-phase approach in all analyses under constant heat flux (q" = 2000 W/m2). The study observed that the nanofluid flowing in the tube with a wave ratio of 4, 5, and 6 resulted in an average enhancement in the Nusselt number of 93.25 %, 86.26 %, and 80.06 %, respectively. The optimal performance evaluation criterion (PEC) for water flowing in the tube with a wave ratio of 6 at Re = 500 exhibited an increase of 11.0 %, whereas the CoFe 2 O 4 /H 2 O flow showed a 9.14 % increment in the average PEC along the Reynolds number. Moreover, the total entropy generation values for water flowing in tubes with wave ratios of 5, 6, and 4 exhibited increases of 101.88 %, 94.66 %, and 51.34 %, respectively, in comparison to the smooth tube. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Guangdong University of Technology is the property of Journal of Guangdong University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

We present the deep learning model for internal forced convection heat transfer problems. Conditional generative adversarial networks (cGAN) are trained to predict the solution based on a graphical input describing fluid channel geometries and initial flow conditions. Without interactively solving the physical governing equations, a trained cGAN model rapidly approximates the flow temperature, Nusselt number (Nu), and friction factor (f) of a flow in a heated channel over Reynolds number ranging from 100 to 27,750. For an effective training, we optimize the dataset size, training epoch, and a hyperparameter ν. The cGAN model exhibited an accuracy up to 97.6% when predicting the local distributions of Nu and f. We also show that the trained cGAN model can predict for unseen fluid channel geometries such as narrowed, widened, and rotated channels if the training dataset is properly augmented. A simple data augmentation technique improved the model accuracy up to 70%. This work demonstrates the potential of deep learning approach to enable cost-effective predictions for thermofluidic processes. [ABSTRACT FROM AUTHOR]

To simulate heat transfer processes, there are numerous numerical methods available; in the meantime, the lattice Boltzmann method is a novel method for analyzing a type of engineering problem that has been very much considered. In the present study, to analyze the heat transfer problem of fluid flow between two horizontal parallel planes and solve the governing equations, such as momentum equations, energy and radiation transfer, the lattice Boltzmann method was used, whereas energy and momentum equations are solved by two relaxation time models to increase stability in the lattice Boltzmann method. For radiation intensity, the radiative transfer equation is solved by the single relaxation time model, and then radiation flux divergence is added into the energy equation. The geometry governing the problem is a horizontal and two-dimensional channel with constant temperature walls. After explaining the lattice Boltzmann method and solving governing equations, the results were validated, and the effect of radiation heat transfer parameters (Planck number–Optical thickness–Scattering albedo) on the heat transfer problem for fluid flow between two horizontal plates was determined. By examining the impact of the related parameters, it was found that increasing the optical thickness, decreasing the Planck number and reducing the scattering albedo tend to enhance the effect of radiative heat transfer. More importantly, the optical thickness parameter has the most influence on the radiative heat transfer. [ABSTRACT FROM AUTHOR]

Copyright of Experimental Technology & Management is the property of Experimental Technology & Management Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

• FIV of a cylinder with an attached splitter plate is numerically studied. • The investigations are performed for Reynolds numbers in a range of 1156 − 9246. • The plate length and mass ratio affect the vibration responses and heat transfer. • The FIV process has both negative and positive effects on heat transfer. • Increasing the plate length and reducing the mass ratio enhance the heat transfer rate. The two-degree-of-freedom (2DOF) flow-induced vibration (FIV) of a circular cylinder with heat transfer in turbulent flow is numerically investigated. The cylinder with an attached splitter plate is elastically supported and allowed to vibrate in both in-line and transverse directions. The unsteady RANS and energy equations along with the SST k-ω turbulent model are coupled with the equation of vibration to study the FIV of the cylinder. The effects of the attached plate length (L/ D = 0.5, 1.0, and 1.5) and the mass ratio (m r = 2 and 6.76) on the heat transfer rate, vortex shedding patterns, vibration trajectories, FFT, and cylinder displacements are studied in a wide range of Reynolds number (1156–9246) and reduced velocity (2–16). The results indicate that FIV can have either a positive or negative effect on heat transfer enhancement, depending on the splitter plate length and the type of cylinder vibration response. At high Reynolds numbers, the cylinder vibration response is observed in the galloping region, accompanied by a significant vibration amplitude. In this region, for L = 0.5D, vibration has a positive effect on heat transfer, while for other lengths, this effect is negative. For L = 1.5D and a reduced velocity of 5.5, contributions of vortex-induced vibration (VIV) and surface area in the heat transfer enhancement are 23.5 % and 44.3 %, respectively. By reducing the mass ratio from 6.76 to 2.6 for L = 0.5D, the heat transfer rate increases by approximately 40 % compared to a stationary cylinder. [Display omitted] [ABSTRACT FROM AUTHOR]

Biomass gasification in supercritical water (SCW) for high energy density gas fuel is a promising method for the efficient usage of biomass resource. Researches have indicated that the gasification efficiency is greatly depended on the heat transfer rate during the practical process of cold biomass particle injected into SCW. So the study of the forced convection heat transfer characteristics of an endothermic-biomass particle placed in SCW crossflow is of great significance. Moreover, the study of the particle surface local heat transfer rate distribution is also necessary for the complete gasification of biomass particles in SCW. Therefore, this work performs particle-resolved direct numerical simulation study on SCW flow past an endothermic sphere. Results demonstrate that the heat transfer gets great enhancement when the heat transfer temperature range comprises the large specific heat capacity zone. For the particle surface local heat transfer distribution, the enhancement at the front of particle is much stronger than that at the rear. Furthermore, the heat transfer characteristics under different pressures are also studied. In the end, a new forced convection heat transfer correlation applicable for SCW flow past an endothermic sphere is obtained. • Forced convection heat transfer of an endothermic sphere in supercritical water. • Flow separation restrained and heat transfer enhancement mainly at particle front. • Similar heat transfer variation tendencies under different pressures. • A new correlation of Nu for supercritical water flow past an endothermic sphere. [ABSTRACT FROM AUTHOR]

In this paper, vortex-induced vibration of a circular cylinder with forced convection heat transfer and entropy generation in pulsating alumina–water nanofluid flow is investigated numerically. Numerical simulation is carried out for a constant mass ratio of 2 and damping ratio of 0.01 at a fixed Reynolds number of 150. The ranges of reduced velocity, particle volume fraction and inlet velocity oscillation amplitude are 3–8, 0–5% and 0–1, respectively. It was found that the lock-in phenomenon, nanofluid concentration and inlet velocity oscillation amplitude have an effective role in increasing heat transfer and decreasing entropy generation. Two wake patterns (2S and 2P) were observed in the present simulation. For velocity oscillation amplitude of 1, the transition from 2S to 2P modes occurs in vortex shedding pattern. [ABSTRACT FROM AUTHOR]

Forced convection heat transfer is a significant factor for the thermal control of a stratospheric airship. However, most of researches were conducted without considering the influence of flight state causing serious errors. In order to accurately predict the forced convection heat transfer of the stratospheric airship at an angle of attack, firstly, an empirical correlation of Nusselt number (Nu) as function of Reynolds number (Re) andlength to diameter ratio (e) is developedunder horizontal state based on a validated computational fluid dynamic (CFD) method. Then, a correction factor K, considering its angle of attack (α), is proposed to modify this correlation. The results show that: (1) Nusselt number increases with the increase of Reynolds number, decreases as the length to diameter ratio changes from 2 ~ 6, and increases as the angle of attack changes from 0° ~ 20°. (2) At higher Reynolds number, the calculated results are 30 percent higher than those of previous studies with α = 20°. (3) Compared with α and e, the effect of Re on correction factor K can be ignored, and K is a strong equation of α and e. The efficiency of heat transfer is increased by 6 percent with α = 20°. The findings of this paper provide a technical reference for the thermal control of a stratospheric airship. [ABSTRACT FROM AUTHOR]

Metal-rubber sandwich cylindrical shell displays a broad range of potential applications in the field of thermal insulation due to its advantages of lightweight, high-temperature stability, and superior high-temperature thermal insulation properties. To optimize the thermal insulation performance of a sandwich cylindrical shell with a metal-rubber core, this study proposes the idea of filling the pores of the metal-rubber with aerogel, thereby forming a composite structure of aerogel and metal-rubber (AMR). Through finite element analysis, the law of internal temperature changes in the AMR composite structure and the distribution laws of the velocity field, viscosity field, and pressure field of the sandwich cylindrical shell under varying wind speeds are investigated. These findings are further verified through heat transfer and forced convection tests. The results reveal that the thermal conductivity of the AMR composite structure at the same density is lower than that of the metal-rubber, and the thermal insulation performance of the AMR composite structure is directly proportional to its density. Meanwhile, through the analysis of forced convection heat transfer in the cylindrical shell, it is found that wind speed has a direct relationship with the pressure field, velocity field, and viscosity field. In addition, there is a relatively high viscosity and a low flow rate near the wall of the cylindrical shell, with a higher flow rate at the axis of the cylindrical shell. At the same wind speed, the temperature rise of the sandwich cylindrical shell shows a positive correlation with an increase in density, and the maximum stable temperature also increases correspondingly. Moreover, at the same density, the thermal conductivity demonstrates a negative correlation with increasing temperature. [Display omitted] • A novel composite structure of metal-rubber filled with aerogel (AMR) was proposed. • The thermal conductivity of AMR structures at different densities was analyzed. • Thermal insulation comparison between AMR and MR cylindrical shell were performed. • The forced convection heat transfer of cylindrical shell was explored. [ABSTRACT FROM AUTHOR]

• The effect of a double wavy geometric disturbance on the heat transfer is originally studied. • The local variations of Nu and the upstream streamwise velocity are strongly correlated. • The DW cylinder attenuates the heat transfer in comparison with the circular cylinder. • The wake modification by the DW cylinder associates to the attenuation of the heat transfer. The present study initially considered the double wavy (DW) shape as the geometric disturbance to control fluid flow and the heat transfer. The large eddy simulation (LES) was performed to solve the filtered momentum and energy equations at the subcritical Reynolds number of 3000 and the Prandtl number of 0.7. In order to evaluate the effect of DW geometry on the force coefficients and the heat transfer, the smooth (CY), and symmetric wavy (SW) and asymmetric wavy (ASW) cylinders are considered for the purpose of the comparison. The DW cylinder achieved the smallest mean drag and the largest suppression of the lift fluctuation among the different geometric disturbances. The Nusselt number of the DW cylinder has the smallest mean and fluctuation values. The spanwise local Nusselt number is strongly correlated to the geometric disturbance, which is consistent with the SW and ASW cylinders. The DW cylinder provided smaller spanwise local Nusselt number over the span than the SW and ASW cylinders. The DW cylinder attenuates the heat transfer in comparison with the circular cylinder. The wake modification by the DW cylinder associates to the attenuation of the heat transfer. [ABSTRACT FROM AUTHOR]

• Heat transfer and nanofluid flow around four sinusoidal side obstacles in a horizontal channel is numerically studied by LBM. • Effects of the Reynolds number and nanoparticles volume fraction at different non-dimensional amplitudes of the wavy wall of the sinusoidal obstacles are studied. • A growth of the Reynolds number leads to a rise of the temperature gradient on the walls of the channel. • An increment of nanoparticles concentration results in the heat transfer enhancement. In the present study, heat transfer by two-dimensional incompressible nanofluids around four sinusoidal side obstacles in a horizontal channel is numerically analyzed via the lattice Boltzmann method (LBM). The liquid in the channel is a water containing copper nano-sized particles. The viscosity and effective thermal conductivity of the nanoliquid are respectively defined through the Brinkman and Patel approaches. Analysis is run for various magnitudes of the Reynolds number (Re = 100, 200, 400) and nano-sized particles concentration (ϕ = 0, 0.03, 0.05) at different non-dimensional amplitudes (A = 0, 10, 20) of the wavy wall of the sinusoidal obstacles. The effects of changing the distance between the obstacles regarding their arrangement inside the channel are also investigated. The obtained data are presented with reference to the streamlines, temperature and Nusselt numbers profiles. The results indicate that, as the magnitude of the nano-sized particles concentration increases and the distance between the obstacles decreases, the mean Nusselt number rises. In addition, decreasing in the wavy border amplitude results to the thermal transmission enhancement. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Forced convection heat transfer of multi-wall carbon nanotubes–iron oxide nanoparticles/water hybrid nanofluid (MWCNT–Fe3O4/water hybrid nanofluid) inside a partially heated τ-shaped channel has been numerically investigated. The effect of magnetic field is taken into account. The governing equations are solved by the lattice Boltzmann method in the domain, and the results were compared with other numerical methods by an excellent agreement between them. The effects of parameters such as Hartmann number (0 ≤ Ha ≤ 60), volume fraction of nanoparticles (0 ≤ ϕ ≤ 0.003) and different location of two heaters on the fluid flow and heat transfer are studied. The results indicate that for all cases, the average Nusselt number of each heater increases as the volume fraction of nanoparticles increases. The heat transfer characteristics were significantly affected by the arrangement of the two heaters. The heaters located on the left half of the top wall is convection-dominant mechanism, and the conduction heat transfer is the primary mechanism when the heater is on the right half of the top wall. The average Nusselt number increases as Ha increases for the heater of dominating convection mechanism but decreases for the heater of dominating conduction mechanism. [ABSTRACT FROM AUTHOR]

A two-dimensional (2D) numerical simulation is performed to simulate the laminar forced convection of a nanofluid in a ribbed channel with apart heating (cooling) sources using lattice Boltzmann method (LBM). The multi-walled carbon nanotubes-iron oxide nanoparticles/water hybrid nanofluid (MWCNT-Fe3O4/water hybrid nanofluid) is used in this simulation. The velocity field, temperature distribution and heat transfer rate are numerically analyzed with the streamlines and isotherm patterns employing of a house code. In addition, the effect of Reynolds number (Re = 25, 50, 75 and 100), nanoparticle solid volume fraction (ϕ = 0, 0.001, 0.003) and ratio of the blocks height (A = 0.2, 0.3, 0.4) are measured. The results are validated against the results reported in the literature, and a good agreement is reported. The obtained results show a maximum value of 16.49% increase in the average heat transfer coefficient for all the considered cases relative to the base fluid. Moreover, the local Nusselt number proves that the use of blocks on the channel walls can increase the amount of heat transfer. Finally, the average Nusselt number shows a linear dependence on the increasing ratio of blocks height for constant solid volume fraction. The results of this study apply to the industrial equipment heating and cooling applications. [ABSTRACT FROM AUTHOR]

Highlights • The effect of an asymmetric wavy disturbance on the heat transfer is originally investigated. • The temperature has a double wavy formation in the wake. • The Nu distribution on the surface forms the invariant and increasing zones. • The ASW cylinder attenuates the heat transfer in comparison with the circular cylinder. Abstract The present study considered the asymmetric wavy (ASW) disturbance which has been confirmed as the passive control to modify the force coefficients Yoon et al. [25]. We evaluated the effect of the asymmetric wavy disturbance on the forced convection heat transfer. For the purpose of the comparison, the smooth (CY) and symmetric wavy (SW) cylinders are considered. Finally, the LES has been carried out to solve the momentum and energy equations governing the flow and thermal fields at the subcritical Reynolds number of 3000. The validation of the present numerical methods were successively done by comparing the force coefficients and the Nusselt number with the previous results. The ASW cylinder provided the smallest mean and fluctuation of the time-and total surface-averaged Nusselt number than the CY and SW cylinders. This dependence of the Nusselt number on the cylinder shape is correlated to the force coefficients. The time-and local spanwise surface averaged Nusselt number of the SW cylinder shows the regional dependent behaviors of an invariant region and an increasing region. The ASW cylinder shows the increasing and decreasing behaviors in the short and long wavelength parts. The double wavy formation of the temperature isosurface in the wake for the ASW cylinder is consistent with the 3D vortical structures. The most significant variation of the time-averaged local Nusselt Number appears in the upstream surface of the SW and ASW cylinders which induce the spanwise dependent incoming flow. [ABSTRACT FROM AUTHOR]

A local thermal non-equilibrium analysis of heat and fluid flow in a channel fully filled with aluminum foam is performed for three cases: (a) pore density of 5 PPI (pore per inch), (b) pore density of 40 PPI, and (c) two different layers of 5 and 40 PPI. The dimensionless forms of fully developed heat and fluid flow equations for the fluid phase and heat conduction equation for the solid phase are solved analytically. The effects of interfacial heat transfer coefficient and thermal dispersion conductivity are considered. Analytical expressions for temperature profile of solid and fluid phases, and also the channel Nusselt number (NuH) are obtained. The obtained results are discussed in terms of the channel-based Reynolds number (ReH) changing from 10 to 2000, and thickness ratio between the channel height and sublayers. The Nusselt number of the channel with 40 PPI is always greater than that of the 5 PPI channel. It is also greater than the channel with two-layer aluminum foams until a specific Reynolds number then the Nusselt number of the channel with two-layer aluminum foams becomes greater than the uniform channels due to the higher velocity in the outer region and considerable increase in thermal dispersion.

Forced convection heat transfer is a significant factor for the thermal control of a stratospheric airship. However, most of researches were conducted without considering the influence of flight state causing serious errors. In order to accurately predict the forced convection heat transfer of the stratospheric airship at an angle of attack, firstly, an empirical correlation of Nusselt number (Nu) as function of Reynolds number (Re) andlength to diameter ratio (e) is developedunder horizontal state based on a validated computational fluid dynamic (CFD) method. Then, a correction factor K, considering its angle of attack (α), is proposed to modify this correlation. The results show that: (1) Nusselt number increases with the increase of Reynolds number, decreases as the length to diameter ratio changes from 2 ~ 6, and increases as the angle of attack changes from 0° ~ 20°. (2) At higher Reynolds number, the calculated results are 30 percent higher than those of previous studies with α = 20°. (3) Compared with α and e, the effect of Re on correction factor K can be ignored, and K is a strong equation of α and e. The efficiency of heat transfer is increased by 6 percent with α = 20°. The findings of this paper provide a technical reference for the thermal control of a stratospheric airship.

A quasi two-dimensional numerical study is performed to analyze the thermo-magneto-convective transport of liquid metal around a square cylinder in a square duct subjected to a strong externally imposed axial magnetic field. The channel bottom wall is considered heated while the top wall is maintained at the free stream temperature keeping the cylinder adiabatic. The Reynolds and Hartmann numbers are kept in the range and . The flow dynamics in the aforementioned range of parameters reveals the existence of four different regimes out of which the first three ones are similar to the classical non-MHD 2-D cylinder wakes while the fourth one is characterized by the vortices evolved from the duct side walls due to the boundary layer separation which strongly disturbs the Kármán vortex street. The flow dynamics and heat transfer rate from the heated channel wall are observed to depend on the imposed magnetic field strength. With increasing magnetic field, the flow becomes stabilized resulting in a degradation in the forced convection heat transfer. A special case at a very high Reynolds number with Ha = 2160 is also considered to show the development of a Kelvin–Helmholtz-type instability that substantially affects the heat transfer rate.

Highlights • Novel convection heat transfer enhancement of a circular cylinder by a flexible fin. • Two-dimensional numerical study using a fluid-structure interaction solver considering heat transfer. • Investigation of different fin lengths and rigidities. • Large-amplitude flow-induced vibration (FIV) of the flexible fin is obtained by the lock-on effect. • Time-averaged Nusselt number through FIV increases up to 11.07% over the cylinder with a rigid fin. Abstract Forced convection heat transfer from a circular cylinder with a flexible fin in laminar flow with Re = 200 and Pr = 0.7 is investigated numerically. The two-dimensional incompressible Navier-Stokes equations and energy equation are coupled with the Euler-Bernoulli beam equation to describe the flow-induced vibration (FIV) of the flexible fin considering the convection heat transfer process. The modified characteristic-based split scheme, Galerkin finite element method, semi-torsional spring analogy method and loosely coupled partitioned approach are employed irrespectively for the flow and convection heat transfer, fin vibration, mesh movement and fluid–structure interaction. The accuracy and stability of the proposed numerical method are validated using three benchmark models including the forced convection heat transfer from a stationary cylinder, forced convection heat transfer from a transversely oscillating cylinder and FIV of a flexible plate behind a square cylinder. Finally, forced convection heat transfer characteristics from a circular cylinder with a flexible fin with fin length l = 0.5 D –1.5 D (D is the cylinder diameter) and elastic modulus E = 104 - 5 × 105 are analyzed in detail. The numerical results show that, when the vortex shedding frequency approaches the natural frequency of the flexible fin, the FIV frequency is locked on the natural frequency and the fin exhibits large-amplitude vibration. As a result, the 'dead water' region behind the cylinder is reduced and the convection heat transfer is improved. In the combinations of parameters considered, a maximum of 11.07% enhancement in heat transfer is obtained by the flexible fin. [ABSTRACT FROM AUTHOR]

Today, increasing the efficiency and optimization of energy systems in terms of economic and environmental conditions is of particular importance. So far, several methods have been proposed to increase the heat transfer in thermal systems, including the use of nanofluids and types of fluid flow turbulators. In this research, the application of both nanofluid and twisted tape to improve the heat transfer coefficient were numerically investigated. Different turbulence models were used to simulate fluid turbulence. The results showed that increasing the nanoparticle volume fraction, reducing the twisting ratio, and increasing the Reynolds number resulted in an increase in heat transfer. By reducing the twisting ratio from 15 to 5, the heat transfer rate increases from 8-16%. With rising Reynolds number from 10,000 to 20,000, maximum temperature differences decreases by 4.5%. Moving downstream of the flow, the difference between the maximum temperature of the sections decreases. Increasing the heat transfer and intensifying the effects of the twisted tape to downward are the reasons for this decline. [ABSTRACT FROM AUTHOR]

Highlights • The effect of a wavelength on the heat transfer at a subcritical Re is originally investigated. • The bifurcation of local peaks of Nusselt number occurs according to wavelength. • The mean Nusselt number along the wavelength correlates with the force coefficients. Abstract Large eddy simulation was carried out to investigate the forced convection around a wavy cylinder at a Reynolds number of 3000 in the subcritical regime and a Prandtl number of 0.7. This is initial research to find the effect of the wavelength (λ / D m ) on the forced convection at a subcritical Reynolds number. A wide wavelength range of 1.136 ⩽ λ / D m ⩽ 6.06 is considered, and the results are compared with those of a smooth cylinder. The local peaks of the time- and total surface-averaged Nusselt numbers for different wavelengths occur at the optimum wavelengths where the minimum and maximum drag occurs. Therefore, the variation of the time- and total surface-averaged Nusselt numbers along the wavelength correlates with the force coefficients on the wavy cylinder. The bifurcation of the location of the maximum Nusselt number from the node to the saddle occurs at the critical wavelength, which is the short optimal wavelength where the maximum drag reduction and suppression of the lift fluctuation appear. The position of the minimum Nusselt number moves from the middle toward the node with increasing wavelength and eventually saturates at the node. These variations of the local Nusselt number are supported by the isotherm distribution, which is strongly governed by wake structures based on shear layer separation. [ABSTRACT FROM AUTHOR]

Numerical results are presented investigating the effect of a gust impulse on the transient fluid flow and forced convection heat transfer from a rotating circular cylinder near a plane boundary in the two-dimensional, in-compressible flow regime. Reynolds numbers of 200, 600 and 1000 have been studied for a fluid of Prandtl number 7. Starting from static, the steady non-dimensional rotation rate is varied up to a maximum value of 5.5, in the counter clockwise direction, such that ( α ∈ { 0 , 0.5 , 1 , 2 , 2.5 , 4.7 , 4.9 , 5 , 5.5 } ) . Gap to diameter ratio for this work is fixed at 3. Typical governing equations namely continuity, momentum and energy have been solved using the Constant Wall Temperature (CWT) boundary condition. This work notes that higher rotation rate of the circular cylinder, in the second vortex shedding regime and slight perturbations in the flow may cause a resultant effect which leads to short term disruption in the plane wall boundary layer dynamics even at larger values of gap to diameter ratio. Moreover, the gust impulse superimposed to the mean flow at the domain inlet causes creation of temporary convection zones in the cylinder wake which have significant impact on the heat transfer from the cylinder surface. Variations in Strouhal number, vorticity contours, peak vorticity trajectory plots, temperature contours and Nusselt number distribution are presented and discussed in comparison with the existing literature. [ABSTRACT FROM AUTHOR]

The present study is an original research for the forced convection heat transfer around a helically twisted elliptic ( HTE ) cylinder inspired by a daffodil stem. Also, this study is an initial investigation to find the effect of the Reynolds number ( Re ) in the laminar flow regime. We carried out numerical simulations to investigate the flow and heat transfer around the HTE cylinder in 60 ⩽ Re ⩽ 150 and Prandtl number ( Pr ) of 0.7. The circular cylinder is considered for the purpose of the comparison. The drag and lift fluctuation for the HTE cylinder are much smaller than those of the smooth cylinder. The decreasing rate of Strouhal number ( St ) for the HTE cylinder to that for the smooth cylinder is about 4–7% in the present Reynolds number range. The smaller St of the HTE cylinder than the smooth cylinder associate a longer vortex formation length of the HTE cylinder. The three-dimensional (3D) geometry of the HTE cylinder formed the spanwise variation of the Nusselt number ( Nu ), resulting in the sinusoidal profiles. This spanwise variation of the Nusselt number is identified by the flow structures and the isotherms distribution. The time- and total surface-averaged Nusselt number of the HTE cylinder decreases from about 1.2% to 2.8% in the present HTE configuration and Re range, compared to the smooth cylinder. [ABSTRACT FROM AUTHOR]

The present study investigates the forced convection heat transfer around a biomimetic elliptic cylinder inspired by a harbor seal vibrissa (HSV). This study is an original research to find the effect of the unique geometry of HSV on the forced convection around the biomimetic cylinder. We carried out large eddy simulation (LES) to investigate the flow and heat transfer around the vibrissa shaped cylinder for the Reynolds number ( Re ) of 500 and Prandtl number ( Pr ) of 0.7. The circular and elliptic cylinders are considered for the purpose of the comparison. The time histories of the surface-averaged Nusselt number showed that the HSV provided the stable behavior of the heat transfer by the significant suppression of its fluctuation. This characteristic of the heat transfer is comparable to the unique ability of the HSV to suppress the lift fluctuation and to role as a detecting device to capture the water movement induced by prey fish. The three-dimensional (3D) geometry of the HSV formed the spanwise variation of the Nusselt number, resulting in the sinusoidal profiles with a maximum and a minimum at the saddle and the node, respectively. This spanwise variation of the Nusselt number is identified by the flow structures. The nearly undetectable vortices in the wake at the node leads to the very weak secondary heat transfer by the recirculation in the near-wake. Thus, the minimum of the Nusselt number appears at the node. Otherwise, the saddle forms the large vortices in the near-wake and improve the heat transfer in this region, forming the maximum of the Nusselt number. [ABSTRACT FROM AUTHOR]

[b]Abstract[/b]. Problem of a heat transfer from a certain solid object under forced convection of thermostatic fluid has been discussed. The analysed objects were a cylinder and a cuboid. They were studied while subjected to a stationary fluid flow at different angles of attack. Several values of the inflow velocity ranging from 0.01 m.s–1 to 1 m.s–1 have been taken into consideration. The analysed fluids were of the water and the ethanol properties, respectively. The analysis has been performed applying the CFD (Computer Fluid Dynamics) ANSYS code. The obtained results complement results of previous analytical studies that had created of a theoretical background for the modified step heating i.e. regular heating regime. In addition, they confirmed a good metrological condition of the developed procedure.[b]Keywords[/b]: thermal diffusivity (TD), temperature equilibration constant, forced convection heat transfer, modified step heating procedure of TD determination, computer fluid dynamics

The heat transfer and flow of nanofluids in microchannel heat sink is usually numerically investigated by the single-phase model. The thermal conductivity and viscosity of nanofluids are calculated in the whole computational region because the single-phase model, assumes the nanofluids is static and nanoparticles concentration is uniform. However for the actual forced flow process, the concentration distribution of the nanofluids is not uniform. So the thermal properties of the nanofluids vary within different computational regions. With the increase of the velocity of the nanofluids, the deviation between the prediction of single-phase model and experimental results increases. In this paper, a new simulation method is proposed to consider the inhomogeneous and dynamic thermophysical properties of the nanofluids by obtaining the nonuniformly distributed nanoparticle concentration in each numerical cell. At the same time, it takes into account the following factors: the interactions between the nanoparticles, the solid wall and the base fluid, the axial conduction, the slip boundary conditions and fluid-solid coupling. The results show that the proposed numerical simulation method further improve the simulation accuracy for the forced flow and heat transfer process of nanofluids in the microchannel in a wider range. The effects of the nanoparticles concentration, Reynolds number and axial heat transfer on the thermophysical properties of the nanofluilds, the flow and heat transfer characteristics of a rectangular microchannels with hydraulic dimensions of 341 μm were analyzed using the proposed simulation model. The main results are as follows: the nanoparticles are enriched at the near wall for the fully developed region; the nonuniformity of the nanofluilds thermal conductivity coefficient distribution at the channel cross section increases with the increase of the mass flow rate and the inlet centration; under the same Reynolds number, the higher the nanofluids concentration the better the heat transfer characteristics, but there is no linear relationship between the enhancement amplitude and concentration; the heat transfer coefficient of nanofluid with 1% and 2% alumina nanoparticles concentration is about 5.86% and 8.49% higher than that of deionized water, respectively; the axial conduction effect cannot be ignored for the microchannel, which significantly affects the inlet and outlet region of the microchannel especially when the Reynolds number is low. The nanofluilds temperature in the microchannel increases with the curve and does not match the conventional linear growth hypothesis. [ABSTRACT FROM AUTHOR]

This paper studies experimentally the forced convection heat transfer of turbulent flow in a cylindrical pebble bed channel with internal heat generation. Exergy and entropy generation analyses are performed to optimize energy conversion in the system identify the destruction of exergy in the pebble bed channel. Stainless steel spheres are used in stacked pebble bed channel. Internal heating is generated uniformly by electromagnetic induction heating method in metallic spheres. Dry air is used as the working fluid in the process of cooling of the heated spheres. The experiment is performed for turbulent flow regimes with Reynolds (Re d ) number (based on the diameter of the spheres) in the range of 920–2570, which is equal to Reynolds (Re) number, based on channel diameter, in the range of 4500–10,000. The effects of different parameters, including spheres diameter ( d = 5.5, 6.5 and 7.5 mm), inlet volumetric flow rate ( V ̇ ) and internal heat generation ( Q ) on the forced convection heat transfer, exergy transfer and entropy generation are studied. For second law and exergy analyses, mean exergy transfer Nusselt number (Nu e ) and entropy generation number ( N s ) are investigated. Results show that for a fixed d and Q , the mean exergy transfer Nusselt number (Nu e ) decreases with the increase of Re d number until it becomes zero for a critical Re d number. This critical Re d number found to be about 1450, 1800 and 2300 for d = 5.5, 6.5 and 7.5 mm, respectively. Further increase in the Re d number, decreases Nu e to negative values. It is found for spheres with diameter of d = 5.5 mm and for a fixed Q , as Re d increases, the entropy generation number N s increases monotonically. While, for d > 5.5 mm and fixed Q , the entropy generation number ( N s ) decreases with the increase of Re d number up to a critical Re d value that makes N s to be minimum. Further increase in Re d number, increases N s . It is also found that for Re d > 1800, among the sphere diameters studied in this work, balls with highest diameters yield the minimum entropy generation in the system. [ABSTRACT FROM AUTHOR]