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The cooling process of a hot rolled strip on the run-out table (ROT) mainly determines the microstructure and mechanical properties of the final product; therefore, a method of investigation that helps companies follow the optimum cooling scenario is a profound issue. This paper develops a 2D finite element model based on industrial data that predicts the cooling pattern of hot rolled strips, with the potential to be formulated for steel grades dealing with complex boundary conditions, flexible to be applied for any cooling table. Meanwhile, this model investigates the thermal behavior of strips facing different heat transfer mechanisms in the full-scale ROT of Mobarakeh Steel Company (MSC). Moreover, coiling temperature (CT) and cooling pattern are validated through experimental data obtained from the Evraz hot rolling mill. Regarding the simulation of various header configurations, each four-header bottom bank, upper laminar, and water curtain headers deliver 10 ∘ C / s , 10.66 ∘ C / s , and 7.85 ∘ C / s of cooling rate, respectively. The simulations also predict the heat flux in the impingement, parallel, and air-cooling zones to be in the range of 4000–12,000, 500–2500, and 80–400 (w / m 2 K) on the top surface, and 21,000–5400, 700–4200, and 380–170 (w / m 2 K) on the bottom surface, respectively. According to the temperature-dependent attitude of steel properties, the effect of strip's thermo-physical properties on the heat transfer along ROT was examined, illustrating the significant impact of specific heat on cooling, which leads to the endorsement of the functionality of early cooling compared to delayed and distributed strategies for the investigated HSLA (high-strength low-alloy) steel. [ABSTRACT FROM AUTHOR]

This study investigates heat transfer and pressure drop in wavy-walled tubes filled with porous media under local thermal equilibrium (LTE) conditions. A two-equation k-ω SST turbulence model is implemented for the simulations. A Darcy–Brinkman–Forchheimer (DBF) model simulates the flow within porous domains. Based on Nusselt number, friction factor, and performance evaluation criteria (PEC), effective parameters such as wave amplitude, Darcy number, and particle diameter of porous media are investigated. As a result of the porous material addition to the wake region of wavy-walled tubes, the center of recirculation vortexes is shifted upstream, and the vortex intensity is reduced. Vortexes disappear in some cases. In these regions, the local Nusselt number increases due to the convergence of this phenomenon due to the placement of porous material in the divergent section of the wavy-walled tube. The results show that heat transfer and pressure drop variations are related to the Darcy number and the design point should be outside this region. Also, it was found that the Darcy number reduction increased the interaction between porous material and flow and PEC number decreases as shear stress increases in the convergent section. As a result of reducing the size of porous media particles, there is increased collision between fluid and particles, resulting in streamlines conforming to the tube wall and no reverse low. The results reveal that in this article, the maximum PEC number increases to 1.364, which indicates that affordable energy supply and improvement in energy efficiency are available with new ideas. [ABSTRACT FROM AUTHOR]

In this paper, hollow glass microspheres (HGMs) are used as fillers to improve the thermal properties of polyester resin. The thermal conductivity coefficient is obtained from experiment and numerical simulations and their results are compared. The thermal conductivity coefficient is measured using KD2 Pro which shows that the thermal conductivity coefficient decreases as the HGM weight fraction increases. For numerical simulations, the HGM sizes are obtained for different weight fractions based on the SEM images, Image J software and the histogram diagram. The RVEs are produced in Digimat and exported into COMSOL Code where the heat transfer problem is solved and the thermal conductivity coefficient is calculated. The HGM size and distribution show no practical effect on the conductivity coefficient. The results of temperature dependent and independent heat capacities and thermal conductivity coefficient are compared which show that the thermal conductivity coefficient using the constant specific heat capacity and thermal conductivity coefficient of matrix shows a better agreement with the experiment. Using the Cooperative rearranging region (CRR) estimate, the interphase width is calculated and added to the model which results show no difference with those without the interphase since its width is much smaller than the HGM size. [ABSTRACT FROM AUTHOR]

This study aimed to numerically evaluate the effects of various encapsulation gas parameters on the powder bed temperature distribution (which is crucial for the quality of the manufactured products' mechanical properties) in the SLS process. The simulations were validated with experimental data obtained from thermal photographs. A parametric study was conducted considering three main factors: gas type, pressure, and heat capacity, which were examined separately. It was observed that among the four gases of argon, ambient air, nitrogen, and helium, the most and the least uniform temperature distributions in the powder were related to helium and argon, respectively. In particular, it was seen that the standard deviation of the temperature of the points located on the powder surface decreased from 3.69 for Argon to 2.98 °C for helium (19.8% decrease). Moreover, the number of points within 4 °C from the final desired temperature increased from about 43 for argon to about 57.2% for helium. As for the gas pressure, it was seen that there is a direct relationship between pressure and the uniformity of the powder temperature distribution. In particular, the standard deviation of the temperature of the points located on the powder surface is decreased from 3.99 for the pressure of 0.4 atm to 3.16 °C for 2 atm (20.8% decrease). Moreover, the number of points within 4 °C from the final desired temperature increased from roughly 40.8 for 0.4 atm to about 48.2% for 2 atm. And finally, as for the gas heat capacity, increasing the gas heat capacity during the preheating process up to a value equal to the heat capacity of the air (while the other gas features were kept unchanged) increases the uniformity of the temperature distribution, whereas increasing the heat capacity beyond that value decreases the uniformity. [ABSTRACT FROM AUTHOR]

The present paper numerically investigates viscoelastic fluid flow in the developing flow regime through both straight and 90-degree curve ducts. The aim is to investigate the effects of the first and second normal-stress differences (N1 and N2) as well as the curvature ratio ( κ = D / R , where R and D are the curvature radius and channel side, respectively) and Reynolds number on the secondary flow patterns. Simulations were carried out in developing flow conditions in curved ducts using the finite volume method. The Reynolds numbers were 10, 20, 30, 40, 50, and 100, and the curvature ratios were 0.05, 0.066, 0.1, and 0.2. The Giesekus constitutive equation was utilized to model the non-linear rheological behavior of a 5.0 wt.% solution of polyisobutylene (PIB) in tetradecane (C14H30). The results reveal that a secondary flow with eight corner vortices is generated in a fully developed flow of viscoelastic fluid through a straight duct. This behavior is attributed to the difference in the second normal stress in the flow field. The results of the current study confirm that the second normal stress difference and change in the sign of N2 around the cross section's corners trigger these corner vortices. Furthermore, the effects of the curvature ratio on the distributions of first and second normal-stress differences in the developing Dean flow were studied for the first time. The vorticity vector method was used for mixing-enhancement assessment. The results show that the intensity of secondary flows was significantly higher in viscoelastic fluid at all curvature ratios and at all considered Reynolds numbers than in Newtonian fluid flow. [ABSTRACT FROM AUTHOR]

The current study investigates the laminar and two-phase nanofluid flow inside a two-dimensional rectangular microchannel with the ratio of length to height of L/H = 120. This study is simulated by using finite volume method in two-dimensional coordinates. Because most of the miniature equipments are affected by the oscillating heat flux, we try to study the hydrodynamical behavior of flow and heat transfer with oscillating heat flux boundary condition. The present research has been carried out in Reynolds numbers of 150-1000 and Ag nanoparticles volume fractions of 0-4% by applying slip and no-slip boundary conditions. Also, in order to estimate the heat transfer behavior and the computational fluid dynamics, two-phase mixture method is employed. The obtained results are analyzed and presented as the contours of Nusselt number, friction coefficient, pressure drop, thermal resistance and temperature. The results also revealed that, applying slip boundary condition on microchannel walls and the enhancement of fluid velocity, Grashof number and volume fraction of nanoparticles cause the improvement of Nusselt number, reduction of thermal resistance and total entropy generation and the augmentation of pressure drop. According to the obtained results, the presence of oscillating heat flux affects the changes of Nusselt number, significantly. In comparison with the pure water fluid with Reynolds numbers of 1000, 700 and 400, in Grashof number of 1000 with no-slip boundary condition on microchannel walls, the enhancement of average Nusselt number in volume fraction of 4% in the same Reynolds numbers is 45%. Also, in mentioned conditions, the pressure drop increases almost 2.8 times further. [ABSTRACT FROM AUTHOR]

In this paper, the effect of internal serrated fins and eccentricity on natural convection heat transfer between annular spaces with the equivalent circular, square, and triangular cross sections has been studied numerically using control volume method. The annuli's inner and outer walls were maintained at different uniform temperatures of 373 and 327 K, respectively, and Rayleigh number ranges were 105 ≤ Ra ≤ 108. According to the results, although heat transfer coefficient was reduced between the space of fins, fins increased the total heat transfer of both inner and outer walls of annuli. The best heat transfer rate belongs to reverse triangular annulus when fins were mounted on the inner wall. As an example, heat transfer of inner wall of reverse triangular annulus was, respectively, increased about 31 and 10% at Ra = 105 and 108, when serrated fins were mounted on the inner wall. In addition, fin efficiency of inner and outer walls was decreased with the increase in Rayleigh number. Nevertheless, thermal efficiency of reverse triangular annulus was uppermost at all Rayleigh numbers compared to other ones. In addition, eccentric annuli showed better heat transfer rate than concentric ones, in which cases 3.5 and 6.7% thermal improvements have been obtained for 0.6 and 1 mm downward movement of the inner wall at Ra = 108, respectively. [ABSTRACT FROM AUTHOR]