Papers by Keyword: Forced Convection

Abstract: In this work, the thermal behavior of a turbulent forced-convection flow of air in a rectangular cross section channel with attached W-shaped obstacles is investigated. The continuity, momentum and energy equations employed to control the heat and velocity in the computational domain. The turbulence model of k-ε is employed to simulate the turbulence effects. The finite volume method with SIMPLE algorithm is employed as the solution method. The results are reported temperature, local and average Nusselt numbers, and mean velocity contours. The subject is relevant and important for industrial applications.

Abstract: This paper deals with a numerical simulation of laminar forced convection heat transfer from a pair of identical circular cylinders placed at the center of square cavity in the line array, the cavity is ventilated with single inlet and outlet ports, the inlet port is located at the middle of left vertical wall and the outlet port is located at the middle of right vertical wall. The work represents the effects of the distance between cylinders and Reynolds number on fluid flow and heat transfer rate. The governing equations of continuity, momentum and energy are solved by using finite-volume method. The obtained results are represented and discussed for following conditions: Reynolds number Re = 1 to 40, Prandtl number Pr = 7.01 and the gap distance S = 0.3L to 0.7L, where L is the cavity length. The main results are potted under the streamline and isotherm contours, the total drag coefficient and average Nusselt number of each cylinder is plotted versus studied parameters. It is found that the increase in the gap space distance between cylinders increases the heat transfer rate.

Abstract: This paper deals with numerical simulations of forced convection from a pair of identical cylinders arranged in tandem manner inside a square cavity of single inlet and outlet ports. The gap distance between the cylinders is fixed with half of square length. The main purpose of this study is to see the effect of inlet and outlet port positions on fluid flow and heat transfer rate. The governing equations of continuity, momentum and energy have been solved using finite-volume method in laminar, steady and two dimensional directions. The work has been done in the range of these conditions: Re = 1 to 40, at fixed Pr = 7.01. Three positions of inlet and outlet port have been selected. The mean results of flow patterns and distribution temperature are illustrated under the contours of streamline and isotherm respectively. The drag and lift coefficients of each cylinder is computed and discussed. The average Nusselt number of both cylinders is also presented and discussed. It was found that the inlet and outlet ports have significant effects on heat transfer from the confined cylinders.

Abstract: In the present work it is performed a study on the geometric evaluation of a pair of elliptical tubes subjected to external flow with forced convection by means of numerical approach. The objectives are the maximization of Nusselt number (Nu_D) and the minimization of drag coefficient (C_D). The degrees of freedom for the pair of tubes arrangement are: the ratio between the transverse pitch and characteristic length of tubes (S_T/D), where D = (A)^1/2, the ratio of the main and secondary axes of the elliptical tube (a/b) and the angle of incidence of the flow on the pair of tubes (α). The simulations were carried out considering two-dimensional forced convective flows, in the laminar regime and incompressible conditions. For all configurations, Reynolds and Prandtl numbers are constant, Re_D = 100 and Pr = 0.71. The Finite Volume Method (FVM) is used to solve conservation equations of mass, momentum and energy. The software Gmsh is used for creation of the geometries and generation of the meshes. Results showed that the degrees of freedom affected the fluid dynamic and thermal performance of the forced convective flow. According to the objectives outlined in this study, the best performance for the maximization of heat transfer was obtained when α = 0o, a/b = 1⁄2 and S_T/D = 3.5. In the case of the fluid dynamics study, the optimal result for C_D minimization occurred when α = 0o, a/b = 2.0 and S_T/D = 4.0. Thus, the optimal geometry will depend on the indicator performance where the problem is evaluated.

Abstract: The purpose of this work is to present a numerical study of a two-dimensional channel with two triangular fins submitted to a laminar flow with forced convection heat transfer, evaluating the geometry of the first fin through the Constructal Design method. The main objectives are to maximize the heat transfer rate and minimize the pressure difference between the inlet and outlet flow of the channel for different dimensions of the first channel fin, considering the same Reynolds (Re_H = 100) and Prandtl numbers (Pr = 0.71). The problem is subjected to three constraints given by the channel area, fin area and maximum occupancy area of ​​each fin. The system has three degrees of freedom. The first is given by the ratio between height and length of the channel, which is kept fixed, H/L = 0.0625. The other two are the ratio between height and width of the upstream fin base (H₃/L₃) positioned on the lower surface of the channel, and the ratio between height and width of the downstream fin (H₄/L₄) positioned on the upper surface of the channel, which is also kept fixed, H₄/L₄ = 1.11. The problem is simulated for three different values ​​of the fraction area of upstream fin (φ₁ = 0.1, 0.2 and 0.3). For the numerical approach of the problem, the conservation equations of mass, momentum and energy are solved using the finite volume method (MVF). The results showed that a ratio of φ₁ = 0.2 is the one that best meets the proposed multi-objective. It was also observed that φ₁ = 0.1 led to a better fluid dynamics performance with a ratio between the best and the worst performance for fluid dynamics case of 25.2 times. For φ₁ = 0.3, the best thermal performance is achieved, where the optimal case has a performance 65.75% higher than that reached for the worst case.

Abstract: The present study consists in a numerical evaluation of an arrangement formed by four cylinders submitted to an unsteady, two-dimensional, incompressible, laminar and forced convective flow. The geometric evaluation is performed through the Constructal Design method. The problem has two restrictions given by the sum of the area of ​​the cylinders and one occupation area and has three degrees of freedom: S_T1/D (the ratio between the transverse pitch of the frontal cylinders and the diameter of the cylinders), S_T2/D (the ratio between the transverse pitch of the posterior cylinders and the diameter of the cylinders) and S_L/D (ratio between the longitudinal pitch of the frontal and posterior cylinders and the diameter of the cylinders). For all simulations the Reynolds number is kept constant, Re_D = 100, and two different Prandtl numbers of Pr = 0.71 and 5.83 are considered, which simulates respectively the use of air and water as a fluid. The conservation equations of mass, momentum and energy are solved with the Finite Volume Method (FVM). The main objective is to evaluate the effect of the degrees of freedom on the drag coefficient (C_D) and the Nusselt number (Nu_D) between the cylinders and the surrounding flow, as well as the optimal S_T2/D values ​​for three ratios of S_T1/D = 1.5, 3.0 and 4.0, these results being obtained for ratios of S_L/D = 1.5 and 4.0. Results showed that the ratio changes of S_T1/D and S_T2/D have a great influence on the drag coefficients and on the Nusselt number of the arrangement formed by the four cylinders, as well as on the geometries leading to the best fluid dynamics and thermal performance.

Abstract: In contrast to the very rich literature on modeling and the determination of the thermal conductivity of nanofluids the forced convection data are limited. This work presents preliminary results of the experimental investigation of the forced convection heat transfer of water-Al₂O₃ nanofluids inside stainless steel tube with 8 mm internal diameter and 2000 mm length. Nanoparticles were tested at the concentrations of 0.01%, 0.1%, 1% and 5% by weight and the Reynolds number range encompasses laminar as well as turbulent flows.

Abstract: The present study focuses on the numerical study of thermal and flow characteristics in a microchannel heat sink with alternating trapezoidal cavities in sidewall (MTCS). The effects of flow rate and heat flux on friction factor and Nusselt are presented. The results showed considerable improvement heat transfer performance micro channel heat sink with alternating trapezoidal cavities in sidewall with an acceptable pressure drop. The heat transfer rate has improved in the cavity area due the greater fluid mixing in fluid vortices and thermal boundary layer disruption. The slipping over the reentrant cavities and pressure gain reduces pressure drop appears as the reason behind of only minor pressure drop due to the cavities.

Abstract: The heat transfer enhancement of the forced convection due to ionic wind over different surface conditions including a smooth, rough ruface and a source array of rectangular blocks surface (representing electronic components) was studied. Under laminar flow, the highest heat transfer rate of 0.0736 W/m².K per minute was observed for the source array surface. The average heat transfer coefficient during steady state of ionic cooling on smooth, rough and source array surfaces were observed to be 19.144 W/m².K, 18.736 W/m².K and 21.126 W/m².K respectively. The heat transfer properties of ionic wind are similar to moving air, generating high heat transfer coefficient and Nusselt number on source array surface due to recirculation eddies.

Abstract: An indirect type solar dryer is fabricated with the components like evacuated tube collector, drying chamber and blower. The performance of the drier is evaluated by carrying out drying experiments with copra at Coimbatore district Tamilnadu, India. A short survey of these showed that applying the indirect type solar dryer not only significantly reduced the drying time but also resulted in many improvements in the quality of the dried products. The temperature of the drying chamber ranges from 55°C to 75°C while the ambient temperature ranges from 28°C to 38°C. Nine basic solar drying models were used to fit the experimental data of copra. For experimental results, the logarithmic model showed the best curve fitting with highest correlation coefficient (R²⁾ and lowest value of RMSE (Root Mean Square Error). Solar dried copra obtained is free from smoke, dust, bird and rodent damage.