Papers by Keyword: Laminar Flow

Abstract: Heat losses from heating air ducts underground are used in many applications such as heating and air conditioning in cold weather. Researchers worked on heat losses to understand different ways to reduce heat losses to the environment. This project studies a 3-dimensional model of heating rectangular duct in cold surroundings. The model was done numerically. The numerical grid was tested to reach a reasonable approximation and a comparison with correlations from literature showed good agreement. Moreover, parametric study was carried out to study the effect of different parameters on heat losses. These parameters were Inlet velocity V_o, Inlet temperature T_o, outer heat transfer coefficient h_o, and surrounding temperature T_∞. Results showed that higher inlet velocity, inlet temperature, and outer heat transfer coefficient increases the total heat loss to the surroundings while higher surrounding temperature decreases the total heat loss to the surroundings.

Abstract: Passive Flow Control in Pipelines is gaining increased importance in the field of fluid transport, particularly in oil and gas applications. This approach relies on the installation of passive devices designed to alter fluid flow paths by generating suppression zones. Among these devices, fins are particularly notable. Hence, the objective of this paper is to provide a numerical investigation into the behavior of laminar flow within a bifurcated backward-facing step (BFS), controlled through the installation of a flexible fin at the lower wall of the enlarged duct part, with varying mechanical stiffness and positioning. The study considers a flow through an expanded conduit, where the fluid enters with a predefined velocity profile and subsequently splits into two sub-conduits. The investigation focuses on examining the influence of fin length (0.5 ≤ L_c/H ≤ 1), position (4 ≤ x₀/H ≤ 7), and elasticity on the elasto-hydrodynamic structure of the flow, including vortex formation, flow separation, the maximum displacement of the flexible fin, and the efficiency of the sub-conduits at the outlet. This analysis is governed by the momentum equations, coupled with solid mechanics equations, using the Arbitrary Lagrangian-Eulerian (ALE) framework. The governing equations are solved using the finite element method, implemented through the simulation and the sliding mesh technique in COMSOL Multiphysics 5.7. The numerical results reveal that installing a flexible or rigid fin within the BFS system significantly impacts the non-isothermal flow behavior within the bifurcation ducts. This configuration effectively allows for flowrate regulation at the BFS outlet, also making it possible to equalize flow rates under specific conditions, particularly when using longer fin that extend halfway across the channel. Moreover, the fin placement on the bottom is important for achieving effective flow rate control and heat transfer, aligning with desired requirements for each branch outlet.

Abstract: This present study is intended for a CFD analysis of hydrodynamic and thermal characteristics of water-based fluid containing TiO₂ or CuO nanoparticles flowing in laminar regime in a 3D uniformly heated horizontal annulus utilizing several. Four distinct models have been developed using various combinations (A, B, C and D) of the available theorical-based and experimental-based thermal conductivity and viscosity correlations. A CFD-Fortran code based on the finite volume technique was elaborated for the numerical solution of the mathematical model of the problem. The implications of Grashof number, volume fraction, and type of nanoparticle on isovelocity, isotherms, mean and wall temperatures, Nusselt number, heat transfer coefficient, pressure drop, and thermal performance evaluation criteria are explored using these different models. The results demonstrate that the Nusselt number and heat transfer coefficient of all developed models improve with the addition of nanoparticles. For 2% of nanoparticles’ concentration, the largest enhancement was reached for model D by about 23.5% with respect to the based liquid, while the smallest enhancement was obtained for model B by about 1.16%. The highest Performance Evaluation Criteria (PEC) are attained by employing model D by about 1.263, followed by model C by about 1.074.

Abstract: The thermophysical properties as well as the thermal performance of a nanofluid can be altered upon varying the nanoparticle type and/or nanoparticle volume concentration. Herein, the effects of variable nanoparticle concentration on water-based TiO₂, SiO₂, TiC, and SiC nanofluids have been studied analytically. The dispersion effects of 1-4% nanoparticle on the single-phase forced convection heat transfer performance of the nanofluids have been investigated. The effective thermophysical properties of the nanofluids are determined adopting the general correlations. The flow velocities of the nanofluids relative to their base fluids are assumed to be constant. Mouromtseff number has been employed as a convenient figure of merit to compare the nanofluids under fully developed internal laminar and turbulent flow conditions. The results indicate an increase in effective density, thermal conductivity, and dynamic viscosity of the nanofluids. Nanofluids containing carbide suspensions exhibit superior heat transfer properties compared to those having oxide suspensions.

Abstract: In this work, we have studied numerically the influence of the nature of nanofluids and the obstacle position, within the mini-channel of dimensions (10 x 10 x 108 mm³) on the electronic component cooling. The power of the electronic component is constant. In these simulations we have considered the Al₂O₃-water, SiO₂-water and TiO₂-water as coolants. The numerical results are obtained by choosing a Reynolds number (Re) between 300 and 500 and considering that the flow regime is stationary. The simulation was performed using the software, ANSYS FLUENT.The analysis of the simulation results shows that the position of obstacles within the mini-channel has considerable effects on the improvement of the electronic component temperature. The results also showed that among the nanofluids studied, the liquid containing nanoparticles Al₂O₃-water is the best for the electronic component cooling.

Abstract: In this paper, the case of the steady two-dimensional flow in a two-sided lid-driven square cavity is numerically investigated by the finite volume method (FVM). The flow motion is due to the top and bottom horizontal walls sliding symmetrically in the opposite direction with equal velocities, U_T and U_B, obtained through three respective Reynolds numbers, Re_1,2=10000, 15000, and 20000. Due to the lack of availability of experimental results in this Reynolds number margin for this type of flow, the problem is first examined by considering that the flow is turbulent with the inclusion of four commonly used RANS turbulence models: Omega RSM, SST k-ω, RNG k-ε and Spalart-Allmaras (SA). Next, the regime is considered being laminar in the same range of Reynolds numbers. A systematic evaluation of the flow characteristics is performed in terms of stream-function contour, velocity profiles, and secondary vortices depth. Examination of the calculation results reveals the existence of a great similarity of the predicted flow structures between the Omega RSM model and those from the laminar flow assumption. On the other hand, the computed flow with the SST k-ω model, the RNG k-ε model, and the SA model reveals a remarkable under-prediction which appears clearly in the size and number of secondary vortices in the near-wall regions. Various benchmarking results are presented in this study.

Abstract: A numerical study of the natural convection of laminar heat transfers in the stationary state in a half-elliptic inclined cavity, which represents a continuation of the work done, we studied the influence of the tilt of the cavity by varying the angle — entered 0 degrees, which corresponds to the horizontal cavity, up to 15 degrees. For each value of δ we varied the Rayleigh number from 2.13 10³ to 10⁶. The system of equations governing the problem solved numerically by the fluent calculation code based on the finite volume method. Based on the Boussinesq approximation. Both bottom and upper walls maintained at a constant temperature. The interest of this study is to see the influence of the tilt of the half-elliptic cavity on the structure of the flow and the distribution of temperature. These results can exploited in semi-elliptic agricultural greenhouses that rest on sloping soils. We chose a Prandtl number 0.71 that corresponds to the air. Keywords: Heat transfer; half-elliptical; Natural convection; Laminar flow; Multicellular; CFD simulation

Abstract: In the present study, heat transfer characteristics of MgO-oil based nanofluid in a miniature counter-flow double-pipe heat exchanger are investigated experimentally and numerically. The nanofluid is a mixture of corn oil as a base fluid and MgO particles in nanorange. The heat exchanger is fabricated from 316 stainless steel with length 500 mm. Cold water flows in the annulus side, and the nanofluid is utilized as the hot medium in the inner tube. ANSYS FLUENT 17,0 commercial software was employed for numerical investigation. The results obtained from using nanofluids are compared with the pure oil base fluid as a hot medium. Effects of inlet flow rate of hot nanofluids and concentration of nanoparticles are considered. It is observed that the average heat transfer rates for nanofluids are higher than those for pure corn oil. The improvement of both MgO concentration and inlet flow rates of nanofluid has a positive impact on the overall heat transfer coefficient and heat transfer rate. In contrast, the pumping power augments as well as the pressure drop increases.

Abstract: Fully developed Mixed Convection through vertical channel in the presence of heat generation/absorption with first order chemical reaction is analyzed.The thermal boundary conditions are isothermal–isothermal for left and right walls of the channel and kept at different temperatures.The effect of thermal buoyancy parameter, concentration buoyancy parameter and heat generation/absorption parameter are studied. Also the flow field with the presence of first order chemical reaction is particularly analyzed. The governing equations are solved using finite element method.Velocity, temperature and concentration profiles are investigated for different values of the flow parameters.

Abstract: In this present study, periodically positioned triangular shaped ribs having a round top corner at the bottom with groove positioned on the top side of the plate is analyzed at laminar flow conditions. The numerical results obtained for the heated plate with rib-groove geometry are compared with that of the flat plate kept under similar conditions. At lower air flow velocity, the Nusselt number of the flat plate improved from 400 to 1407 with the provision of triangular ribs-groove arrangement in it. Similarly, it improved from 850 to 6420 at higher air flow velocity with triangular ribs-groove arrangement. Higher Nusselt number values leads to a higher heat transfer coefficient values. Therefore, the triangular ribs-groove geometry gives an enhanced rate of heat transfer with minimum pressure drop. The study shows that irrespective of geometry, the rate of heat transfer is relying on fluid (air in this present case) flow velocity over heated plate, fluid flow contact with the heated plate and surface area of the heated plate.