Study Of Laminar Forced Convection Research Articles

Numerical Study of Forced Convection of Nanofluid Flow Over a Backward Facing Step With a Corrugated Bottom Wall in the Presence of Different Shaped Obstacles

In this paper, a numerical study of laminar forced convection of nanofluid flow over a backward facing step with a corrugated bottom wall in the presence of different shaped obstacles placed behind the step was performed. The bottom corrugated wall of the channel downstream of the step is isothermally heated and the other walls of the channel and obstacle surface are assumed to be adiabatic. The governing equations are solved with a finite-element method. The influences of the Reynolds number (between 10 and 200), solid volume fraction of the nanoparticle (between 0 and 0.05), and obstacle type (circular, square, and diamond shaped) on fluid flow and heat transfer are numerically investigated. It is observed that among different obstacles, the diamond shaped obstacle provides better local heat transfer enhancement characteristic in the vicinity of the step compared to the circular or square obstacle at high Reynolds number. Heat transfer enhancement of 6.66% is achieved in terms of maximum values with a diamond shaped obstacle compared to the no-obstacle case of the corrugated channel. Adding an obstacle deteriorates heat transfer in terms of average values for the backward facing step geometry with a corrugated wall. When the solid volume fraction of nanoparticle is increased, maximum and average heat transfer rate increase. Heat transfer enhancements of 7.45%, 7.42%, 6.94%, and 6.64% are obtained for the average values for circle, diamond, square, and no-obstacle cases, respectively, when solid volume fraction of 0.05 is compared to pure fluid.

Influence of inclination angle of magnetic field on mixed convection of nanofluid flow over a backward facing step and entropy generation

In this paper, numerical study of laminar forced convection of nanofluid flow over a backward facing step for different inclination angles of magnetic field is performed. The bottom wall of the channel downstream of the step is isothermally heated and the other walls of the channel are assumed to be adiabatic. Finite element method was used to solve the governing equations. The influence of the Reynolds number (between 20 and 200), Hartmann number (between 0 and 50) and solid volume fraction of the nanoparticle (between 0 and 0.04) on the fluid flow and heat transfer are numerically investigated for different orientation angles of the magnetic field. It is observed the averaged heat transfer increases as the Reynolds number increases and this effect is more pronounced with higher values of inclination angle of the magnetic field. As the value of the Hartmann number decreases for horizontally aligned magnetic field and volume fraction of the nanoparticles increases averaged and local enhancement of heat transfer are observed. For the inclined and vertical magnetic field, suppression of the recirculation zone behind the step is observed as the value of Ha increases which results in heat transfer enhancement. The total entropy generation ratio increases with increasing values of Reynolds number, solid volume fraction of nanoparticles and decreasing values of Hartmann number for horizontally oriented magnetic field.

The experimental and theoretical study of laminar forced convection of nanofluids in the round channel

The experiment-calculated investigation of forced convection of nanofluids based on CuO nanoparticles was carried out. Nanoparticle concentration varied in the range from 0.25 to 2 vol.% in the experiments. The considerable heat transfer intensification was obtained. The power applied to the pump for pumping the nanofluid was measured. A strong influence of the polymer used to stabilize the transport properties of nanofluids was shown. The Newtonian behavior for 0.25%-nanofluid, and non-Newtonian behavior, that described well with power-law model, for all other cases, were obtained. The hydrodynamic description and the model of homogeneous nanofluids are used for modelling. As is shown by the results, such a model satisfactorily describes in some cases the data of full-scale experiment of nanofluids forced convection in laminar flow regimes.

Numerical study of heat transfer performance of single-phase heat sinks with micro pin-fin structures

This paper presents a numerical study of laminar forced convection in heat sinks with micro pin-fin structure. A water cooled heat sink on a 1 cm × 1 cm substrate has been studied. Both pin-finned microchannel heat sinks (MCHSs) and pin fin heat sinks (PFHSs) are investigated. The distribution patterns of the fabricated pin-fins are either oblique or staggered. The Navier–Stokes and energy equations for the liquid region and the energy equation for the solid region are solved simultaneously to find the hydraulic and heat transfer performance of the heat sinks. The heat removal fluxes in finned MCHSs and PFHSs with different height of micro pin fins are compared with that in an optimum simple MCHS in equal pumping powers. It is shown that for the same pumping powers, the heat removal of the finned heat sinks is lower than that in the optimum simple MCHSs at medium and high pumping powers. The finned heat sinks, however, perform slightly better than an optimum simple MCHS for small pumping powers. It is also shown that studied heat sinks can be optimized using entropy generation minimization.

Numerical Study of Laminar Forced Convection of Water/Al2o3 Nanofluid in an Annulus with Constant Wall Temperature

Laminar forced convection of a nanofluid consisting of water and Al2O3 in a horizontal annulus has been studied numerically. Two-phase mixture model has been used to investigate thermal behaviors of the nanofluid over constant temperature thermal boundary condition and with different volume concentration of nanoparticles. Comparisons with previously published experimental and analytical works on flow behavior in horizontal annulus show good agreements between the results as volume fraction is zero. In general convective heat transfer coefficient increases with nanoparticle concentration. ABSTRAK: Kertaskerja ini mengkaji secara numerik olakan paksa bendalir lamina yang menganduangi air dan Al2O3 didalam anulus mendatar. Model campuran dua fasa digunakan bagi mengkaji tingkah laku haba bendalir nano pada keadaan suhu malar dengan kepekatan nanopartikel berbeza. Perbandingan dengan karya eksperimen dan analitikal yang telah diterbitkan menunjukkan bahawa kelakuan aliran didalm anulus mendatar adalah baik apabila pecahan isipadu adalah sifar. Pada amnya, pekali pemindahan haba olakan meningkat dengan kepekatan nanopartikel. KEYWORDS: nanofluid; volume concentration; heat transfer enhancement; laminar flow convection; annulus

Application of integral transform technique to the transient laminar flow heat transfer in the ducts

In this paper, a theoretical study of laminar forced convection inside ducts, subjected to periodically varying inlet temperature is presented. A thermal diffusion in the duct walls and a boundary condition which accounts for external convection are considered. In the first part, this problem is solved by applying a Generalized Integral Transform Technique (GITT). The complex eigenvalues and coefficients results are listed and compared with the literature. In the second part, the Quasi-steady Approach (QSA) which employs a constant heat transfer coefficient at liquid–solid interface is also investigated and compared with the GITT solution. The bulk temperature, Nusselt number, the damping and phase lag coefficients as function of the inlet temperature frequency are plotted.

Numerical Study of Laminar Forced Convection in Entrance Region of a Wavy Wall Channel

A numerical study of laminar forced convection in entrance region of a wavy-channel is presented. The wavy walls are described by a sinusoidal profile and maintained to a uniform temperature. Transfer equations are solved numerically with an iterative finite-volume. The PISO algorithm handles the linkage between the velocity and the pressure field. The effects of the Prandtl number, the Reynolds number and the amplitude of the corrugation on transfers have been analysed. In the entrance zone of the channel, shear stresses and Nusselt numbers increase as the Reynolds number increases. The lengths for which the flow and the thermal transfer are established depend on the Reynolds number, the amplitude of corrugation and the Prandtl number. The optimal amplitude for the heat transfer is found equal to 0.12 for water.

Optimized mass flux ratio of double-flow solar air heater with EHD

The numerical study of laminar forced convection inside double-flow solar air heater with electrohydrodynamic technique is investigated by finite difference method. The electric field is generated by the wire electrodes charged with DC high voltage. The mathematical modeling of computational fluid dynamics includes the interactions among electric field, flow field, and temperature field. It can be perceived that augmented heat transfer with presence of an electric field increases with the supplied voltage but decreases with the total mass flux. The optimized mass flux ratio is expressed incorporating with concerning parameter comprising of the electrode arrangement, the number of electrodes, the total heat flux at an absorbing plate, and the channel geometry.

Numerical study of three‐dimensional non‐Darcy forced convection in a square porous duct

The objective of the present work was to perform a detailed numerical study of laminar forced convection in a three‐dimensional square duct packed with an isotropic granular material and saturated with a Newtonian fluid. Hydrodynamic and heat transfer results are reported for three different thermal boundary conditions. The flow in the porous medium was modeled using the semi‐empirical Brinkman‐Forchheimer‐extended Darcy model which also included the effects of variable porosity and thermal dispersion. Empirical models for variable porosity and thermal dispersion were determined based on existing three‐dimensional experimental measurements. Parametric studies were then conducted to investigate the effects of particle diameter, Reynolds number, Prandtl number and thermal conductivity ratio. The results showed that channeling phenomena and thermal dispersion effects are reduced considerably in a three‐dimensional duct compared with previously reported results for a two‐dimensional channel. It was found that the Reynolds number affects mainly the velocity gradient in the flow channeling region, while the particle diameter affects the width of the flow channeling region. As the Reynolds number increases or as the particle diameter decreases (i.e., when the inertia and thermal dispersion effects are enhanced), the Nusselt number increases. The effects of varing the Prandtl number on the magnitude of the Nusselt number were found to be more significant than those of the thermal conductivity ratio. Finally, the effects of varing the duct aspect ratio on the friction factor can be neglected for small particle diameter (Dp ≤ 0.01) or for high particle Reynolds number (Red ≥ 1000) due to the dominant bulk damping resistance from the porous matrix (Darcy term) or strong inertia effects (Forchheimer term), respectively.

Forced convection of a power-law fluid in a porous channel - numerical solutions

A detailed numerical study of laminar forced convection in a porous channel which contains a fibrous medium saturated with a power-law fluid was performed. Hydrodynamic and heat transfer results are presented for a configuration that has uniform heat flux or uniform temperature heating at the walls. The flow in the porous medium was modeled using the modified Brinkman-Forchheimer-extended Darcy model for power law fluids in which the non-Darcy effects of inertia and boundary were considered. Parametric studies were conducted to examine the effects of Darcy number, power law index, inertia parameter and Prandtl number. The results indicate that when the power law index is decreased, the velocity gradient near the walls increases but these effects are reduced gradually as the Darcy number decreases until the Darcy regime (Da≤10−6) is reached in which case the effects of power law index become negligible. As the power law index is decreased, the thermal boundary layer thickness decreases significantly only in the non-Darcy regime. Consequently, as the power law index decreases, the fully developed Nusselt number increases considerably in the non-Darcy regime whereas in the Darcy regime the change in Nusselt number is very small. As the Prandtl number increases, the local Nusselt number increases and this effect is more significant for shear thinning fluids (n<1.0).

Réponse a un signal thermique sinusoïdal dans le cas d'un écoulement laminaire a plan directeur

A theoretical and numerical study of laminar forced convection in both parallel-plate channels, subjected to a sinusoidally varying inlet temperature, is presented. The plate's thermal response is coupled to the fluid via the congugation conditions at the interface (boundary condition of the fourth kind). A thermal diffusion in the plate and a boundary condition that accounts for external convection are considered. The temperature amplitude and phase lag are determined as a function of four parameters. The results are compared at the classical hypothesis of isothermal plates used by several authors. Exactness of the numerical scheme solutions are established by comparison with exact solutions for slug flows.

Unsteady thermal entrance heat transfer in laminar flow with a periodic variation of inlet temperature

A theoretical study of laminar forced convection in the thermal entrance region of a rectangular duct, subjected to a sinusoidally varying inlet temperature, is presented. Several boundary conditions that account for uniform wall heat flux and/or external convections with or without wall thermal capacitance effects are considered. Analytical expressions for these problems are obtained through extending the generalized integral transform technique. The centerline temperature amplitudes are determined as a function of Biot number, fluid-to-wall thermal capacitance ratio and dimensionless inlet frequency of inlet heat input oscillations. The effects of these variables on the solution are discussed. The eigenvalues and corresponding coefficients are given in tabular forms.

Unsteady Laminar Forced Convection in Ducts With Periodic Variation of Inlet Temperature

A theoretical and experimental study of laminar forced convection in the thermal entrance region of a rectangular duct, subjected to a sinusoidally varying inlet temperature, is presented. A general boundary condition of the fifth kind that accounts for both external convection and wall thermal capacitance effects is considered, and an analytical solution is obtained through extending the generalized integral transform technique. The variations of amplitudes and phase lags of centerline and bulk temperatures are determined as functions of modified Biot number, fluid-to-wall thermal capacitance ratio, and dimensionless inlet frequency. An apparatus has been designed, built, and used for the experimental study to provide validation of the mathematical modeling employed. Good agreement is obtained when the nonuniform sinusoidally varying inlet temperature profile obtained by experiments is incorporated into the theoretical model.

A lumped study of laminar forced convection in pipes with circular transverse fins at the outer surface

A simplified analysis of laminar forced convection heat transfer in an externally finned horizontal pipe was performed using a lumped energy balance formulation. Local values for both the internal and external Nusselt numbers via correlations have been employed, leading to a simple ordinary differential equation which is solved numerically by a standard Runge-Kutta method. Results are presented for the distribution of the dimensionless total heat transferQT/Qmax plotted against the dimensionless axial stationX in the region of thermal development of the pipe. A sample of typical cases covering a wide variety of combinations of geometrical and thermal parameters in the finned pipe are discussed at length. It is found that results for all cases tested compared favorably with other more laborious numerically and analytically-oriented papers published recently in the open literature.