Search

Graphical abstract The physical model is intended to portray the schematic of the problem and behaviour of skin friction and Nusselt number. Highlights • The review describe the physical properties of Carreau nanofluids. • Flow past a wedge shaped geometry is studied. • Heat and mass transfer characteristics are further analyzed. • Effect of thermal radiation on heat transfer rate are investigated. • Numerical solutions are computed via collocated numerical method. Abstract In this article, an innovative revised Buongiorno's model is employed to investigate the flow of Carreau nanofluids generated by a wedge-shaped geometry. Moreover, heat and mass transfer characteristics are explored under the influence of non-linear thermal radiation. At first, the developed flow equations are made dimensionless via suitable transformations and then resulting set of nonlinear ordinary differential equations are solved numerically using built-in MATLAB solver bvp4c. It is observed that the solution of current flow problem is highly dependent on the contribution of several physical parameters like Weissenberg number, power-law index, wedge angle parameter, velocity ratio parameter, non-linear radiation parameter, suction parameter, Brownian motion and thermophoresis parameters, Lewis and Prandtl numbers. Detailed analysis for the novel results of dimensionless velocity, temperature and nanoparticles concentration with in the boundary layer region is exhibited graphically. The core physical implication of the computed results is that the thermal boundary layer is thinned by higher radiation parameter. This study reveals that an enhancement in the local Nusselt number is noted with higher temperature ratio parameter. On the other hand, an incremental skin friction ate the wall can be achieved by growing values of power-law index. The obtained data is distinguished with earlier studies and admirable agreement has been noted. [ABSTRACT FROM AUTHOR]

Highlights • Boiling flow phases are identified to obtain stable two-phase flow. • The flow rate decreases when the two-phase frictional resistance is large enough. • Existing models are roughly unsuitable for the natural circulation in rod bundle. • A new correlation for two-phase frictional pressure drop in rod bundle is fitted. Abstract Natural circulation boiling flow resistance characteristics in a 3 × 3 rod bundle channel are experimentally studied in this paper. In order to achieve a stable two-phase natural circulation flow, the boiling flow phases are identified and measures such as decreasing the inlet fluid subcooling degree and increasing the inlet local resistance are adopted. The ONB during the experiment is determined by the wall temperature drop. The variation of pressure drop components, including the gravity pressure drop, the frictional pressure drop and the acceleration pressure drop, is given. For high mass quality conditions, the mass flow rate is observed declining with the increasing heat flux when the frictional pressure drop and the acceleration pressure drop grow faster than the gravity pressure drop reduction. A few homogeneous flow models and separated flow models for the two-phase frictional pressure drop are compared against experimental results. The homogeneous flow models can well predict the frictional pressure drops for low mass quality conditions and the Duckler model predictions are the most accurate with a mean relative error of 15.7%. In terms of the separated flow models, the Mishima and Sun models predictions are in good agreement with experimental results respectively for low and high mass quality conditions. Based on the Chisholm correlation, a new correlation is fitted by experimental results. The friction factors obtained in single-phase experiments are used to calculate the liquid phase frictional pressure drops. The comparison against experimental results and data from other literatures shows the new correlation can well predict the two-phase frictional pressure drops under given flow conditions. [ABSTRACT FROM AUTHOR]

This paper investigates the bioconvection in rotating system between two rotating plates immersed in a nanofluid with temperature dependent viscosity and thermal conductivity. The passively controlled model is introduced to characterize the nanoparticle concentration on the upper plate. By means of the similarity transformation, the proposed governing equations are reduced to a class of coupled ODEs with boundary conditions and then the numerical solutions are obtained by the Matlab bvp4c ODE solver. Some important characteristics of velocity, temperature, nanoparticle concentration and density of the motile microorganisms are displayed graphically and discussed in detail. Results show that the viscosity variation parameter has remarkable influence on the local skin friction coefficient and Sherwood number, while local Nusselt number and wall motile microorganisms flux are more sensitive to the thermal conductivity variation parameter. Higher bioconvection Péclet number leads to the aggregation of the motile microorganisms in the middle of the two plates. Moreover, the aggregation of motile microorganisms is weakened by the intense Brownian motion, but improved by the thermophoresis effect. [ABSTRACT FROM AUTHOR]

In consideration of the effects of the local resistance and the frictional resistance in the natural circulation loop, the analytical relation between the natural circulation mass flow rate G and the heating power Q can be express as G ∼ Q m , m = f ( Re, R n ) , where the R n is the ratio of the local pressure loss coefficient and the friction coefficient. The relation of flow-resistance to the natural circulation mass flow rate can be expressed as Δ p f ∼ G r , r = f ( t , m ) . These correlations is tested with experimental data from the experimental facility of HRTL-200 II and showed reasonable agreement. [ABSTRACT FROM AUTHOR]

This work investigates transition to turbulence using laminar kinetic energy modeling based in single-point RANS approach. Transport equations are discretized using the cell centered control-volume method and the system of algebraic equations is relaxed using SIMPLE algorithm. A modified version of the most known laminar kinetic energy model is proposed and compared with the original version and with an experimental correlation transition model. The numerical results show that the laminar kinetic energy approach has reasonable experimental correlation. The modified version presents improvements in prediction of skin friction coefficient in flows subjected to pressure gradients. However, the use of the laminar kinetic energy concept has shown weakness when dealing with detached induced transition. Probably the cause of that is the lack of physical modeling of this phenomenon. Laminar kinetic energy modeling is in continuous evolution and is a good alternative to deal with engineering simulation that needs a good prediction of wall shear stress in transitional flows. [ABSTRACT FROM AUTHOR]

Abstract: The present study considers the effect of heat and mass transfer on free convective flow of a visco-elastic incompressible electrically conducting fluid past a vertical porous plate through a porous medium with time dependent oscillatory permeability and suction in presence of a uniform transverse magnetic field and heat source. The novelty of the present study is to analyze the effect of time dependant fluctuative suction and permeability of the medium on a visco-elastic fluid flow. The necessity of the present analysis arises as the most industrial fluids exhibit the visco-elastic behavior. The coupled nonlinear partial differential equation are turned to ordinary by super imposing a solution with steady and time dependant transient part. Finally, the set of ordinary differential equations is solved with a perturbation scheme to meet the inadequacy of boundary condition. Elasticity of the fluid and the Lorentz force reduce the velocity and it is more pronounced in case of heavier species. Most interesting observation is the fluctuation of velocity appears near the plate due to the presence of sink and presence of elastic element as well as heat source reduce the skin friction. [Copyright &y& Elsevier]

Abstract: Numerical modeling of Prandtl equations was undertaken in order to investigate into the effect of mainstream acceleration on characteristics of dynamic and thermal boundary layers. Unlike in dynamic boundary layer, nondimensional characteristics of thermal boundary layer proved to be rather conservative to the action of the favorable pressure gradient. It was found that, unlike the skin-friction coefficient and the momentum-thickness Reynolds number, the Stanton number and the energy-thickness Reynolds number both exhibit no saturation with increasing the Kays acceleration parameter. Also, an analysis of the violation of Reynolds analogy by the stream acceleration is given. [Copyright &y& Elsevier]

Abstract: This study investigates the thermal-diffusion and diffusion-thermo effects on the two-dimensional magnetohydrodynamics (MHD) axisymmertric flow of a second grade fluid. Mathematical analysis has been carried out in the presence of Joule heating and first order chemical reaction. Using momentum, energy and concentration laws, the governing partial differential equations have been reduced to the ordinary differential equations by suitable transformations. Series solutions are constructed by homotopy analysis method (HAM). Convergence of the derived series solutions is ensured. Plots are displayed in order to examine the influence of emerging parameters on the dimensionless components of velocity, temperature and concentration fields. Numerical computations for skin friction coefficient, Nusselt number and Sherwood number are tabulated. [Copyright &y& Elsevier]

Abstract: An experimental investigation of forced convection heat transfer in a rectangular channel (aspect ratio AR=5) with angled rib turbulators, inclined at 45°, is presented. The angled ribs were deployed with parallel orientations on one or two surfaces of the channel. The convective fluid was air, and the Reynolds number varied from 9000 to 35,500. The ratio of rib height to hydraulic diameter (e/D) was 0.09, while four rib pitch-to-height ratios (p/e) were studied: 6.66, 10.0, 13.33, and 20.0. The aim of the work was to study the effect of rib spacing on the thermal performance of the ribbed channel. The maps of local heat transfer coefficient in the inter-rib regions have been reconstructed by liquid crystal thermography. The thermal performance of each ribbed channel is identified by the average Nusselt number and by the friction factor. Superior heat transfer performance was found at the optimal rib pitch-to-height ratio of 13.33 for the one-ribbed wall channel and at p/e =6.66–10 for the two-ribbed wall channel. [Copyright &y& Elsevier]

Abstract: This study examines the airside performance of the wavy fin-and-tube heat exchangers having a larger diameter tube (Dc =16.59mm) with the tube row ranging from 1 to 16. It is found that the effect of tube row on the heat transfer performance is quite significant, and the heat transfer performance deteriorates with the rise of tube row. The performance drop is especially pronounced at the low Reynolds number region. Actually more than 85% drop of heat transfer performance is seen for Fp ∼1.7mm as the row number is increased from 1 to 16. Upon the influence of tube row on the frictional performance, an unexpected row dependence of the friction factor is encountered. The effect of fin pitch on the airside performance is comparatively small for N =1 or N =2. However, a notable drop of heat transfer performance is seen when the number of tube row is increased, and normally higher heat transfer and frictional performance is associated with that of the larger fin pitch. [Copyright &y& Elsevier]

Abstract: An unsteady mixed convection flow over a moving vertical plate in a parallel free stream is considered to investigate the combined effects of buoyancy force and thermal diffusion in presence of heat generation or absorption. The unsteadiness is introduced by the time dependent free stream velocity as well as by the moving plate velocity. The governing boundary layer equations are transformed into a non-dimensional form by a special group of non-similar transformations. The resulting system of coupled non-linear partial differential equations is solved by an implicit finite difference scheme in combination with the quasi-linearization technique. Computations are performed and numerical results are displayed graphically to illustrate the influence of the buoyancy (mixed convection) parameter, Prandtl number, the ratio of free stream velocity to the composite reference velocity and heat generation or absorption parameter on the velocity and temperature profiles. The numerical results for the local skin-friction coefficient and local Nusselt number are also presented. Present results are compared with previously published work and are found to be in excellent agreement. It is found that in presence of buoyancy force (λ >0), the velocity profile exhibits velocity overshoot 80% more for lower Prandtl number (Pr =0.7) as compared to the magnitude of the velocity overshoot for higher Prandtl number (Pr =7.0). [ABSTRACT FROM AUTHOR]

Abstract: The objective of the paper is to investigate the numerical study of an unsteady two-dimensional mixed convection flow along a vertical semi-infinite power-law stretching sheet in a parallel free stream with a power-law wall temperature distribution of the form T W(x)= T ∞ + Ax 2 m −1. The unsteadiness is caused by the free stream velocity as well as by the stretching sheet velocity. The governing non-linear partial differential equations in the velocity and temperature fields are written in non-dimensional form using suitable transformations. The resulting final set of coupled non-linear partial differential equations is solved using an implicit finite difference scheme in combination with a quasi-linearization technique. The effects of various governing parameters on the velocity and temperature profiles are discussed in the present numerical study. In addition, the numerical results for the local skin friction coefficient and local Nusselt number are also presented. The numerically computed results are compared with previously reported work and are found to be in excellent agreement. [ABSTRACT FROM AUTHOR]

Abstract: The behavior of unsteady mixed convection flow of an incompressible viscous fluid over a vertical wedge with constant suction/injection have been investigated. The unsteadiness is due to the time-dependent free stream velocity. The governing boundary layer equations along with the boundary conditions are first converted into dimensionless form by a non-similar transformation, and then resulting system of coupled non-linear partial differential equations is solved by an implicit finite-difference scheme in combination with the quasi-linearization technique. Numerical results for the effects of various parameters on velocity, temperature and concentration profiles and on their gradient at the wall are reported in the present study. The buoyancy force causes considerable velocity overshoot for low Prandtl number (Pr) fluids. Skin friction coefficient, heat and concentration transfer rates are found to alter significantly due to injection/suction for both accelerating and decelerating flow. [Copyright &y& Elsevier]