Heat transfer in fluctuating flow of an elastico-viscous fluid past an infinite plate with constant suction

An analysis of heat transfer in a two dimensional flow of an elastico-viscous fluid (Walters liquid B) past an infinite porous plate has been carried out under the following conditions: (1) constant suction, (2) free stream oscillates in time about a constant mean, (3) the plate is thermally insulated. Approximate solutions to the temperature field have been derived on taking into consideration viscous dissipative terms. The mean wall temperature has been shown graphically and it is observed that it decreases with increasing frequency.     

MHD laminar thin-film flow along a vertcal wall

An accelerating magnetohydrodynamic laminar flow of an electrically conducting fluid under the influence of gravity and in presence of transverse magnetic field is investigated in the paper. Using a cubic polynomial for the velocity profile inside the boundary layer, the momentum integral equation is solved numerically by Runge-Kutta method to determine the boundary layer thickness and the corresponding film thickness is then calculated for the entrance region. The effect of magnetic field on these solutions is shown in graphical form.List of symbols u, v local velocity components - p pressure - density - kinematic viscosity - viscosity= - electrical conductivity - g acceleration due to gravity - U _s (x) inviscid core velocity - h(x) film thicknes - (x) boundary layer thickness - M Hartmann number - B ₀ external magnetic field The authors remain thankful to the referee for some helpful criticisms.     

Series solution of unsteady free convection flow with mass transfer along an accelerated vertical porous plate with suction

The problem of unsteady free convection flow is considered for the series solution (analytic solution). The flow is induced by an infinite vertical porous plate which is accelerated in its own plane. The series solution expressions for velocity field, temperature field and concentration distribution are presented. The influence of important parameters is seen on the velocity, temperature, concentration, skin friction coefficient and temperature gradient with the help of graphs and tables. Convergence is also properly checked for different values of the important parametes for velocity field, temperature and concentration with the help of ħ-curves.     

Heat transfer in magneto-hydrodynamic couette flow with variable wall temperature

Heat transfer in magneto-hydrodynamic Couette flow as affected by wall electrical conductance is discussed. The flow is bounded by two moving walls with temperature linearly varying along their lengths. The exact solutions obtained indicate that an increase in the conductivity ratio at the lower wall leads to a sharp rise in the Nusselt numbers at the upper wall.     

Heat transfer enhancement of laminar nanofluids flow in a triangular duct using vortex generator

In this work, two dimensional laminar flow of different nanofluids flow inside a triangular duct with the existence of vortex generator is numerically investigated. The governing equations of mass, momentum and energy were solved using the finite volume method (FVM). The effects of type of the nanoparticles, particle concentrations, and Reynolds number on the heat transfer coefficient and pressure drop of nanofluids are examined. Reynolds number is ranged from 100 to 800. A constant surface temperature is assumed to be the thermal condition for the upper and lower heated walls. In the present work, three nanofluids are examined which are Al₂O₃, CuO and SiO₂ suspended in the base fluid of ethylene glycol with nanoparticles concentrations ranged from 1 to 6%. The results show that for the case of SiO₂–EG, at ? = 6% and Re = 800, it is found that the average Nusselt number is about 50.0% higher than the case of Re = 100.     

Stratification of a two-phase monodisperse system in a plane laminar flow

A thermodynamic approach is used to describe the distribution of particles of a disperse phase in a plane laminar flow. The effect of the density, shape, and velocity of disperse particles in the flow is considered. Conditions are described under which various modes of stratification of the flow (near-wall, central, intermediate, and multilayer modes) arise. The equilibrium distributions obtained are self-similar; this allows one to compare the behavior of colloidal, highly disperse, coarsely disperse, and coarse-grain systems for various shear velocities and flow widths.     

Heat transfer behaviour of nanofluids in a uniformly heated circular tube fitted with helical inserts in laminar flow

The CFD simulation of heat transfer characteristics of a nanofluid in a circular tube fitted with helical twist inserts under constant heat flux has been explained using Fluent version 6.3.26 in laminar flow. Al₂O₃ nanoparticles in water of 0.5%, 1.0% and 1.5% concentrations and helical twist inserts of twist ratios 2.93, 3.91 and 4.89 has been used for the simulation. All thermophysical properties of nanofluids are temperature dependent. The heat transfer enhancement increases with Reynolds number and decreases with twist ratio with maximum for the twist ratio 2.93. By comparing the heat transfer rates of water and nanofluids, the increase in Nusselt number is 5%–31% for different helical inserts and different volume concentrations. The maximum heat transfer enhancement is 31.29% for helical insert of twist ratio 2.93 and for the volume concentration of 1.5% corresponding to the Reynolds number of 2039. The data obtained by simulation match with the literature value of water with the discrepancy of less than ±10% for plain tube and tube fitted with helical tape inserts for Nusselt number.     

Heat transfer at a laminar free convection and separated flow past a rib in a vertical channel with isothermal walls

The results of numerical computations of a free laminar convection and heat transfer between two parallel isothermal plates in the presence of a single rib on the channel surface are presented. The investigations have been conducted for a channel with the aspect ratio AR = L/w = 10, where L is the channel height, and w is the distance between the plates. An infinitely thin adiabatic rib was located on one of the channel walls in the middle of its height. The relative rib height l/w was varied in the range 0÷0.8. The wall temperature was higher than the ambient temperature, and the Rayleigh number was varied in the range Ra = 10²÷10⁵. The main attention has been paid to the study of the influence of the rib height and the Rayleigh number on local and integral heat transfer and the Reynolds number in the channel (the convective thrust). A fundamental difference in the heat transfer over the channel height has been shown on the ribbed wall and on a smooth surface. The computational results have been compared with the case of a symmetric distribution of the ribs on the both walls with the integral height equal to a single rib.     

On flow of an elastico-viscous fluid past an oscillating porous plate

A solution for the flow problem of an elastico-viscous fluid (Walters liquid B) due to an oscillating infinite porous plate with constant suction has been obtained. It has been observed that the magnitude of velocity decreases with increase in suction velocity. The shearing stress increases with increase in suction.We thank the referee for his useful suggestions.     

Heat transfer of an oscillating cylinder in a viscous incompressible fluid flow

Unsteady flow and heat transfer of the heated cylinder with transverse and longitudinal oscillations in unbounded flow of viscous incompressible heat conducting fluid are considered. Influence of amplitude, frequency and direction of harmonic oscillations of the cylinder on the near-wake structure and heat transfer are investigated.     

Liquid entrainment by gas flow along the interface of a liquid bridge

We report the results of numerical and experimental studies of two-phase flows in an annulus. The geometry corresponds to a cylindrical liquid column co-axially placed into an outer cylinder with solid walls. Gas enters into the annular duct and entrains the initially quiescent liquid. The internal column consists of solid rods at the bottom and top, while the central part is a liquid bridge from a viscous liquid and kept in its position by surface tension. Silicone oil 5cSt was used as a test liquid and air and nitrogen as gases. An original numerical approach was developed to study the problem in complex geometry. The flow structure in the liquid is analyzed for a wide range of gas flow rates.     

Heat and mass transfer on MFD flow through porous media over an accelerating surface in the presence of suction and blowing

The heat and mass transfer of electrically conducting fluid through porous media over an accelerating surface subject both to power law surface temperature and power law heat flux variations with a temperature-dependent heat source in the presence of a transverse uniform magnetic field is studied. A series solution to the energy and species concentration equation in terms of Kummer’s function is studied. The effect of Prandtl number and Schmidt number is studied with the help of graphs.     

Heat transfer in tubes with periodic draft under supercritical conditions

The temperature mode of a wall was studied experimentally for sub-and supercritical pressures of water in tubes with turbulence stimulators; these data were compared with similar results obtained for a smooth tube. An increase in heat transfer inside a turbulizing tube was revealed for a single-and two-phase water flows. Correlation dependencies for determination of heat transfer coefficient in a single-phase flow inside a tube with turbulence stimulators were obtained.     

Heat transfer and flow characteristics of turbulent slot jet impingement on plane and ribbed surfaces

A computational study is carried out to assess the suitability of various RANS based turbulence models for slot jet impingement on flat and ribbed surfaces with various values of Reynolds number and jet to plate spacing. The com-puted results are compared with the reported experimental data. It was observed that none of the turbulence models considered predicted the heat transfer data accurately. However, some models predicted the experimental data with good trends, e.g., secondary peak and several spikes in Nusselt number for ribbed surface, with a precise computation of the stagnation point Nusselt number. Further, the effects of slot width, rib pitch and jet to ribbed surface spacing were investigated for jet impingement on a ribbed surface. It was observed that the local Nusselt number increased with slot width and rib to plate spacing. It was also observed that increasing Reynolds number had a positive effect on the local heat transfer. With increasing rib pitch the local Nusselt number increased near the stagnation zone but de-creased downstream. The observed flow pattern was different for jet impingement on a ribbed surface than that on a flat surface.     

Heat transfer for boundary layers with cross flow

An analysis is presented to study the dual nature of solutions for the forced convective boundary layer flow and heat transfer in a cross flow with viscous dissipation terms in the energy equation. The governing equations are transformed into a set of three self-similar ordinary differential equations by similarity transformations. These equations are solved numerically using the very efficient shooting method. This study reveals that the dual solutions of the transformed similarity equations for velocity and temperature distributions exist for certain values of the moving parameter, Prandtl number, and Eckert numbers. The reverse heat flux is observed for larger Eckert numbers; that is, heat absorption at the wall occurs.     

Turbulent periodic flow and heat transfer in a rectangular channel with detached V-baffles

This paper presents a numerical analysis of turbulent periodic flow and heat transfer in a rectangular channel with detached V-baffles. The computations are based on the finite volume method with the SIMPLE algorithm for handling the pressure–velocity coupling and using the QUICK scheme for the convection terms. Air is used as the test fluid with the air flow rate in terms of Reynolds numbers ranging from 3000 to 20,000. The effects of different detached-clearance ratios (c/H, CR) of 0.0, 0.05, 0.1, 0.15, and 0.2, baffles-pitch to square channel-diameter ratio (pitch ratio (p/H), PR) is 1.0, baffles-height to square channel-diameter ratio (blockage ratio (b/H), BR) is 0.10, and attack angle (α) is 45? on heat transfer, friction factor and thermal enhancement factor are investigated numerically. It is found that a pair of counter-rotating vortices (P-vortex) caused by the baffles can induce impingement/attachment flows repeatedly on the rectangular channel walls leading to a greater increase in the heat transfer over the test channel. The maximum thermal performance and heat transfer are found to be about 1.5 and 3.3, respectively for CR = 0.05 and Re = 3000, while the highest pressure loss is about 21.5 in the case of CR = 0.2 and Re = 20,000.     

Numerical investigation of laminar flow and heat transfer in a radial flow cooling system with the use of nanofluids

Nanofluids, because of their enhanced heat transfer capability as compared to normal water/glycol/oil based fluids, offer the engineer opportunities for development in areas where high heat transfer, low temperature tolerance and small component size are required. In this present paper, the hydrodynamic and thermal fields of a water–γAl₂O₃ nanofluid in a radial laminar flow cooling system are considered. Results indicate that considerable heat transfer enhancement is possible, even achieving a twofold increase in the case of a 10% nanoparticle volume fraction nanofluid. On the other hand, an increase in wall shear stress is also noticed with an increase in particle volume concentration.