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Article
Publication date: 4 November 2019

C. Jawali Umavathi and Mikhail Sheremet

The purpose of this study is a numerical analysis of steady-state heat transfer behavior of couple-stress nanofluid sandwiched between viscous fluids. It should be noted…

Abstract

Purpose

The purpose of this study is a numerical analysis of steady-state heat transfer behavior of couple-stress nanofluid sandwiched between viscous fluids. It should be noted that this research deals with the development of a cooling system for the electronic devices.

Design/methodology/approach

Stokes model is used to define the couple-stress fluid and the single-phase nanofluid model is used to define the nanofluid transport processes. The fluids in all regions are assumed to be incompressible, immiscible and the transport properties in all the three layers are assumed to be constant. The governing coupled linear ordinary differential equations are made dimensionless by using appropriate fundamental quantities. The exact solutions obtained for the velocity and temperature fields are evaluated numerically for various model parameters.

Findings

The results are demonstrated using different types of nanoparticles such as copper, silver, silicon oxide (SiO2), titanium oxide (TiO2) and diamond. The investigations are carried out using copper–water nanofluid for different values of couple-stress parameter a with a range of 0 = a = 12, solid volume fraction ϕ with a range of 0.0 ≤ ϕ ≤ 0.05, Eckert number Ec with a range of 0.001 ≤ Ec ≤ 6 and Prandtl number Pr with a range of 0.001 ≤ Pr ≤ 6. It was found that the Nusselt number increases by increasing the couple stress parameter, Eckert number and Prandtl number and it decreases with a growth of the solid volume fraction parameter. It was also observed that using SiO2–water nanofluid, the optimal Nusselt number is obtained. Further, using copper, silver, diamond and TiO2, nanoparticles and water as a base fluid does not show any significant changes in the rate of heat transfer. The couple-stress parameter enhances the velocity and temperature fields whereas the solid volume fraction suppresses the flow field for both Newtonian and couple-stress fluid.

Originality/value

The originality of this work is to analyze the heat transfer behavior of couple-stress nanofluid sandwiched between viscous fluids. The results would benefit scientists and engineers to become familiar with the analysis of convective heat transfer and flow structures in nanofluids and the way to predict the heat transfer rate in advanced technical systems, in industrial sectors including transportation, power generation, chemical sectors, electronics, etc.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 29 no. 11
Type: Research Article
ISSN: 0961-5539

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Article
Publication date: 2 December 2019

Boualem Chetti and Wael Ahmed Crosby

The purpose of this paper is to present the effect of the preload on the static characteristics of three-lobe bearings lubricated with a fluid blended with high polymer…

Abstract

Purpose

The purpose of this paper is to present the effect of the preload on the static characteristics of three-lobe bearings lubricated with a fluid blended with high polymer additives modeled as a couple stress fluid.

Design/methodology/approach

Based on the micro-continuum theory, the modified Reynolds equation for couple stress fluids is solved using a finite difference method to obtain the distribution of the pressure, the load-carrying capacity, the attitude angle, the friction coefficient and the side leakage for various values of the couple stress parameter and the preload factor.

Findings

The results show that the presence of a couple stress in the lubricants improves the static characteristics of this type of bearing compared to those lubricated with Newtonian fluids for any value of the preload factor. Thus, it is found that the preload significantly affects the performance of the three-lobe journal bearing lubricated with a couple stress fluid or a Newtonian fluid. Moreover, the investigation showed that increasing the preload factor exhibits an increase in the load carrying capacity and the attitude angle, but it decreases the friction coefficient and the side leakage especially at a lower preload factor. Furthermore, using a couple stress fluid and a higher preload factor led to a significant rise in the load carrying capacity and a significant reduction in the friction coefficient.

Practical implications

This study helped improve the performance characteristics of the three-lobe journal bearing.

Originality/value

The presence of couple stress in the lubricants improves the static characteristics of this type of bearing compared to those lubricated with Newtonian fluids for any value of the preload factor. The usage of the couple stress fluid and the higher preload factor led to a significant rise in the load carrying capacity and a significant reduction in the friction coefficient.

Details

Industrial Lubrication and Tribology, vol. 71 no. 10
Type: Research Article
ISSN: 0036-8792

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Article
Publication date: 11 April 2016

Boualem Chetti

This paper presents an analysis of the static characteristics of two-lobe journal bearings lubricated with couple stress fluids operating in a turbulent regime. The…

Abstract

Purpose

This paper presents an analysis of the static characteristics of two-lobe journal bearings lubricated with couple stress fluids operating in a turbulent regime. The modified Reynolds equation for a couple stress fluids taking into consideration the effect of turbulence is solved using finite difference method. The load-carrying capacity, attitude angle, friction coefficient and side leakage are determined for various values of the couple stress parameter and Reynolds number. It is found that the couple stress fluids affect significantly on the performance of a two-lobe journal bearing in laminar and turbulent regime.

Design/methodology/approach

The modified Reynolds equation for a couple stress fluids taking into consideration the effect of turbulence is solved using finite difference method.

Findings

It is found that the couple stress fluids affect significantly on the performance of a two-lobe journal bearing in laminar and turbulent regime.

Originality/value

A couple stress fluid is used for lubrication of a two-lobe journal bearing in turbulent regime and laminar.

Details

Industrial Lubrication and Tribology, vol. 68 no. 3
Type: Research Article
ISSN: 0036-8792

Keywords

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Article
Publication date: 2 December 2019

Shitendu Some and Sisir Kumar Guha

In the application of hydrostatic double-layered porous journal bearings, misalignment of bearing systems is a major problem. On the other hand, the use of coupled-stress

Abstract

Purpose

In the application of hydrostatic double-layered porous journal bearings, misalignment of bearing systems is a major problem. On the other hand, the use of coupled-stress fluid as a lubricant is more practical in the present days. Furthermore, in case of porous bearing, neglecting slip effect and percolation effect of additives into the pores may lead to erroneous result. Hence, this paper aims to address the effect of journal misalignment and coupled-stress lubricant on the steady-state film pressure of the double-layered porous journal bearing with tangential velocity slip and percolation effect.

Design/methodology/approach

First, considering the tangential velocity slip, the most general modified Reynolds type equation has been derived for the film region and the governing equations for flow in the coarse and fine layers of porous medium, incorporating the percolation effect for a double-layered porous bearing. Here, considering the misalignment caused by shaft displacement. Film thickness expression established considering the effect of misalignment. Steady-state film pressures are obtained by solving modified Reynolds equation based on the coupled-stress lubrication theory. Effects of journal misalignment and coupled-stress lubricant on the pressure profiles in the film region are discussed and demonstrated in the graphical form.

Findings

In this paper, effects of journal misalignment and coupled-stress lubricant on the pressure profiles in the film region are obtained. In general, higher degree of misalignment gives higher steady-state pressure value in the film region, and this pressure increases due to increase in coupled-stress parameter up to a certain limit.

Originality/value

To the best of the author’s knowledge, there is no literature available, so far, that addresses the analysis of the steady-state pressure in the film region of a doubled–layered porous journal bearing under misaligned condition with coupled-stress lubricant. But in this paper all these points are included, which makes this article valuable in design purpose.

Details

Industrial Lubrication and Tribology, vol. 72 no. 3
Type: Research Article
ISSN: 0036-8792

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Article
Publication date: 3 April 2017

Jawali Umavathi, Jada Prathap Kumar, Ioan Pop and Murudappa Shekar

The purpose of this paper is to consider the problem of fully developed laminar mixed convection flow of a couple stress fluid in a vertical channel with the third-kind…

Abstract

Purpose

The purpose of this paper is to consider the problem of fully developed laminar mixed convection flow of a couple stress fluid in a vertical channel with the third-kind boundary conditions in the presence or absence of heat source/sink effect.

Design/methodology/approach

Through proper choice of dimensionless variables, the governing equations are developed. These governing equations are solved analytically by the differential transform method and numerically by the Runge–Kutta shooting method. Analytical solutions for the velocity and temperature profiles for heat generation and absorption of the problem are reported.

Findings

The mass flow rate and Nusselt numbers at both the left and right channel walls on mixed convection parameter, Brinkman number, couple stress parameter and heat generation/absorption parameter for equal and unequal Biot numbers are presented. Favorable comparisons of special cases with previously published work are obtained. It is found that velocity, temperature, mass flow rate and Nusselt number decrease with couple stress parameter and increase with mixed convection parameter and Brinkman number.

Originality/value

The work done in this paper is not done earlier to the authors’ knowledge. This is the first paper in which the sixth-order differential equation is solved using the semi-numerical method, which is a differential method.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 27 no. 4
Type: Research Article
ISSN: 0961-5539

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Article
Publication date: 1 October 2003

Cheng‐Hsing Hsu, Jaw‐Ren Lin and Hsiu‐Lu Chiang

According to the Stokes microcontinuum theorem and Christensen's stochastic model, the main objective of this paper is to theoretically predict the combined influences of…

Abstract

According to the Stokes microcontinuum theorem and Christensen's stochastic model, the main objective of this paper is to theoretically predict the combined influences of couple stresses and surface roughness on the lubrication performance of journal‐bearing systems. To take account of the presence of both the surface roughness of bearings and the couple stress effect due to the lubricant containing the polar suspensions, the generalized stochastic non‐Newtonian Reynolds‐type equation is derived. Compared to the Newtonian‐lubricant smooth‐bearing case, the couple stress effects and the longitudinal roughness improve the load carrying capacity, and thus decrease the attitude angle and friction parameter, while the effect of transverse roughness is opposite to that of the longitudinal one in the journal‐bearing system.

Details

Industrial Lubrication and Tribology, vol. 55 no. 5
Type: Research Article
ISSN: 0036-8792

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Article
Publication date: 10 October 2016

Rajneesh Kumar, Shaloo Devi and Veena Sharma

The purpose of this paper is to investigate the two-dimensional axisymmetric problem in a homogeneous, isotropic modified couple stress thermoelastic diffusion (TD) medium…

Abstract

Purpose

The purpose of this paper is to investigate the two-dimensional axisymmetric problem in a homogeneous, isotropic modified couple stress thermoelastic diffusion (TD) medium in the context of dual-phase-lag model.

Design/methodology/approach

The Laplace and Hankel transforms have been applied to find the general solution to the field equations. The components of displacement, stresses, temperature change and chemical potential are obtained in the transformed domain. The resulting quantities are obtained in the physical domain by using numerical inversion technique.

Findings

The components of normal stress, tangential stress, tangential couple stress, temperature change and chemical potential are obtained numerically and depicted graphically to see the effect of dual-phase-lag diffusion (DLD), dual-phase-lag heat transfer (DLT) and TD models in the absence and presence of couple stress parameter.

Originality/value

Comparisons are made in the absence and presence of couple stress DLD, DLT and TD models.

Details

Multidiscipline Modeling in Materials and Structures, vol. 12 no. 3
Type: Research Article
ISSN: 1573-6105

Keywords

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Article
Publication date: 14 November 2016

Rajneesh Kumar and Shaloo Devi

The purpose of this paper is to deal with the study of plane waves and fundamental solution in a modified couple stress generalized thermoelastic solid with…

Abstract

Purpose

The purpose of this paper is to deal with the study of plane waves and fundamental solution in a modified couple stress generalized thermoelastic solid with three-phase-lag (TPL) model of thermoelasticity.

Design/methodology/approach

It is found that for two-dimensional model, there exists two longitudinal waves, namely, longitudinal wave (P-wave), thermal wave (T-wave), and a set of coupled transverse waves (SV1 and SV2 waves). In addition, the fundamental solution for the system of differential equations for steady oscillations in terms of elementary functions has been constructed. Some properties of fundamental solution are also established. Various particular cases of interest are also deduced from the present investigations and compared with the known results.

Findings

The phase velocity, attenuation coefficient, specific loss and penetration depth are computed numerically and presented graphically to see the effect of TPL model, dual-phase-lag (DPL) model and GN-III model in the presence of couple stress parameter.

Originality/value

The results are compared with couple stress TPL model, couple stress DPL model and GN-III model.

Details

Multidiscipline Modeling in Materials and Structures, vol. 12 no. 4
Type: Research Article
ISSN: 1573-6105

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Article
Publication date: 1 February 2005

Won‐Hsion Liao, Rong‐Fang Lu, Rean‐Der Chien and Jaw‐Ren Lin

The purpose of the present study is to provide the dynamic characteristics of long journal bearings lubricated with couple stress fluids.

Abstract

Purpose

The purpose of the present study is to provide the dynamic characteristics of long journal bearings lubricated with couple stress fluids.

Design/methodology/approach

Based upon the micro‐continuum theory generated by Stokes, the dynamic Reynolds‐type equation governing the film pressure is derived to account for the couple stress effects resulting from the non‐Newtonian behavior of complex fluids. By applying the linear stability theory to the non‐linear equations of motion the journal rotor, the equilibrium positions and dynamic characteristics of the system are evaluated.

Findings

As compared to the classical Newtonian model, the effects of couple stresses signify enhanced stiffness and damping coefficients (including KXX, KXY , BXX and BXY) at moderate values of the steady eccentricity ratio. Totally, as the rotor center operates at an eccentricity ratio about εs≤0.71, long bearings lubricated with couple stress fluids under small disturbance results in a higher stability threshold speed than that of the Newtonian‐lubricant case.

Originality/value

These findings provide engineers useful information in designing journal‐bearing systems.

Details

Industrial Lubrication and Tribology, vol. 57 no. 1
Type: Research Article
ISSN: 0036-8792

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Article
Publication date: 16 September 2013

Jaw-Ren Lin, Rong-Fang Lu, Li-Ming Chu and Chi-Ren Hung

– The purpose of this paper is to investigate the effects of non-Newtonian rheology on the dynamic characteristics of a secant-shaped couple-stress lubricated slider bearing.

Abstract

Purpose

The purpose of this paper is to investigate the effects of non-Newtonian rheology on the dynamic characteristics of a secant-shaped couple-stress lubricated slider bearing.

Design/methodology/approach

By applying the linear dynamic theory to the film force equation, a closed-form solution of the stiffness and damping coefficients is obtained for the secant-shaped bearing taking into account the non-Newtonian effects of Stokes couple stress fluids.

Findings

Comparing with the secant-shaped Newtonian-lubricant bearing, the effects of non-Newtonian couple stresses provide an apparent improvement in the dynamic stiffness and damping characteristics, especially for the secant-shaped slider bearing operating at lower squeezing-film heights and with larger non-Newtonian couple stress parameters.

Originality/value

Comparing with those of the inclined plane-shaped non-Newtonian slider bearings, better dynamic stiffness and damping performances are provided for the secant-shaped non-Newtonian slider bearing designed at larger values of the shoulder parameters. The advantages of secant-shaped slider-bearing types provide engineers useful information in bearing selection and engineering application.

Details

Industrial Lubrication and Tribology, vol. 65 no. 6
Type: Research Article
ISSN: 0036-8792

Keywords

1 – 10 of 297