In this article, the effect of lubricant inertia on the thermohydrodynamic behaviour of journal bearings is studied. Many researchers have analysed the inertia effect on lubricant flow in bearings using different simplifying assumptions. The purpose of this study is to eliminate most of those assumptions, using computational fluid dynamics (CFD) techniques to solve the exact governing equations. The bearing has a finite length and operates under incompressible laminar flow and steady conditions. Numerical solutions of the full three-dimensional Navier-Stokes equations with and without inertia terms, coupled with the energy equation in the lubricant flow and the heat conduction equations in the bearing and the shaft are obtained. Cavitation effects are also considered using an appropriate three-dimensional cavitation model. In order to study the effect fluid inertia under several different conditions, solutions are obtained for different values of the eccentricity and radial clearance and also for different values of the rotational speed of the shaft. To validate the computational results, comparison with the experimental data of other investigators is made, and reasonable agreement is obtained.
In this paper, a thermohydrodynamic (THD) analysis of vapour cavitation in steady loaded and finite length journal bearing has been developed using three different cavitation models. It involves the simultaneous solution of the three-dimensional Navier-Stokes and energy equations by CFD technique. An orthogonal grid is generated using analytic transformation functions and the governing equations are transformed for use in the computational plane. These equations are made discrete by means of control volume method and the well-known SIMPLE algorithm is used for the pressure-velocity calculation. In the cavitated part of the lubricant flow with a mixture of vapour and liquid, three different cavitation models are used to obtain the thermal behaviour of lubricant flow in this region. In all of the three cavitation models, an attempt is made to replace a single phase fluid with equivalent properties instead of the mixture of liquid and vapour. The calculated results are compared with the theoretical results of other investigators and also with experiment, and the abilities of the proposed cavitation models to predict THD characteristics of journal bearings are examined. The numerical results show that the third model in which the liquid fraction is calculated based on continuity requirement for three-dimensional cavitated flow, predicts well the lubricant pressure and temperature fields in journal bearings.can either be a result of: (1) dissolved gas coming out of the solution or (2) evaporation of the fluid. Both types of cavitation are commonly observed in journal bearings. The occurrence of cavitation in journal bearings is shown to result in reduced power loss, friction coefficient, bearing torque and load capacity [1].Computed performance characteristics of a journal bearing depend significantly on the cavitated model and the related boundary conditions used in the analysis. For the steadily loaded journal bearings under laminar flow and isothermal conditions, several boundary conditions in the cavitated region have been proposed, some of which are listed in a paper by Mori and Mori [2].A computational cavitation algorithm was introduced by Elrod [3] which can be used in liquidfilm lubrication problems with or without cavitation region. In that work, a single 'universal' differential equation for the whole lubrication region was derived JET238 Fig. 7 Bush inner surface temperature distribution of the Mistry's bearing c/r s = 0.004, Re = 7.2, ε = 0.15, L/D = 0.5 JET238
This paper presents the heat transfer characteristics of a new type of gas-to-gas heat exchanger that operates on the basis of energy conversion between gas enthalpy and thermal radiation. A theoretical analysis is conducted for the one-dimensional system where convection and radiation take place simultaneously in three porous layers. In the high-temperature section, the enthalpy of gas flow converts to thermal radiation and the reverse direction of this process occurs in two recovery sections. The porous medium is assumed to be a homogeneous continuum that absorbs, emits and scatters thermal radiation. In order to investigate the thermal behaviour of gas flows and porous layers, the coupled energy equations for the gas and porous media, based on a two-flux radiation model, are solved numerically using an iterative method. Computational results show that this type of heat exchanger has a very high efficiency, especially when the porous layers have a high optical thickness and a low scattering coefficient. To confirm the validity of the present analysis, the numerical results for a simple energy recovery system are compared with theoretical results of other investigators and reasonable agreement is found.A surface area (m 2 ) b backscattered fraction factor B incoming radiation (W/m 2 ) B 0 non-dimensional incoming radiation ¼ B=sT 4 g0 c specific heat (J/kg K) h heat transfer coefficient (W/m 2 K) k thermal conductivity (W/m K) N S number density of solid particles (m 23 ) P dimensionless group ¼ h w =r g c g u g q þ,2 forward and backward radiative heat flux3 g0 R 0 radius of the porous layer (m) T temperature (K) u velocity (m/s) x coordinate along the flow direction (m) d thickness of the porous layer (m) u p,g non-dimensional temperature ¼ T p,g =T g0 r density (kg/m 3 ) s Stefan -Boltzman constant (W/m 2 K 4 ) s a absorbing coefficient (m 21 ) s e summation of the absorbing and scattering coefficients (m 21 ) s s scattering coefficient (m 21 ) t optical depth ¼ s e (x À x 1 ) t 0 optical thickness ¼ s e d v scattering albedo ¼ s s =s e
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