Faculty Publications
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Item Asymptotic approach to obtain nusselt number correlation for laminar mixed convection in a vertical channel(Dalian University of Technology, 2018) Nakate, P.; Kotresha, B.; Gnanasekaran, N.In this paper, a general methodology is proposed for treating mixed convection problems in a vertical channel by the concept of asymptotic computational fluid dynamics (ACFD). Average Nusselt number is developed based on the limiting solutions of natural and forced convection.These correlations are then blended to find a unified composite correlation that work very well for extreme limits of mixed convection. For the purpose of demonstration, the problem of 2-D laminar, mixed convection in a vertical channel that comprises of a heater sandwiched between two aluminum plates has been used. Numerical simulations are performed with ANSYS-FLUENT to generate the required correlation. The study proposed in this work reveals that with minimum CFD solutions one can obtain a reasonably good composite correlation for the Nusselt number. © 2018 by the authors of the abstracts.Item Numerical analysis of mixed convection in a lid-driven cavity with Cu-water nanofluid using artificial compressibility method(Dalian University of Technology, 2018) Katti, A.S.; Maniyeri, R.In this paper, we present a computational model based on an artificial compressibility method to study mixed convection in a lid-driven square cavity containing Cu-water nanofluid for two cases: i) adiabatic vertical walls and horizontal walls kept at constant temperature, and ii) adiabatic horizontal walls and sinusoidal temperature heating along vertical walls. The artificial compressibility method is used to couple pressure and velocity, and solve the momentum and continuity equations. This method is used because of its simplicity in solving steady state incompressible flow problems. The streamlines, isotherms, variation of local Nusselt number at hot walls, and variation of average Nusselt number with change in Cu-nanoparticle concentration are presented. Also, the variation of local Nusselt number with change in Richardson number (0.1 < Ri < 10), keeping Grashof number constant (Gr = 100), is obtained. For both cases, it is found that heat transfer increases with increase in Cu-nanoparticle concentration, keeping Richardson number constant, and also with a decrease in Richardson number, keeping Grashof number constant. © 2018 by the authors of the abstracts.Item Numerical Study of Mixed Convection in Single and Double Lid Driven Cavity Using LBM(Springer Science and Business Media Deutschland GmbH, 2021) Sen, S.; Arumuga Perumal, D.; Yadav, A.K.The lattice Boltzmann method (LBM) has been gaining popularity over the last two decades and the method has been extended from simple fluid flow problems to problems involving heat transfer. In the present work, an attempt is made to model cases involving mixed convection. Two types of problems are considered in this study; the first one dealing with mixed convection in a single-sided lid-driven cavity and the second one dealing with mixed convection in a double-sided lid-driven cavity in parallel and anti-parallel configurations at constant Prandtl number and various values of Richardson number. For the first problem, a square domain is considered with a moving lid at a lower temperature while the stationary wall at the bottom at a higher temperature. The cavity side walls are treated with an adiabatic boundary condition. In LBM, a forcing term dependent on temperature difference is utilized to vary the value of y-velocity in order to satisfy the effects of gravity on mixed convection. A grid independence study is conducted to show that the results are independent of the grid chosen, and good agreement with literature is achieved. The second problem is an extension of the first one; the cavity bottom wall is first given a velocity in the opposite direction, and then in the same direction, and the velocity streamlines, temperature contours and local Nusselt number variation in the top wall for these cases are plotted. The developed method helps in the visualization of various phenomena such as splitting of flow into two halves for the parallel configuration and formation of secondary vortices with high Reynolds number. © 2021, Springer Nature Singapore Pte Ltd.Item Behavioral study of alumina nanoparticles in pool boiling heat transfer on a vertical surface(2011) Hegde, R.N.; Reddy, R.P.; Rao, S.S.Experiments were carried out to investigate the pool boiling of alumina-water nanofluid at 0.1 g/l to 0.5 g/l of distilled water, and the nucleate pool boiling heat transfer of pure water and nanofluid at different mass concentrations were compared at and above the atmospheric pressure. At atmospheric pressure, different concentrations of nanofluids display different degrees of deterioration in boiling heat transfer. The effect of pressure and concentration of nanoparticles revealed significant enhancement in heat flux and deterioration in pool boiling. The heat transfer coefficient of 0.5 g/l alumina-water nanofluid was compared with pure water and clearly indicates deterioration. At all pressures the heat transfer coefficients of the nanofluid were lower than those of pure water. Experimental observation revealed particles coating over the heater surface and subsequent SEM inspection of the heater surface showed nanoparticles coating on the surface forming a porous layer. To substantiate the nanoparticle deposition and its effect on heat flux, investigation was done by measuring the surface roughness of the heater surface before and after the experiment. While SEM images of the heater surface revealed nanoparticle deposition, surface roughness of the heater surface confirmed it. Based on the experimental investigations it can be concluded that an optimum thickness of nanoparticles coating favors an increase in heat flux. Higher surface temperature due to the presence of nanoparticles coating results in the deterioration of boiling heat transfer. © 2011 Wiley Periodicals, Inc.Item Experimental study on CuO nanoparticles in distilled water and its effect on heat transfer on a vertical surface(2011) Hegde, R.N.; Rao, S.S.; Reddy, R.P.The pool boiling characteristics of dilute dispersions of CuO nanoparticles in water were studied at atmospheric pressure on a vertical heating surface. Experimental investigation of different weight concentrations of nanoparticles revealed significant enhancement in heat flux and deterioration in pool boiling. Out of many reasons, nanoparticles coating the heater surface was believed to be the reason behind this. Subsequent inspection of the heater surface showed nanoparticles coating the surface, forming a porous layer. To substantiate the nanoparticle deposition and its effect on heat flux, an investigation was performed by measuring the surface roughness of the heater surface before and after the experiment. While SEM images of the heater surface revealed nanoparticle deposition, measurement of surface roughness of the heater surface confirmed it. Formation of the porous layer on the heater surface as revealed by SEM images provided an excellent location for nucleation sites enhancing heat transfer. However, deterioration in nucleate boiling at different weight concentrations indicated some phenomenon is working behind this. © 2011 The Korean Society of Mechanical Engineers and Springer-Verlag Berlin Heidelberg.Item Influence of mixed convection in an exponentially decreasing external flow velocity(Elsevier Ltd, 2017) Patil, P.M.; Ramane, H.S.; Roy, S.; Hindasageri, V.; Momoniat, E.This article explores the influence of mixed convection in a steady incompressible laminar boundary layer flow for an exponentially decreasing free stream velocity in presence of surface mass transfer and heat source or sink. The nonlinear partial differential equations governing the flow and thermal fields are expressed in dimensionless form with the help of suitable non-similar transformations. The mathematical complexities in obtaining non-similar solutions at the leading edge of the streamwise coordinate as well as non-similarity variable ? have overcome by using the implicit finite difference scheme in conjunction with Quasi-linearization technique by choosing an appropriate finer step sizes along the streamwise direction. The effects of various dimensionless physical parameters on velocity and thermal fields are analysed. © 2016 Elsevier LtdItem Investigation of Mixed Convection Heat Transfer Through Metal Foams Partially Filled in a Vertical Channel by Using Computational Fluid Dynamics(American Society of Mechanical Engineers (ASME) infocentral@asme.org, 2018) Kotresha, B.; Gnanasekaran, N.Two-dimensional computational fluid dynamics simulations of mixed convection heat transfer through aluminum metal foams partially filled in a vertical channel are carried out numerically. The objective of the present study is to quantify the effect of metal foam thickness on the fluid flow characteristics and the thermal performance in a partially filled vertical channel with metal foams for a fluid velocity range of 0.05-3 m/s. The numerical computations are performed for metal foam filled with 40%, 70%, and 100% by volume in the vertical channel for four different pores per inch (PPIs) of 10, 20, 30, and 45 with porosity values varying from 0.90 to 0.95. To envisage the characteristics of fluid flow and heat transfer, two different models, namely, Darcy Extended Forchheirmer (DEF) and Local thermal non-equilibrium, have been incorporated for the metal foam region. The numerical results are compared with experimental and analytical results available in the literature for the purpose of validation. The results of the parametric studies on vertical channel show that the Nusselt number increases with the increase of partial filling of metal foams. The thermal performance of the metal foams is reported in terms of Colburn j and performance factors. © Copyright 2018 by ASME.Item Forced convection through discrete heat sources and simple thermal model - A numerical study(International Journal of Mathematical, Engineering and Management Sciences, 2019) Hasavimath, K.; Naik, K.; Kotresha, B.; Gnanasekaran, N.In this work a forced convection through discrete heat sources and simple thermal model placed inside the vertical channel is analyzed numerically. The problem considered for the investigation comprises of a vertical channel with distinct heat source assembly located at the center of the channel. The novelty of the present work is to replace the discrete heat source assembly by a simple thermal model to obtain uniformly distributed temperature and streamlines. A conjugate heat transfer investigation is carried out because the problem domain consists of aluminum solid strips as well as Bakelite strips in discrete heat source assembly which are replaced by a aluminum solid in case of simple thermal model. The numerically obtained data are initially compared with experimental data for the purpose of validation. The temperature of each discrete sources decrease with increase in inlet velocity of the fluid and bottom heat source is able to take higher heat load. The results in terms excess temperature obtained for both discrete heat source and simple thermal model is presented and discussed. © International Journal of Mathematical, Engineering and Management Sciences.Item Determination of interfacial heat transfer coefficient for the flow assisted mixed convection through brass wire mesh(Elsevier Masson SAS 62 rue Camille Desmoulins Issy les Moulineaux Cedex 92442, 2019) Kotresha, B.; Gnanasekaran, N.In this work, a numerical investigation of Darcy?Forchheimer mixed convection from a heated vertical flat plate embedded in a brass wire mesh porous medium is carried out to determine the coupled effects of flow and thermal diffusion. The numerical model consists of a two dimensional computational domain in which conjugate heat transfer analysis is performed to predict the hydrodynamic and thermal performance of the brass wire mesh in a vertical channel using Local Thermal Non-Equillibrium (LTNE) model. The novelty of the present study is to acquire the interfacial heat transfer coefficient, an as yet another challenging task, of the wire mesh porous medium so as to provide a quick and feasible solution to modeling of fluid flow and heat transfer through brass wire mesh porous media. The results of heat transfer through brass wire mesh are reported in terms of Colburn j factor, performance factor and are compared with other porous mediums available in literature. The present study not only opens up new vistas for more parametric studies but also provides practical and cost effective assessment to design new porous materials. © 2018 Elsevier Masson SASItem Inexpensive computations using computational fluid dynamics combined with asymptotics applied to laminar mixed convection in a vertical channel(American Society of Mechanical Engineers (ASME), 2019) Nakate, P.; Kotresha, B.; Gnanasekaran, N.In this work, a solution technique is proposed by synergistically combining asymptotics and computational fluid dynamics to ascertain a problem of laminar mixed convection heat transfer in a vertical channel. First, numerical simulation is carried out on a vertical channel that consists of an aluminum heater plate assembly at the center of the channel. The numerical model is treated as a conjugate heat transfer problem, and the concept of perturbation and blending is incorporated wherein the limiting solution of natural and forced convection is obtained in terms of average Nusselt number. These correlations are then blended to find a unified composite correlation that work very well for extreme limits of mixed convection. The Richardson number is chosen as an independent variable in the present analysis; as a result, the Nusselt number correlation is cogent for the mixed convection region. Upon performing the numerical simulations, the results of the mixed convection are then compared with experimental results available in the literature for the purpose of validation of the numerical solution. The results of the present work emphasize that, with minimum computational fluid dynamics (CFD) solutions, one can obtain a reasonably good composite correlation for the Nusselt number for mixed convection and also a substantial reduction of computations is possible ensuing an asymptotically flawless solution. © © 2019 by ASME.