In the present study, fluid flow, heat transfer and entropy generation in impingement cooling system with an array of air jets for different values of Reynolds number (Re), Velocity Ratio (VR) and Channel Height (H/L) are investigated. The magnitude of overall Nusselt number (Nuov‾) and global total entropy generation (Stot,Ω) is found to increase with increasing Re,VR and decreasing H/L. Further, spectral and proper orthogonal decomposition analyses are performed to analyze spatio-temporal dynamics of vortex structures for unsteady configurations of impingement cooling system. It is observed that, along the interface of jet (both primary and secondary) and ambient fluid, the destabilizing effect of shear forces overcome the stabilizing effect of momentum diffusion. This results in evolution of counter-rotating vortex rings along the interfaces of jet and ambient fluid due to shear layer instability. Finally, Multi-Objective Genetic Algorithm (MOGA) has been implemented to obtain optimum configurations of impingement cooling system where a trade-off between two performance parameters, Nuov‾ and Stot,Ωis obtained. © 2016 Elsevier Ltd

Arul Prakash Karaiyan

Department of Applied Mechanics

Prasanth Anand Kumar Lam

Cooling

Cooling systems

Diffusion in liquids

Economic and social effects

entropy

finite element method

Genetic algorithms

Jets

Principal component analysis

Reynolds number

Shear flow

Thermoelectric equipment

COUNTER-ROTATING VORTICES

entropy generation

Impinging jet

Multi-objective genetic algorithm

Numerical investigations

Proper orthogonal decompositions

SHEAR LAYER INSTABILITY

SPATIO-TEMPORAL DYNAMICS

Vortex flow

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

International Journal of Heat and Mass Transfer

In the present study, a multi-objective optimization procedure combining finite element modeling of impingement cooling system, Response Surface Approximation (RSA) of objective functions and optimization based on Multi-Objective Genetic Algorithm (MOGA), to achieve maximum heat transfer and minimum entropy generation is demonstrated. For the purpose, numerical simulations are performed for impingement cooling system with Al2O3/water nanofluid, to investigate the influence of Reynolds number (Re), non-dimensional channel height (H/L) and nanoparticle volume fraction (Pdbl) on fluid flow, heat transfer and entropy generation. The simulated results illustrate that, a secondary recirculation bubble observed on upper surfaces of fourth (at Re ≥ 500) and fifth (for Re ≥ 800) heat sources, lead to an accumulation of heat. The magnitude of local Nusselt number (Nu) is found to be maximum along stagnation region whereas in the regions of secondary recirculation a minimum value is observed. Further, an increase in overall surface averaged Nusselt number (Nuov) and global total entropy generation (Stot,Ω) is observed with increasing Re,Pdbl and decreasing H/L. Subsequently, Nuov and Stot,Ω are selected as objective functions and are modeled using RSA. Furthermore, MOGA has been implemented to obtain optimum configurations of impingement cooling system encapsulating in the functional space lying on the Pareto-optimal frontier where a trade-off between two performance parameters, Nuov and Stot,Ω are obtained. © 2015 Elsevier Ltd. All rights reserved.

Energy Conversion and Management

Thermodynamic investigation and multi-objective optimization for jet impingement cooling system with Al2O3/water nanofluid

In the present study, fluid flow and thermal characteristics associated with forced convection cooling of an array of discrete protruding heat sources mounted on impingement plate of channel by an impinging laminar jet is investigated for various Reynolds number (Re) and channel height (H/L). It is observed that, the magnitude of average Nusselt number for all heat sources increases with increasing Re and decreasing H/L, except the regions of heat sources covered by recirculation bubbles which may be due to accumulation of heat resulting in hot spots. In order to eliminate these hot spots, a porous layer is attached to the impingement plate. A parametric study is conducted to predict the performance of porous layer on fluid flow pattern, heat transfer and entropy generation for various values of Darcy number (Da), Reynolds number (Re), channel height (H/L), porosity (∈) and porous layer thickness (h/H). For the purpose, equations governing two-dimensional, time-dependent, incompressible and laminar flow are solved in a Cartesian framework by using Streamline Upwind Petrov-Galerkin (SUPG) Finite Element (FE) method. The generalized Darcy-Forchheimer-Brinkman model is adopted to model the flow in porous medium. The recirculation bubbles on heat sources are completely eliminated with the inclusion of porous layer at Darcy number, Da=10-2. The magnitude of overall Nusselt number and global entropy generation due to heat transfer (Sθ,Ω¯) and fluid friction (Sψ,Ω¯) increases with increasing Da,Re,h/H and decreasing ∈ and H/L. The optimum configuration for maximum heat transfer and minimum entropy generation is observed at Da=10-2,Re=1000,H/L=1.0,h/H=0.75 and ∈=0.5. © 2014 Elsevier Ltd. All rights reserved.

A numerical investigation of heat transfer and entropy generation during jet impingement cooling of protruding heat sources without and with porous medium

In this paper, fluid flow and thermal characteristics associated with natural convection heat transfer in a porous enclosure containing high temperature heat sources placed on top and bottom walls are studied. For this purpose, two-dimensional, time-dependent Navier-Stokes equations with Darcy-Brinkman-Forchheimer terms are solved in a Cartesian framework by using Streamline Upwind Petrov-Galerkin (SUPG) based finite element method. The effect of heat sources on flow pattern, entropy generation and temperature distribution are studied for different Darcy numbers, porosities and Rayleigh numbers. The results show that maximum entropy generation due to heat transfer irreversibility is observed in the vicinity of heat sources due to the presence of high thermal gradient. The global entropy generation due to fluid friction is found to increase in convection dominated regime. It is also observed that with increasing Darcy number, porosity and Rayleigh number the surface averaged Nusselt number for both top and bottom heat sources is increased. © 2013 Elsevier Ltd. All rights reserved.

A numerical study on natural convection and entropy generation in a porous enclosure with heat sources

One of the important objectives of thermal systems engineering is to analyze the utilization of thermal energy in an efficient manner. Analysis on entropy generation may give an insight about thermal efficiency of various thermal systems. Entropy generation analysis during natural convection in a porous trapezoidal structures of various inclination angles (φ) with isothermal (case 1) and non-isothermal (case 2) hot bottom wall has been performed. Simulations have been done to obtain solutions in terms of isotherms (θ), streamfunction (ψ) and entropy generation maps (S θ and Sψ) for various ranges of modified Darcy number (Da), Prandtl number (Pr) at modified Rayleigh number, Ra = 10 6. It is observed that Sθ,max occurs near bottom corners for case 1 whereas that occurs near middle part of the left and right portions of the bottom wall for case 2. The entropy production due to fluid flow irreversibilities (Sψ,max) occurs either at the top wall, or side walls or along the interface between two counter-rotating cells. It is found that, square cavities may be the optimal geometry in comparison to trapezoidal cavities for both cases. Also, trapezoidal cavities with φ = 60 may be the alternative optimal design in comparison with φ = 45 for all Pr fluids. © 2013 Elsevier Ltd. All rights reserved.

Role of entropy generation on thermal management due to thermal convection in porous trapezoidal enclosures with isothermal and non-isothermal heating of wall

Analysis of entropy generation has been carried out for square cavities with distributed heated sources filled with various materials involving wide range of Pr(=0.015, 0.7, 10, 1000) during the conduction and convection regime within Ra(=103 - 105). Entropy generation terms involving thermal and velocity gradients are evaluated accurately based on elemental basis set via Galerkin finite element method. Local entropy maps are analyzed in detail for various cases and the dominance of thermal and frictional irreversibilities is studied via average Bejan number. The heat transfer irreversibility is found to dominate during conduction regime while the fluid friction irreversibility dominates the entropy generation in the convection regime, except for the low Pr fluid based on the heating configuration of the cavity. Further, the variation of total entropy generation has been observed to be similar for different heating configurations for higher Pr fluids (=10, 1000) whereas, the configuration of cavity has been found to have little effect on total entropy generation for fluids with Pr = 0.7 during both conduction and convection regimes. Thermal mixing and degree of temperature uniformity due to distributed heating in various cases are also reported and optimum cases for processing of various fluids are presented based on minimum entropy generation. © 2011 Elsevier Ltd. All rights reserved.

Analysis of entropy generation for distributed heating in processing of materials by thermal convection

A numerical investigation and design optimization of impingement cooling system with an array of air jets

Journal	Data powered by TypesetInternational Journal of Heat and Mass Transfer
Publisher	Data powered by TypesetElsevier Ltd
ISSN	00179310
Open Access	No