Arunn Narasimhan

The interplay between internal heat generation and externally driven natural convection inside a porous medium annulus is studied in detail using numerical methods. The axisymmetric domain is bounded with adiabatic top and bottom walls and differentially heated side walls sustaining steady natural convection of a fluid with Prandtl number, Pr=5, through a porous matrix of volumetric porosity, Φ=0.4. The generalized momentum equation with Brinkman-Darcy-Forchheimer terms and the local thermal non-equilibrium based two-energy equation model are solved to determine the flow and the temperature distribution. Beyond a critical heat generation value defined using an internal Rayleigh number, RaI,cr*, the convection transits from unicellular to bicellular mode, as the annulus Tmax becomes higher than the fixed hot-wall temperature. The RaI,cr* increases proportionately when the permeability based external Rayleigh number RaE* and the solid-fluid thermal conductivity ratio γ are independently increased. A correlation is proposed to predict the overall annulus Nu as a function of RaE*, RaI*, Da and γ. It predicts the results within ±20% accuracy. © 2010 Elsevier Ltd.

Thermal management of heat generating electronics using the Bi-Disperse Porous Medium (BDPM) approach is investigated. The BDPM channel comprises heat generating micro-porous square blocks separated by macro-pore gaps. Laminar forced convection cooling fluid of Pr = 0.7 saturates both the micro- and macro-pores. Bi-dispersion effect is induced by varying the porous block permeability DaI and external permeability DaE through variation in number of blocks N2. For fixed Re, when 10-5 ≤ DaI ≤ 10-2, the heat transfer Nu is enhanced four times (from ∼200 to ∼800) while the pressure drop Δp reduces almost eightfold. For DaI < 10-5, Nu decreases quickly to reach a minimum at the Mono-Disperse Porous Medium (MDPM) limit (Da I → 0). Compared to N2 = 1 case, Nu for BDPM configuration is high when N2 ≫ 1, i.e., the micro-porous blocks are many and well distributed. The pumping power increase is very small for the entire range of N2. Distributing heat generating electronics using the BDPM approach is shown to provide a viable method of thermo-hydraulic performance enhancement χ. © 2010 Elsevier Ltd. All rights reserved.

A novel approach of treating near-compact heat exchangers (NCHX) (surface to volume ratio, α= 100-300 m2/m3 with hydraulic diameter DM∼6 mm) as a "global" porous media, whose thermohydraulic performance is being influenced by the presence of "local" tube-to-tube porous medium interconnectors, connecting the in-line arrangement of tubes (D=2 mm) having square pitch of XT=XL=2.25, is investigated in this study using numerical methods. The thermohydraulics of the global porous media (NCHX) are characterized by studying the effect of transverse thickness (δ) and permeability (represented by Dai) of the local metal foam type porous medium interconnectors on the global heat transfer coefficient (Nu) and nondimensional pressure drop (ξ). The fluid transport in the porous medium interconnectors is governed by the Brinkman-Darcy flow model while the volume averaged energy equation is used to model energy transport, with the tube walls kept at constant temperature and exchanging heat with the cooling fluid having Pr= 0.7 under laminar flow (10

Microlithography, the fabrication process for microchips and Micro-Electro-Mechanical Systems (MEMS) devices, involves a series of manufacturing processes performed on a silicon wafer, each in separate stations of a microlithography cluster. Bake (heating) and chill (cooling) of silicon wafers comprise an important manufacturing step in microlithography. Thermal analysis of an actual combination bake-chill station design using two-and three-dimensional numerical simulations are presented. In this bake-chill station, the wafer is heated to the desired bake temperature and chilled back to room temperature before being moved by the robot, resulting in tight temperature control of the wafer throughout the process. Two models, axi-symmetric and three-dimensional (geometrically similar to the new station), are generated for analyzing the thermal performance of the above station. The numerical simulations solving the transport equations in the computational domain are performed using the commercial CFD software Fluent®. Methods to improve wafer surface temperature uniformity, in light of bake-chill-station mechanical and thermal design losses, are discussed. Copyright © Taylor & Francis, Inc.

The haemodynamics of the Fontan connection is studied both numerically and experimentally by placing porous media across the connection. The 1D-offset total cavopulmonary connection (TCPC) configuration is considered for the present study with steady, laminar and newtonian assumptions. The inlet caval flow rates are varied by increasing the total cardiac output from 2LPM to 6LPM. The TCPC with porous media provides 7% reduction in pressure drop penalty, compared with no-porous medium case. Hence the introduction of porous media helps in improving the hydraulic efficiency by curtailing the recirculation zones across the connection.

The pressure drop for steady uniform flows (UF) through low permeability porous media - packed bed of particles (balls and rods) and sand (K<10-7m2) - is predicted using the existing global Hazen-Dupuit-Darcy (HDD) hydraulic model, composed of the viscous and form drag terms. In this work, experiments are performed to generate pressure drop data for accelerated steady flows through porous media for a wide range of low permeability (10-9

Pan Retinal photocoagulation (PRP), a retinal laser surgical process, is simulated using a three-dimensional bio-heat transfer numerical model. Spots of two different type of array, square array of 3 × 3 spots and a circular array of six spots surrounding a central spot, are sequentially irradiated. Pennes bio-heat transfer model is used as the governing equation. Finite volume method is applied to find the temperature distribution due to laser irradiation inside the human eye. Each spot is heated for 100 ms and subsequently cooled for 100 ms with an initial laser power of 0:2W. Based on the outcome of temperature distribution, the laser is pulsated in subsequent simulations to reduce the average peak temperature of spots to minimize the temperature induced cell damage. A method to reduce the laser power to attain the peak temperature towards photocoagulation temperature (60 °C) is also presented.

Heat and mass transport processes in humans occur at cellular, tissue, organ, and whole-body levels. The subfield of heat and mass transfer in the human eye provides the context for understanding the functions of the eye and to develop protective, diagnostic, and therapeutic processes. The eye is sensitive to the environment because of the absence of blood flow through parts such as cornea and lens, and the absence of thermal sensors and protective reflexes beyond blinking. Heat transfer processes in the eye comprise the continuous evaporation of the tear layer coating the corneal region of a normal eye, the thermal massage across the pupils called the transpupillary thermotherapy (TTT), and the several methods of internal tissue ablation involving lasers. Drug delivery inside the eye is an important man-made mass transfer process that includes the intravitreous and transscleral routes to medicate the retina. This chapter focuses on the exposition of heat transfer processes that drive laser surgical methods and the mass transfer processes that govern drug delivery methods to the retina. In a bridging section, discussion on the combined heat and mass transfer processes involved in the TTT-based convection-assisted drug diffusion to the retina through the vitreous humor is also provided.

Using an approach that couples genetic algorithm (GA) with conventional numerical simulations, optimization of the geometric configuration of a phase-change material based heat sink (PBHS) is performed in this paper. The optimization is done to maximize the sink operational time (SOT), which is the time for the top surface temperature of the PBHS to reach the critical electronics temperature (CET). An optimal solution for this complex multiparameter problem is sought using GA, with the standard numerical simulation seeking the SOT forming a crucial step in the algorithm. For constant heat dissipation from the electronics (constant heat flux) and for three typical PBHS depths (A), predictive empirical relations are deduced from the GA based simulation results. These correlations relate the SOT to the amount of phase change material to be used in the PBHS (φ), the PBHS depth (A), and the heat-spreader thickness (s), a hitherto unconsidered variable in such designs, to the best of the authors' knowledge. The results show that for all of the typical PBHS depths considered the optimal heat-spreader thickness is 2.5% of the PBHS depth. The developed correlations predict the simulated results within 4.6% for SOT and 0.32% for φ and empowers one to design a PBHS configuration with maximum SOTfor a given space restriction or the most compact PBHS design for a given SOT. Copyright © 2008 by ASME.