D. Poulikakos
University of Illinois at Chicago
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Featured researches published by D. Poulikakos.
Physics of Fluids | 1995
Jun Fukai; Y. Shiiba; Tsuyoshi Yamamoto; Osamu Miyatake; D. Poulikakos; Constantine M. Megaridis; Z. Zhao
In this paper an experimental and theoretical study of the deformation of a spherical liquid droplet colliding with a flat surface is presented. The theoretical model accounts for the presence of inertia, viscous, gravitation, surface tension, and wetting effects, including the phenomenon of contact‐angle hysteresis. Experiments with impingement surfaces of different wettability were performed. The study showed that the maximum splat radius decreased as the value of the advancing contact angle increased. The effect of impact velocity on droplet spreading was more pronounced when the wetting was limited. The experimental results were compared to the numerical predictions in terms of droplet deformation, splat radius, and splat height. The theoretical model predicted well the deformation of the impacting droplet, not only in the spreading phase, but also during recoiling and oscillation. The wettability of the substrate upon which the droplet impinges was found to affect significantly all phases of the spre...
Physics of Fluids | 1993
Jun Fukai; Z. Zhao; D. Poulikakos; Constantine M. Megaridis; Osamu Miyatake
This article presents a theoretical study of the deformation of a spherical liquid droplet impinging upon a flat surface. The study accounts for the presence of surface tension during the spreading process. The theoretical model is solved numerically utilizing deforming finite elements and grid generation to simulate accurately the large deformations, as well as the domain nonuniformities characteristic of the spreading process. The results document the effects of impact velocity, droplet diameter, surface tension, and material properties on the fluid dynamics of the deforming droplet. Two liquids with markedly different thermophysical properties, water and liquid tin, are utilized in the numerical simulations because of their relevance in the industrial processes of spray cooling and spray deposition, respectively. The occurrence of droplet recoiling and mass accumulation around the splat periphery are standout features of the numerical simulations and yield a nonmonotonic dependence of the maximum splat radius on time.
Journal of Heat Transfer-transactions of The Asme | 1987
D. Poulikakos; M. Kazmierczak
This paper presents a theoretical study of fully developed forced convection in a channel partially filled with a porous matrix. The matrix is attached at the channel wall and extends inward, toward the centerline. Two channel configurations are investigated, namely, parallel plates and circular pipe. For each channel configuration, both the case of constant wall heat flux and constant wall temperature were studied. The main novel feature of this study is that it takes into account the flow inside the porous region and determines the effect of this flow on the heat exchange between the wall and the fluid in the channel. The Brinkman flow model which has been proven appropriate for flows in sparsely packed porous media and for flows near solid boundaries was used to model the flow inside the porous region. Important results of engineering interest were obtained and are reported in this paper. These results thoroughly document the dependence of the Nusselt number on several parameters of the problem. Of particular importance is the finding that the dependence of Nu on the thickness of the porous layer is not monotonic. A critical thickness exists at which the value of Nu reaches a minimum.
International Journal of Heat and Mass Transfer | 1996
Z. Zhao; D. Poulikakos; Jun Fukai
Abstract This paper presents a numerical study of the fluid dynamics and heat transfer phenomena during the impingement of a liquid droplet upon a substrate. The theoretical model, based on the Lagrangian formulation, is solved numerically utilizing the finite element method. A deforming mesh is utilized to simulate accurately the large deformations, as well as the domain nonuniformity characteristic of the spreading process. The occurrence of droplet recoiling and mass accumulation around the splat periphery are standout features of the numerical simulations and yield a nonmonotonic dependence of the maximum splat radius on time. The temperature fields developing in both the liquid droplet and the substrate during the impingement process are also determined. To this end, liquid metal and water droplet collisions on different substrates were investigated. Convection effects on the temperature field development were found to be important for the entire history of spreading. These effects resulted sometimes in a practically radial temperature variation at late stages of spreading, particularly so in the cases of high impact velocities.
International Journal of Heat and Mass Transfer | 1997
J.M. Waldvogel; D. Poulikakos
A predominantly theoretical study is presented of the impact and solidification of molten solder droplets on a multi-layer substrate. This problem is of central importance to the novel micromanufacturing process called solder jetting, in which picoliter-size solder droplets are dispensed for the attachment of microelectronic components. The theoretical model is based on a Lagrangian formulation, and accounts for a host of thermal-fluid phenomena, including surface tension and heat transfer with solidification. Deforming finite elements with integrated automatic mesh generation are utilized to accommodate the large deformations which develop during the computations. An experimental investigation is also presented in which deposits produced by a prototype solder jetting apparatus are analysed using scanning electron microscopy. Results of simulations are presented in which variations of the initial droplet temperature, impact velocity, thermal contact resistance and initial substrate temperature are studied to demonstrate their impact on droplet spreading, on final deposit shapes and on the times to initiate and complete freezing. In many cases, non-intuitive results are observed, such as the non-monotonic dependence of the solidification time on variations of many of the parameters considered. Detailed study of the final solidified shapes, as well as the droplet configuration and flow filed at the onset of phase change, indicate strong coupling between the droplet dynamics and the freezing behavior.
International Journal of Heat and Mass Transfer | 1988
K.J. Renken; D. Poulikakos
Abstract This paper presents an experimental investigation of forced convective heat transport in a packed bed of spheres occupying a heated channel. A parallel plate channel configuration with the channel walls maintained at constant temperature is employed. The experiments document the dependence of the temperature field as well as the heat flux from the wall (represented by the Nusselt number) on the problem parameters, in the thermally developing region. Numerical simulations for the same problem are also performed. A general model for the momentum equation accounting for flow inertia, macroscopic shear and variable porosity is used. The experimental and numerical findings are in good agreement and they predict an overall heat transfer enhancement between the wall and the fluid/porous matrix composite when compared to the predictions of the popular Darcy flow model.
International Journal of Heat and Mass Transfer | 1995
S.K. Rastogi; D. Poulikakos
Abstract In this paper, a theoretical study is presented for the problem of double-diffusion from a vertical plate embedded in a porous matrix that is saturated with a non-Newtonian (power law) fluid. The study consists of two parts: In the first part, scaling analysis is utilized to obtain estimates of the quantities of interest and to identify the various possible flow regimes depending on the values of the buoyancy ratio and the Lewis number. This task is performed for both the case of a wall with constant temperature and concentration and the case of a wall with constant heat and species flux. In the second part of the study, a numerical solution of the problem is presented for the general case of a wall with arbitrarily varying temperature and concentration. The values of the relevant parameters resulting in a constant heat and species flux or a constant temperature and concentration at the wall are identified. The dependence of the flow, temperature, and concentration fields as well as of the local heat and species fluxes at the wall on the power law exponent, the buoyancy ratio and the Lewis number is documented for the two cases: (a) constant temperature and concentration, (b) constant heat and species flux.
Physics of Fluids | 1986
D. Poulikakos
In this study a series of numerical simulations is reported that aims to document the phenomenon of buoyancy‐driven flow instability in a fluid layer extending over a porous substrate. The numerical simulations focus primarily on the parametric domain in which the flow in the system is well established, i.e., the value of the Rayleigh number is larger than critical. A general flow model is used to describe the flow inside the porous bed. This flow model accounts for friction caused by macroscopic shear [Brinkman extension of the Darcy model; Appl. Sci. Res. Sect. A 1, 27 (1947)], as well as for the phenomenon of flow inertia [Forchheimer’s extension of the Darcy model; Dtsch. Ingenieure 45, 1782 (1901)]. Several important characteristics of the flow and temperature fields inside the composite layer (porous/fluid) are reported and the dependence of these characteristics on the problem dimensionless groups is documented.
International Journal of Heat and Mass Transfer | 1985
D. Poulikakos
Abstract This paper reports an analytical study of natural convection heat and mass transfer, induced by a concentrated source, located in an infinite porous medium. The transient and steady-state flow, temperature and concentration fields are obtained in terms of series expansions in the Rayleigh number based on the permeability of the porous medium and the heat generation rate from the source. The impact of the chemical species created by the source is to either aid or retard the flow induced by thermal buoyancy. Expressions determining the effect of species generation on the resulting transient and steady-state temperature and flow fields in the porous medium are reported in the course of the study. All discussions in this paper focus on the case where the net flow is upwards. Even though heat was specified to be one of the two diffusion mechanisms, the results of the present study apply as well to the case of buoyancy induced flow from a concentrated source generating simultaneously two different chemical components.
Journal of Thermophysics and Heat Transfer | 1998
D. Getachew; D. Poulikakos; W. J. Minkowycz
A numerical and theoretical study of double-diffusive natural convection within a rectangular porous cavity saturated by a non-Newtonian e uid and characterized by a power-law model is conducted. The conditions on the vertical walls are of a constant temperature and concentration. The theoretical method utilizes the pure scaling arguments to estimate, in an order-of-magnitude sense, the type of e ow and the heat and mass transfer patterns that can develop in the enclosure. The results obtained using the scaling arguments are then verie ed by performing a series of numerical experiments. Numerical solutions for the e owe eld, the temprature and concentration distributions, and the heat and mass transfer rates are obtained for a wide range of parameters. Results are presented for 50 # Ra # 500, 0 # N # 20, 0.1 # Le # 500, and 0.5 # n # 1.6. The order-of-magnitude predictions for the overall heat and mass transfer rates and their respective domains of validity are shown to be in agreement with the results produced by discrete numerical experiments.