Young I. Cho

Bio: Young I. Cho is an academic researcher from Drexel University. The author has contributed to research in topics: Fouling & Blood viscosity. The author has an hindex of 42, co-authored 266 publications receiving 12349 citations. Previous affiliations of Young I. Cho include California Institute of Technology & Thomas Jefferson University Hospital.

Changes in whole blood viscosity at low shear rates correlate with intravascular volume changes during hemodialysis.

Abstract: Background:Elevated blood viscosity has been shown to be independently correlated with cardiovascular risk factors and associated with increased risk of major cardiovascular events, including death

Physical Water Treatment Using Oscillating Electric Fields to Mitigate Scaling in Heat Exchangers

Abstract: This chapter presents an environment-friendly method to mitigate scaling in heat exchangers. A new physical water treatment (PWT) using high-frequency oscillating electric fields produced directly in water was used to mitigate scaling of heat transfer surfaces. The new method of using high-frequency oscillating electric fields directly in water is a major improvement over the previous PWT methods (i.e., low electric field strength, about ~1 mV/cm, and low allowable frequency, ~2 kHz). Both artificial and natural hard water at varying calcium carbonate hardness were used. Different combinations of voltages and frequencies were investigated to get the optimum values for the mitigation of scaling. It is hypothesized that the oscillating electric fields in the present PWT method precipitate the dissolved mineral ions such as calcium to mineral salts in bulk water. As the mineral ions continue to precipitate and adhere on the surfaces of the suspended particles, the particles grow in size and adhere to the solid heat transfer surface in the form of soft sludge or particulate fouling. This type of fouling is believed to be easily removed by shear forces created by flow than those deposits produced from the precipitation of mineral ions directly on the solid heat transfer surface, i.e., precipitation fouling. The new PWT method using oscillating electric fields presents a valid tool to mitigate scaling in heat exchangers from cooling water. The work in this book is based from the PhD dissertation of the first author at the Division of Mechanical Design Engineering at Chonbuk National University. Section 3.1 presents an overview of mineral fouling and the different methods to mitigate the fouling formation in heat exchangers, focusing on physical water treatment. Sections 3.2, 3.3, 3.4 and 3.5 give in detail the experimental work and discussion of the use of oscillating electric fields as a means to mitigate mineral fouling in a double-pipe heat exchanger. Section 3.6 summarizes the present study.

Non-equilibrium plasma in liquid water -dynamics of generation and quenching

Abstract: In most cases, the electric breakdown of liquids is initiated by the application of high electric field on the electrode, followed by rapid propagation and branching of plasma channels. Typically plasma is only considered to exist through the ionization of gases and typical production of plasmas in liquids has generated bubbles through heating or via cavitation and sustains the plasmas within those bubbles. The question appears: is it possible to ionize the liquid without cracking and voids formation?

The effect of patient-specific non-newtonian blood viscosity on arterial hemodynamics predictions

Abstract: Blood flow simulations can identify arterial regions that are vulnerable to atherosclerotic or thrombotic evolution. To accurately define vulnerable arterial regions, hemodynamic parameters such as...

Flow Resistance in Curved Femoral Artery Flow Models of Man for Steady Flow

Abstract: Etude des flux liquidiens sur un modele d'artere femorale. Simulation du flux en fonction du rayon de courbure

Convective Transport in Nanofluids

Abstract: Nanofluids are engineered colloids made of a base fluid and nanoparticles (1-100 nm) Nanofluids have higher thermal conductivity' and single-phase heat transfer coefficients than their base fluids In particular the heat transfer coefficient increases appear to go beyond the mere thermal-conductivity effect, and cannot be predicted by traditional pure-fluid correlations such as Dittus-Boelter's In the nanofluid literature this behavior is generally attributed to thermal dispersion and intensified turbulence, brought about by nanoparticle motion To test the validity of this assumption, we have considered seven slip mechanisms that can produce a relative velocity between the nanoparticles and the base fluid These are inertia, Brownian diffusion, thermophoresis, diffusioplwresis, Magnus effect, fluid drainage, and gravity We concluded that, of these seven, only Brownian diffusion and thermophoresis are important slip mechanisms in nanofluids Based on this finding, we developed a two-component four-equation nonhomogeneous equilibrium model for mass, momentum, and heat transport in nanofluids A nondimensional analysis of the equations suggests that energy transfer by nanoparticle dispersion is negligible, and thus cannot explain the abnormal heat transfer coefficient increases Furthermore, a comparison of the nanoparticle and turbulent eddy time and length scales clearly indicates that the nanoparticles move homogeneously with the fluid in the presence of turbulent eddies so an effect on turbulence intensity is also doubtful Thus, we propose an alternative explanation for the abnormal heat transfer coefficient increases: the nanofluid properties may vary significantly within the boundary layer because of the effect of the temperature gradient and thermophoresis For a heated fluid, these effects can result in a significant decrease of viscosity within the boundary layer, thus leading to heat transfer enhancement A correlation structure that captures these effects is proposed

Investigation on Convective Heat Transfer and Flow Features of Nanofluids

Abstract: Low thermal conductivity is a primary limitation in the development of energy-efficient heat transfer fluids that are required in many industrial applications. In this paper we propose that an innovative new class of heat transfer fluids can be engineered by suspending metallic nanoparticles in conventional heat transfer fluids. The resulting {open_quotes}nanofluids{close_quotes} are expected to exhibit high thermal conductivities compared to those of currently used heat transfer fluids, and they represent the best hope for enhancement of heat transfer. The results of a theoretical study of the thermal conductivity of nanofluids with copper nanophase materials are presented, the potential benefits of the fluids are estimated, and it is shown that one of the benefits of nanofluids will be dramatic reductions in heat exchanger pumping power.

Hydrodynamic and heat transfer study of dispersed fluids with submicron metallic oxide particles

Abstract: Turbulent friction and heat transfer behaviors of dispersed fluids (i.e., uttrafine metallic oxide particles suspended in water) in a circular pipe were investigated experimentally. Viscosity measurements were also conducted using a Brookfield rotating viscometer. Two different metallic oxide particles, γ-alumina (Al2O3) and titanium dioxide (TiO2), with mean diameters of 13 and 27 nm, respectively, were used as suspended particles. The Reynolds and Prandtl numbers varied in the ranges l04-I05 and 6.5-12.3, respectively. The viscosities of the dispersed fluids with γ-Al2O3 and TiO2 particles at a 10% volume concentration were approximately 200 and 3 times greater than that of water, respectively. These viscosity results were significantly larger than the predictions from the classical theory of suspension rheology. Darcy friction factors for the dispersed fluids of the volume concentration ranging from 1% to 3% coincided well with Kays' correlation for turbulent flow of a single-phase fluid. The Nusselt n...

Thermal Conductivity of Nanoparticle -Fluid Mixture

Abstract: Effective thermal conductivity of mixtures of e uids and nanometer-size particles is measured by a steady-state parallel-plate method. The tested e uids contain two types of nanoparticles, Al 2O3 and CuO, dispersed in water, vacuum pump e uid, engine oil, and ethylene glycol. Experimental results show that the thermal conductivities of nanoparticle ‐e uid mixtures are higher than those of the base e uids. Using theoretical models of effective thermal conductivity of a mixture, we have demonstrated that the predicted thermal conductivities of nanoparticle ‐e uid mixtures are much lower than our measured data, indicating the dee ciency in the existing models when used for nanoparticle ‐e uid mixtures. Possible mechanisms contributing to enhancement of the thermal conductivity of the mixtures are discussed. A more comprehensive theory is needed to fully explain the behavior of nanoparticle ‐e uid mixtures. Nomenclature cp = specie c heat k = thermal conductivity L = thickness Pe = Peclet number P q = input power to heater 1 r = radius of particle S = cross-sectional area T = temperature U = velocity of particles relative to that of base e uids ® = ratio of thermal conductivity of particle to that of base liquid ¯ = .® i 1/=.® i 2/ ° = shear rate of e ow Ω = density A = volume fraction of particles in e uids Subscripts