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.

A new scanning capillary tube viscometer

Abstract: The present study introduces a new scanning capillary tube viscometer for measuring fluid viscosity continuously over a range of shear rates including a low shear regime. Using a charge-coupled device sensor array, one could measure the changes in fluid level in a rising tube h(t) from which viscosity and shear rate were mathematically calculated. The concept of the new scanning capillary tube viscometer was validated by measuring viscosities of Newtonian fluids and comparing the results with those obtained with reference data and a rotating viscometer. Furthermore, the present method overcomes one of the major drawbacks of the capillary tube viscometer, the inability to produce viscosity data in a low shear range, by extending the shear rate range as low as 5 s−1 for water and diluted glycerin solutions at room temperature.

High efficiency refrigeration system

Abstract: An improved refrigeration system utilizing one or more vortex tubes. Vortex tubes produce liquid refrigerant from saturated-state vapor refrigerant in a vapor-compression refrigeration cycle. The efficiency of a refrigeration system can be improved by placing a vortex tube before the evaporator. The efficiency of a refrigeration system may also be improved by placing a vortex tube in the condenser approximately one-quarter of the way from the inlet of the condenser. The efficiency of a refrigeration system may also be improved by placing a vortex tube before the compressor.

Effect of Blood Viscosity on Oxygen Transport in Residual Stenosed Artery Following

Abstract: The effect of blood viscosity on oxygen transport in a stenosed coronary artery during thepostangioplasty scenario is studied. In addition to incorporating varying blood viscosityusing different hematocrit (Hct) concentrations, oxygen consumption by the avascularwall and its supply from vasa vasorum, nonlinear oxygen binding capacity of the hemo-globin, and basal to hyperemic flow rate changes are included in the calculation ofoxygen transport in both the lumen and the avascular wall. The results of this study showthat oxygen transport in the postangioplasty residual stenosed artery is affected by non-Newtonian shear-thinning property of the blood viscosity having variable Hct concentra-tion. As Hct increases from 25% to 65%, the diminished recirculation zone for the in-creased Hct causes the commencement of p

Effects of Whole Blood Viscosity on Atherogenesis.

Abstract: There is a high correlation between high whole blood viscosity and the well known risk factors for arterial occlusive disease: hypertension, hyperlipidemia, diabetes, male sex, age, smoking, and obesity. These risk factors increase whole blood viscosity, whereas the preventive factors of arterial occlusive disease such as fish oil, aspirin, alcohol, and exercise probably tend to reduce whole blood viscosity. The protective adaptation theory recently presented by Kensey and Cho1 proposed high whole blood viscosity as one of the major factors that make up the mechanical injury possibly inducing arterial occlusive disease. New diagnostic and prophylactic treatments for arterial occlusive disease are suggested. An accurate, convenient, and cost-effective blood viscometer that can be used in a clinical environment might become a useful diagnostic screening device for patients at risk for arterial occlusive disease, and it would help discover new prophylactic treatments.

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