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.

Stretched arc discharge in produced water

Abstract: The objective of the present study was to investigate the feasibility of stretching an arc discharge in produced water to increase the volume of produced water treated by plasma. Produced water is the wastewater generated by hydraulic fracturing of shale during the production phase in shale-oil or shale-gas exploration. The electric conductivity of produced water is in the range of 50-200 mS/cm, which provides both a challenge and opportunity for the application of plasmas. Stretching of an arc discharge in produced water was accomplished using a ground electrode and two high-voltage electrodes: one positioned close to the ground electrode and the other positioned farther away from the ground. The benefit of stretching the arc is that the contact between the arc and water is significantly increased, resulting in more efficient plasma treatment in both performance and energy cost.

The hydrodynamics of a bent cylinder in a viscoelastic fluid

Abstract: The hydrodynamics of a bent cylinder specimen moving in a viscoelastic fluid and a Newtonian fluid has been studied experimentally by observing the falling motion of the specimen with different initial orientations. The effect of the end-to-end distance on the terminal velocity of the specimen was also investigated in both fluids. In the Newtonian fluid, no matter what the initial position or the bend angle of the specimen was, it always reoriented to the open-end-up position and kept this shape while it fell. In the viscoelastic fluid, however, the open-end-up specimen always fell down as it was, while open-end-down specimen did not always flip to the open-end-up position as in the Newtonian fluid, but, if the bend angle was smaller than a critical value, it fell down with open-end-down shape. The effect of the end-to-end distance on the specimen terminal velocity was found to be significantly different between the Newtonian and the viscoelastic fluid. These observations represent new experimental findings, unique to a viscoelastic fluid, and may be attributed to the existence of a polymer network in viscoelastic solutions created by high molecular-weight polymer chains.

Apparatus and method for determining in vivo the instantaneous velocity of the flow of blood in a living being

Abstract: Apparatus (20) and a method of determining in vivo the instantaneous velocity of the blood flowing within the body of a living being. The apparatus (20) basically comprises respective first and second sensors (42, 44) which are arranged to be disposed at spaced apart locations within a blood vessel (26). The sensors (42, 44) are coupled to a control/analysis unit (24) located externally of the body of the being. The first sensor (42) is arranged to provide a heat pulse to the blood flowing thereby and to provide a first signal at that time. The second sensor (44) is located downstream of said first sensor and is arranged for providing a second signal when the first blood portion passes thereby. The control/analysis unit (24) measures the time period between those signals and based on that value and data representative of the distance separating the sensors, calculates the instantaneous blood velocity.

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