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.

Steady shear viscosity measurements of viscoelastic fluids with the falling needle viscometer

Abstract: Previous measurements by other investigators of the purely viscous properties of viscoelastic fluids using the falling ball viscometer have been shown to yield anomalous results. These occur because the ball falling through the viscoelastic fluid creates a stress field which requires up to one hour to relax to its stress free state before another ball can be dropped. This is experimentally inconvenient. To further investigate this effect for a variety of viscometers, time interval measurements were made on a viscoelastic fluid (AP-273 Separan) using falling ball, falling needle and rotating cylinder viscometers. Although the falling ball measurements showed considerable time interval effects, the falling needle and rotating cylinder measurements did not. Thus the falling needle and rotating cylinder viscometers can be used to conveniently measure the steady shear viscosity of viscoelastic fluids.

Effect of hydration on whole blood viscosity in firefighters.

Abstract: ContextCardiovascular disease (CVD) is the leading cause of on-duty death among firefighters, totaling 45% of on-duty fatalities. Heat stress and fluid losses can result in decreases in cardiac output of firefighters, despite sus- tained tachycardia and maximally elevated heart rate dur- ing emergencies. Measurements of whole blood viscosity (WBV) may serve as an independent biomarker of the hydration and dehydration states of on-duty firefighters. ObjectiveThe current pilot study investigates the effects of a strenuous firefighting simulation and subsequent rehydration on WBV and other biological metrics in nine healthy, nonsmoking firefighters to (1) determine whether dehydration and rehydration result in detectable changes in WBV and (2) compare WBV with the results from a range of conventional medical tests. DesignThe research team designed a single-center, unblinded pilot study. SettingFire Training Division, 1900 Lind Ave SW, Renton, WA, 98057. ParticipantsParticipants were 9 healthy, nonsmoking firefighters who were volunteers. Outcome Measure(s) • Vital signs, traditional medical blood tests, and WBV were measured for each firefighter (1) at baseline, (2) after exercise but before rehydration with alkaline water, and (3) postexercise and after rehy- dration. Hematocrit (HCT), hemoglobin (Hb), and WBV increased after exercise and before rehydration. ResultsDehydration during the mock fire drill resulted in elevated WBV at both low- and high-shear rates. HCT and Hb increased due to dehydration and hemoconcen- tration. Hb and HCT returned to baseline values after exercise and rehydration, and while WBV improved, base- line values were not restored. After exercise but before rehydration, WBV changes were significantly larger than HCT and Hb changes, suggesting the profound influence of hydration states on WBV. ConclusionsWBV measurements were better determi- nants of hydration states than HCT or Hb and should be performed to monitor the cardiovascular health of at-risk firefighters. (Altern Ther Health Med. 2013;19(4):44-49.)

Method and apparatus for increasing the efficiency of a refrigeration system

Abstract: A refrigeration system utilizing a vortex generator and a diffuser to reduce the pressure differential between the head pressure and suction pressure across a compressor

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