Showing papers by "Young I. Cho published in 1999"

Catheter obstruction effect on pulsatile flow rate--pressure drop during coronary angioplasty.

Abstract: The coupling of computational hemodynamics to measured translesional mean pres­ sure gradients with an angioplasty catheter in human coronary stenoses was evalu­ ated. A narrowed flow cross section with the catheter present effectively introduced a tighter stenosis than the enlarged residual stenoses after balloon angioplasty; thus elevating the pressure gradient and reducing blood flow during the measurements. For resting conditions with the catheter present, flow was believed to be about 40 percent of normal basal flow in the absence of the catheter, and for hyperemia, about 20 percent of elevated flow in the patient group. The computations indicated that the velocity field was viscous dominated and quasi-steady with negligible phase lag in the Ap(t) — u(t} relation during the cardiac cycle at the lower hydraulic Reynolds numbers and frequency parameter. Hemodynamic interactions with smaller catheterbased pressure sensors evolving in clinical use require subsequent study since artifactually elevated translesional pressure gradients can occur during measurements with current angioplasty catheters.

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.

Multiple coil assembly for use with electronic descaling unit

Abstract: An apparatus for imparting an electric field to water travelling within a pipe. The apparatus includes a plurality of rectangularly-shaped coils of electric wire connected in an electrically parallel arrangement. Each coil is sandwiched between flexible cover sheets. The resulting assembly is applied to the outer circumference of the pipe, with the lengthwise dimension of the coil extending perpendicularly to the flow inside the pipe. A time-varying electric current is applied to the coil to produce a corresponding electric field. This, in turn, produces controlled precipitation of mineral ions from the water.

Combined use of an electronic antifouling technology and brush punching for scale removal in a water-cooled plain tube

Abstract: The objective of the present study was to investigate the benefit of the combined use of an electronic antifouling (EAF) technology and brush punching for scale removal in a shell-and-tube heat exchanger. Two fouling experiments were conducted with new plain tubes: one without an EAF treatment and the other with it. Scale inside the two tubes was produced in a recirculation-flow system with an artificially hardened water of 7.5 mol/m3. After passing tap water through each tube for 4 days, the fouling resistance in the tube with the EAF treatment was measured and found to be 46% less than in the one without the EAF treatment. Subsequent brush punching of the tube for the case with the EAF treatment cleaned almost all of the remaining scale, thus recovering the initial overall heat transfer coefficient values, resulting in zero fouling resistance. However, for the case without the EAF treatment, brush punching was not effective in removing scale. Both the present experiment and earlier SEM photographs suppo...

An innovative electronic descaling technology for scale prevention in a chiller

Abstract: The present study introduces an innovative method called electronic descaling (ED), which was developed as a means to prevent precipitation fouling in a heat exchanger. The operating principle of the ED technology is presented using fundamental physics laws. The validity of the ED technology was tested by evaluating the performance of a full-scale chiller over an entire cooling season. The ED technology eliminated scales in the condenser tubes, resulting in the improvement of chiller performance and in energy savings.