Showing papers by "Young I. Cho published in 1995"

Radiative heat transfer by the Monte Carlo method

Abstract: Part 1 Principles of radiation: thermal radiation radiation heat transfer. Part 2 Principles of Monte Carlo methods: formulation methods of solution special treatises. Part 3 Applications of the Monte Carlo method: two-dimensional systems some industrial applications references applications on disk list of variables in computer programs.

Current driver for electronic descaling

Abstract: An electronic descaling system to prevent or remove mineral deposits by exposing moving fluids to magnetic and electric fields includes an improved power supply. In particular, the power supply adapts to the varying length, diameter and impedance of attached coil and cable combinations, and still provides the proper current and power levels to effectuate electronic descaling. A constant current D.C. power supply having a regulated D.C. current output level is provided. The substantially constant D.C. current output is then switched in a switching circuit responsive to a switching control signal to provide a bi-directional current through the coil in one direction and then switched to conduct current through the coil in the other direction. The switching frequency of the switching control signal is time variable or constant. The present improved current driver adapts for such varying frequencies while providing a substantially constant D.C. current output level as the frequency of switching control signal varies. The descaling coil provides the proper induced electric and magnetic fields, and the resulting induced electromotive force, for different switching frequencies and for cables with varying lengths and coils with varying diameters.

Reduced corrosion electronic descaling technology

Abstract: A method for minimizing localized corrosion of fluid containers that occurs as a consequence of most non-chemical procedures for removing scale deposits is described. It counteracts the unavoidable side-effect of the lowering of the local pH in the vicinity of the bubbles of CO 2 that are generated during an electromagnetically-induced controlled precipitation procedure. The method is a simple and facile procedure for curbing the localized corrosion occurring as a result of most non-chemical procedures for removing scales. The method is desirably performed by an induction coil wrapped around a fluid container such as a pipe encrusted with scale through which hard water is flowing. A pulsing electrical current is successively applied through the coil and halted, preferably for 3 to 10 minutes each. When the current is applied, a transitory induced magnetic field is generated in the solution, and scale encrusted on the fluid container dissolves in the solution. When the pulsing current is stopped, the induced magnetic field in the solution ceases and so the scale stops dissolving, allowing a protective layer of scale to form over potential points of corrosion. Optionally permanent magnets may be used in the process, alone or with an induction coil.

Local Friction and Heat Transfer Behavior of Water in a Turbulent Pipe Flow With a Large Heat Flux at the Wall

Abstract: We investigate the behavior of friction and heat transfer coefficients of water flowing turbulently in a relatively long (i.e., 950 diameter long) circular pipe. When a large heat flux was applied at the wall, the viscosity of water significantly decreased along the axial direction due to the increasing temperature of water. A concept of a redeveloping region was introduced, where the local heat transfer coefficient increased while the local friction coefficient decreased due to the above-mentioned viscosity change. We propose the use of local bulk-mean temperature to determine local Nusselt numbers by using local Reynolds (Re LB ) and Prandtl numbers (PT LB ), a method that automatically took into account the effect of axial viscosity change on the evaluation of local heat transfer coefficients. A new turbulent heat transfer correlation for the prediction of the local Nusselt number is given as Nu x = 0.00425 Re LB 0.079 Pr LB O.4 (μ w /μ h ) -0.11 .

Recurrence of balloon treated intracranial terminal aneurysm: a study with pulsatile blood flow

Abstract: ABSIRAcr To identify the hemodynamic mechanisms associated with recurrence of intracranial aneurysms following the treatment with balloon or coil occlusion. Pulsatile flow in a terminal recurrent intracranial aneurysm was numerically simulated based on the physiological pulsatile flow observed in the middle cerebral artery. In order to quantify the reason for recurrence of terminal aneurysm. flow parameters including local maximum wall shear stress and pressure drop at the neck of the aneurysm was calculated. Though the maximum shear stress at the right neck of the aneurysm after the insertion of the balloon is significantly reduced. it is still two and a half times more than the normal maximum shear stress. It is observed that due to the residual neck left after the insertion of the balloon an inadequate reduction in shear stress is achieved at the right neck where the recurrence of aneurysm is initiated. It is clear that the structural alteration of the endothelial layers in the aneurysm neck, where the shear stress was high. was critical.