Young I. Cho

Effects of the non-Newtonian viscosity of blood on flows in a diseased arterial vessel. Part 1: Steady flows.

Effects of the non-Newtonian viscosity of blood on a flow in a coronary arterial casting of man were studied numerically using a finite element method. Various constitutive models were examined to model the non-Newtonian viscosity of blood and their model constants were summarized. A method to incorporate the non-Newtonian viscosity of blood was introduced so that the viscosity could be calculated locally. The pressure drop, wall shear stress and velocity profiles for the case of blood viscosity were compared for the case of Newtonian viscosity (0.0345 poise). The effect of the non-Newtonian viscosity of blood on the overall pressure drop across the arterial casting was found to be significant at a flow of the Reynolds number of 100 or less. Also in the region of flow separation or recirculation, the non-Newtonian viscosity of blood yields larger wall shear stress than the Newtonian case. The origin of the non-Newtonian viscosity of blood was discussed in relation to the viscoelasticity and yield stress of blood.

Non-Newtonian Fluids in Circular Pipe Flow

Publisher Summary This chapter focuses on heat transfer behavior of viscoelastic fluid in turbulent pipe flow. Although the asymptotic values of the heat transfer and friction factor can be calculated, there exist no firm criteria for determining whether asymptotic conditions exist. Predictions of the intermediate values of the friction and heat transfer are not yet possible, even if the rheology and the thermal properties of the aqueous polymer solution are known. To deals with the problems, the Weissenberg or Deborah number has to be taken into account. The behavior of viscoelastic fluids flowing turbulently in noncircular channels or over external surfaces represents a relatively unexplored area of fluid mechanics. Open channel flow of viscoelastic fluid is another interesting field currently being investigated. The chapter concludes that to approach turbulent heat transfer behavior analytically, the usual and simplest method is to solve the uncoupled energy equation using the empirically determined velocity profile. Hence, it is essential to understand the fluid mechanics of non-Newtonian fluids as well as the rheology.

Hemorheological Disorders in Diabetes Mellitus

The objective of the present study is to review hemorheological disorders in diabetes mellitus. Several key hemorheological parameters, such as whole blood viscosity, erythrocyte deformability, and aggregation, are examined in the context of elevated blood glucose level in diabetes. The erythrocyte deformability is reduced, whereas its aggregation increases, both of which make whole blood more viscous compared to healthy individuals. The present paper explains how the increased blood viscosity adversely affects the microcirculation in diabetes, leading to microangiopathy.

Forced convection heat transfer with phase-change-material slurries: Turbulent flow in a circular tube

Abstract The present study investigates the increase in the convective heat transfer coefficient as well as the increase in the thermal capacity of a working fluid by using the latent heat from a solid-liquid phase change of particles. A long heating test section (627 diameters) with a uniform heat flux boundary condition is constructed in order to study the effects of the phase-change phenomenon produced by a phase-change-material (PCM)—water slurry on the convective heat transfer coefficient in a turbulent flow. The study introduces a method to generate very fine PCM particles inside a flow loop using an emulsifier. With such fine PCM particles, the flow loop did not clog. Local pressure drops and local heat transfer coefficients are measured along the test section. The pressure drop significantly decreased at the point where the PCM particles in the slurry melted. The local convective heat transfer coefficient was found to vary significantly when the particles melted. This made it difficult to apply the LMTD method to the analysis of the PCM slurry flow heat transfer. The study proposes a new three-region melting model, and provides an explanation of the physical mechanism of the convective heat transfer enhancement due to the PCM particles.

Non-equilibrium plasma in liquid water: dynamics of generation and quenching

In most cases, the electric breakdown of liquids is initiated by the application of high electric field on the electrode, followed by rapid propagation and branching of plasma channels. Typically plasmas are only considered to exist through the ionization of gases and typical production of plasmas in liquids generates bubbles through heating or via cavitation and sustains the plasmas within those bubbles. The question arises: is it possible to ionize the liquid without cracking and void formation?To answer this question we used a pulsed power system with 32–220 kV pulse amplitude, 0.5–12 ns pulse duration, 150 ps rise time. The discharge cell had a point-to-plate geometry with a tip diameter of 100 µm. These parameters allowed us to observe non-equilibrium plasma generation. The measurements were performed with the help of a 4Picos ICCD camera. It was found that the discharge in liquid water forms on a picosecond time scale. The increase of emission intensity and plasma formation took 200–300 ps. The diameter of the excited region near the tip of the high-voltage electrode was ~1 mm. After this initial stage emission rapidly decreased and the plasma region became almost invisible after 500 ps. The absence of emission during the rest of the pulse is explained by a decrease of the electrical field on the boundary of the conductive zone.Thus we have demonstrated the possibility of formation of non-equilibrium plasma in the liquid phase and investigated the dynamics of excitation and quenching of non-equilibrium plasma in liquid water.

Separation and reattachment of non-newtonian fluid flows in a sudden expansion pipe

Abstract In the current flow visualization studies, the role of non-Newtonian characteristics (such as shear-rate-dependent viscosity and viscoelasticity) on flow behavior across the sudden expansion step in a circular pipe is investigated over a wide range of Reynolds numbers including the turbulent flow. The expansion ratios tested are 2.000 and 2.667 and the range of the Reynolds number covered in the current flow visualization tests are 10–35 000 based on the inlet diameter. The reattachment lengths for the viscoelastic fluids in the laminar flow regime are found to be much shorter than those for the Newtonian fluid. In addition they decrease significantly with increasingly concentration of viscoelastic fluid at the same Reynolds number. However, in the turbulent flow regime, the reattachment length for the viscoelastic fluids is two or three times longer than those for water, and gradually increases with increasing concentration of viscoelastic solutions, resulting in 25 and 28 step-height distances for 500 ppm and 1000 ppm polyacrylamide solutions respectively. This may be because the elasticity in polyacrylamide solutions suppresses the eddy motion and controls separation and reattachment behavior in the sudden expansion pipe flow. The reattachment lengths for the purely viscous non-Newtonian fluids are found to be almost the same as those for water.

Gliding arc in tornado using a reverse vortex flow

The present article reports a new gliding arc (GA) system using a reverse vortex flow (“tornado”) in a cylindrical reactor (gliding arc in tornado, or GAT), as used to preserve the main advantages of traditional GA systems and overcome their main drawbacks. The primary advantages of traditional GA systems retained in the present GAT are the possibility to generate transitional plasma and to avoid considerable electrode erosion. In contrast to a traditional GA, the new GAT system ensures much more uniform gas treatment and has a significantly larger gas residence time in the reactor. The present article also describes the design of the new reactor and its stable operation regime when the variation of GAT current is very small. These features are understood to be very important for most viable applications. Additionally the GAT provides near-perfect thermal insulation from the reactor wall, indicating that the present GAT does not require the reactor wall to be constructed of high-temperature materials. The...

The effect of header shapes on the flow distribution in a manifold for electronic packaging applications

Abstract The present paper investigates the effects of header shapes and the Reynolds number on the flow distribution in a parallel flow manifold to be used in a liquid cooling module for electronic packaging. The flow distribution in the manifold greatly depends on the header shape and the Reynolds number. Of the three different headers (i.e., rectangular, triangular, and trapezoidal), the triangular header produces the best flow distribution regardless of the Reynolds number.

Effect of Mild Atherosclerosis on Flow Resistance in a Coronary Artery Casting of Man

An in-vitro flow study was conducted in a mildly atherosclerotic main coronary artery casting of man using sugar-water solutions simulating blood viscosity. Steady flow results indicated substantial increases in pressure drop, and thus flow resistance at the same Reynolds number, above those for Poiseuille flow by 30 to 100 percent in the physiological Reynolds number range from about 100 to 400. Time-averaged pulsatile flow data showed additional 5 percent increases in flow resistance above the steady flow results. Both pulsatile and steady flow data from the casting were found to be nearly equal to those from a straight, axisymmetric model of the casting up to a Reynolds number of about 200, above which the flow resistance of the casting became gradually larger than the corresponding values from the axisymmetric model.

The effect of area ratio on the flow distribution in liquid cooling module manifolds for electronic packaging

Abstract The proper selection of the geometry of a manifold is important to obtain a uniform coolant distribution which is necessary to eliminate local hot spots in a liquid cooling module for electronic packaging. The effect of an area ratio, defined as ratio of the total channel cross-sectional area to the dividing flow header cross-sectional area, on the coolant distribution in a parallel flow manifold was studied numerically for a Reynolds number of 50, a typical flow condition observed in the electronic packaging. Of the three area ratios (4,8, and 16), the case of AR =4 produced the best coolant distribution. However, the flow rate in the last channel was 2.75 times that in the first channel. It is concluded that the area ratio is one of the most important parameters affecting the coolant distribution and should be carefully examined in the design of a liquid cooling module.