Recently completed Research Projects include :

• Particle-hemodynamics simulations and virtual prototyping of branching blood vessels
  
• Air flow and particle deposition in lung airway models
  
• Turbulent air flow and pollutant distributions in occupied inhalation test chambers
  
• Fluid-structure interaction project: Stented abdomainal aortic aneurysms
• Gas and liquid flows in microchannels

• Home Page
• Basic Information
• Research Projects
• Research Results and Background
• Selected Links

Particle-Hemodynamics Simulations and Virtual Prototyping of Branching Blood Vessel

Presently, the branching blood vessels of interest are the rabbit's abdominal aorta as an atherosclerotic model to understand the onset of the disease, the human carotid artery bifurcation and its geometric alternatives to reduce or eliminate restenosis/thrombosis, the arterio-venous graft end for hemodialysis patients, and femoral graft-to-artery anastomoses to reduce the high graft-failure rates.

The underlying hypotheses for these projects are that aggravating physical factors trigger a cascade of abnormal biological events and that, in turn, geometric changes mitigate or eliminate the physico-biological impact, resulting in blood vessels of higher sustained patency rates. The block schematic below illustrates factors, events, and solutions in this research area.

In a complementary study, fluid-structure interactions are investigated as applied to optimal stent design and location to repair aneurysms, etc.

A) Carotid Artery Bifurcation Redesign

Click image to enlarge

B) Arterio-Venous Graft Connectors for Hemodialysis

Click image to enlarge

Selected Publications :

• Longest, P.W., Kleinstreuer C. and Buchanan, J.R. (2004), "Efficient computation of micron-particle dynamics including wall effects," Computers and Fluids, 33, 577-601
• Kleinstreuer C., and Longest, P. W. (2003) “Particle-hemodynamics analyses of end-to-side anastomoses: A computational comparison study,” in Vascular Grafts-Experiment and Modeling, A. Tura (ed.), WIT Press, Ashurst , UK .
  
• Longest, P. W., and Kleinstreuer, C. (2003) “Comparison of blood particle deposition models for non-parallel flow domains,” Journal of Biomechanics, 36, 421-430
  
• Longest, P. W., Kleinstreuer, C., Truskey, G.A., and Buchanan, J.R. (2003) “Relation between near-wall residence times of monocytes and early lesion growth in the rabbit aorto-celiac junction,” Annals of Biomedical Engineering, 31, 53-64
  
• Longest, P. W. and Kleinstreuer, C. (2003) Numerical simulation of wall shear stress conditions and platelet localization in realistic end-to-side arterial anastomoses,” ASME Journal of Biomechanical Engineering, 125, 671-681
  
• Longest, P. W., Kleinstreuer, C., and Archie, J.P. (2003) “Particle-hemodynamics analysis of the Miller-cuff arterial anastomosis,” Journal of Vascular Surgery, (in press)
  
• J.R. Buchanan, C. Kleinstreuer, S. Hyun, and G.A. Truskey (2003), "Hemodynamics simulation and identification of susceptible sites of atherosclerotic lesion formation in a model abdominal aorta," Journal of Biomechanics, 36, 1185-1196
  
• S. Hyun, C. Kleinstreuer, and J. P. Archie Jr (2003), "Computational Analysis of the Effect of External Carotid Artery Flow and Occlusion on Adverse Carotid Bifurcation Hemodynamics," Journal of Vascular Surgery, 37, 1248-1254
  

Animations : Click here to see selected animations

Click image to enlarge

Air Flow and Particle Deposition in Lung Airway Models

Realistic and accurate simulations of micron- and sub-micron-particle depositions in the human respiratory system play very important roles : (i) for dosimetry-and-health-effct studies of toxic particles and (ii) in combating lung and other diseases with drug aerosols employing "smart inhalers". Model validation with detailed experimental data sets, and use of multiprocessor machines are imperative for this complex two-phase flow project.

Selected Publications :

• Zhang, Z., Kleinstreuer, C, Donohue, J.F. and Kim, C. S., 2005, “Comparison of Micro- and Nano-Size Particle Depositions in a Human Upper Airway Model”, Journal of Aerosol Science, Vol. 36, 211-233.
  
• Zhang, Z., Kleinstreuer, C., Kim, C. S. and Cheng, Y. S., 2004, "Vaporizing Micro-Droplet Inhalation, Transport and Deposition in a Human Upper Airway Model", Aerosol Science and Technology, Vol.38, 36-49
  
• Zhang, Z., and Kleinstreuer, C, 2004, “Airflow Structures and Nano-Particle Deposition in a Human Upper Airway Model”, Journal of Computational Physics, Vol. 198, 178-210.
  
• Zhang, Z., Kleinstreuer, C, Donohue, J.F. and Kim, C. S., 2004, “Comparison of Micro- and Nano-Size Particle Depositions in a Human Upper Airway Model”, Journal of Aerosol Science, in press.
  
• Shi, H., Kleinstreuer, C., Zhang, Z. and Kim, C. S. 2004, “Nano-particle transport and deposition in bifurcating tubes with different inlet conditions”, Physics of Fluids, Vol. 16, 2199-2213.
  
• Zhang, Z. and Kleinstreuer, C. (2003) “Modeling of Low Reynolds Number Turbulent Flows in Locally Constricted Conduits: A Comparison Study,” AIAA Journal, Vol. 41, 831-840
  
• Kleinstreuer, C., and Zhang, Z. (2003) “Laminar-to-Turbulent Fluid-Particle Flows in a Human Airway Model,” Int. J. Multiphase Flow, Vol. 29, 271-289
  
• Zhang, Z. and Kleinstreuer, C. (2003) “Species Heat and Mass Transfer in a Human Upper Airway Model,” International Journal of Heat and Mass Transfer, Vol. 46, 4755-4768
  
• Zhang, Z. and Kleinstreuer, C., Kim, C. S., and Cheng, Y. S. (2003) “Vaporizing Micro-Droplet Inhalation, Transport and Deposition in a Human Upper Airway Model,” Aerosol Science and Technology, Vol. 38, 36-49
  
• Kleinstreuer, C., and Zhang, Z. (2003) “Targeted Drug Aerosol Deposition Analysis for a Four-Generation Lung Airway Model with Hemispherical Tumors,” ASME Journal of Biomechanical Engineering, Vol. 125, 197-206
  

Animations : Click here to see selected animations

Turbulent Air Flow and Pollution Distributions in Occupied Inhalation Test Chamber

Proper airflow and tracer gas or aerosil distributions as well as contaminant ventilation are of great importance in biomedical test chambers or for industrial workrooms. The focus is on two-phase flow in a Rochester-style inhalation test chamber with breating subjects exposed to a tracer gas (CO) or micron-particle environment. This is realistic set-up for dosimetry-and-health-effect studies, which require controlled, near-uniform pollutant concentrations. However, unmodified test chambers exhibit a strong single vortex in the larger breathing zone and measurable buoyancy effects. Depending upon the subjects location that implies possible depletion during inhalation, foreign particle entrainment, excessive air velocities, etc. Employing a commercial finite-volume code with user-enhanced Fortran programs, the transient three-dimensional turbulent momentum, mass and heat transfer equations have been solved and the configurations of a suitable flow redirection device, the characteristics of a new porous ceiling, different man-machine locations, and thermal effects have been analyzed. As a result, the best air flow device configuration and subject locations orientations have been determined to achieve high and consistent test pollutant concentrations inhaled by the subjects.

Click image to enlarge

Selected Publications :

• S, Hyun and C. Kleinstreuer (2002), "Computational Analysis of Human Inhalation Test Chamber for Dosinetry-and-health-effect studies," Applied Occupational and Environmental Hygiene, 17(8), 561-572
• S, Hyun and C. Kleinstreuer (2001), "Numerical Simulation of Mixed Convection Heat and Mass Transfer in a Human Inhalation Test Chamber," Int. J. Heat & Mass Transfer, 44(12), 2247-2260
• P. W. Longest, C. Kleinstreuer, and J. S. Kinsey (2000), "Turbulent 3-D Air Flow and Trace Gas Distribution in an Inhalation Test Chamber," ASME J. Fluids Eng., 122(2), 403-411

Animations : Click here to see selected animations

Fluid-structure interaction project: Stented abdominal aortic aneurysms

Realistic simulations of fluid-structure interactions in (stented) AAAs are important for AAA-rupture prediction, optimal stent-graft placement, new stent-graft designs, and quantitative Endo-vascular Aortic Repair (EVAR) recommendations.

• Coupled ANSYS fluid structure interaction (FSI) simulations of stented abdominal aortic aneurysms (AAAs):
• Rupture predication for abdominal aortic aneurysms.
• Effects of stent-graft placement to restore “normal” blood flow.
• Stent migration, endoleaks and other problems in stent-graft applications
  

Selected Publications :

• Li Z., Kleinstreuer C. A new wall stress equation for aneurysm-rupture prediction. Annals of Biomedical Engineering, 33, 209-213, 2005.
• Li Z., Kleinstreuer C. Fluid-structure Interaction Effects on Sac-blood Pressure and Wall Stress in a Stented Aneurysm. Journal of Biomechanical Engineering (ASME), 2005 (In press).
• Li Z., Kleinstreuer C. Blood Flow and Structure Interactions in a Stented Abdominal Aortic Aneurysm Model. Medical Engineering & Physics, 2005 (In press).
  
• Li Z., Kleinstreuer C. Computational Fluid-structure Interaction ANALYSES Applied to A Stented Abdominal Aortic Aneurysm. 2005 Summer Bioengineering Conference (ASME), June, Vail Cascade Resort&Spa, Vail Colorado.
• Li Z., Kleinstreuer C. Computational Analysis of Fluid-Structure Interactions in a Stented Aneurysm Model. Computer Methods in Biomechanics and Biomedical Engineering (In review).
  
• Li Z., Kleinstreuer C. A Comparison between Axisymmetric and Asymmetric Abdominal Aortic Aneurysm Morphologies Employing Computational Fluid-structure Interaction Analysis. Computers & Structures (In review).
  
• Li Z., Kleinstreuer C. Analysis of Biomechanical Factors Affecting Stent-graft Migration in an Abdominal Aortic Aneurysm Model. Journal of Biomechanics (In review).
  
• Li Z., Kleinstreuer C., Farber M. Computational Analysis of Biomechanical Contributors to Possible Endovascular Graft Failure. Journal of Endovascular Therapy (In review).
  
• Li Z., Kleinstreuer C. Effects of Blood Flow and Vessel Geometry on Wall Stress and Rupture Risk of Abdominal Aortic Aneurysms. Journal of Medical Engineering & Technology (In review).
  
• Li Z., Kleinstreuer C. Computational Analysis of Fluid-Structure Interactions in a Stented Aneurysm Model. Journal of Biomechanical Engineering(ASME), 2003, (accepted)
  
• Li Z., Kleinstreuer C. and Farber M., Analysis of Stent-graft and Arterial Wall Dynamics in an Axisymmetric Aneurysm Model, Journal of Vascular Surgery, 2003, (submitted)
  
• Li Z., Kleinstreuer C. "A new Wall Stress Equation for Aneurysm-rupture Prediction," J. Biomechanics, (in review)

Animations : Click here to see selected animations

Microfluidics and its applications to bio-MEMS

Microfluidics deals with fluid flows and micro/nano-particle suspensions in micro-conduits where the Knudsen number, Kn=λ/l_system, is relatively large. Hence the continuum assumption may be invalid and the Navier-Stokes equations and boundary conditions have to be modified, or new solution approaches (DSMC, MD, etc.) have to be applied.

Experimental observations of liquid microchannel flows are reviewed and results of computer experiments concerning channel entrance, wall slip, non-Newtonian fluid, surface roughness, viscous dissipation, and turbulence effects on the friction factor are discussed. Significant surface roughness effects are a function of the Darcy number, the Reynolds number, and cross-sectional configurations. For relatively low Reynolds numbers, Re < 2,000, onset to turbulence has to be considered important because of possible geometric non-uniformities, e.g., a contraction and/or bend at the inlet to the microchannel. Channel-size effect on viscous dissipation turns out to be important for conduits with D_h < 100 μm.

Selected Publications :

• Koo, J. and Kleinstreuer, C. (2003) “Liquid flow in microchannels: experimental observations and computational analyses of microfluidics effects,” Journal of Micromechanics and Microengineering, 13, 568-579
  
• Kleinstreuer, C. and Koo, J. (2004) “Computational Analysis of Wall Roughness Effects for Liquid Flow in Micro-Conduits,” Journal of Fluids Engineering, 126, 1-9
  
• Koo, J. and Kleinstreuer, C. (2004) “Viscous dissipation effects in microtubes and microchannels,” International Journal of Heat and Mass Transfer, 47, 3159-3169
  
• Koo, J. and Kleinstreuer, C. (2004) “A new thermal conductivity model for nanofluids,” Journal of Nanoparticle Research, 6, in press

Animations : Click here to see selected animations

Nanofluid flow applied to a micro-heat sink

In a quiescent suspension, nanoparticles move randomly and thereby carry on a micro-scale relatively large volumes of surrounding liquid with them. This Brownian-motion induced interaction may occur between hot and cold regions, resulting in a lower local temperature gradient for a given heat flux when compared to the pure liquid case. Thus, the effective thermal conductivity, keff , which is composed of the particles’ conventional static part and the Brownian motion part, increases, resulting in a lower temperature gradient for a given heat flux. To capture these transport phenomena, a new thermal conductivity model for nanofluids has been developed, i.e., keff = kstatic + kBrownian, which takes the effects of particle size, particle volume fraction and temperature dependence as well as properties of base liquid and particle phase into consideration.

In response to the ever increasing demand for smaller and lighter high-performance cooling devices, steady laminar liquid nanofluid flow in microchannels is simulated and analyzed. Considering two types of nanofluids, i.e., copper-oxide nano-spheres at low volume concentrations in water or ethylene glycol, the conjugated heat transfer problem for micro heat-sinks has been numerically solved. Employing new models for the effective thermal conductivity and dynamic viscosity of nanofluids, the impact of nanoparticle concentrations in these two mixture flows on the microchannel pressure gradients, temperature profiles and Nusselt numbers are computed, in light of aspect ratio, viscous dissipation, and enhanced temperature effects. Based on these results, the following can be recommended for micro heat-sink performance improvements: Use of large high Prandtl-number carrier fluids, nanoparticles at high
volume concentrations of about 4 [%] with elevated thermal conductivities and dielectric constants very close to that of the carrier fluid, microchannels with high aspect ratios, and treated channel walls to avoid nanoparticle accumulation.

Selected Publications :

• Koo, J. and Kleinstreuer, C. (2004) “A new thermal conductivity model for nanofluids,” Journal of Nanoparticle Research, 6, in press
  
• Koo, J. and Kleinstreuer, C. (2005) “Laminar Nanofluid Flow in Micro Heat-sinks,” International Journal of Heat and Mass Transfer, in press
  
• Koo, J. and Kleinstreuer, C. (2005) “Impact analysis of nanoparticle motion mechanisms on the thermal conductivity” International Communications in Heat and Mass Transfer, sumitted