Sampling of Research at the Advanced Materials and Technologies Laboratory
Ranga Pitchumani Advanced Materials and Technologies Laboratory Department of Mechanical Engineering Virginia Tech Blacksburg, Virginia 24061-0238 pitchu@vt.edu • http://www.me.vt.edu/amtl • (540) 231-1776
Presented at the VBI Faculty Meeting • November 10, 2009
Advanced Materials and Technologies Laboratory Prof. Ranga Pitchumani • pitchu@vt.edu • http://www.me.vt.edu/amtl Bio Transport Phenomena
Microfabrication
Blood flows through stenosed carotid and coronary arteries with a complete bypass graft are investigated by using computational fluid dynamics tools. Different anastomotic angles, bypass graft length and locations of the stenosis are analyzed as function of the extent of plaque occlusion in the artery. The effects of type-II diabetes mellitus is also investigated. The results show that the flow features, including pressure drop cross the stenosis and the shear stress on artery walls, are all influenced by these parameters; a systematic analysis is conducted to derive information on graft design so as to minimize the possibility of the restenosis in the host artery with bypass graft implantation.
Composite Materials and Nanocomposites
A/W=1709 m2/g
100%
Research focuses on the fundamentals of multiscale, multiphysics phenomena in the fabrication of composite materials via liquid molding and other methods. The emphasis is on filling gaps in understanding of the phenomena, bridging them across a cascade of scales, and using computational physics-based models for realtime sensing and control, design, optimization, and analysis under uncertainty. Use of carbon nanotubes in structural fiber-reinforced composites is studied for their damping characteristics for applications in vibrating and rotating structures (such as rotorcraft and wind turbine blades). Related issues on characterizing the complex rheology and cure kinetics of resin systems with carbon nanotubes are also addressed.
As microsystem technologies and application prospects continue to grow, it is of interest to fabricate high aspect ratio microstructures from a broad range of metals and ceramics. The objective of the work is to investigate a new technique based on capillarydriven microcasting and curing of an epoxy-based metallic or ceramic nanoparticulate slurry into a sacrificial plastic mold, and subsequent sintering of the nanoparticulate ceramic or metallic phase to form the micropart. Fundamentals of microchannel filling, nanoparticle settling during flow, and nanoparticulate preform sintering are investigated to arrive at operating windows on slurry formulations, mold design, mold filling parameters, and sintering conditions so as to maximize feature fidelity.
A novel process for replication of electroforming micromolds for use in high aspect ratio micropart fabrication is being studied in collaboration with Sandia National Laboratories. A combined computational and experimental study on the fundamental phenomena governing the fabrication process is used to systematically elucidate the effects of the various process, material, and geometric parameters, including the interactive effects of uncertainty inherent in the materials and the process toward predicting the resulting process variability and the micropart quality. Optimum processing conditions are derived for robust and reliable processing.
Energy
Programs in the area of energy focus on fuel cells, hybrid systems, photovoltaics and thermal energy storage. The projects on fuel cells are aimed at designing the cell and the systems for uniformity of current density through optimal design of the operating conditions as well as through novel material designs such as graded material microarchitectures. Passive airbreathing fuel cell designs are developed for reduced system complexity and novel microfuel cells that combine microfabrication and fuel cell technologies are investigated for micropower generation at high power density. Transient operation of fuel cells and fuel cell/battery and fuel cell/gasoline hybrid systems are also being investigated to design systems for tracking varying power requirements in different applications. Research on photovoltaics is on understanding the fundamentals of dye-sensitized solar cells (DSSC) or Grätzel cells with a view to develop design maps for applications in different terrestrial locations. Thermal energy storage technologies based on phase change materials are being developed for concentrating solar power systems. The novel approach involves embedding thermosyphons or heat pipes to reduce the resistance to heat transfer between the location where phase change occurs and the working fluid of the power cycle.
Blood Flow Through Stenosed Arteries with Complete Bypass
Atherosclerosis—the constriction of an artery through plaque buildup—is a leading cause of human mortality in developed countries. Bypass surgery is used to improve blood flow around a diseased artery.
The goal is to study blood flow in a stenosed artery with bypass with the objective of developing bypass design guidelines.
Bypass parameters were varied in a computational simulation study to assess their influence on the pressure drop and wall shear stress
r v
r v Artery
Anastomosis Angle: α, Anastomosis Length: L Occlusion:
Astenosis 1 1 Ahost
d D
2
Blood Rheology
0 r v
r Ý v
p
r vT
Carotid (D = 6 mm; 370
Coronary (D = 3 mm; 35
ml/min flux)
ml/min flux)
Carreau model:
20%, 50%, 75% and 100% 15o, 30o, 45o, and 60o L/D
4, 6 and 8
Advanced Materials and Technologies Laboratory
Axial Velocity Profiles Carotid Artery
o
45
Carotid Artery
= 75% L 4D
L = 4D
Bypass Ratio 1.77
L = 6D
Bypass Ratio 1.61
L = 8D
Bypass Ratio 1.48
Coronary Artery
45o
= 75%
Advanced Materials and Technologies Laboratory
Axial Velocity Profiles in the Carotid Artery = 20%
= 15o
= 50%
= 30o
= 75%
= 45o
= 100%
= 60o
45o L = 4D
75% L = 4D Advanced Materials and Technologies Laboratory
Pressure Drop in the Carotid Artery
Advanced Materials and Technologies Laboratory
Minimum Wall Shear Stress in the Carotid Artery
min
Minimum Wall Shear Stress,
[Pa]
min
Minimum Wall Shear Stress,
[Pa]
min
Advanced Materials and Technologies Laboratory
Bypass Design Plots po is the pressure drop in a healthy non-stenosed artery without bypass
po 129.3Pa
p
p
po
po
Carotid Artery
Carotid Artery p
po
po 101.5Pa
p
Coronary Artery
po
Coronary Artery
Advanced Materials and Technologies Laboratory
Bypass in Patients with Type 2 Diabetes Mellitus
Advanced Materials and Technologies Laboratory