Ira M. Cohen

Phone: 215.898.7076
Email: imcohen@seas.upenn.edu
Office: 306 Towne Building

EDUCATION:

Ph.D. Aeronautical Engineering. Princeton University, 1963.

B.Aero.E. Polytechnic University, 1958.

RESEARCH:

When a gas is sufficiently ionized that the Debye length is the smallest characteristic length, we may call it plasma. Plasmas are used for illumination as glow and arc discharges, for melting and welding materials, and for etching, deposition, and spray coating. We have studied the heating, melting, rollup into a ball, cooling and solidification of very fine wires used for microelectronic interconnections. The heat is supplied by a low current electric arc discharge struck between the wire anode and a cathode. We are also interested in plasmas that occur in combustion flames as well as high intensity plasmas used for spray deposition to create temperature or corrosion resistant coatings. Finally, breakdown characteristics of gases may be used in diagnostics of gas composition.

The classical problem of the decay of a laminar shear layer, starting from a velocity discontinuity at the origin, has never been solved. A basic question related to the solution of this problem is the following. The Navier-Stokes equations which describe the problem are elliptic. Why is it that the Navier-Stokes equations require downstream boundary conditions on the velocity components for an unique solution, but the boundary layer equations, which are purported to be the downstream limit of the Navier-Stokes equations, being parabolic, cannot accept a downstream boundary condition?

SELECTED PUBLICATIONS:

"Numerical Methods for Two-Dimensional Analysis of Electrical Breakdown in a Non-Uniform Gap" (with K. Ramakrishna and P.S. Ayyaswamy). J. Comp. Phys., 104, 173-184 (1993).

"Decay of a Laminar Shear Layer" (with T.M. Alston). Phys. Fluids, A4, 2690-2699 (1992).

"Electrode Heating in a Wire-to-Plane Arc" (with M.A. Jog and P.S. Ayyaswamy). Phys. Fluids, B3, 465-472 (1992).

"Overview of Flow Hemodynamics" (second author with John Listerud). Neuroimaging Clinics of North America, 2, 719-742 (1992).

"Fixed Wand Electronic Flame Off for Ball Formation in the Wirebonding Process - Side Discharge" (with W. Qin and P.S. Ayyaswamy). Trans. ASME, J. Electronic Packaging, 116, 212-219 (1994).

"Melting and solidification of thin wires: a class of phase-change problems with a mobile interface - I. Analysis, II. Experimental confirmation" (with L. J. Huang and P.S. Ayyaswamy). Int. J. Heat Mass Transfer 38, I:1637-1645, II: 1647-1659 (1995).

"Weakly Ionized Plasma Arc Heat Transfer Between Geometrically Dissimilar Electrodes" (with S. S. Sripada and P. S. Ayyaswamy). Trans. ASME, J. Heat Trans., 120, 939-942 (1998).

"Interfacial Motion of a Molten Layer Subject to Plasma Heating" (with S. S. Sripada and P. S. Ayyaswamy). In Fluid Dynamics at Interfaces, Wei Shyy and Ranga Narayanan, Editors, Cambridge University Press (1999), pp. 320-338.

"A Multigrid Simulation of the Rapid Solidification of a Pendent Molten Layer" (with S.S. Sripada and P.S. Ayyaswamy). Presented at ASME 1998 IMECE, Anaheim, Nov. 15-20. In Heat Transfer in Materials Processing, HTD-Vol. 361-4, Eds: R.A. Nelson, Jr. and U. Chandra, pp. 281-286.

"Charged Particle Distribution and Heat Transfer in a Discharge Between Geometrically Dissimilar Electrodes: From Breakdown to Steady State" (with W. Qin and P.S. Ayyaswamy). Phys. Plasmas, 7, 719-728 (2000)

“Low energy plasma heat transfer as applied to microelectronic manufacturing” (with P.S. Ayyaswamy) invited for Annual Review of Heat Transfer, Vol. XII (2000).