Professor; PhD, University of Minnesota

Condensing/Phase-change flows, Computational and Experimental Fluid Mechanics/Heat Transfer

Dr. Narain’s current research interest is both computational and experimental in nature and emphasizes the area of internal condensing flows. Fluid mechanics and heat transfer issues along with free-surface phenomena are being investigated in the context of a condenser’s performance in a thermal system. NSF and NASA fund these investigations. His secondary interests are in related areas of transport processes such as: cavitation signatures in an automobile’s torque-converter, computational simulations of turbulent flows through heat exchangers, displacement pumps, etc. The condensing flow research has demonstrated the significance of exit conditions on condenser operations. The experiments also demonstrate how exit-condition effects can lead to system-instabilities. Such system-instabilities may arise in ground and space thermal management systems, looped heat pipes, Rankine power cycles, etc. Research and recent publications also emphasizes integration of experimental results with state of the art nearly exact computational code development and simulations for two dimensional internal condensing flows - both in steady and unsteady (i.e. wavy-interface) regimes. The simulations identify various instability mechanisms and flow regimes. For condensation inside vertical tubes and inclined channels, the ongoing experiments employ modern electronic flow control techniques, fiber-optic flow visualization techniques, a fluorescence and fiber-optic based sensor (developed at MTU) for measuring real time values of condensate thickness, etc.

Ongoing condensing flow research has achieved significant milestones. These are: state of the art computational code capable of simulating these flows including the time-varying locations of the wavy interface, development of a new state of the art experimental facility for investigating internal condensing flows, and our own invention of a well tested fluorescence and fiber-optic based film thickness sensor capable of measuring time-varying thicknesses of a dynamic film. Recent publications discuss results obtained from accurate direct computational simulations and experiments for two dimensional internal condensing flows - both in steady and unsteady (i.e. wavy-interface) regimes. The simulations and experiments (funded by NSF and NASA) identify various instability mechanisms and flow regimes/categories. For condensation inside vertical tubes and channels, the ongoing experiments employ modern electronic flow control techniques, fiber-optic flow visualization techniques, our own fluorescence and fiber-optic based sensor for measuring local time varying thickness of the liquid film, etc.

Publications

• Phan, L., X. Wang, and A. Narain, 2006, “Exit Condition, Gravity, and Surface-Tension Effects on Stability and Noise-sensitivity Issues for Steady Condensing Flows inside Tubes and Channels,” International Journal of Heat and Mass Transfer, Vol. 49, Issues 13-14, pp. 2058-2076.
  
• Narain, A., A. Siemionko, J. H. Kurita, M. Kivisalu, N. Kim, T. W. Ng, L. Phan, and S. D. Kulkarni, 2007, “Internal Condensing Flows Inside a Vertical Pipe – Experimental/Computational Investigations of Effects of Specified and Unspecified (Free) Exit Conditions,” submitted for publication in the ASME Journal of Heat Transfer.
  
• Phan, L. and A. Narain, 2007 “Non-linear Stability of the Classical Nusselt Problem of Film Condensation and Wave-Effects,” in press for publication in the ASME Journal of Applied Mechanics, Vol. 74, No.2.
  
• Narain, A., Q. Liang, G. Yu, and X. Wang, “Direct computational simulations for internal condensing flows and results on attainability/stability of steady solutions, their intrinsic waviness, and their noise-sensitivity, ” Journal of Applied Mechanics, Jan. 2004, Vol. 71, pp. 69-88.
  
• Liang, Q., X. Wang, and A. Narain, “Effect of Gravity, Shear and Surface Tension in Internal Condensing Flows - Results from Direct Computational Simulations.” ASME Journal of Heat Transfer, Oct. 2004, 126 (4), pp. 676 – 686.
  
• C. L. Anderson, L. Zeng, P. Sweger, A. Narain, and J. R. Blough: “Experimental Investigation of Cavitation Signatures in an Automotive Torque Converter Using a Microwave Telemetry Technique,” International Journal of Rotating Machinery, Vol. 9, pp. 1 - 8, 2003.
  
• Narain, A. and Joseph, D. D., "Linearized Dynamics for Step Jumps of Velocity and Displacement of Shearing Flows of a Simple Fluid," Rheologica Acta, 21, pp. 228-50, 1983.