The Woodruff School

SUMMARY

Under certain circumstances pulse combustors have been shown to improve both heat transfer and drying rate when compared to steady flow impingement. The research presented here utilized experimental and numerical techniques to study the heat and mass transfer characteristics of these types of oscillating jets when impinging on solid surfaces and porous media. The numerical methods were validated using laboratory data, as well as correlations from literature. It was found that the pulsating flows yielded elevated heat and mass transfer compared to similar steady flow jets. However, the numerical simulations were also used to analyze the details of the fluid flow in the impingement zone that resulted in said heat and mass transport. It was found that the key mechanisms of the enhanced transfer were the vortices produced by the oscillating flow. The characteristics of these vortices such as the size, strength, and temperature, determined the extent of the improvement. The effects of five parameters were studied: the velocity amplitude ratio, oscillation frequency, the time-averaged bulk fluid velocity at the tailpipe exit, the hydraulic diameter of the tailpipe, and the impingement surface velocity. Analysis of the resulting fluid flow revealed three distinct flow types as characterized by the vortices in the impingement zone. These flow types were: a single strong vortex that dissipated before the start of the next oscillation cycle, a single persistent vortex that remained relatively strong at the end of the cycle, and a strong primary vortex coupled with a short-lived, weaker secondary vortex. It was found that the range over which each flow type was observed could be classified into distinct flow regimes. The secondary vortex and persistent vortex regimes were found to enhance heat transfer. Subsequently, transition criteria dividing these regimes were formed based on dimensionless parameters. The critical dimensionless parameters appeared to be the Strouhal number, a modified Strouhal number, the Reynolds number, the velocity amplitude ratio, and the H/Dh ratio. Additionally, jet-to-jet interactions were studied using multiple nozzle systems.

SUBJECT:	Ph.D. Dissertation Defense

BY:	Michael Psimas

TIME:	Thursday, April 1, 2010, 1:00 p.m.

PLACE:	IPST Building, 521

TITLE:	Experimental and Numerical Investigation of Heat and Mass Transfer Due to Pulse Combustor Jet Impingement

COMMITTEE:	Dr. Tim Patterson, Co-Chair (ME) Dr. Cyrus Aidun, Co-Chair (ME) Dr. Sujit Banerjee (ChBE) Dr. Preet Singh (MSE) Dr. William Wepfer (ME)

SUMMARY Under certain circumstances pulse combustors have been shown to improve both heat transfer and drying rate when compared to steady flow impingement. The research presented here utilized experimental and numerical techniques to study the heat and mass transfer characteristics of these types of oscillating jets when impinging on solid surfaces and porous media. The numerical methods were validated using laboratory data, as well as correlations from literature. It was found that the pulsating flows yielded elevated heat and mass transfer compared to similar steady flow jets. However, the numerical simulations were also used to analyze the details of the fluid flow in the impingement zone that resulted in said heat and mass transport. It was found that the key mechanisms of the enhanced transfer were the vortices produced by the oscillating flow. The characteristics of these vortices such as the size, strength, and temperature, determined the extent of the improvement. The effects of five parameters were studied: the velocity amplitude ratio, oscillation frequency, the time-averaged bulk fluid velocity at the tailpipe exit, the hydraulic diameter of the tailpipe, and the impingement surface velocity. Analysis of the resulting fluid flow revealed three distinct flow types as characterized by the vortices in the impingement zone. These flow types were: a single strong vortex that dissipated before the start of the next oscillation cycle, a single persistent vortex that remained relatively strong at the end of the cycle, and a strong primary vortex coupled with a short-lived, weaker secondary vortex. It was found that the range over which each flow type was observed could be classified into distinct flow regimes. The secondary vortex and persistent vortex regimes were found to enhance heat transfer. Subsequently, transition criteria dividing these regimes were formed based on dimensionless parameters. The critical dimensionless parameters appeared to be the Strouhal number, a modified Strouhal number, the Reynolds number, the velocity amplitude ratio, and the H/Dh ratio. Additionally, jet-to-jet interactions were studied using multiple nozzle systems.