SUBJECT: Ph.D. Proposal Presentation
   
BY: Bo Lu
   
TIME: Wednesday, April 15, 2009, 10:30 a.m.
   
PLACE: Love Building, 109
   
TITLE: Application of Convection Heat Transfer in Near-Wall Jets to Electron-Beam-Pumped Gas Lasers
   
COMMITTEE: Dr. Said I. Abdel-Khalik, Chair (ME)
Dr. Seyed M. Ghiaasiaan (ME)
Dr. Sheldon M. Jeter (ME)
Dr. Narayanan M. Komerath (AE)
Dr. Michael F. Schatz (Phy.)
 

SUMMARY

Heating of the transmission foil separating the vacuum diodes from the laser cell in electron-beam-pumped gas lasers due to electron beam attenuation necessitates an cooling scheme to prevent its failure under repetitively pulsed operating conditionss. Attenuation of the electron beam (typically 500kV, 100kA and 100ns) produces a strong and pulsed volumetric heat source in the relatively thin (~25μm thick) stainless-steel foil causing failure. An experimental and numerical investigation will be conducted to study the cooling effectiveness of high-speed jets for a single stainless-steel foil strip simulating the geometry between two hibachi ribs in the Electra KrF gas laser developed by the Naval Research Laboratory. The foil is placed inside a duct with continuous gas flow simulating the circulating laser gas. Heating of foil is controlled to achieve the same foil temperatures observed in Electra without active cooling. Detailed studies include two jet types (planar and circular) and two injection methods (parallel and impinging) for two hibachi foil designs (flat and scalloped). The planar jet flows parallel to the circulating laser gas along the entire foil span. The other configuration uses small-diameter circular jets positioned in two staggered rows located on the foilís two edges along the height of the foil (~30 cm). The jets are issued obliquely towards the foil. For both jet configurations, experiments will be conducted at different jet velocities, impingement angles and jet-foil spacing to identify the optimal parameters to be used in the actual hibachi foil cooling. Experimental results will be compared to the predictions from CFD simulations using FLUENT. The objective is to show quantitatively that near-wall jets can effectively cool the foil separating the vacuum diodes from the laser cell under prototypical pulsed (5Hz) operating conditions in order to assure the foilís survival and minimize impact on electron beam quality and laser efficiency.