Determination of dissipation rate direct measurement of fluctuating in stirred vessels through velocity gradients

2-D and 3-D PIV and 4-channel LDA techniques were employed to measure the turbulence energy dissipation rate in vessels stirred by Rushton impellers. The measurements were made in vessels of diameter T=100 mm and 294 mm and stirred by impellers of diameter D=T/3. The impellers were rotated at speeds corresponding to Reynolds number of 40,000 to ensure fully-turbulent flow in the vessels. epsilon was determined directly from measurements of the Reynolds stress gradients by analyzing the PIV images over interrogation areas down to 0.1 mm. Similar LDA data were obtained in the larger 294 mm vessel, with a resolution of around 50 mum. The fluctuating gradient results obtained with the two techniques compare well and show that direct measurement of the epsilon distribution is feasible with both PIV and LDA methods.