Thien Duy Nguyen

Mass and Heat Transfer Inside the Air Gap of a Discoidal and Unshrouded Rotor Stator System With a Jet Impingement

Mass and heat transfer are experimentally investigated in a discoidal and unshrouded rotor-stator cavity where an air jet passes through the stator and impinges on the rotor center. Using a jet impingement is a way to bring fresh air inside the air gap and to increase shear stresses and so heat transfer over the rotor. This study focuses on comparisons between heat transfer coefficients and velocity fields obtained inside the air gap for the case of a dimensionless spacing interval G = 0.02 and a low aspect ratio for the jet e/D = 0.25. Two jet Reynolds numbers ranging from 16000 to 42000 and three rotational Reynolds numbers between 30000 and 516000 are considered. Mass transfers are investigated by Particle Image Velocimetry technique while the radial distribution of heat transfer coefficients over the rotor is obtained using a thick wall method and temperature measurements by infrared thermography.© 2012 ASME

POD-Based Estimations of the Flowfield From PIV Wall Gradient Measurements in the Backward-Facing Step Flow

In this paper, particle image velocimetry (PIV) results from a backward-facing step flow, of which Reynolds number is 2800 based on free stream velocity and step height (h = 16.5 mm), are used to demonstrate the capability of proper orthogonal decomposition (POD)-based estimation models. Three-component PIV velocity fields are decomposed into a set of spatial basis functions and a set of temporal coefficients. The estimation models are built to relate the low-order POD coefficients, determined from an ensemble of 1050 PIV fields by the “snapshot” method, and the time-resolved wall gradients, measured by a near-wall measurement technique called stereo interfacial PIV. These models are evaluated in terms of reconstruction and prediction of the low-order temporal POD coefficients of the velocity fields. In order to determine the coefficients of the estimation models, linear stochastic estimation (LSE), quadratic stochastic estimation (QSE), principal component regression (PCR) and kernel ridge regression (KRR) are applied. In addition, we introduce a possibility of multi-time POD-based estimations in which past and future information of the wall gradient events is used separately or combined. The results show that the multi-time estimation approaches can improve the prediction process. Among these approaches, the proposed multi-time KRR-POD estimation with optimized time duration of wall gradient information in the past yields the best prediction.Copyright

Application of an Integrated Microfluidic Total Internal Reflection (TIR)-based Chip to Nano-Particle Image Velocimetry (nano-PIV)

A polymer TIR-based chip has been developed. The chip is monolithically fabricated using Si bulk micromachining and PDMS casting at very low cost. A PDMS microchannel is attached to the chip by van-der-Waals contact through a common thin glass slide to form an integrated microfluidic (TIR)-based chip. The slide-format of the microfluidic TIR-based chip can be employed with both inverted and upright fluorescent microscope. This paper reports the first application of this microfluidic TIR-based chip to study microfluidic flow by nano-PIV with an upright fluorescent microscope. Pressure-driven flows of carboxylate-modified Nile-red nanotracers are generated inside the microchannel of the microfluidic TIR-based chip. The time-sequenced fluorescent images of tracers, illuminated by evanescent field, are recorded onto a CCD camera and are cross-correlated by a PIV program to obtain the near-wall velocity field at various shear rates. Our integrated system could be an important component of a micro-total analysis system (mu-TAS) to study nanoparticles or bio-molecules transport and their near-wall interactions in a microchannel.