SIMULATIONS OF NEWTONIAN AND NON-NEWTONIAN FLOWS IN DEFORMABLE TUBES

Computational models for the investigation of flows in deformable tubes are developed and implemented in the open source computing environment OpenFOAM. Various simulations for Newtonian and non-Newtonian fluids under various flow conditions are carried out and analyzed. First, simulations are performed to investigate the flow of a shear-thinning, non-Newtonian fluid in a collapsed elastic tube and comparisons are made with experimental data. The fluid is modeled by means of the Bird-Carreau viscosity law. The computational domain of the deformed tube is constructed from data obtained via computer tomography imaging. Comparison of the computed velocity fields with the ultrasound Doppler velocity profile measurements show good agreement, as does the adjusted pressure drop along the tube's axis. Analysis of the shear rates show that the shear-thinning effect of the fluid becomes relevant in the cross-sections with the biggest deformation. The peristaltic motion is simulated by means of upper and lower rollers squeezing the fluid along a tube. Two frames of reference are considered. In the moving frame the computational domain is fixed and the coordinate system is moving with the roller speed, and in the fixed frame the roller is represented by a deforming mesh. Several two-dimensional simulations are carried out for Newtonian and non-Newtonian fluids. The effect of the shear-thinning behavior of the fluid on the transport efficiency is examined. In addition, the influence of the roller speed and the gap width between the rollers on the xxvii transport efficiency is discussed. Comparison with experimental data is also presented and different types of moving waves are implemented. In addition, the influence of the roller speed and the gap width between the rollers on the transport efficiency is discussed. Comparison with experimental data is also presented and different types of moving waves are implemented.

Non-intrusive pressure measurement in microchannels

A non-intrusive interferometric measurement technique has been successfully developed to measure fluid compressibility in both gas and liquid phases via refractive index (RI) changes. The technique, consisting of an unfocused laser beam impinging a glass channel, can be used to separate and quantify cell deflection, fluid flow rates, and pressure variations in microchannels. Currently in fields such as microfluidics, pressure and flow rate measurement devices are orders of magnitude larger than the channel cross-sections making direct pressure and fluid flow rate measurements impossible. Due to the non-intrusive nature of this technique, such measurements are now possible, opening the door for a myriad of new scientific research and experimentation. This technique, adapted from the concept of Micro Interferometric Backscatter Detection (MIBD), boasts the ability to provide comparable sensitivities in a variety of channel types and provides quantification capability not previously demonstrated in backscatter detection techniques. Measurement sensitivity depends heavily on experimental parameters such as beam impingement angle, fluid volume, photodetector sensitivity, and a channel’s dimensional tolerances. The current apparatus readily quantifies fluid RI changes of 10-5 refractive index units (RIU) corresponding to pressures of approximately 14 psi and 1 psi in water and air, respectively. MIBD reports detection capability as low as 10-9 RIU and the newly adapted technique has the potential to meet and exceed this limit providing quantification in the place of detection. Specific device sensitivities are discussed and suggestions are provided on how the technique may be refined to provide optimal quantification capabilities based on experimental conditions.

Non-invasive method to predict viscosity and size using total internal reflection fluorescence microscopy (TIRFM) system

This study develops an automated analysis tool by combining total internal reflection fluorescence microscopy (TIRFM), an evanescent wave microscopic imaging technique to capture time-sequential images and the corresponding image processing Matlab code to identify movements of single individual particles. The developed code will enable us to examine two dimensional hindered tangential Brownian motion of nanoparticles with a sub-pixel resolution (nanoscale). The measured mean square displacements of nanoparticles are compared with theoretical predictions to estimate particle diameters and fluid viscosity using a nonlinear regression technique. These estimated values will be confirmed by the diameters and viscosities given by manufacturers to validate this analysis tool. Nano-particles used in these experiments are yellow-green polystyrene fluorescent nanospheres (200 nm, 500 nm and 1000 nm in diameter (nominal); 505 nm excitation and 515 nm emission wavelengths). Solutions used in this experiment are de-ionized (DI) water, 10% d-glucose and 10% glycerol. Mean square displacements obtained near the surface shows significant deviation from theoretical predictions which are attributed to DLVO forces in the region but it conforms to theoretical predictions after ~125 nm onwards. The proposed automation analysis tool will be powerfully employed in the bio-application fields needed for examination of single protein (DNA and/or vesicle) tracking, drug delivery, and cyto-toxicity unlike the traditional measurement techniques that require fixing the cells. Furthermore, this tool can be also usefully applied for the microfluidic areas of non-invasive thermometry, particle tracking velocimetry (PTV), and non-invasive viscometry.

DEVELOPMENT OF AN IONIC LIQUID FERROFLUID ELECTROSPRAY SOURCE AND MODE SHAPE STUDIES OF A FERROFLUID IN A NON-UNIFORM MAGNETIC FIELD

An electrospray source has been developed using a novel new fluid that is both magnetic and conductive. Unlike conventional electrospray sources that required microfabricated structures to support the fluid to be electrosprayed, this new electrospray fluid utilizes the Rosensweig instability to create the structures in the magnetic fluid when an external magnetic field was applied. Application of an external electric field caused these magnetic fluid structures to spray. These fluid based structures were found to spray at a lower onset voltage than was predicted for electrospray sources with solid structures of similar geometry. These fluid based structures were also found to be resilient to damage, unlike the solid structures found in traditional electrospray sources. Further, experimental studies of magnetic fluids in non-uniform magnetic fields were conducted. The modes of Rosensweig instabilities have been studied in-depth when created by uniform magnetic fields, but little to no studies have been performed on Rosensweig instabilities formed due to non-uniform magnetic fields. The measured spacing of the cone-like structures of ferrofluid, in a non-uniform magnetic field, were found to agree with a proposed theoretical model.