In this thesis work fluid flow and heat transfer in two-dimensional microchannels are studied numerically. A computer code based on Lattice Boltzmann Method (LBM) is developed for this purpose. The code is written using MATLAB and Jacket software and has the important feature of being able to run parallel on Graphics Processing Units (GPUs). The code is used to simulate flow and heat transfer inside micro and macro channels. Obtained velocity profiles and Nusselt numbers are compared with the Navier-Stokes based analytical and numerical results available in the literature and good matches are observed. Slip velocity and temperature jump boundary conditions are used for the micro channel simulations with Knudsen number values covering the slip flow regime. Speed of the parallel version of the developed code running on GPUs is compared with that of the serial one running on CPU and for large enough meshes more than 14 times speedup is observed.

Microfluidics deals with the behavior, control and manipulation of fluids which are confined at micrometer length scale. It has important application in lab-on-a chip technology, micro-propulsion, additive manufacturing, and micro-thermal technologies. Microfluidics has been widely used in detection, separation, transportation, and mixing of fluids and particles. The work carried out for the thesis to study the fluid-structure interaction in micro-channel involves an experimental part and a simulation part. In the experimental part the characterization of biofluid (RBC in BSA) is carried out based on the power law of fluid and flow behavior is studied. Also the dependence of fluid concentration on the viscosity in the channel is studied. The results are analyzed. Transition of fluid behavior from non-Newtonian shear thickening to non-Newtonian shear thinning is observed when the RBC concentration varies from 5.5×106 to 5.5×107 cells/ml in the channel. From the viscosity measurements of the biofluid it is observed that the average viscosity in the channel increases on increasing concentration of the fluid for shear thickening fluids. In the simulation part, interaction behavior of biomolecule DNA is studied in the channel containing biofluid which is characterized in the experimental part. Cell free DNAs are common problem in infectious disease detection. Based on the assumptions of the WLC model, DNA strand is assumed as a one dimensional elastic member with its one end fixed at the channel wall and the other end free to move in the fluid. Bent and straight DNAs are considered for the study. Multiple scales are involved in this problem which is not fully understood. DNA strands in the channel are exposed to different forces in the channel which are mainly due to the pressure and viscous effects. Numerical simulations are carried out for the multiphysics problem of DNA in the fluid using a coupled multiphysics finite element scheme and the results are obtained. Same procedure is carried out considering smaller channels and also for PBS solution as background fluid to obtain consistent results. It is found that when the channel width increases the tip displacement of DNA decreases. It was observed that DNA tip displacement is more in the channel when its end-to-end length is approximately half the width of the channel. Potential application of these modeling and simulation are in molecular screening processes to improve the performance of microfluidic DNA chips, and in design of micro-channel structures of microfluidic devices.