Kravchuk O. Hydrodynamics, mass and heat transfer of homogeneous and nanofluids in microchannels with different configuration

The dissertation is devoted to the research of microprocesses of heat and mass transfer and hydrodynamics of homogeneous liquids and nanofluids in channels of different geometry. In this paper, we describe the stochastic method of studying the heat transfer in the microchannel and the boundary layer in the presence of nanoparticles based on the Monte Carlo method. Computer-aided research of heat transfer of nanofluids in a planar microchannel and in a boundary layer was carried out. Monte Carlo calculations have shown that with the increase of the longitudinal coordinate, the profile of temperature and concentration is aligned. When increasing the volume fraction of nanoparticles at the channel entrance, linear growth is observed, but nonlinear growth is observed with an increase in the thermal conductivity of nanofluids. And a nonlinear drop is observed with the increase in the Prandtl number, as the viscosity increases. The main result obtained with the Monte Carlo method is that the addition of a small amount of nanoparticles to the fluid leads to an increase in heat transfer (with 0.05 volume fraction of nanoparticles heat transfer is increased by 10%). Similar effects are observed for both the flat microchannel and the boundary layer. Hydrodynamics and heat exchange under mixed convection in vertical planar and cylindrical microchannels using Lattice Boltzmann method have been investigated, as well as a comparison with analytical calculations. Changing the values of the Rayleigh number leads to a change in the characteristics of the flow in the central part of the channel, the change in the values of the Knudsen number primarily affects the changes in characteristics in the wall area. At high Prandtl values, high flow rate. With such parameters, the temperature jump disappears, and the slip effect does not work, which results in an increase in the value of the Nusselt number. Computer experiments were conducted to investigate the centrifugal instability of nanofluids with radial temperature and heterogeneity of concentration. The turbulent incompressible flow in a planar rotating microchannel is investigated. Increasing the Coriolis force leads to the appearance of reverse flows that lead to instability. With an increase in the angular speed of rotation, the growth of hydraulic resistance is observed, but the greater the value of Knudsen, the growth of hydraulic resistance decreases due to the effect of slipping. The results of the work can be used to select the mode of operation of various micro devices, such as: sensors, motors, pumps, turbines, ducts and valves.