Convective Heat Transfer to Non-Newtonian Fluids
Mechatronics Engineering, MSc. Thesis Dissertation, 2015
Assoc. Prof. Ali Koşar (Thesis Advisor), Assoc. Prof. Mehmet Yildiz,
Prof. Pinar Mengüç
Date & Time: July, 21th, 2015 – 13:00-14:30
Place: FENS L067
Keywords : Heat transfer, Non-Newtonian fluid, Slip flow, Microchannel,
Nucleate pool boiling
In this thesis, the perturbation method was implemented to analytically solve the governing equations relevant to both hydrodynamically and thermally fully developed power-law fluid and plug flows through parallel-plates and circular microchannels under constant isoflux thermal and slip boundary condition. It is well accepted that the physical properties are a function of temperature and taking them as constant might lead to remarkable deviations. The slip condition, on the other hand, has shown a prominent effect on heat transfer and fluid flow characteristics. Therefore, to get more accurate results, temperature-dependent properties, being viscosity and thermal conductivity, were considered along with non-linear slip condition in the analysis in addition to viscous dissipation. The velocity, temperature and constant property Nusselt number closed form expressions were derived and then the Nusselt number corresponding to temperature-dependent thermophysical properties was numerically obtained due to their complexity nature. Numerical simulations were also performed for verifying the analytical results. The results indicated that the property variations and slip condition significantly affected thermo-fluid characteristics, and these parameters should be included to achieve a better thermal design for microdevices. The second law analysis was further performed for both constant and variable properties.
Furthermore, an experimental study was performed on nucleate pool boiling of polymeric solutions as a subcategory of non-Newtonian fluids, which are prepared by the dissolution of polymeric additives into a solvent and find applications in many areas. Their advantage over new generation fluids such as nanofluids is that they have no side effects such as agglomeration and sedimentation of particles, which is common for nanofluids. Therefore, this thesis presents an experimental study on nucleate pool boiling of aqueous Xanthan gum solutions of different concentrations. The results revealed that heat transfer coefficients of prepared polymeric solutions were lower than those of pure water, while concentration played a significant role in the performance of the heat transfer. In visualization studies, different pool boiling patterns were recorded particularly for high concentrations, which bolsters the heat transfer results.