Visualization Measurement And Investigation Of Fluid Flow And Heat Transfer In Silicon Microchannels

Understanding the fundamentals of fluid flow and heat transfer of Microfluidics has become crucial for the rapid development of all kinds of Micro Systems. In this study, systematic experimental investigation was carried out on single-phase fluid flow and vapor-liquid two-phase flow heat transfer in silicon microchannels.Two silicon microchannel test sections were designed and fabricated using the standard Micro- Electro- Mechanical Systems techniques. One is the conventional parallel silicon microchannel test section; the other is the new parallel silicon microchannel test section which was designed based on the thermal boundary layer redeveloping concept. Both of the two types of microchannels have the same hydraulic diameters of 155.3 microns, and have comparability. A Microfluidics optic platform and an experimental system were set up.An experimental study of forced convective heat transfer through conventional microchannels was performed using the water and methanol as the working fluids. The experimental correlations of friction constant and Nusselt number were gained based on the experimental results.Using water as the working fluid, comparative experiments were carried out between the two test sections. And experimental results show that the new structure microchannels can enhance heat transfer and reduce pressure drop across microchannels at the same time.Boiling heat transfer experiments in conventional microchannels were performed using acetone as the working fluid. All microchannels display the transient flow pattern behavior in milliseconds. A full cycle can be subdivided into three stages. Four different vapor-liquid two-phase flow patterns were observed. The statistical analysis shows that the occurring probabilities of the four flow patterns satisfy the statistical principle for successive cycles. And the bubble explosive phenomenon was observed.By plotting the curves of wall superheat and mass flux versus heat flux, the boiling incipiencies were obtained. In terms of the observed transient flow patterns in microchannels, five heat transfer mechanisms are identified.Three different boiling heat transfer regions were divided by the non-dimensional boiling number, and the transition criteria among the three heat transfer regions are given. The dominant boiling heat transfer mechanisms are different in different boiling heat transfer regions, and the unified law that controls the microscale boiling heat transfer was discovered. A uniform chip temperature field could be acquired by selecting the suitable boiling number ranges.When the nucleate boiling heat transfer is dominant, both the boiling heat transfer coefficients and chip temperatures are dependent on the heat fluxes only. Two new correlations were put forward, which all can predict the nucleate boiling heat transfer results well.When the forced convective boiling heat transfer is dominant, the boiling heat transfer coefficients are mainly dependent on mass fluxes and less dependent on heat...