Study On Micro-nanoscale Thin Film Heat Transfer And Micro-Bubble Dynamics

Devices Minimization is a new research field for sciences and engineering technologies.Micro devices such as MEMS are widely used in many industries. However,it is investigated that many phenomenon are difficult to be explained by regular physical mechanism,which are called microscale effects.Since great amount of heat and mass are transferred through micro devices,microscale heat transfer is critical for understanding the microscale effects.Since devices such as microsensors and microactuators use thin film microheaters as the heating-driven component,it has been studied by many researchers.In this paper,the investigation focuses on the following aspects:1.the temperature field of thin film microheater under pulse heating before bubble nucleationThe temperature field on a thin film microheater differs from that of a normal-sized film heater.Regularly the thin film temperature is indirectly measured, and it is often an averaged value.In chapter 2,an analytical solution is deduced for the temperature of the thin film microheater,thus the three dimensional temperature distribution is available.The analytical results are compared with the existed experimental values and are proved reasonable.2.The thin liquid film study under micro bubbleAs the thin film microheater is heated,bubbles are generated from above,and there is a thin liquid film between bubble and the microheater underneath.The existed studies mainly focus on the liquid film between vapor slug and the heated channel wall,and seldom is discussed on thin liquid film between heated surface and boiling bubble.A high order runge-kutta method is used to calculate the film thickness and under given heat flux,and the data were analyzed with good results.3.Micro bubble dynamics under forced convectionTo design a better microactuator in a microfluidic system,it is important to understand the bubble dynamics on the microheaters.At present micro bubble dynamics under forced convection is not fully studied.Based on MEMS technology,a platinum film microheater fabricated with the size of 100μm×20μm×10nm is placed in the silicon channel.With working liquid flowing through the pulse heated microheater,the bubble patterns generated are classified,and the effect of parameters such as pulse frequency f,Ï„₁/Ï„_cycle as well as the working liquid flow rate on micro bubble dynamics is discussed.Moreover,the flow patterns after bubble detachment is analyzed,and the boiling curves are compared with those pool boiling ones.