טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentKlein Daniel
SubjectHeat Transfer in Micro-Channels in the Presence of Surface
Active Agents
DepartmentDepartment of Mechanical Engineering
Supervisor Professor Emeritus Gad Hetsroni (Deceased)


Abstract

Increasing heat generation in electronic and optical components, such as computer CPUs, automotive chips, miniaturized lasers, transmission windows for accelerator and others, have lead numerous researchers to look for improved ways to remove the generated heat. For example, one could consider low thermal resistant methods: the micro impinging jets, the micro heat pipes and the micro channel forced convection. The current research focuses on forced convection, while using low Reynolds, single and two-phase flow, combined with surfactant (surface active agents) additives. Surfactants are known for their ability to reduce drag in turbulent single-phase flows and for enhancing the boiling mechanism, therefore improving heat transfer rates in pool boiling. The effects of surfactant solution on heat transfer capabilities using single- and two-phase (boiling) flow in microchannels are still unclear. In order to shed some light on these matters, while improving existing microchannel heat exchangers, some test modules were fabricated. The modules included a double-sided silicon chip, which was used for simulating an electronic chip. On one of its sides, an aluminum resistor was deposited, produced uniform heat flux. On the other side, a number of etched parallel triangular microchannels convected various fluids. The chip was connected to a flow loop by two collectors, which distributed the entering fluid to the microchannels and collected the exiting fluid from the microchannels. A thermal map of the resistor was acquired using an IR camera, while inlet and outlet temperatures and pressures were acquired by thermocouples and pressure transducers.

            As expected, the use of surfactant solutions in two-phase flows, lead to heat transfer enhancement while maintaining quasi-stable surface temperatures. In addition, it turned out that the attached collectors' material and shape were meaningful as well, to heat removal capability. Furthermore, it become evident that the etched silicon micro-channels must be further treated by coating their surfaces with a thin layer of metal, as proposed for other miniature heat sinks. This procedure will decelerate or even stop surface flaking and micro-channel blocking, as a result of highly applied heat fluxes.