M.Sc Thesis

M.Sc StudentGridish Yaakov
SubjectFluid Flow and Heat Transfer in Micro-Channels
DepartmentDepartment of Mechanical Engineering
Supervisor PROFESSOR EMERITUS Gad Hetsroni (Deceased)
Full Thesis text - in Hebrew Full thesis text - Hebrew Version


Micro-channels heat sinks are used today in high power diode lasers arrays and in personal computers or servers, where the thermal requirements can not be alleviated by air convection systems. Silicon based micro-channels devices which match better the thermal expansion coefficient of the microelectronic device than the usual used copper based micro - channels. This fact ensures more reliability and higher environmental stability of the silicon based micro - channel compares to the copper one. Despite the above, silicon based micro-channels devices are not yet in regular use. The present work explores the heat transfer and fluid flow in silicon micro-channels of rectangular cross section.

The micro-channels were produces on the back side of a silicon wafer, using reactive ions beam etching technique. Various shapes and channels width to height aspect ratios were designed and fabricated. Electrical resistors produced by thin films technology, used to simulate heat load source during the thermal experimental measurements.

A Pyrex glass wafer was bonded to the silicon wafer by anodic bonding process. Metal electrodes were fabricated over the cover glass chip before the anodic bonding step. During flow experiments, the electrodes were connected to a pulse generator that generates square shape voltage to create hydrogen bubbles in the slightly saline water flowing in the micro-channels. The hydrogen bubbles within the liquid flow emphasize the fluid velocity profile.

The research focuses on single-phase, laminar, fluid flow and heat transfer. The research explores the effect of micro-channel path shape and rectangular cross section aspect ratios on the friction factor along the channels and on the heat transfer coefficient. The research shows good correlation between the micro-channels friction factor and Nusselt number to the conventional theory of standard size channels.

Due to the micro scales and high fluid flow, the pressure drop in the micro-channel chip is high. This requires a common tool for comparing the heat dissipation efficiency between different shapes of micro-channels. The work unravels that curved path micro - channels has better heat dissipation efficiency compares to 84 and 300 microns width straight channels.