| Summary: | 博士 === 國立成功大學 === 航空太空工程學系碩博士班 === 92 === The development and fabrication of a MEMS at a low temperature process is required if the MEMS system is to be made on top of an IC system. The current work presents a novel low temperature fabrication process for a microchannel system that is integrated with the heaters and arrays of temperature and pressure sensors inside. This channel system can be used to study the local micro-scale heat transfer process at different Reynolds number flow conditions. Understanding of local flow and heat transfer process is very important not only for the basic research but also for practical application in MEMS thermal system. Unfortunately, most of the current micro-channel used or fabricated could not provide local heat transfer measurements due to the improper control of the heat loss. The channels fabricated in the past will lead to a large amount of axial conduction and heat loss; therefore, local heat transfer data could not be obtained accurately.
The current channel designed and fabricated has an inside dimension of 4000 µm in length, 500 µm in width and 80 µm in height. Several important design considerations for the control of heat loss, the pressure sensors and the channel fabrication process will be analyzed and discussed. Initially, the heaters and the arrays of temperature sensors and pressure sensors selected are made of polysilicon layers doped with different concentration of boron, which are deposited and patterned on a 6 inch P-type (100) silicon wafer by LPCVD, photolithography process and RIE dry etching, respectively. Then, all the devices fabricated were moved onto a low thermal conductivity epoxy-glass substrate by using the low temperature epoxy bonding process and the TMAH wet etching process. The final step is to construct a relatively thick and compact channel structure, by using the techniques of SU-8 lithography and a second low temperature epoxy bonding process, which can readily allow for water or other viscous flows through the channel. In this way, all the wall materials used have a very low thermal conductivity that can significantly minimize both the axial conduction and the heat loss. Therefore, very accurate local heat transfer data can be measured and obtained for the first time in the literature. Many fabrication techniques developed in this work will be presented and discussed.
The local Nusselt numbers obtained along the channel flow direction at each Reynolds number are compared with the results for the case of large-scale channel. It is found that the local Nusselt numbers is significantly smaller than the results of large-scale channel, and the reason for this deviation is attributed to the micro-scale effect. In addition, the local Nusselt numbers increases with increasing Re and the heat flux, respectively, in both the case of air and DI water flow. Detailed discussion on the measurements and analysis of the heat transfer results will be presented in this work.
|
|---|
