E-Thesis 87 views 33 downloads
Experimental and numerical study of an electro-osmotic flow based heat spreader. / Connie Pey Fen Eng
Swansea University Author: Connie Pey Fen Eng
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In this thesis, experimental and numerical analysis of an electro-osmosis (EO) based cooling system are presented. Heat spreader with EO pump is proposed to remove heat from a microprocessor. The EO micro-pump is formed by 152 straight micro-channels and used to force the electrolyte to circulate th...
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In this thesis, experimental and numerical analysis of an electro-osmosis (EO) based cooling system are presented. Heat spreader with EO pump is proposed to remove heat from a microprocessor. The EO micro-pump is formed by 152 straight micro-channels and used to force the electrolyte to circulate through the elliptical micro-channels. This arrangement is expected to reduce hot spots and temperature of the microprocessor. The fabrication of the EO heat spreader is discussed in detail in this thesis. Different channel depths are etched and tested on a silicon wafer. Besides, an isolation layer is deposited between the EO heat spreader and the microprocessor to avoid the electrical interference. The experiments of the EO heat spreader with and without isolation layer are carried out and silicon dioxide has been found to have good electrical insulation properties. The flow rate through the EO heat spreader is obtained l)y monitoring the distance travelled by a particle in an EO flow channel which is subjected to an external electric potential. At higher electric potential difference, electrolysis occurs and results in the bubble generation near the electrodes. To reduce the bubble generation, a pulse like voltage cycle is introduced for the first time. Finally, the experiments are carried out to study the influence of the EO heat spreader on the cooling system. The proposed EO heat spreader can reduce both the size of the heat sink and the temperature of the microprocessor. In the latter part of the thesis, the numerical modelling of the EO heat spreader is presented. The electric potentials in the EO flow are solved explicitly and global time stepping is used. The converged electric potential solutions are added into the momentum equation. The Navier Stokes equations (NSE) which are used to govern the EO flow are non-dimensionalised. A new non-dimensional scale is selected to avoid introducing Reynolds number into the non-dimensional form. Local time stepping is used to solve the NSE. The governing equations are temporally discretised by using Artificial Compressibility - Characteristic Split (AC-CBS) algorithm is used to reduce the oscillation which is caused by the pressure and convection terms. Standard Galerkin finite element method is used for spatial discretisation. The numerical EO flow solution obtained is compared with experimental data and good agreement is obtained between the results.
College of Engineering