Michael P. Beck B.S. Chemical Engineering 1999 University of Wisconsin at Madison B.S. Biochemistry 1999 University of Wisconsin at Madison Michael.Beck@chbe.gatech.edu

Project:

1. Formulation and characterization of nanofluids for improved heat transfer.

Advances in microelectronics require improved heat transfer strategies. It has been suggested that only forced convection of liquids and/or phase change will provide adequate heat transfer for high performance electronic devices. However, heat transfer characteristics are not the only factors that must be considered for direct immersion cooling. The primary concern is the chemical compatibility of the liquid with the chip and packaging materials. Typical heat transfer liquids such as water may have favorable heat transfer characteristics, but have unsuitable chemical characteristics. Fluorocarbons are generally considered to be the most suitable for microelectronics devices, but they have a low thermal conductivity as well as surface tension. These thermal and wetting characteristics lead to temperature overshoot, a common problem in pool boiling. Adding nanoparticles to fluorocarbons will increase the thermal conductivity and possibly provide nucleation sites for pool boiling.

A fluid containing dispersed nanoparticles is referred to as a nanofluid. In general, solid-liquid mixtures have a higher thermal conductivity than the liquid alone. Moreover, when the solid consists of nanoparticles, the increase in thermal conductivity is much higher than a mixture containing larger particles (greater than 1 mm). An important aspect of nanofluids is the stability of the dispersion. Brownian motion keeps the nanoparticles suspended due to their small size. However, flocculation will occur in an unstable nanofluid which will effectively create larger particles that will settle from the solution. This would cause accumulation of solid in a heat exchanger or plugging of microchannels. Flocculation will also cause a decreased thermal conductivity since it effectively creates larger particles.

My work involves mixing the nanoparticles with a fluid containing a surfactant to ensure stability. These nanofluids are then characterized with the transient hot wire method to determine the thermal conductivity as well as TEM to observe the size of the particles. My focus is on nanofluids that can be used for microelectronic cooling such as fluorocarbons containing non-polar nanoparticles. I am also attempting to create a model to predict the increase the thermal conductivity as a function of the particle size, volume fraction, and thermal conductivities of the individual solid and liquid.