MTL Annual Report

Nanofluids have often been investigated for their ability to enhance heat-transfer-related characteristics. This investigation concerns the application of phase-change nanofluids to solar thermal-power generation. As the intensity of sunlight varies due to weather conditions, solar thermal-power generation systems must have sufficient thermal storage to continue operating during periods of low sunlight. One approach to this problem is to seed the heat-transfer fluid with nanosized phase-change particles. By taking advantage of the large latent heat involved in phase change we can increase the effective heat capacity of the heat-transfer fluid. Heat-transfer characteristics must be measured, as it is no longer clear that the fluid can be modeled by bulk properties. It is expected that the region of most interest will be that region in which the nanoparticles are changing phase from solid to liquid. Since manufacture of nanofluids in large quantities is difficult, a microfluidic flow cell is designed for the testing of phase-change nanofluids. A patterned aluminum heater will provide the heat flux necessary to cause melting of the nanoparticles, and doped silicon resistors act as the temperature measurement devices. In the melting regime, the temperature change of the fluid should be small, and it is therefore imperative to have precise temperature-measurement capabilities. Although platinum resistance thermometers are commonly used to measure temperature, their relatively small temperature coefficient of resistance makes them impractical for measuring 0.1K temperature differences at this scale. Low-dosage Boron-doped silicon resistors, however, have a much higher temperature coefficient of resistance and are appropriate for this application.

References

1. L. Zhang, et al., “Measurements and modeling of two-phase flow in microchannels with nearly constant heat flux boundary conditions,” Journal of Microelectromechanical Systems, vol. 11, pp. 12-19, Feb. 2002.
2. L. Zhang, et al., Study of boiling regimes and transient signal measurements in microchannels. Berlin: Springer-Verlag Berlin, 2001.
3. S. Kuravi, et al., “Numerical Investigation of Flow and Heat Transfer Performance of Nano-Encapsulated Phase Change Material Slurry in Microchannels,” Journal of Heat Transfer-Transactions of the Asme, vol. 131, June 2009.
4. S. Reggiani, et al., “Electron and hole mobility in silicon at large operating temperatures – Part I: Bulk mobility,” IEEE Transactions on Electron Devices, vol. 49, pp. 490-499, Mar. 2002