Research in High Heat Flux Spray Cooling
(Sergio Escobar Vargas, R. Sharma, J. Gonzalez, D. Fabris)
A thermal ink jet (TIJ) print head is used to provide a controllable monodisperse water spray on to a hot surface. Experiments have been conducted to determine the physical mechanism of heat transfer, efficiency, and potential maximum heat flux. No maximum heat flux has been reached, current results achieved ~ 4kW/cm2, literature has reported maximum of 1-2kW/cm2. Droplet Reynolds number does not show significant effect on the heat flux efficiency. Heat losses are significant close to 70% of the heat flux at the fin base. Efficiency has a correlation to the liquid film thickness and the wetted area, thinner liquid films result in higher efficiencies i.e. d~5um → h~0.9.
Research into the Design of a Coal to Syngas Reformer.
(Matthew Brubaker, D. Fabris collaboration with M. Alyaser, Eventix)
A numerical model is used to design and that calculated flow rates, energy balances, reaction rates, and thermodynamic states for a compact parallel plate heat exchanger and reformer. The model will be used to determine design parameters. The concept uses high temperature steam and external heat input to achieve coal reformation without a separate combustion. This concept could potentially lead to cleaner and less expensive coal. “Clean coal” is a potential energy source that can greatly reduce carbon emissions over current coal technology but has been limited by cost. In 2006 coal supplied 51.6% of the US energy need.
Center for Nanostructures
(D. Fabris in collaboration with C. Yang)
As an interdisciplinary center for research and integrated education in the diverse field of nanoscale science and technology, CNS builds upon existing SCU faculty strengths and initiatives, and incorporates established partnerships in nanotechnology with NASA Ames Research Center and Hitachi High Technologies America (HHTA), as well as ongoing relationships with the Stanford Nanofabrication Facility. For more information see Center for Nanostructures.
CNS-Research into Thermal Interface Materials (TIM)
Multi-walled carbon nanotubes (CNTs), which possess both a high aspect ratio and high thermal conductivity, hold great promise as potential high-conductivity fillers in advanced TIM. Polymeric TIM with CNT inclusions may exhibit lower thermal resistance as a result of an increase in more highly conductive percolation paths across the interface at lower filler concentrations than traditional TIM. Using an advanced ASTM D5470-06 standard steady-state TIM testing apparatus developed in-house approach we measure the thermal resistance of TIM samples at a constant heat rate while varying the externally applied pressure. Our thermal resistance measurements indicate that improved TIM performance is achieved with less viscous composites at lower CNT loadings.
CNS-Research in Submicron Temperature Measurement
A quasi-steady state thermoreflectance measurement is performed to acquire the 2-D spatial temperature of a model thin film gold system undergoing Joule heating. Reproduced and repeatable thermoreflectance coefficients are obtained under narrowband LED peak illumination wavelengths used to perform the experiment at κ470nm = 2x10-4 K-1 and κ530nm = -2x10-4 K-1, respectively. By comparing a steady state continuum treated 2-D heat transport model accounting for thermal dissipation heat transfer and uniform volumetric energy generation due to Joule heating, the experiment allows for measurement thermal resistance between the gold film and the SiO2 substrate values for the model system studied. Further, by assuming 1-D conduction heat transfer to the substrate, the thermal dissipation is shown to easily convert to overall thermal resistance, ΣR. Thermal resistances are compared with existing published data that are acquired through parallel pump-probe thermoreflectance experiments and are found to be in good agreement.
Hydrodynamic Trap-and-Release Microfluidic Device for Single Cell Analysis
This work focuses on developing a microfluidic chip for single cell trapping and release. The work explores hydrodynamic trapping and other concepts, a design stage review of possible configurations, CFD modeling of these configurations to determine the variation in parameters, and a fabrication of several PDMS test chips. The experimental work is supported by the Stephen Quake lab in the Bioengineering Department at Stanford University.
Research into the Development of New Numerical Methods
(Matthew Green, D. Fabris)
This work is on the analysis of algorithms to solve partial differential equations on segmented domains (domain decomposition). The goal is develop a technique that distribute the computational load on a multiprocessor computer. This work will stem from the prior algorithm development work.