Micro- and Nanoscale Measurement Methods for Phase Change Heat Transfer on Planar and Structured Surfaces

In this opinion piece, we discuss recent advances in experimental methods for characterizing phase change heat transfer. We begin with a survey of techniques for high-resolution measurements of temperature and heat flux at the solid surface and in the working fluid. Next, we focus on diagnostic tools for boiling heat transfer and describe techniques for visualizing the temperature and velocity fields, as well as measurements at the single bubble level. Finally, we discuss techniques to probe the kinetics of vapor formation within a few molecular layers of the interface. We conclude with our outlook for future progress in experimental methods for phase change heat transfer.United States. Dept. of Energy (Advanced Research Projects Agency-Energy Grant DE-AR0000363)National Science Foundation (U.S.) (Grant 1261824)United States. Office of Naval Research (Grant N00014-13-1-0324

Predicting the Outcome through a Fluidic-Mechanical System Analogy Approved by Supervising Committee: Supervisor: ____________________________________

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Humidity Effects on the Wetting Characteristics of Poly(N-isopropylacrylamide) during a Lower Critical Solution Transition

Poly(N-isopropylacrylamide) (PNIPAM) is expected to find utility in tissue engineering and drug delivery, among other biomedical applications. These applications capitalize on the intrinsic lower critical solution temperature (LCST) of the polymer: below the LCST, enthalpic gain from intermolecular hydrogen bonding between PNIPAM and water molecules dominates the solvation; above the LCST, entropic effects resulting from the intramolecular hydrogen bonding between the carboxyl and amide groups of PNIPAM lead to water expulsion. The dependence of the LCST upon the molecular weight, solvent, and solution activity (i.e., solute concentration) has been studied extensively. However, what has not been previously explored is the effect of humidity on the characteristic properties of the polymer. Herein, we show that the relative humidity affects the water adsorption dynamics of PNIPAM as well as the magnitude of the transition that occurs at the LCST of the polymer. In short, the magnitude of the LCST transition decreases with an increasing relative humidity, and the time period over which adsorption occurs decreases with the temperature

MICROCHANNEL EXPERIMENTAL STRUCTURE FOR MEASURING TEMPERATURE FIELDS DURING CONVECTIVE BOILING

ABSTRACT This work designs and fabricates a microchannel structure for measurement of wall temperature fields in two-phase flow. The microchannel with hydraulic diameter of 100 micrometers is etched into a suspended beam of silicon with three independently heated regions and integrated doped silicon resistors sensitive to channel temperature. Doped silicon resistors are also sensitive to strain in the silicon caused by pressure transients in the channel, so sensors are designed with two different orientations and thus two different piezoresistive coefficients to allow decoupling of pressure and temperature effects. Use of a 400 micrometer wide suspended beam reduces side-wall conduction compared to a bulk sample and provides better opportunities to measure the influence of flow regimes on heat transfer coefficients in future work. Use of the central heater reduces fluid preheating in the inlet plenum. The measured temperature distributions at flowrates up to 0.25 ml/min with heat fluxes into the silicon beam up to 78 W/cm 2 show initial capabilities of the structure

Micro- and Nanoscale Measurement Methods for Phase Change Heat Transfer on Planar and Structured Surfaces

In this opinion piece, we discuss recent advances in experimental methods for characterizing phase change heat transfer. We begin with a survey of techniques for high-resolution measurements of temperature and heat flux at the solid surface and in the working fluid. Next, we focus on diagnostic tools for boiling heat transfer and describe techniques for visualizing the temperature and velocity fields, as well as measurements at the single bubble level. Finally, we discuss techniques to probe the kinetics of vapor formation within a few molecular layers of the interface. We conclude with our outlook for future progress in experimental methods for phase change heat transfer