Brian D. Iverson

Heat and Mass Transport in Heat Pipe Wick Structures

temperature field,areobtainedfortheporouswicksundertheactionofadiscreteheatsource(evaporator)mounted on one end. The working fluid, supplied from a condenser pool, evaporates from the wick surface primarily in the evaporator region and is condensed and collected into a container separate from the pool, to yield mass flow rates. Thus the liquid-pumping capability of the wick, coupled with flow impedance, is measured as a function of applied heat flux.Repeatableresultswithlowuncertaintyareobtained.Acarefulanalysisofthetransportpathsforheatand masstransferin thewickstructure confirmsthatmasstransfer duetovaporization oftheworking fluidisthelargest contributor to heat dissipation from the wick. The expected and measured values of evaporation rate are in good agreement. Results are also presented in terms of overall effective conductance based on measured temperatures.

High Aspect Ratio Carbon Nanotube Membranes Decorated with Pt Nanoparticle Urchins for Micro Underwater Vehicle Propulsion via H2O2 Decomposition

The utility of unmanned micro underwater vehicles (MUVs) is paramount for exploring confined spaces, but their spatial agility is often impaired when maneuvers require burst-propulsion. Herein we develop high-aspect ratio (150:1), multiwalled carbon nanotube microarray membranes (CNT-MMs) for propulsive, MUV thrust generation by the decomposition of hydrogen peroxide (H2O2). The CNT-MMs are grown via chemical vapor deposition with diamond shaped pores (nominal diagonal dimensions of 4.5 × 9.0 μm) and subsequently decorated with urchin-like, platinum (Pt) nanoparticles via a facile, electroless, chemical deposition process. The Pt-CNT-MMs display robust, high catalytic ability with an effective activation energy of 26.96 kJ mol(-1) capable of producing a thrust of 0.209 ± 0.049 N from 50% [w/w] H2O2 decomposition within a compact reaction chamber of eight Pt-CNT-MMs in series.

Economic Optimization of a Concentrating Solar Power Plant With Molten-Salt Thermocline Storage

System-level simulation of a molten-salt thermocline tank is undertaken in response to year-long historical weather data and corresponding plant control. Such a simulation is enabled by combining a finite-volume model of the tank that includes a sufficiently faithful representation at low computation cost with a system-level power tower plant model. Annual plant performance of a 100 MWe molten-salt power tower plant is optimized as a function of the thermocline tank size and the plant solar multiple (SM). The effectiveness of the thermocline tank in storing and supplying hot molten salt to the power plant is found to exceed 99% over a year of operation, independent of tank size. The electrical output of the plant is characterized by its capacity factor (CF) over the year, which increases with solar multiple and thermocline tank size albeit with diminishing returns. The economic performance of the plant is characterized with a levelized cost of electricity (LCOE) metric. A previous study conducted by the authors applied a simplified cost metric for plant performance. The current study applies a more comprehensive financial approach and observes a minimum cost of 12.2 ¢/kWhe with a solar multiple of 3 and a thermocline tank storage capacity of 16 h. While the thermocline tank concept is viable and economically feasible, additional plant improvements beyond those pertaining to storage are necessary to achieve grid parity with fossil fuels. [DOI: 10.1115/1.4025516]

Experimental characterization of induction electrohydrodynamics for integrated microchannel pumping

Microscale fluid flow using traveling-wave induction electrohydrodynamics is demonstrated. A three-phase traveling-wave device fabricated for the experiments provides a temporally and spatially varying electric field which helps induce ions in a fluid that is subjected to a temperature gradient. These ions are moved as the traveling wave propagates, resulting in a drag force being exerted on the surrounding fluid. Repulsion-type electrohydrodynamic flow is visualized in a microchannel of depth 50 µm, and results are presented in terms of velocity measurements using particle image velocimetry. The effects of voltage, traveling-wave frequency and the addition of externally applied heat are demonstrated and heat transfer capabilities of the micropump are discussed. (Some figures in this article are in colour only in the electronic version)

Thermal Property Testing of Nitrate Thermal Storage Salts in the Solid-Phase

Implementation of molten salt compounds as the heat transfer fluid and energy storage medium provides specific benefits to energy collection and conversion. Nitrate salts have been identified as a strong candidate for energy transfer and storage and have been demonstrated for use in these applications over time. As nitrate salts have solidification temperatures above ambient, concern for recovery from salt freezing events has instigated efforts to understand and predict this behavior. Accurate information of salt property behavior in the solid-phase is necessary for understanding recovery from a freeze event as well as for phase change thermal energy storage applications. Thermal properties for three representative salts (that span the range of melting temperatures from approximately 90–221 °C), have been obtained. These properties include specific heat, coefficient of thermal expansion, and thermal conductivity. Specific heat and thermal conductivity were measured using differential scanning calorimetry.Copyright

Noise analysis and sensitivity enhancement in immunomagnetic nanomechanical biosensors

We report noise and detection limitations in cantilever-based immunomagnetic biosensors. A differential cantilever system with sensing and control arms was used whereby the control arm was passivated with bovine serum albumin (BSA) and the sensing arm was functionalized with biotin-BSA. Streptavidin-coated magnetic beads were exposed to cantilever arms. An oscillatory magnetic field induced a magnetic force on the beads which caused a relative deflection of the sensing arm. Increasing the excitation frequency suppressed the 1∕f noise by 100-fold, resulting in a deflection resolution of 0.065A in air.

Temperature-dependent mechanical property testing of nitrate thermal storage salts.

Three salt compositions for potential use in trough-based solar collectors were tested to determine their mechanical properties as a function of temperature. The mechanical properties determined were unconfined compressive strength, Youngs modulus, Poissons ratio, and indirect tensile strength. Seventeen uniaxial compression and indirect tension tests were completed. It was found that as test temperature increases, unconfined compressive strength and Youngs modulus decreased for all salt types. Empirical relationships were developed quantifying the aforementioned behaviors. Poissons ratio tends to increase with increasing temperature except for one salt type where there is no obvious trend. The variability in measured indirect tensile strength is large, but not atypical for this index test. The average tensile strength for all salt types tested is substantially higher than the upper range of tensile strengths for naturally occurring rock salts.

Note: Thermal analog to atomic force microscopy force-displacement measurements for nanoscale interfacial contact resistance

Thermal diffusion measurements on polymethylmethacrylate-coated Si substrates using heated atomic force microscopy tips were performed to determine the contact resistance between an organic thin film and Si. The measurement methodology presented demonstrates how the thermal contrast signal obtained during a force-displacement ramp is used to quantify the resistance to heat transfer through an internal interface. The results also delineate the interrogation thickness beyond which thermal diffusion in the organic thin film is not affected appreciably by the underlying substrate.

Numerical Investigation of the Flow and Heat Transfer Due to a Miniature Piezoelectric Fan

Piezoelectric fans have emerged as a viable alternative for electronics cooling applications requiring low input power and noiseless operation. A piezoelectric fan is a cantilever actuated by a piezoelectric ceramic material bonded to it. The fan oscillates back and forth creating airflow when an alternating electric field is applied to this bonded piezoelectric ceramic. Forced convection induced by such an oscillating fan in an enclosure is numerically investigated. The computational model is capable of sustaining deforming fluid cells that allow large boundary movement. The moving wall boundary, modeled as large-amplitude beam deflection, initiates flow in the fluid domain which enhances convection to varying extents depending on the heat source-to-fan distance and beam deflection amplitude. The effects of these parameters on heat transfer are studied. Transition between distinct convection patterns is observed with changes in the parameters. Results are validated against experimental measurements, with good agreement.Copyright

FREEZE-THAW TESTS OF TROUGH RECEIVERS EMPLOYING A MOLTEN SALT WORKING FLUID

Several studies predict an economic benefit of using nitrate-based salts instead of the current synthetic oil within a solar parabolic trough field. However, the expected economic benefit can only be realized if the reliability and optical performance of the salt trough system is comparable to today’s oil trough. Of primary concern is whether a salt-freeze accident and subsequent thaw will lead to damage of the heat collection elements (HCEs). This topic was investigated by experiments and analytical analysis. Results to date suggest that damage will not occur if the HCEs are not completely filled with salt. However, if the HCE is completely filled at the time of the freeze, the subsequent thaw can lead to plastic deformation and significant bending of the absorber tube.Copyright