Impact of current speed on mass flux to a model flexible seagrass blade

National Science Foundation (U.S.) (Grant EAR 1140970

Miniature fiber‐optic refractometer for measurement of salinity in double‐diffusive thermohaline systems

This is the published version. Copyright © 1985 American Institute of PhysicsInformation on salinity and temperature distributions is important in the study of thermohaline systems. In order to overcome difficulties associated with existing measurement methods, a miniature fiber‐optic probe has been developed. The probe, which is capable of local quasisteady and fluctuating salinity and temperature measurements, is easily constructed, calibrated, and utilized. Probe measurements compare favorably with results obtained using a slant‐wire shadowgraph technique and clearly show local phenomena in double‐diffusive thermohaline systems

Thermal Dissipation and Variability in Electrical Breakdown of Carbon Nanotube Devices

We study high-field electrical breakdown and heat dissipation from carbon nanotube (CNT) devices on SiO2 substrates. The thermal "footprint" of a CNT caused by van der Waals interactions with the substrate is revealed through molecular dynamics (MD) simulations. Experiments and modeling find the CNT-substrate thermal coupling scales proportionally to CNT diameter and inversely with SiO2 surface roughness (~d/{\Delta}). Comparison of diffuse mismatch modeling (DMM) and data reveals the upper limit of thermal coupling ~0.4 W/K/m per unit length at room temperature, and ~0.7 W/K/m at 600 C for the largest diameter (3-4 nm) CNTs. We also find semiconducting CNTs can break down prematurely, and display more breakdown variability due to dynamic shifts in threshold voltage, which metallic CNTs are immune to; this poses a fundamental challenge for selective electrical breakdowns in CNT electronics

Reducing thermal transport in electrically conducting polymers: Effects of ordered mixing of polymer chains

Reducing the phonon thermal conductivity of electrically conducting polymers can facilitate their use as potential thermoelectric materials. Thus, the influence of the coupling between the longitudinal and transverse phonon modes on overall thermal conductivity is explored for binary mixtures of polyaniline (PANI) and polyacetylene (PA) chains by considering various geometricpolymer mixture configurations. The molecular simulations reveal that an increase in the interfacial area available for transverse interactions between dissimilar chains enhances atomic interactions that are orthogonal to the heat transfer direction. As transverse collisions between PA and PANI chains are enhanced, the motion of longitudinal phonons is disrupted, impeding thermal transport. This enhances phonon scattering and reduces longitudinal thermal transport. While there is a nonlinear decrease in the phonon thermal conductivity with increasing interfacial contact area, there is a corresponding linear growth in the nonbonded interaction energies between the different polymers

Unique Thermal Properties of Clothing Materials.

Cloth wearing seems so natural that everyone is self-deemed knowledgeable and has some expert opinions about it. However, to clearly explain the physics involved, and hence to make predictions for clothing design or selection, it turns out to be quite challenging even for experts. Cloth is a multiphased, porous, and anisotropic material system and usually in multilayers. The human body acts as an internal heat source in a clothing situation, thus forming a temperature gradient between body and ambient. But unlike ordinary engineering heat transfer problems, the sign of this gradient often changes as the ambient temperature varies. The human body also perspires and the sweat evaporates, an effective body cooling process via phase change. To bring all the variables into analysis quickly escalates into a formidable task. This work attempts to unravel the problem from a physics perspective, focusing on a few rarely noticed yet critically important mechanisms involved so as to offer a clearer and more accurate depiction of the principles in clothing thermal comfort

Measurement of salinity distributions in salt‐stratified, double‐diffusive systems by optical deflectometry

This is the published version. Copyright © 1986 American Institute of PhysicsReliable salinity measurements in double‐diffusive thermohaline solutions are necessary to understand relevant system behavior. An optical technique, which has previously been used to investigate solutediffusion in isothermal systems, is employed to measure the salinity distribution in a double‐diffusive thermohaline system. The technique is verified by comparison with independent salinity measurements, and its use in a double‐diffusive system reveals detailed salinity distribution information. When used with the shadowgraph method of flow visualization, the salinity measurement technique permits a more quantitative interpretation of the shadowgraphic results

Modifying thermal transport in electrically conducting polymers: Effects of stretching and combining polymer chains

If their thermal conductivity can be lowered, polyacetylene (PA) and polyaniline(PANI) offer examples of electrically conducting polymers that can have potential use as thermoelectrics. Thermal transport in such polymers is primarily influenced by bonded interactions and chain orientations relative to the direction of heat transfer. We employ molecular dynamics simulations to investigate two mechanisms to control the phonon thermal transport in PANI and PA, namely, (1) mechanical strain and (2) polymer combinations. The molecular configurations of PA and PANI have a significant influence on their thermal transport characteristics. The axial thermal conductivity increases when a polymer is axially stretched but decreases under transverse tension. Since the strain dependence of the thermal conductivity is related to the phonon scattering among neighboring polymer chains, this behavior is examined through Herman\u27s orientation factor that quantifies the degree of chain alignment in a given direction. The conductivity is enhanced as adjacent chains become more aligned along the direction of heat conduction but diminishes when they are orthogonally oriented to it. Physically combining these polymers reduces the thermal conductivity, which reaches a minimum value for a 2:3 PANI/PA chain ratio

Electrical and Thermal Transport in Metallic Single-Wall Carbon Nanotubes on Insulating Substrates

We analyze transport in metallic single-wall carbon nanotubes (SWNTs) on insulating substrates over the bias range up to electrical breakdown in air. To account for Joule self-heating, a temperature-dependent Landauer model for electrical transport is coupled with the heat conduction equation along the nanotube. The electrical breakdown voltage of SWNTs in air is found to scale linearly with their length, approximately as 5 V/um; we use this to deduce a thermal conductance between SWNT and substrate g ~ 0.17 +/- 0.03 W/K/m per tube length, which appears limited by the SWNT-substrate interface rather than the thermal properties of the substrate itself. We examine the phonon scattering mechanisms limiting electron transport, and find the strong temperature dependence of the optical phonon absorption rate to have a remarkable influence on the electrical resistance of micron-length nanotubes. Further analysis reveals that unlike in typical metals, electrons are responsible for less than 15% of the total thermal conductivity of metallic nanotubes around room temperature, and this contribution decreases at high bias or higher temperatures. For interconnect applications of metallic SWNTs, significant self-heating may be avoided if power densities are limited below 5 uW/um, or if the SWNT-surrounding thermal interface is optimized.Comment: accepted for publication in J. Appl. Phys. (2007

Modelling of single bubble-dynamics and thermal effects

This paper evaluates the solution effects of different Rayleigh-Plesset models (R-P) for simulating the growth/collapse dynamics and thermal behaviour of homogeneous gas bubbles. The flow inputs used for the discrete cavitation bubble calculations are obtained from Reynolds-averaged Navier-Stokes simulations (RANS), performed in high-pressure nozzle holes. Parametric 1-D results are presented for the classical thermal R-P equation [1] as well as for refined models which incorporated compressibility corrections and thermal effects [2, 3]. The thermal bubble model is coupled with the energy equation, which provides the temperature of the bubble as a function of conduction/convection and radiation heat-transfer mechanisms. For approximating gas pressure variations a high-order virial equation of state (EOS) was used, based on Helmholtz free energy principle [4]. The coded thermal R-P model was validated against experimental measurements [5] and model predictions [6] reported in single-bubble sonoluminescence (SBSL)

Thermal Probing of Energy Dissipation in Current-Carrying Carbon Nanotubes

The temperature distributions in current-carrying carbon nanotubes have been measured with a scanning thermal microscope. The obtained temperature profiles reveal diffusive and dissipative electron transport in multi-walled nanotubes and in single-walled nanotubes when the voltage bias was higher than the 0.1-0.2 eV optical phonon energy. Over ninety percent of the Joule heat in a multi-walled nanotube was found to be conducted along the nanotube to the two metal contacts. In comparison, about eighty percent of the Joule heat was transferred directly across the nanotube-substrate interface for single-walled nanotubes. The average temperature rise in the nanotubes is determined to be in the range of 5 to 42 K per micro watt Joule heat dissipation in the nanotubes