Kenneth D. Kihm

Empirical correlation finding the role of temperature and particle size for nanofluid (Al2O3) thermal conductivity enhancement

In this letter, we report an experimental correlation [Eqs. (1a) and (1b) or (1c)] for the thermal conductivity of Al2O3 nanofluids as a function of nanoparticle size (ranging from 11nmto150nm nominal diameters) over a wide range of temperature (from 21to71°C). Following the previously proposed conjecture from the theoretical point-of-view (Jang and Choi, 2004), it is experimentally validated that the Brownian motion of nanoparticles constitutes a key mechanism of the thermal conductivity enhancement with increasing temperature and decreasing nanoparticle sizes.

PIV flow measurements for heat transfer characterization in two-pass square channels with smooth and 90° ribbed walls

Abstract Particle image velocimetry (PIV) experiments have been carried out to study the correlation between the high-Reynolds number turbulent flow and wall heat transfer characteristics in a two-pass square channel with a smooth wall and a 90° rib-roughened wall. Detailed averaged velocity distributions and turbulent kinetic energy for both the main and the secondary flows are given for a representative Reynolds number (Re) of 30,000. The PIV measurement results were compared with the heat transfer experimental data of Ekkad and Han [International Journal of Heat Mass Transfer 40 (11) (1997) 2525–2537]. The result shows that the flow impingement is the primary factor for the two-pass square channel heat transfer enhancement rather than the flow turbulence level itself. The characteristics of the secondary flow, for example, vortexs shape, strength, rotating-direction and positions, are closely correlated with the wall heat transfer enhancements for both smooth and ribbed wall two-pass square channels. The rib-induced flow turbulence increases the heat transfer mainly because of the enhanced local flow impingement near the rib.

Examination of ratiometric laser induced fluorescence thermometry for microscale spatial measurement resolution

Ratiometric laser induced fluorescence (LIF) thermometry technique has been quantitatively examined for its capability for a microscale field-of-view. The goal of the study is to quantitatively examine the measurement accuracy of the ratiometric LIF technique at sub-millimeter and micron scales for its potential use as a microscale temperature mapping tool. Measurements have been made for the steady temperature fields established by thermal buoyancy inside 1-mm wide closed test cell with low Grashof–Prandtl numbers (86 < GrwPr < 301), and the detailed measured data have been compared with the well-known predictions. The smallest measurement resolution could be achieved being equivalent to the CCD pixel size of 4.7 lm in the present experiment, but with large data uncertainties. The measurement uncertainties show persistent improvement to better than ±1 � C when measurement resolution is equivalent to 76 lm.

Temperature measurement for a nanoparticle suspension by detecting the Brownian motion using optical serial sectioning microscopy (OSSM)

A concept of nonintrusive thermometry is presented based on the correlation of the Brownian motion of suspended nanoparticles with the surrounding fluid temperature. Detection of fully three-dimensional Brownian motion is possible by the use of optical serial sectioning microscopy (OSSM). This technique measures optically diffracted particle images, the so-called point spread function (PSF), and determines the defocusing or line-of-sight location of the imaged particle measured from the focal plane. A dry objective lens (40×, 0.75 NA) is used to detect the diffraction patterns of 500 nm polystyrene fluorescent (505/515) nanoparticles suspended in water at a volume concentration of 4 × 10−6, for a range of temperatures from 5 to 70 °C. The measured mean square displacement (MSD) data (figure 8, table 1) agree fairly well with the well-known Einstein predictions. Differentials of 5.54%, 4.26% and 3.19% were found for the 1D, 2D and 3D cases, respectively. In summary, the line-of-sight Brownian motion detection using the OSSM technique is proposed in lieu of the more cumbersome two-dimensional Brownian motion tracking on the imaging plane as a potentially more effective tool to nonintrusively map the temperature fields for nanoparticle suspension fluids.

How to Reliably Determine the Complex Refractive Index (RI) of Graphene by Using Two Independent Measurement Constraints

Reliable determination of the complex refractive index (RI) of graphene inherently requires two independent measurement realizations for two independent unknowns of the real (nG) and imaginary (kG) components, i.e., RI = nG + i kG. Thus, any single set of measurement realization provides only one constraint that is insufficient to uniquely determine the complex RI of graphene. Tandem uses of two independent measurement techniques, namely the surface plasmon resonance (SPR) angle detection and the attenuated total reflection (ATR) intensity measurement, allow for the unique determination of the complex RI of CVD-synthesized graphene. The presently measured graphene RI is determined to be 2.65 + 1.27i for the E-field oscillating parallel to graphene at 634 nm wavelength, with variations for different numbers of L (1, 3 and 5) remaining within ±3%. Thus, our demonstration results for the specified wavelength serve as an impetus to suggest the need for two independent measurement techniques in determining both the real and imaginary RI values for graphene. Additional efforts have been made to characterize graphene layers using the density function theory (DFT): this calculation provides RIG = 2.71 + 1.41i.

Laser Speckle Photography Technique Applied for Heat and Mass Transfer Problems

Publisher Summary The speckle photography refers to an optical method that measures the refractive index gradients of a phase object based on the optically created and refractively dislocated speckle patterns. The chapter introduces the operating principle of the speckle photography technique and discusses its unique features compared with other competing optical methods. Several different natural heat convection problems are presented for that speckle photography successfully measures the heat transfer coefficients without the need of corrections for the conduction and radiation losses. Speckle results provide data with high spatial resolution and make the experimental processes more reliable. Speckle photography measures the statistical properties for turbulent flows with density and temperature fluctuations. The chapter presents the tomographic reconstruction of a density field from multiple specklegrams. The potential of speckle photography for high-temperature applications such as combusting flames is discussed in the chapter. The viability of the technique emerges from its applications for premixed Bunsen flames of axisymmetric and laminar configuration. The chapter explores an example application of speckle photography for a liquid flow with density variation where the refractive index behaves quite differently from that of air or other gases.

Opto-Electric Cellular Biosensor Using Optically Transparent Indium Tin Oxide (ITO) Electrodes

Indium tin oxide (ITO) biosensors are used to perform simultaneous optical and electrical measurements in order to examine the dynamic cellular attachment, spreading, and proliferation of endothelial cells (ECs) as well as cytotoxic effects when exposed to cytochalasin D. A detailed description of the fabrication of these sensors is provided and their superior optical characteristics are qualitatively shown using four different microscopic images. Differential interference contrast microscopy (DICM) images were acquired simultaneously with micro-impedance measurements as a function of frequency and time. A digital image processing algorithm quantified the cell-covered electrode area as a function of time. In addition, cytotoxicity effects, produced by the toxic agent cytochalasin D, were examined using micro-impedance measurements, confocal microscopy images of stained actin-filaments, and interference reflection contrast microscopy (IRCM) capable of examining the bottom morphology of a cell. The results of this study show (1) the dynamic optical and electrical cellular characteristics using optically thin ITO biosensors; (2) qualitative agreement between cell-covered electrode area and electrical impedance during cellular attachment; (3) in vitro cytotoxicity detection of ECs due to 3 μM cytochalasin D. The present opto-electric biosensor system is unique in that a simultaneous and integrated cellular analysis is possible for a variety of living cells.

Femtosecond Laser Fabrication of Cavity Microball Lens (CMBL) inside a PMMA Substrate for Super-Wide Angle Imaging.

Since microlenses have to date been fabricated primarily by surface manufacturing, they are highly susceptible to surface damage, and their microscale size makes it cumbersome to handle. Thus, cavity lenses are preferred, as they alleviate these difficulties associated with the surface-manufactured microlenses. Here, it is shown that a high repetition femtosecond laser can effectively fabricate cavity microball lenses (CMBLs) inside a polymethyl methacrylate slice. Optimal CMBL fabrication conditions are determined by examining the pertinent parameters, including the laser processing time, the average irradiation power, and the pulse repetition rates. In addition, a heat diffusion modeling is developed to better understand the formation of the spherical cavity and the slightly compressed affected zone surrounding the cavity. A micro-telescope consisting of a microscope objective and a CMBL demonstrates a super-wide field-of-view imaging capability. Finally, detailed optical characterizations of CMBLs are elaborated to account for the refractive index variations of the affected zone. The results presented in the current study demonstrate that a femtosecond laser-fabricated CMBL can be used for robust and super-wide viewing micro imaging applications.

Comparison of wire—plate and plate—plate electrostatic precipitators in turbulent flow

Abstract The transport of pre-charged particles in a wire—plate precipitator in turbulent flow is investigated by numerical solution of the convective diffusion equation. For ease of computation the high voltage wire electrodes are replaced by strip electrodes giving essentially the same potential distribution. It is shown that for equivalent values of the Deutsch and Peclet numbers, the efficiency of the wire—plate system agrees closely with that of a plate—plate system, provided the comparison is made on the basis of equal values of the space-averaged field at the collector. The study does not include corona charging as normally encountered.

Microscale Heat and Mass Transport of Evaporating Thin Film of Binary Mixture

Analytical and computational studies are presented to examine the effect of binary mixture (pentane/decane) on the microscale heat and mass transport of an evaporating meniscus formed inside a two-dimensional slotted pore. Mass conservation in the liquid film is combined with the momentum equations, energy balance, and normal stress balance and then scaled yielding two constitutive equations: 1) a fourth-order, nonlinear, ordinary differential equation for thin-film profile [Eq. (27)] and 2) a first-order, linear, ordinary differential equation for concentration profile [Eq. (30)]. The numerical results showed that the magnitude of distillation-driven capillary stress due to the composition gradient of a binary mixture can be larger than the thermocapillary stress due to temperature gradient while they are acting in opposite direction. Henceforth, the proof-of-concept has been established in that the binary mixture could facilitate improvement of the evaporating thin-film stability. It was also shown that the resulting stress elongated the length of the evaporating thin-film region without degradation of heat transport effectiveness.