Cascaded Thermodynamic and Environmental Analyses of Energy Generation Modalities of a High-Performance Building Based on Real-Time Measurements.

This study presents cascaded thermodynamic and environmental analyses of a high-performance academic building. Five different energy efficiency measures and operation scenarios are evaluated based on the actual measurements starting from the initial design concept. The study is to emphasize that by performing dynamical energy, exergy, exergoeconomic, and environmental analyses with increasing complexity, a better picture of building performance indicators can be obtained for both the building owners and users, helping them to decide on different investment strategies. As the first improvement, the original design is modified by the addition of a ground-air heat exchanger for pre-conditioning the incoming air to heat the ground floors. The installation of roof-top PV panels to use solar energy is considered as the third case, and the use of a trigeneration system as an energy source instead of traditional boiler systems is considered as the fourth case. The last case is the integration of all these three alternative energy modalities for the building. It is determined that the use of a trigeneration system provides a better outcome than the other scenarios for decreased energy demand, for cost reduction, and for the improved exergy efficiency and sustainability index values relative to the original baseline design scenario. Yet, an integrated approach combining all these energy generation modalities provide the best return of investment.

Image registration method for mobile-device-based multispectral optical diagnostics for buildings.

The recent advances in mobile device hardware and software introduced new opportunities to perform more advanced computation and measurements for buildings. Multispectral optical imaging is a widely recognized technique for building diagnostics, as it is non-destructive, quick, and provides rich spatial-spectral information about the different surfaces for decisions related to building energy performance. However, such implementations require an accurate image fusion. The purpose of this study is to introduce a practical and robust image registration method for mobile-device-based multispectral imaging analysis for building diagnostics. Considering the complicated building geometries including walls, floors, ceilings, roofs, windows, and doors, a new approach based on planar homography is chosen for determining the feature points that are required to perform image fusion between different images. The results obtained are compared against the other available methods, which show that the current method provides multispectral images enhanced with accurate qualitative information, as long as the constraints are satisfied. The results are compared with the state-of-the-art methods. The possible impact of the multispectral imaging to the future of building diagnostics is also discussed.

Publisher Correction: A biomimicry design for nanoscale radiative cooling applications inspired by Morpho didius butterfly.

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has been fixed in the paper.

Plasmon coupling between complex gold nanostructures and a dielectric substrate.

Intercoupling of an incident electric field in metal nanoparticles causes asymmetric distribution of surface charges, which eventuates in shifting of the surface plasmon resonance frequency. This feature can be used in tuning the surface plasmon resonance and controlling the light absorption in a desired wavelength. This work provides a theoretical study of the plasmonic properties of complex gold nanostructures on a dielectric substrate where the nanoparticles have different morphologies. For analysis, we have developed a discrete dipole approximation with surface interactions-z, which is the third version of the MATLAB-based DDA-SI toolbox. In this version, lower-upper decomposition of the interaction matrix is used as a preconditioning of the LSQR iterative solver. This method accelerates the DDA-SI calculations by decreasing the total number of iteration steps and decreases the relative residual to achieve more accurate results. In the analysis, nanostructures are assumed to be gold dimers, trimers, and quadrumers with different sizes and elongations of cubical or spherical geometries on a BK7 substrate. The results show that absorption spectra exhibit both red- and blueshifted plasmon resonances in array, depending on the particle shape and elongation. The cubic structure of gold array provides the highest absorption efficiency, while the spherical structures give wider bandwidth; the combination of these structures could be used to design a system with intended features. We demonstrate that the geometrical symmetry plays an important role in the plasmon resonance of gold arrays, and it is shifted when the symmetry of the array is broken.

A biomimicry design for nanoscale radiative cooling applications inspired by Morpho didius butterfly.

In nature, novel colors and patterns have evolved in various species for survival, recognizability or mating purposes. Investigations of the morphology of various butterfly wings have shown that in addition to the pigmentation, micro and nanostructures within the wings have also allowed better communication systems and the pheromone-producing organs which are the main regulators of the temperature within butterfly wings. Within the blue spectrum (450-495 nm), Morpho didius butterfly exhibit iridescence in their structure-based wings' color. Inspired by the rich physics behind this concept, we present a designer metamaterial system that has the potential to be used for near-field radiative cooling applications. This biomimicry design involves SiC palm tree-like structures placed in close proximity of a thin film in a vacuum environment separated by nanoscale gaps. The near-field energy exchange is enhanced significantly by decreasing the dimensions of the tree and rotating the free-standing structure by 90 degrees clockwise and bringing it to the close proximity of a second thin film. This exchange is calculated by using newly developed near-field radiative transfer finite difference time domain (NF-RT-FDTD) algorithm. Several orders of enhancement of near-field heat flux within the infrared atmospheric window (8-13 µm bandwidth) are achieved. This spectrally selective enhancement is associated with the geometric variations, the spatial location of the source of excitation and the material characteristics, and can be tuned to tailor strong radiative cooling mechanisms.

Entropy Generation Analysis of Laminar Flows of Water-Based Nanofluids in Horizontal Minitubes under Constant Heat Flux Conditions.

During the last decade, second law analysis via entropy generation has become important in terms of entropy generation minimization (EGM), thermal engineering system design, irreversibility, and energy saving. In this study, heat transfer and entropy generation characteristics of flows of multi-walled carbon nanotube-based nanofluids were investigated in horizontal minitubes with outer and inner diameters of ~1067 and ~889 µm, respectively. Carbon nanotubes (CNTs) with outer diameter of 10-20 nm and length of 1-2 µm were used for nanofluid preparation, and water was considered as the base fluid. The entropy generation based on the experimental data, a significant parameter in thermal design system, was examined for CNTs/water nanofluids. The change in the entropy generation was only seen at low mass fractions (0.25 wt.% and 0.5 wt.%). Moreover, to have more insight on the entropy generation of nanofluids based on the experimental data, a further analysis was performed on Al2O3 and TiO2 nanoparticles/water nanofluids from the experimental database of the previous study of the authors. The corresponding results disclosed a remarkable increase in the entropy generation rate when Al2O3 and TiO2 nanoparticles were added to the base fluid.

Near-field thermal radiation transfer by mesoporous metamaterials.

In this work, we investigate the impact of nano-scale pores within structured metamaterials on spectral near-field radiative transfer. We use Finite Difference Time Domain Method (FDTD) and consider uniform and corrugated SiC substrates filled with rectangular nano-scale vacuum inclusions having equivalent diameters of 10, 37 and 57 nm. We report the appearance of the secondary and tertiary resonance peaks at different frequencies as a function of changing pore diameter, which cannot be predicted if an effective medium theory approximation is used.

Near- to far-field coherent thermal emission by surfaces coated by nanoparticles and the evaluation of effective medium theory.

Near-field thermal radiation may play significant role in the enhancement of energy harvesting and radiative cooling by new types of designer materials, which in turn can be crucial in the development of future devices. In this work, we present a case study to explore near- to far-field thermal emission and radiative flux from a thin polar SiC film coated by different size and shape nanoparticles. The same geometry with nano-particles is also considered as a layered medium, which is analyzed using Effective Medium Theory (EMT). A significant enhancement of emission, particularly at the far infrared, is observed when nanoparticles are placed on the surface of a SiC film with certain periodicities, which shows potential use of these structures for radiative cooling applications. Yet, these enhancements are not observed when the EMT approach is adapted, which is questioned for its accuracy of predicting near-to-far field transition regime of radiation transfer from corrugated surfaces.

Effects of a silicon probe on gold nanoparticles on glass under evanescent illumination.

We have numerically investigated the influence of a nanoscale silicon tip in proximity to an illuminated gold nanoparticle. We describe how the position of the high-permittivity tip and the size of the nanoparticle impact the absorption, peak electric field and surface plasmon resonance wavelength under different illumination conditions. We detail the finite element method (FEM) approach we have used, whereby we specify a volume excitation field analytically and calculate the difference between this source field and the total field (i.e., scattered-field formulation). We show that a nanoscale tip can locally enhance the absorption of the particle as well as the peak electric field at length scales far smaller than the wavelength of the incident light.

Surface waves and atomic force microscope probe-particle near-field coupling: discrete dipole approximation with surface interaction.

Evanescent waves on a surface form due to the collective motion of charges within the medium. They do not carry any energy away from the surface and decay exponentially as a function of the distance. However, if there is any object within the evanescent field, electromagnetic energy within the medium is tunneled away and either absorbed or scattered. In this case, the absorption is localized, and potentially it can be used for selective diagnosis or nanopatterning applications. On the other hand, scattering of evanescent waves can be employed for characterization of nanoscale structures and particles on the surface. In this paper we present a numerical methodology to study the physics of such absorption and scattering mechanisms. We developed a MATLAB implementation of discrete dipole approximation with surface interaction (DDA-SI) in combination with evanescent wave illumination to investigate the near-field coupling between particles on the surface and a probe. This method can be used to explore the effects of a number of physical, geometrical, and material properties for problems involving nanostructures on or in the proximity of a substrate under arbitrary illumination.

Geometry dependence of the electrostatic and thermal response of a carbon nanotube during field emission.

In this paper we present an analysis to simulate heating within an isolated carbon nanotube (CNT) attached to an etched tungsten tip during field emission of an electron beam. The length, radius, wall thickness and shape of the tip (closed with a hemispherical shape or open and flat) of the CNT and its separation distance from the flat surface are considered as variables. Using a finite element method, we predict the field enhancement, emission current and temperature of the CNT as a function of these parameters. The electrostatic and transient thermal analyses are integrated with the field-emission models based on the Fowler-Nordheim approximation and heating/cooling due to emitting energetic electrons (the Nottingham effect). These simulations suggest that the main mechanism responsible for heating of the CNT is Joule heating, which is significantly larger than the Nottingham effect. Results also indicate that the electrostatic characteristics of CNTs are very sensitive to the considered parameters whereas the transient thermal response is only a function of the CNT radius and wall thickness. Further, the thermal response of the CNT is independent of its geometry, meaning that, as long as a given set of geometrical conditions are present that result in a given emission current, the maximum temperature a CNT attains will be the same.

Derivatives of scattering profiles: tools for nanoparticle characterization.

This paper presents a new approach to characterize nanoparticles using derivatives of scattering profiles of evanescent waves/surface plasmons. We start the procedure using the scattering profiles for an unknown configuration of nanoparticles, either from physical experiments or numerical simulations conducted for different nanoparticles on surfaces. We apply the statistical technique of compound estimation to recover the derivatives of scattering profiles. The L(1) discrepancies with the corresponding curves from known configurations are used to identify the most plausible configuration of particles that could yield the "experimental" profiles. We conduct a simulation study to see how often the new procedure correctly recovers the agglomeration level for gold spherical nanoparticles on a thin gold film. The results suggest that first derivatives are much more effective for characterization than undifferentiated profiles and that M(33) is the most useful element for distinguishing among configurations. The proposed compound estimation technique is more effective than typical inverse analyses based on look-up tables and can be used effectively in nanoparticle characterization platforms.

Growth of tungsten oxide nanorods with carbon caps.

Hybrid nanostructures consisting of tungsten oxide nanorods with mushroom-shaped carbon caps were grown on electrochemically etched tungsten tips by thermal chemical vapor deposition with methane and argon. These nanorods grow along the radial direction and are very straight and smooth. Electron microscopy revealed a dominant diameter and length of approximately 50 nm and approximately 0.6 microm, respectively. High-resolution transmission electron microscopy (HRTEM), and electron energy loss spectroscopy (EELS) revealed the presence of crystalline monoclinic W18O49 in the nanorods, and the cap was entirely amorphous carbon. A plausible growth mechanism involves the reduction of tungsten oxide WO3, present on the tungsten surface, by methane at 900 degrees C.

Light-scattering and dispersion behavior of multiwalled carbon nanotubes.

Elliptically polarized light-scattering measurements were performed to investigate the dispersion behavior of multiwalled carbon nanotubes (MWNT). Xylene- and pyridine-derived MWNT powders were dispersed in water and ethanol in separate optic cells and allowed to sit undisturbed over a two-week time period after probe sonication. Continuous light-scattering measurements taken between scattering angles of 10-170 deg and repeated over several days showed that the nanotubes formed fractal-like networks. The pyridine-derived MWNTs showed greater dispersion variation over time, tending to aggregate and clump much faster than the xylene-derived tubes. The water suspensions appeared much more stable than the ethanol suspensions, which transformed into nonfractal morphology after a few hours. We relate the dispersion stability to size and fringe patterns on the outer surface of the nanotubes. Measured values of fractal dimension were distinctly lower than those in previous studies of single-walled carbon nanotubes. Profiles of both diagonal and off-diagonal scattering matrix elements are presented.

Convective-diffusion-based fluorescence correlation spectroscopy for detection of a trace amount of E. coli in water.

Fluorescence correlation spectroscopy (FCS) is adapted for a new procedure to detect trace amounts of Escherichia coli in water. The present concept is based on convective diffusion rather than Brownian diffusion and employs confocal microscopy as in traditional FCS. With this system it is possible to detect concentrations as small as 1.5 x 10(5) E. coli per milliliter (2.5 x 10(-16) M). This concentration corresponds to an approximately 1.0-nM level of Rhodamine 6G dyes. A detailed analysis of the optical system is presented, and further improvements for the procedure are discussed.

Characterization of milk properties with a radiative transfer model.

To characterize milk through light-scattering measurements, a semianalytical radiative transfer model was used to simulate the backscatter of light in milk having homogenized fat levels from 0.05 to 3.2 wt. %. The input parameters to the model include the incident wavelength, refractive index of particles and medium, and particle number densities. By varying the wavelength, we can obtain a reasonable fit between experimental data and the model for lower fat milks. Results indicate that the model is most sensitive to the particle diameter and size distribution and less sensitive to the number and index of refraction of the particles.