There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Titanium Dioxide Nanomaterials: Synthesis, Properties, Modifications, and Applications

Metal-organic frameworks (MOFs) are an emerging class of porous materials with potential applications in gas storage, separations, catalysis, and chemical sensing. Despite numerous advantages, applications of many MOFs are ultimately limited by their stability under harsh conditions. Herein, the recent advances in the field of stable MOFs, covering the fundamental mechanisms of MOF stability, design, and synthesis of stable MOF architectures, and their latest applications are reviewed. First, key factors that affect MOF stability under certain chemical environments are introduced to guide the design of robust structures. This is followed by a short review of synthetic strategies of stable MOFs including modulated synthesis and postsynthetic modifications. Based on the fundamentals of MOF stability, stable MOFs are classified into two categories: high-valency metal-carboxylate frameworks and low-valency metal-azolate frameworks. Along this line, some representative stable MOFs are introduced, their structures are described, and their properties are briefly discussed. The expanded applications of stable MOFs in Lewis/Bronsted acid catalysis, redox catalysis, photocatalysis, electrocatalysis, gas storage, and sensing are highlighted. Overall, this review is expected to guide the design of stable MOFs by providing insights into existing structures, which could lead to the discovery and development of more advanced functional materials.

Stable Metal-Organic Frameworks: Design, Synthesis, and Applications.

http://csmres.co.uk/cs.public.upd/article-downloads/lynch.pdf

Protein-nanoparticle interactions

Atmospheric water is a resource equivalent to ~10% of all fresh water in lakes on Earth. However, an efficient process for capturing and delivering water from air, especially at low humidity levels (down to 20%), has not been developed. We report the design and demonstration of a device based on a porous metal-organic framework {MOF-801, [Zr6O4(OH)4(fumarate)6]} that captures water from the atmosphere at ambient conditions by using low-grade heat from natural sunlight at a flux of less than 1 sun (1 kilowatt per square meter). This device is capable of harvesting 2.8 liters of water per kilogram of MOF daily at relative humidity levels as low as 20% and requires no additional input of energy.

https://science.sciencemag.org/content/sci/early/2017/04/12/science.aam8743.full.pdf

Water harvesting from air with metal-organic frameworks powered by natural sunlight

Thermal energy storage has received significant interest for delivering both heating and cooling in electric vehicles, to minimize the use of the on-board electric batteries for heating, ventilation and air-conditioning (HVAC). An advanced thermo-adsorptive battery (ATB) is currently being developed, to provide both heating and cooling for an electric vehicle. We present a detailed thermophysical and physicochemical characterization of adsorptive materials for the development of the ATB. We discuss the feasibility of using contemporary adsorptive materials, such as zeolite 13X, by carrying out a detailed experimental characterization. In this study, zeolite 13X is combined with aluminum hydroxide (Al(OH)3) as a binder to improve the thermal conductivity. We also investigate the effect of densification on the overall transport characteristics of the adsorbent-binder composite material. Accordingly, the effective thermal conductivity, surface area, adsorption capacity and surface chemistry were characterized using the laser flash technique, surface sorption analyzer, thermogravimetric analyzer, and x-ray scattering technique. Thermal conductivity predictions of both zeolite 13X and its combination with the binder were made with existing conductivity models. Thermal conductivity in excess of 0.4 W/mK was achieved with the addition of 6.4 wt.% of Al(OH)3. However, a 10.6 % decrease in adsorption capacity was also observed. The experimental characterization presented herein is an essential step towards the development of the proposed ATB for next-generation electric vehicles.Copyright © 2013 by ASME

Experimental Characterization of Adsorption and Transport Properties for Advanced Thermo-Adsorptive Batteries

This study quantifies the evaporation rate of sessile droplets using a quartz crystal microbalance (QCM). Specifically, we analyze the evaporation of water droplets on a gold-coated flat surface exposed to dry nitrogen at different temperatures. In this approach, we use the QCM as a radius sensor and determine the contact angle by droplet imaging, which allows calculating the instantaneous volume and the evaporation rate. For comparison, we quantify evaporation using computational modeling and an experimental technique based on droplet imaging alone. In general, the QCM-based approach was found to provide higher accuracy and a better agreement with the model predictions compared to the approach using imaging only. With modeling and experiments, we also elucidate the role of droplet self-cooling, vapor advection, and diffusion on the net rate of evaporation of sessile droplets. For all the conditions analyzed in this study, the evaporation rate was found to decrease monotonically. We found this reduction to take place even in the presence of a steadily increasing droplet temperature due to a shrinking evaporation area. Considering the vapor transport mechanisms occurring in the ambient, we find diffusion to be the rate-limiting process controlling the net evaporation rate of the droplet.

Quantifying the evaporation rate of sessile droplets using a quartz crystal microbalance

Planck’s law predicts the distribution of radiation energy, color and intensity, emitted from a hot object at thermal equilibrium. The Law also sets the upper limit of radiation intensity, the blackbody limit. Recent experiments reveal that micro-structured tungsten can exhibit significant deviation from the blackbody spectrum. However, whether thermal radiation with weak non-equilibrium pumping can exceed the blackbody limit in the far field remains un-answered experimentally. Here, we compare thermal radiation from a micro-cavity/tungsten photonic crystal (W-PC) and a blackbody, which are both measured from the same sample and also in-situ. We show that thermal radiation can exceed the blackbody limit by >8 times at λ = 1.7 μm resonant wavelength in the far-field. Our observation is consistent with a recent calculation by Wang and John performed for a 2D W-PC filament. This finding is attributed to non-equilibrium excitation of localized surface plasmon resonances coupled to nonlinear oscillators and the propagation of the electromagnetic waves through non-linear Bloch waves of the W-PC structure. This discovery could help create super-intense narrow band thermal light sources and even an infrared emitter with a laser-like input-output characteristic.

/pdf/an-in-situ-and-direct-confirmation-of-super-planckian-2k01g4giw7.pdf

An In-situ and Direct Confirmation of Super-Planckian Thermal Radiation Emitted From a Metallic Photonic-Crystal at Optical Wavelengths.

This study quantitatively compares the finite element (FE) and lumped modeling techniques to analyze phase-change and multiphase flow in a microchannel evaporator. We compare the one- and two-zone models in the lumped modeling approach by considering both pressure drop and phase change in the evaporator. The study investigates the deviation in results from the lumped model relative to the FE model for various evaporator heat loads. For the one-zone model, the relative errors in predicting the average density, pressure, temperature, and vapor quality increase with the evaporator heat load. This increase is mainly due to the nonlinear variation in the heat transfer coefficient and pressure drop, which are calculated with higher inaccuracies at larger evaporator heat loads. On the other hand, the liquid-phase region and the exit vapor quality are predicted more accurately. The overall errors using one- and two-zone lumped models were less than 30% when the exit qualities do not exceed 0.5. Since strategies involving flow boiling in evaporators typically avoid high exit vapor qualities to circumvent dry-out and critical heat flux, the use of lumped models under these conditions is favorable. This approach also avoids the computational costs associated with FE models while achieving sufficient accuracy to predict the evaporator’s performance.

A Comparison of Finite Element and Lumped Modeling Techniques to Analyze Flow Boiling in Microchannels

A new cooling scheme utilizing evaporation from an ultrathin, spatially confined liquid film is described and analyzed for thermal management of hot spots with local heat fluxes in excess of 600 W/cm2. This is achieved by a stable monolayer of liquid maintained on the surface and using fully dry sweeping gas (e.g., air) blown at high velocity (50–100 m/s) above this liquid monolayer. We also demonstrate how dielectric coolants like FC72 can outperform water as an evaporative coolant for this scheme. This work presents the conceptual system design, the results of performance analysis supporting the feasibility of the proposed cooling scheme, and experimental results that demonstrate the idea as well as validate the computational results. The analysis allows one to elucidate the salient physical features of evaporative cooling from spatially confined thin films subjected to a sweeping gas and to identify the key parameters resulting enhanced performance. The simplified model provides results in a form suitable for designing a full-scale cooling device (perspiration nanopatch) that exploits the unique advantages of the proposed cooling scheme.

Shankar Narayanan

Papers

Experimental Characterization of Adsorption and Transport Properties for Advanced Thermo-Adsorptive Batteries

Quantifying the evaporation rate of sessile droplets using a quartz crystal microbalance

An In-situ and Direct Confirmation of Super-Planckian Thermal Radiation Emitted From a Metallic Photonic-Crystal at Optical Wavelengths.

A Comparison of Finite Element and Lumped Modeling Techniques to Analyze Flow Boiling in Microchannels

Gas assisted thin-film evaporation from confined spaces