A. G. Agwu Nnanna

Local Heating with Lithographically Fabricated Plasmonic Titanium Nitride Nanoparticles

Titanium nitride is considered a promising alternative plasmonic material and is known to exhibit localized surface plasmon resonances within the near-infrared biological transparency window. Here, local heating efficiencies of disk-shaped nanoparticles made of titanium nitride and gold are compared in the visible and near-infrared regions numerically and experimentally with samples fabricated using e-beam lithography. Results show that plasmonic titanium nitride nanodisks are efficient local heat sources and outperform gold nanodisks in the biological transparency window, dispensing the need for complex particle geometries.

Long-range and rapid transport of individual nano-objects by a hybrid electrothermoplasmonic nanotweezer

Plasmon-enhanced optical trapping is being actively studied to provide efficient manipulation of nanometre-sized objects. However, a long-standing issue with previously proposed solutions is how to controllably load the trap on-demand without relying on Brownian diffusion. Here, we show that the photo-induced heating of a nanoantenna in conjunction with an applied a.c. electric field can initiate rapid microscale fluid motion and particle transport with a velocity exceeding 10 μm s(-1), which is over two orders of magnitude faster than previously predicted. Our electrothermoplasmonic device enables on-demand long-range and rapid delivery of single nano-objects to specific plasmonic nanoantennas, where they can be trapped and even locked in place. We also present a physical model that elucidates the role of both heat-induced fluidic motion and plasmonic field enhancement in the plasmon-assisted optical trapping process. Finally, by applying a d.c. field or low-frequency a.c. field (below 10 Hz) while the particle is held in the trap by the gradient force, the trapped nano-objects can be immobilized into plasmonic hotspots, thereby providing the potential for effective low-power nanomanufacturing on-chip.

Thermal Transport Phenomena in Buoyancy-Driven Nanofluids

This paper presents an experimental investigation of the thermal transport phenomena in buoyancy-driven nanofluids. The experimental model for this study is a rectangular enclosure with differentially heated vertical walls and adiabatic horizontal walls. The nanofluids were confined within the enclosure. Simulations were performed to measure the transient and steady-state temperature response of the nanofluids to applied load. Experimental observation shows settling of the nanoparticle at low heat loads and a remixing of the nanofluid at higher loads. At high loads, the buoyancy force increased hence increasing the re-circulatory motion of the nanofluid. This may be one method of addressing the settling of nanoparticles in nanofluid. For natural convection in an enclosure, this paper shows that the thermal behavior of nanofluids is identical to pure fluids. Temperature data collected during the experiment were used to study the variation of Nusselt number with Rayleigh number.Copyright

Removal of Trace Pharmaceuticals from Water using coagulation and powdered activated carbon as pretreatment to ultrafiltration membrane system.

In this study, the efficacy of water treatment technologies: ultra-filtration (UF), powdered activated carbon (PAC), coagulation (COA) and a combination of these technologies (PAC/UF and COA/UF) to remove target pharmaceuticals (Acetaminophen, Bezafibrate, Caffeine, Carbamazepine, Cotinine, Diclofenac, Gemfibrozil, Ibuprofen, Metoprolol, Naproxen, Sulfadimethoxine, Sulfamethazine, Sulfamethoxazole, Sulfathiazole, Triclosan and Trimethoprim) was investigated. Samples of wastewater from municipal WWTPs were analyzed using direct aqueous injection High Performance Liquid Chromatography with Tandem Quadrupole Mass Spectrometric (LC/MS/MS) detection. On concentration basis, results showed an average removal efficiency of 29%, 50%, and 7%, respectively, for the UF, PAC dosage of 50ppm, and COA dosage of 10ppm. When PAC dosage of 100ppm was used as pretreatment to the combined PAC and UF in-line membrane system, a 90.3% removal efficiency was achieved. The removal efficiency of UF in tandem with COA was 33%, an increase of 4% compared with the single UF treatment. The adsorption effect of PAC combined with the physical separation process of UF revealed the best treatment strategy for removing pharmaceutical contaminant from water.

Fabrication and calibration of Oxazine-based optic fiber sensor for detection of ammonia in water

This paper presented the fabrication and calibration of a clad-modified evanescent based plastic optical fiber (POF) sensor for the detection of ammonia in both stagnant and dynamic aqueous media. This optochemical sensor was based on Oxazine 170 perchlorate (sensing material) and polydimethylsiloxane (PDMS) (protective material) thin layers. A special chemical solution was developed for the etching removal of cladding and a methodology for trapping moisture was exercised. Experimental results on dissolved ammonia detection exhibited short response time (≤10 s), low detection limit (minimum detection limit 1.4 ppm), high sensitivity, and excellent reversibility (over 99%).

Meeting world's most stringent Hg criterion: A pilot-study for the treatment of oil refinery wastewater using an ultrafiltration membrane process

A membrane ultrafiltration (UF) technology was tested using an oil refinerys end-of-pipe effluent to demonstrate the proof of concept, i.e. can the Great Lakes Initiative criterion of less than 1.3 ppt be consistently met at the pilot-scale, and to provide the data necessary for preliminary full-scale process design. This study presents the successful pilot test conducted with continuous but varying feed conditions over a protracted period. The UF membrane process consistently provided a constant permeate quality at all tested operating conditions, virtually independent of the feed water characteristics and the feed Hg concentration (0.5-22.7 ppt). The treatment target of less than 1.3 ppt of Hg was met and exceeded for all tested conditions during the pilot study. Turbidity measurements were <0.5 NTU (with a MDL of 0.5 NTU) 85% of the time and <0.16 NTU 95% of the time when analyzed on-line. The TMP values were below the specification of (negative) 7-12 psi at all tested conditions during the pilot-study. Weekly maintenance cleans and monthly clean in place (CIP) events were very effective in consistently restoring the membrane permeability during the pilot-study.

Experimental Study of Fluid Flow in Microchannel

This paper presents a study of fluid flow through microchannel. Based on the work of Senta and Nnanna, [23], a trapezoidal-shaped manifold is used to ensure uniform flow distribution in the microchannel. Analysis further shows that flow uniformity among the channels largely depends on shape of the manifolds, length and location of inlet and outlets, and the inlet flow rate. The test setup consists of one hundred twenty-six 14.5μm-width channels, flow loop, heat source, thermal sensors and pressure transducers. Flow of fluid through the channels is regulated using a peristaltic pump. Experiments were conducted from various flow rates and heat loads. According to experimental data, microchannel has significant impact in the heat transfer rate for all the flow rates considered. This enhancement could be attributed to laminar flow in the microchannels, conduction heat transfer through the walls of the channel, fluid-channel wall interaction, and microconvection within the channel. Results show raises some concerns on the use of empirical correlations for flow between two parallel plates to predict heat transfer behavior in microchannels. In the absence of experimental data, f ≈ −2(dp/dx)dh /ρum 2 provides a reasonable estimate of friction factor in microchannel.Copyright

Design of Manifold for Nanofluid Flow in Microchannel

This paper presents a study of nanofluid flow through microchannel. Its focus is on the design and optimization of microchannel assembly with emphasis on the design of manifold or jacket. The test setup consists of ninety-nine 120μm×120μm×20mm channels, nanofluid flow loop, heat source, thermal sensors and pressure transducers. Flow of nanofluid through the channels is regulated using a peristaltic pump. Numerical iterations were performed to study the effect of inlet and exit flow locations and shape of the jacket on uniform distribution of nanofluid in the channels. Based on the numerical results, it is recommended that for uniform flow distribution in the microchannel, a trapezoidal shaped jacket should be used. The results obtained from this work provided an insight on the variation of the flow patterns within the channel. It reveals that flow uniformity among the channels largely depends on the shape of the manifolds, length and location of inlet and outlets, and the inlet flow rate.© 2007 ASME

Thermo-Hydraulic Behavior of Microchannel Heat Exchanger System

This article presents an experimental study of thermo-hydrodynamic phenomena in a microchannel heat exchanger system. The aim of this investigation is to develop correlations between flow/thermal characteristics in the manifolds and the heat transfer performance of the microchannel. A rectangular microchannel fabricated by a laser-machining technique with channel width and hydraulic diameter of 87 μm and 0.17 mm, respectively, and a trapezoidal-shaped manifold are used in this study. The heat sink is subjected to iso-flux heating condition with liquid convective cooling through the channels. The temporal and spatial evolutions of temperature as well as total pressure drop across the system are monitored using appropriate sensors. Data obtained from this study were used to establish relationships between parameters such as longitudinal wall conduction factor, residence and switching time, and thermal spreading resistance with Reynolds number. Result shows that there exist an optimum Reynolds number and con...This article presents an experimental study of thermo-hydrodynamic phenomena in a microchannel heat exchanger system. The aim of this investigation is to develop correlations between flow/thermal characteristics in the manifolds and the heat transfer performance of the microchannel. A rectangular microchannel fabricated by a laser-machining technique with channel width and hydraulic diameter of 87 μm and 0.17 mm, respectively, and a trapezoidal-shaped manifold are used in this study. The heat sink is subjected to iso-flux heating condition with liquid convective cooling through the channels. The temporal and spatial evolutions of temperature as well as total pressure drop across the system are monitored using appropriate sensors. Data obtained from this study were used to establish relationships between parameters such as longitudinal wall conduction factor, residence and switching time, and thermal spreading resistance with Reynolds number. Result shows that there exist an optimum Reynolds number and conditions for the microchannel heat exchanger system to result in maximum heat transfer performance. The condition in which the inlet manifold temperature surpasses the exit fluid temperature results in lower junction temperature. It further shows that for a high Reynolds number, the longitudinal wall conduction parameter is greater than unity and that the fluid has sufficient dwelling time to absorb heat from the wall of the manifold, leading to high thermal performance.

Dye Doped Clad Modified Evanescent Optical Fiber (CMEOF) Sensor Array for the Detection of Aqueous-Ammonia

We are currently developing pH sensitive dye doped clad modified evanescent optical fiber (CMEOF) sensor array for the detection of aqueous-ammonia. The quasi-distribution of CMEOF ammonia sensors allows efficient measurement of aqueous-ammonia at several locations using a single fiber optic line. CMEOF sensors are fabricated by immobilized pH sensitive dyes in sol-gel and applying the dye doped sol-gel as a thin film around a bare core optical fiber. The CMEOF sensors are then sealed from water using a gas permeable membrane, PDMS-vinyl. The dyes in each CMEOF sensor are tailored to operate at slightly different wavelengths by appropriate choice of dyes. Wavelength-division-multiplexing (WDM) and linear system of equations (LSE) are used to interrogate each CMEOF sensor and determine the concentration of aqueous-ammonia at each sensor location.Copyright