Effect of surface tension on nanotube nanofluids

This letter presents heat transfer results that single-walled carbon nanotube (CNT) suspensions in a boiling environment can extend the saturated boiling regime and postpone catastrophic failure of the material even further than previously reported if the surface tension of the nanofluid is carefully controlled. The maximum enhancement in the critical heat flux is nearly four times for a surfactant to CNT concentration ratio of 1:5. The experimental results show that the material burnout is a strong function of the relaxation of the nanofluid surface tension with the base fluid

An enhanced CRISPR repressor for targeted mammalian gene regulation.

The RNA-guided endonuclease Cas9 can be converted into a programmable transcriptional repressor, but inefficiencies in target-gene silencing have limited its utility. Here we describe an improved Cas9 repressor based on the C-terminal fusion of a rationally designed bipartite repressor domain, KRAB-MeCP2, to nuclease-dead Cas9. We demonstrate the system's superiority in silencing coding and noncoding genes, simultaneously repressing a series of target genes, improving the results of single and dual guide RNA library screens, and enabling new architectures of synthetic genetic circuits

Next generation heat transfer fluids : experimental study of nano-oxide and carbon nanotube suspensions in water

Complex or smart fluids, made of evenly and stably suspended nanoparticles, have been an object of considerable research in the last decade due to their promising applications in a number of applications such as micro-electronic cooling, high power demands in nuclear plants, smaller and more efficient heat exchangers, oil recovery, and transportation. Nanofluids consist of typically less than 100nm sized particles dispersed in base fluids. The heat transfer characteristics of several nano-oxide suspensions in pool boiling with a suspended heating NiChrome wire have been analyzed. The pH value of the nanosuspensions is important from the point of view that it determines the stability of the particles and their mutual interactions towards the suspended heated wire. Heat transfer in silica nanofluids at different acidity and base is measured for various ionic concentrations in a pool boiling experiment. Nanosilica suspension increases the critical heat flux by up to 300% compared to conventional fluids. The l0 nm particles possess a thicker double diffuse layer compared to 20 M particles. The catalytic properties of nanofluids decrease in the presence of salts, allowing the particles to cluster and minimize the potential increase in heat transfer. Nanofluids in a strong electrolyte, i.e., in high ionic concentration, allow a higher critical heat flux than in buffer solutions because of the difference in surface area. The formation and surface structure of the deposition affect the thermal properties of the liquid. When there is no particle deposition on the wire, the nanofluid increases CHF by about 50% within the uncertainty limits, regardless of pH of the base fluid or particle size. The extent of oxidation on the wire impacts CHF, and is influenced by the chemical composition of nanofluids in buffer solutions. The boiling regime is further extended to higher heat flux when there is agglomeration on the wire. This agglomeration allows high heat transfer through inter-agglomerate pores, resulting in a nearly 3-fold increase in burnout heat flux. The pool boiling heat transfer has been even higher (- up to 4 times that of the base fluid) for Double Walled Carbon Nanotubes (DWNTs). A comparison study between Single and Double Walled Carbon Nanotube suspensions has been performed. A closed flow loop has been designed and fabricated to study the thermal transport characteristics of nanosilica suspensions in heated flow. The heat transfer coefficient and pressure drop data are provided for laminar and turbulent regimes (200

Heat Transfer Behavior Of Silica Nanoparticles In Pool Boiling Experiment

The heat transfer characteristics of silica (SiO2) nanofluids at 0.5 vol % concentration and particle sizes of 10 nm and 20 nm in pool boiling with a suspended heating Nichrome wire have been analyzed. The influence of acidity on heat transfer has been studied. The pH value of the nanosuspensions is important from the point of view that it determines the stability of the particles and their mutual interactions toward the suspended heated wire. When there is no particle deposition on the wire, the nanofluid increases critical heatflux (CHF) by about 50% within the uncertainty limits regardless of pH of the base fluid or particle size. The extent of oxidation on the wire impacts CHF and is influenced by the chemical composition of nanofluids in buffer solutions. The boiling regime is further extended to higher heatflux when there is agglomeration on the wire. This agglomeration allows high heat transfer through interagglomerate pores, resulting in a nearly threefold increase in burnout heatflux. This deposition occurs for the charged 10 nm silica particle. The chemical composition, oxidation, and packing of the particles within the deposition on the wire are shown to be the reasons for the extension of the boiling regime and the net enhancement of the burnout heat flux. Copyright © 2008 by ASME

Dispersion And Surface Characteristics Of Nanosilica Suspensions

Nanofluids consisting of nanometer-sized particles dispersed in base liquids are known to be effective in extending the saturated boiling regime and critical heat flux in pool boiling. The heat transfer characteristics of nanosilica suspensions with particle sizes of 10 and 20 nm in pool boiling with a suspended heating Nichrome wire have been analyzed. The pH value of the nanosuspensions is important from the point of view that it determines the stability of the particles and their mutual interactions toward the suspended heated wire. When silica is suspended in water with no additives, the surface potential of the nanoparticles determines their movement toward the electrodes. Particles continuously deposit on the wire and extend the burnout heat flux, influenced by the chemical composition of the nanofluids. This agglomeration allows high heat transfer through interagglomerate pores, resulting in a nearly threefold increase in burnout heat flux. Particle size, zeta potential, and the burnout heat flux values under different volume concentrations are provided. The burnout heat flux of the wire does not increase monotonically with concentration, but depends on the agglomeration characteristics, particle shape, and the hydroxylated surface of the nanoparticles. © 2009 New York Academy of Sciences

Functionalized Single Walled And Double Walled Carbon Nanotubes For Thermal Enhancement

Our investigation in this study focuses on the chemical and thermal characteristics of Single Walled Nanotubes (SWNTs) in comparison with Double Walled Nanotubes (DWNTs) for their potential to extend the heat flux in the boiling regime. SWNTs and DWNTs were successfully dispersed in an aqueous medium by reducing the surface tension, i.e. adsorption of anionic surfactant (NaDDBS). Two mechanisms of stabilization have been adopted: electrosteric and steric stabilization, and the suspensions were seen to be stable for longer periods. DWNTs have better heat transfer performance in the pool boiling experiment due to their unique structure. Functionalization and surfactant coating of SWNTs may reduce the heat flow because of modification of the structure. The burnout heat flux of the immersed Nichrome wire in water under pool boiling conditions was increased by up to 170% over that for the pure base liquid for DWNT nanofluid. In contrast, SWNT nanofluid enhanced burnout heat flux by 30%. The nature of the deposition on the heating element affects the surface wetting and therefore the pool boiling curve. DWNT coating on the wire is much thinner than SWNT coating; however, it is more porous and enhances CHF. Copyright © 2007 by ASME

Functionalized Single Walled And Double Walled Carbon Nanotubes For Thermal Enhancement

Our investigation in this study focuses on the chemical and thermal characteristics of Single Walled Nanotubes (SWNTs) in comparison with Double Walled Nanotubes (DWNTs) for their potential to extend the heat flux in the boiling regime. SWNTs and DWNTs were successfully dispersed in an aqueous medium by reducing the surface tension, i.e. adsorption of anionic surfactant (NaDDBS). Two mechanisms of stabilization have been adopted: electrosteric and steric stabilization, and the suspensions were seen to be stable for longer periods. DWNTs have better heat transfer performance in the pool boiling experiment due to their unique structure. Functionalization and surfactant coating of SWNTs may reduce the heat flow because of modification of the structure. The burnout heat flux of the immersed Nichrome wire in water under pool boiling conditions was increased by up to 170% over that for the pure base liquid for DWNT nanofluid. In contrast, SWNT nanofluid enhanced burnout heat flux by 30%. The nature of the deposition on the heating element affects the surface wetting and therefore the pool boiling curve. DWNT coating on the wire is much thinner than SWNT coating; however, it is more porous and enhances CHF

Role of ions in pool boiling heat transfer of pure and silica nanofluids

Heat transfer in silica nanofluids at different acidity and base is measured for various ionic concentrations in a pool boiling experiment. Nanosilica suspension increases the critical heat flux 3 times compared to conventional fluids. The 10-nm particles possess a thicker double diffuse layer compared to 20-nm particles. The catalytic properties of nanofluids decrease in the presence of salts, allowing the particles to cluster and minimize the potential increase in heat transfer. Nanofluids in a strong electrolyte, i.e., in high ionic concentration, allow a higher critical heat flux than in buffer solutions because of the difference in surface area. The formation and surface structure of the deposition affect the thermal properties of the liquid

Luminescence Properties of Gd₂(MoO₄)₃ Modified with Sm(III) and Tb(III) for Potential LED Applications

Light-emitting phosphors, doped with lanthanide ions of Tb(III) and Sm(III) of the type Gd1.97−y SmyTb0.03(MoO4)3 (y = 0.01–0.11, step 0.02) and Gd1.95−xSm0.05Tbx(MoO4)3 (x = 0.01–0.09, step 0.02), were synthesized and characterized by X-ray diffraction, UV-Vis spectroscopy, scanning and transmitting electron microscopy (SEM, TEM) as well as photoluminescence spectroscopy. The effect of the doping content of Tb/Sm was followed. The unit cell parameters for Gd1.97−ySmyTb0.03(MoO4)3 and Gd1.95−xSm0.05Tbx(MoO4)3 changed with the increase in the Tb/Sm content. The microstrain values also increased, proposing an increased concentration of defects. The mean particle size was estimated to be approximately 0.6 µm. Based on a Williamson–Hall plot, the size of the crystallites was determined to be in the range of 42–60 nm for modified and pure Gd2(MoO4)3 samples, respectively. The samples excited at 406 nm exhibited characteristic emission lines of Sm (485, 555, 646 nm). The host material Gd2(MoO4)3 emission in visible light was explained by the crystal structure defects, namely, oxygen vacancies. The CIE x/y color coordinates of the phosphors were determined and the related points were located in the green-yellow/pale yellow region of the visible light. The excited state lifetimes were determined for both groups of the samples, showing values in the millisecond range and indicating the samples as promising phosphors

Effect Of Surface Hydration And Interfusion Of Suspended Silica Nanoparticles On Heat Transfer

Experimental results of silica nanofluids consisting of 10nm or 20nm silica particles have been performed. Particle size, zeta potential and the CHF values under different volume concentrations are provided, and agglomeration structures are seen to affect the critical heat flux of NiChrome wire immersed in a pool of water. The critical heat flux (CHF) of the wire does not increase monotonically with concentration. CHF decreases when particle concentration is increased depending on the particle shape and the hydroxylated surface of the nanoparticles