Comparison of different conductivity detector geometries on an isotachophoresis PMMA-microchip

Conductivity detection is one of the most often employed means of detection in isotachophoresis. In microanalytical devices, thin-film platinum electrodes can be used for conductivity detection and for other electrochemical methods of detection. The design and the performance of different electrode geometries for on-column contact conductivity detection with thin-film platinum electrodes integrated on an isotachophoresis PMMA-microchip is described. Three different electrode geometries for direct conductivity detection were used for the investigation of isotachophoretic separations. The influence of the width of the electrodes and their positioning relative to the separation channel was investigated. The performance of the different detectors is compared for the analysis of organic carboxylic acid anions.     

Development of a thermal conductivity cell with nanolayer coating for thermal conductivity measurement of fluids

Various techniques and methodologies of thermal conductivity measurement have been based on the determination of the rate of directional heat flow through a material having a unit temperature differential between its opposing faces. The constancy of the rate depends on the material density, its thermal resistance and the heat flow path itself. The last of these variables contributes most significantly to the true value of steady-state axial and radial heat dissipation depending on the magnitude of transient thermal diffusivity along these directions. The transient hot-wire technique is broadly used for absolute measurements of the thermal conductivity of fluids. Refinement of this method has resulted in a capability for accurate and simultaneous measurement of both thermal conductivity and thermal diffusivity together with the determination of the specific heat. However, these measurements, especially those for the thermal diffusivity, may be significantly influenced by fluid radiation. Recently developed corrections have been used to examine this assumption and rectify the influence of even weak fluid radiation. A thermal conductivity cell for measurement of the thermal properties of electrically conducting fluids has been developed and discussed.     

Role of the Debye temperature in the lattice thermal conductivity of silicon

This paper is a theoretical study of the effect of the variation in the Debye temperature _D with temperature on the lattice thermal conductivity of Si in the temperature range 2–300 K. Expressions for the three-phonon scattering relaxation rates previously proposed by Shermaet al. are used here. The percentage changes in the lattice thermal conductivity due to the Debye temperature for the transverse and the longitudinal phonons are studied separately.

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Zusammenfassung Dieses Manuskript ist eine theoretische Untersuchung des Einflusses der Veränderung der Debey-Temperatur D mit der Temperatur auf die Gitterwärmeleitfähigkeit von Si im Temperaturbereich 2–300 K. Unlängst von Shermaet al. vorgeschlagene Ausdrücke für die drei Phononen-Streuungsrelaxations-Geschwindigkeiten fanden dabei Anwendung. Die prozentuelle Änderung der Gitterwärmeleitfähigkeit in Abhängigkeit von der Debey-Temperatur wurde für transversale als auch für longitudinale Phononen separat untersucht.

     

A thermal conductivity model for two phase media

A model is proposed for the calculation of effective thermal conductivity of two phase media with a single continuous phase. This model has been shown to satisfy the limiting conditions and also to correlate the experimental data well. Though this model is based on the Ohm's law, it is in very good agreement with rigorously derived results based on the Fourier law.     

Model for thermal conductivity of composites with carbon nanotubes

This paper presents a model for evaluation of effective thermal conductivity for the composites with carbon nanotubes (CNT) having log-normal function of distribution of CNT, with direct effect over depolarization factor. The CNT are considered having cylindrical shape with L/d ratio very high. The model parameters are calculated in function of the data from literature. The influence of volume fraction of reinforced materials, of the aspect ratio of the particles included and of the ratio of the two thermal conductivities is presented.     

A new semi-analytical model for effective thermal conductivity of nanofluids

A new theoretical model for thermal conductivity of nanofluids is developed incorporating effective medium theory, interfacial layer, particle aggregation and Brownian motion-induced convection from multiple nanoparticles/aggregates. The predicated result using aggregate size, which represents the particle size in the actual condition of nanofluids, fits well with the experimental data for water-, R113- and ethylene glycol (EG)-based nanofluids. The present model also gives much better predictions compared to the existing models. A parametric analysis, particularly particle aggregation, is conducted to investigate the dependence of effective thermal conductivity of nanofluids on the properties of nanoparticles and fluid. Aggregation is the main factor responsible for thermal conductivity enhancement. The dynamic contribution of Brownian motion on thermal conductivity enhancement is surpassed by that of static mechanisms, particularly at high volume fraction. Predication also indicated that the viscosity increases faster than the thermal conductivity, causing the highly aggregated nanofluids to become unfavourable, especially for d_f = 1.8.     

A new equation for the thermal conductivity of organic compounds

This work presents a wide literature survey of the available data of the experimental thermal conductivity data of organic liquids. The experimental data were collected for 136 compounds belonging to the following families: refrigerants, alkanes, alkenes, aromatics, cycloalkanes, cycloalkenes, ethers, esters, ketones, carboxylic acids, and alcohols. The experimental data were regressed with the most reliable semi-empirical correlating methods existing in the literature and a reliable set of 4,584 experimental data was finally selected. The influence of several physical parameters on the thermal conductivity calculation is discussed and a new equation to represent the thermal conductivity of organic liquids at atmospheric pressure for temperatures below normal boiling point and at saturation for temperatures above the normal boiling point is presented. To minimize the deviation between the predictions and the experimental data and to find the optimal coefficients for the proposed equation, a statistical analysis was performed. The resulting equation is simple and is able to predict the thermal conductivities with low deviations for the major part of the collected data for the studied families.     

A simple solution route to single-crystalline Sb2O3 nanowires with rectangular cross sections

We report a simple solution route to large-scale synthesis of uniform, single-crystalline, and well-faceted orthorhombic antimony trioxide (Sb(2)O(3)) nanowires with rectangular cross sections by direct air oxidation of bulk metal antimony (Sb) in a mixed solution made of ethylenediamine (EDA) and deionized water (DIW). The as-synthesized products were analyzed by range of methods, such as XRD, SEM, EDX, TEM, SAED, HRTEM, FTIR, Raman, UV-vis absorption, and photoluminescence (PL) spectra. The as-synthesized Sb(2)O(3) nanowires with rectangular cross sections are usually hundreds of micrometers in length, typically 80-100 nm in width, and 60-80 nm in thickness. The novel room temperature photoluminescence properties of Sb(2)O(3) nanowires with rectangular cross sections displayed a significant UV luminescence with a strong emission band at 374 nm, which was reported for the first time, indicating the as-synthesized products with an optical band gap E(g) = 3.3 eV. It is expected that as-synthesized Sb(2)O(3) nanowires would be a new member of functional materials and used in the manufacture of advanced nanodevices.     

Intercomparison of thermal conductivity and thermal diffusivity methods for plastics

An intercomparison of measurements of the thermal conductivity and thermal diffusivity of two poly(methyl methacrylates) is reported. A wide variety of methods were used: temperature wave analysis, laser flash, transient plane source (Hot Disk^®), transient line-source probe, and heat flux meter methods. Very good agreement of thermal conductivity results and, separately, of thermal diffusivity results was obtained. Similarly, good agreement between thermal conductivity and thermal diffusivity results, when converted using specific heat capacity and density values, was also obtained. Typically, the values were within a range of approximately ±10%. Considering the significant differences between the methods and the requirements on specimen dimensions, the level of agreement between results was considered to be good.     

Combustion analysis of biodiesel blends with different piston geometries

Journal of Thermal Analysis and Calorimetry - Shallow reentrant piston (SRP) and deep cylindrical piston (DCP) geometries were designed by modifying the compression ratio of an engine with baseline...     

A binary array method for calculating thermal conductivity of porous materials

The present research on thermal conductivity of porous materials is hampered by their highly random internal structure. Until now, the researches could not describe internal structure of porous materials, but macro calculation expressions were established. In order to solve the above problem, this paper presents a method of calculation that applies a binary array. This method can describe the internal structure of porous materials, reflects its randomness, and calculates the thermal conductivity of porous materials. The technique selects large enough porous material models and divides them in small enough grids. Each grid needs a binary conversion process to determine if the grid is matrix or pore. Finally, a grid array composed of matrix and pore is established. Based on this grid array, this study sets the initial and boundary conditions, and then calculates the thermal conductivity of porous materials by a numerical calculation according to internal heat-transfer mechanism. This research adopts the described method to calculate the thermal conductivity of porous aluminum. The result is consistent with that of the experimental measurement, thereby verifying the accuracy and reliability of this method.     

A multiparameter thermal conductivity equation for R134a with an optimized functional form

A new multiparameter equation λ = λ(T, ρ) for the thermal conductivity of R134a has been developed from the available experimental data using a technique for the optimization of the functional form. The equation is valid in the temperature range from 200 to 540 K and for pressure up to 70 MPa, including also the near-critical region. The satisfactory performances of the equation are summarized by an average absolute deviation of 2.04% for the selected 5102 primary data points, with a significant improvement with respect to the present reference equation from the literature.The conversion of the independent variables of the experimental data into those of the equation, i.e. (T, P) into (T, ρ), is performed with a high accuracy equation of state for the fluid.     

Enhanced growth of crystalline-amorphous core-shell silicon nanowires by catalytic thermal CVD using in situ generated tin catalyst

In this work,we prepared silicon nanowires(Si NWs) on both fluorine-doped SnO 2(FTO) coated glass substrate and common glass substrate by catalytic thermal chemical vapor deposition(CVD) using indium film as the catalyst.It is confirmed that indium can catalyze the growth of Si NWs.More importantly,we found that tin generated in situ from the reduction of SnO 2 by indium can act as catalyst,which greatly enhances the growth of Si NWs on FTO substrate.The obtained Si NWs have a uniform crystalline-amorphous core-shell structure that is formed via vapor-liquid-solid and vapor-solid growth of silicon sequentially.This work provides a strategy to prepare Si NWs in high yield by catalytic thermal CVD using the low melting point metal catalysts.     

Effect of empty spaces on the lattice thermal conductivity of polyethylene with different degrees of crystallinity

A study is presented of the effect of empty space scattering in the estimation of the lattice thermal conductivity of four samples of polyethylene with different degrees of crystallinity at temperatures between 0.4 and 20 K. This study was performed by considering different values of the empty space fraction. It is found that empty space scattering plays a very important role in the calculation of the lattice thermal conductivity of semicrystalline polymers.     

A universal strategy for fast,scalable, and aqueous synthesis of multicomponent palladium alloy ultrathin nanowires

Noble metal alloy nanowires(NWs)with ultrathin diameters(2–3 nm)and precisely controllable elemental compositions have attracted dramatically growing attention for(electro)catalysis.Despites numerous achievements in past two decades,noble metal alloy NWs are mostly synthesized with the traditional oil-phase methods that suffer from some undesirable drawbacks.Here,we report a general strategy for fast,scalable,and aqueous synthesis of multicomponent Pd-based alloy ultrathin NWs with an average diameter of 2.6 nm,ranging from bimetallic PdM(PdFe,PdCo,PdNi,PdCu,PdZn,PdRu,PdRh,PdAg,PdCd,PdIr,PdPt,PdAu)and binary PdS/PdP NWs,to trimetallic PdM1M2 NWs(PdAuCu,PdCoNi,PdCuZn,PdCuNi,PdAgCu,PdAuCu,PdRuAg,PdAuRu,and PdPtAu),and to tetrametallic PdM1M2M3 NWs(PdAuAgCu,PdCoCuNi,PdAuCuNi,PdPtAuCu,and PdIrPtAu).The key to the success of this aqueous synthesis is the utilization of N2H4 as the extremely strong reducing agent that directs the synchronous reduction and anisotropic nucleation growth of multicomponent Pd alloy NWs along nanoconfined columnar phase assembled with amphiphilic dioctadecyldimethylammonium chloride.As-resultant Pd-based alloy ultrathin NWs exhibit multiple structural and compositional synergies,which remarkably optimize the removal of poisoning ethoxy intermediates and thus improve electrocatalytic performance towards ethanol oxidation reaction(EOR).Among them,tetrametallic PdAuCuNi alloy ultrathin NWs hold a high EOR activity of 5.14 A mg-1 Pd and a low activation energy of 13.1 kJ mol^-1,both of which are much better than its counterpart catalysts alloyed with less elements.This work represents an important advance in precise aqueous synthesis of multicomponent noble metal alloy ultrathin NWs as the high-performance electrocatalysts for various targeted applications.     

Evaluation of different tubing geometries for high-speed counter-current chromatography

Different tubing geometries were evaluated for use in high-speed counter-current chromatography. Standard round tubing was compared to rectangular and twisted rectangular tubing. The number of theoretical plates for a standard anthocyanin mixture from black currant was determined for each experiment. The results of twisted rectangular tubing were superior to a standard setup.     

Applying different types of artificial neural network for modeling thermal conductivity of nanofluids containing silica particles

Journal of Thermal Analysis and Calorimetry - Nanofluids are widely applicable in thermal devices with porous structures. Silica nanoparticles have been dispersed in different heat transfer fluids...