Improving the heat transfer efficiency of synthetic oil with silica nanoparticles

The heat transfer properties of synthetic oil (Therminol 66) used for high temperature applications was improved by introducing 15 nm silicon dioxide nanoparticles. Stable suspensions of inorganic nanoparticles in the non-polar fluid were prepared using a cationic surfactant (benzalkonium chloride). The effects of nanoparticle and surfactant concentrations on thermo-physical properties (viscosity, thermal conductivity and total heat absorption) of these nanofluids were investigated in a wide temperature range. The surfactant-to-nanoparticle (SN) ratio was optimized for higher thermal conductivity and lower viscosity, which are both critical for the efficiency of heat transfer. The rheological behavior of SiO(2)/TH66 nanofluids was correlated to average agglomerate sizes, which were shown to vary with SN ratio and temperature. The conditions of ultrasonic treatment were studied and the temporary decrease of agglomerate size from an equilibrium size (characteristic to SN ratio) was demonstrated. The heat transfer efficiencies were estimated for the formulated nanofluids for both turbulent and laminar flow regimes and were compared to the performance of the base fluid.     

A note on the equation of heat transfer

Liquids with properties βpv/c_p ⪡ 1 and p²vκ/c_pT ⪡ 1 are defined as “incompressible liquids”. The compression work in motion of incompressible liquid is negligibly small. The change in the internal energy of incompressible liquids with respect to the temperature is, however, proportional to c_p. Motions of perfect gases in open systems under appropriate conditions and in closed systems with no net heat addition (or removal) are prescribed by the energy equation with c_p as the appropriate specific heat. Otherwise, either no reduction is possible or both c_p and c_v may become the appropriate specific heats in the energy equation.     

A simple variant of the Michaelis-Becker phase transfer reaction

Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, p. 1196, May, 1990.     

A new and simple method for sulfur nanoparticles synthesis

Sulfur nanoparticles were successfully synthesized via novel water-in-oil microemulsion system. The microemulsion system contained cyclohexane as an oil phase, Triton X-100 as a surfactant, butanol as a co-surfactant and sodium polysulfide solution or hydrochloric acid solution as aqueous phase, respectively. The sulfur nanoparticles were characterized by X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy and Fourier transform infrared spectroscopy. The results showed that the as-prepared monoclinic sulfur nanoparticles exhibited high purity and spherical shape with an average size of about 22 nm.     

A review on heat transfer characteristics of cryogenic heat pipes

Journal of Thermal Analysis and Calorimetry - Heat pipes are broadly applied for thermal management of devices with high heat flux. Due to the dependency of their efficient operating range on the...     

A numerical analysis of heat transfer in an evacuated flexible multilayer insulation material

In this article, the theoretical heat transfer of flexible multilayer insulation material which can be used in high (<433 K) and low temperature (>123 K) environments has been analyzed. A mathematical model has been developed to describe the heat flux through flexible multilayer insulation material, where the heat transfer consists of thermal radiation, solid spacers and gas heat transfer. The equations for heat transfer model have been solved by iterative method combining with dichotomy method using Matlab. Comparison between the experimental results and the calculated values which are obtained from the model shows that the model is feasible to be applied in practical estimation. The investigation on the flexible multilayer thermal insulation material will present active instruction to improve the performance and accomplish optimum design of the material.     

Atom transfer cyclization of simple hexenyl iodides. A caution on the use of alkenyl iodides as probes for the detection of single electron transfer processes

The trialkyltin initiated isomerization of 1-iodo-5-hexene to (iodomethyl)cyclopentane is reported. Rapid and reversible iodine atom transfer between alkyl radicals is the key chain transfer step. The results suggest an important caution in the use of hexenyl iodides as SET probes: a good mechanism exists whereby the yield of rearranged products may be much greater than the amount of radicals produced by the reaction under study!     

A simple urea-based route to ternary metal oxynitride nanoparticles

Ternary metal oxynitrides are generally prepared by heating the corresponding metal oxides with ammonia for long durations at high temperatures. In order to find a simple route that avoids use of gaseous ammonia, we have employed urea as the nitriding agent. In this method, ternary metal oxynitrides are obtained by heating the corresponding metal carbonates and transition metal oxides with excess urea. By this route, ternary metal oxynitrides of the formulae MTaO₂N (M=Ca, Sr or Ba), MNbO₂N (M=Sr or Ba), LaTiO₂N and SrMoO_3−xN_x have been prepared successfully. The oxynitrides so obtained were generally in the form of nanoparticles, and were characterized by various physical techniques.     

A study on the heat transfer geometry in MBDTA

This paper presents the quantitative application of the Metal Blocked Differential Thermal Analysis (MBDTA). Calibrations have been electrically carried out by using three types of calibration heaters (pen, ring and spiral), which are placed inside the sample. By means of this arrangement, thermophysical properties of the samples make the quantitative evaluation of the results easy. The influence of the size and sample diameter, the types of heater, the space between heater and thermocouple, in other words, the factors affecting calibration and the effect of the heat transfer geometry on the determination of the fusion heat have been investigated.

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Zusammenfassung Vorliegende Arbeit stellt eine quantitative Anwendung der Metallblock-DTA (MBDTA) dar. Es wurden elektrisch Kalibrationen mit verschiedenen, innerhalb der Probe befindlichen Kalibrationserhitzern (Stift, Ring, Spirale) durchgeführt. Mit Hilfe dieser Anordnung wird die Auswertung der Ergebnisse durch die thermophysischen Eigenschaften der Probe erleichtert. Es wurde der Einfluß von Größe und Probendurchmesser, von Erhitzertyp, von Abstand zwischen Erhitzer und Thermoelement, mit anderen Worten von denjenigen Faktoren, die die Kalibration beeinflussen sowie der Einfluß der Wärmetransportgeometrie auf die Bestimmung der Schmelzwärme untersucht.

     

A simple method for the evaluation of heat resistant property of elastomers

The paper shows a simple method that provides us the induction period, rate of weight increase at an earlier stage of thermal oxidation of elastomer and the rate of weight loss by oxidative degradation from a certain period of aging time. Ethylene-propylene elastomer (EPR) was aged in air at various constant temperatures ranged from 90 °C to 130 °C. The weight of samples was measured periodically at room temperature. The weight increased after a certain period of induction period at the early stage of aging. The activation energy obtained from the reciprocal of the induction period and that of the rate of weight increase was the same. The values were 113 kJ/mol. The weight started to decrease from the maximum point. The activation energy for the tangent of decrease curve was 60.3 kJ/mol. This method was applied to study the effect of pre-irradiation of EPR in air on the heat resistant property of the sample. The relatively low dose of 40 kGy decreased the induction period.     

Convective heat transfer performance of hybrid nanofluid in a horizontal pipe considering nanoparticles shapes effect

Journal of Thermal Analysis and Calorimetry - In the present paper, the first and second laws of thermodynamics are utilized to select the optimized position of porous insert to achieve maximum...     

A simple method to ordered mesoporous carbons containing nickel nanoparticles

A series of ordered mesoporous carbons containing magnetic Ni nanoparticles (Ni-OMCs) with a variety of Ni loadings was made by a simple one-pot synthetic procedure through carbonization of phenolic resin-Pluronic block copolymer composites containing various amount of nickel nitrate. Such composite materials were characterized by N₂ sorption, XRD, and STEM. Ni-OMCs exhibited high BET surface area, uniform pore size, and large pore volume without obvious pore blockage with a Ni loading as high as 15 wt%. Ni nanoparticles were crystalline with a face-center-cubic phase and observed mainly in the carbon matrix and on the outer surface as well. The average particle size of Ni nanoparticles was dependent on the preparation (carbonization) temperature and Ni loading; the higher the temperature was used and the more the Ni was incorporated, the larger the Ni nanoparticles were observed. One of the applications of Ni-OMCs was demonstrated as magnetically separable adsorbents. Dedicated to Professor Mietek Jaroniec on the occasion of his 60th birthday.     

A simple two-phase route to silver nanoparticles/polyaniline structures

Novel silver nanoparticles/polyaniline composites were obtained through a two-phase water/toluene interfacial reaction. We show that by rigorously controlling the reaction time, different structures of the nanocomposites can be obtained, such as a thin sheet of polyaniline around the silver nanoparticles or a polymer mass with nanoparticles homogeneously embedded within it. Samples were characterized by FT-IR, UV-vis-NIR and Raman spectroscopy, X-ray diffraction, cyclic voltammetry, TEM, and HRTEM. Conductivity and current-voltage characteristics of the nanocomposites were measured, and the results indicate that different properties result from the different structures in which the nanocomposites were formed.     

Evaluating energy efficiency and economic effect of heat transfer in copper tube for small solar linear Fresnel reflector

Journal of Thermal Analysis and Calorimetry - An experimental and numerical investigation of a small linear Fresnel for water heating application has been carried out in Blida, Algeria. The...     

Nonlinear analysis of heat transfer in an insulator application to NaBr

Using nonlinear heat transfer theory and following Kazakov and Nagaev, a simple expression for the lattice thermal conductivity has been derived for an insulator having resonance-producing impurities. The expression obtained has been used to analyse the lattice thermal conductivity of pure and doped samples of NaBr in the entire temperature range 0.05-5 K. Good agreement has been found between the calculated and experimental values of phonon conductivity at low temperatures.

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Zusammenfassung An Hand der nicht linearen Wärmeübertragungstheorie, sowie nach Kazakow und Nagaew wurde ein einfacher Ausdruck für die thermische Gitterleitfähigkeit für ein Isolator mit resonanzbildenen Verunreinigungen abgeleitet. Der erhaltene Ausdruck wurde zur Analyse der Gitter-Wärmeleitfähigkeit reiner und Zusatzstoffe enthaltender NaBr-Proben im ganzen Temperaturbereich von 0.05 bis 5 K eingesetzt. Eine gute Übereinstimmung der berechneten und Versuchswerte der Phononleitfähigkeit wurde bei niedrigen Temperaturen erhalten.

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Résumé En se servant de la théorie du transfert de chaleur non-linéaire et suivant Kazakov et Nagaev, on a trouvé une expression simple pour la conductibilité thermique du réseau dans le cas d'un isolant à impuretés produisant la résonance. L'expression obtenue a été utilisée pour analyser la conductibilité thermique du réseau d'échantillons de NaBr purs ou contenant des additifs, dans tout l'intervalle de température allant de 0.05 à 5 K. Un bon accord a été observé entre les valeurs expérimentales et calculées de la conductibilité des phonons aux basses températures.

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, , - . 0.05–5 . .

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Part of the thesis to be submitted for the requirement of the M. Sc. degree in Physics by H. H. B.

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The authors wish to express their thanks to Dr. R. H. Misho and Dr. R. A. Rashid for their interest in the present project.     

Parametric analysis of direct contact sensible heat transfer in spray columns

The present investigation deals with a theoretical analysis of direct contact sensible heat transfer between two immiscible liquids in a countercurrent spray column. The non-dimensional parameters governing the heat transfer process are identified and a study of the effects of the variation of these parameters is made. The predicted column heights and the temperature profiles of both the phases along the column compare favourably with the available experimental data.     

A simple visual method for DNA detection based on the formation of gold nanoparticles

A simple visual method for DNA detection during the formation of gold nanoparticles (AuNPs) was developed based on different electrostatic properties of single strand DNA (ssDNA) and double strand DNA (dsDNA). Since the ssDNA is easy to bind to AuNPs due to its exposed bases which could prevent salt-induced aggregation of AuNPs. The dsDNA always present negative charge because its negatively charged phosphate backbone is exposed. In this case, the dsDNA could disturb the adsorption between dsDNA and AuNPs and result in non-aggregation of AuNPs. After hybridization, chloroauric acid and ascorbic acid were added to the mixture solution, and the solution changed to red immediately and turned to purple in 10 min in the present of target DNA. TEM results confirmed that the change of color stemed from aggregation of AuNPs. In order to obtain accurate results by naked eye, the DNA detection assay should be conducted under pH 7.0.     

Effect of conjugate heat transfer on the thermo-electro-hydrodynamics of nanofluids: entropy optimization analysis

Journal of Thermal Analysis and Calorimetry - We investigate, in this analysis, the entropy generation characteristics associated with the transport of nanofluid in a microfluidic channel under the...     

A simple visual method for DNA detection based on the formation of gold nanoparticles

A simple visual method for DNA detection during the formation of gold nanoparticles (AuNPs) was developed based on different electrostatic properties of single strand DNA (ssDNA) and double strand DNA (dsDNA). It could identify target DNA in 10 min.