Thermal conductance of nanofluids: is the controversy over?

Over the last decade nanofluids (colloidal suspensions of solid nanoparticles) sparked excitement as well as controversy. In particular, a number of researches reported dramatic increases of thermal conductivity with small nanoparticle loading, while others showed moderate increases consistent with the effective medium theories on well-dispersed conductive spheres. Accordingly, the mechanism of thermal conductivity enhancement is a hotly debated topic. We present a critical analysis of the experimental data in terms of the potential mechanisms and show that, by accounting for linear particle aggregation, the well established effective medium theories for composite materials are capable of explaining the vast majority of the reported data without resorting to novel mechanisms such as Brownian motion induced nanoconvection, liquid layering at the interface, or near-field radiation. However, particle aggregation required to significantly enhance thermal conductivity, also increases fluid viscosity rendering the benefit of nanofluids to flow based cooling applications questionable.     

Isotope-dependent crystalline phases at ambient temperature: Spectroscopic and calorimetric evidence for a deuteration-induced phase transition at 320 K in α-DCrO2

The heat capacities of HCrO₂ and DCrO₂ have been measured at temperatures between 5 and 360 K. A lambda anomaly occurred at 320 K for DCrO₂ but not for HCrO₂. Infrared spectra were recorded at temperatures between 5 and 405 K. The spectrum of DCrO₂ changed at 320 K with respect to the peak wave-number and splitting of some of the vibrations, while those of HCrO₂ depended smoothly on temperature. These experimental results are discussed in terms of a deuteration-induced phase transition.     

Time-dependent heat capacity of water-lysozyme solution

Summary We report here the first observation of the time-dependent heat capacity of water-lysozyme solution. The observed increase of heat capacity in time occurs independently of the lysozyme concentration and thepH value of the solvent. The time necessary to attain the heat capacity equilibrium value and the amplitude of the effect are not well reproducible; the former tends to increase with temperature, while the amplitude decreases and practically disappears about 35°C. Evolution of a spatial order of the proteins in water and/or of water molecules interacting with the proteins is considered as a possible explanation for the results. The phenomenon promises to be an important tool to study the role of water in biological organization and activity.     

The integral mean diffusivity for particle-gas mass transfer calculations under thermal plasma conditions

Plasma Chemistry and Plasma Processing - A new integral mean diffusivity is proposed for the calculation of the mass transfer rate around a small particle immersed in a thermal plasma gas....     

Synthesis of Heterocyclic Ring Systems for Heat-Resistant Plastics from Polyisocyanates

Investigations on space flight and rockets carried out in particular in the United States have aroused great interest in plastics with enhanced thermal stability. It has become possible to pass far beyond the expected limits of thermal stability with organic plastics, and to synthesize plastics and polymers that can be used at temperatures between about 200 and about 500 °C, a range that formerly appeared to be the exclusive province of inorganic materials.     

Heats of displacement of hydrogen from palladium by noble gases

It has been observed that noble gases, such as helium, neon and argon produce heat evolution when contacted with Pd powder partially saturated with hydrogen. These phenomena have been studied with flow-through adsorption microcalorimetry. The observed exothermic effects are comparable to those usually associated with the heat of sorption of hydrogen in palladium. It is suggested that the noble gases displace the adsorbed H species from the surface of Pd, causing their reabsorption in the Pd lattice with the exothermic heat of PdH bonds formation, or the formation of H₂, both heat evolutions being observed with a flow-through microcalorimeter.     

Development of an optical trap for microparticle clouds in dilute gases

Long-duration experiments with clouds of microparticles are planned for the ICAPS facility on board the International Space Station ISS. The scientific objectives of such experiments are widespread and are ranging from the simulation of aerosol behaviour in Earths atmosphere to the formation of planets in the early solar system. It is, however, even under microgravity conditions, impossible to sustain a cloud of free-floating, microscopic particles for an extended period of time, due to thermal diffusion and due to unavoidable external accelerations. Therefore, a trap for dust clouds is required which prevents the diffusion of the particles, which provides a source of relative velocities between the dust grains and which can also concentrate the dust to higher number densities that are otherwise not achievable. We are planning to use the photophoretic effect for such a particle trap. First short-duration microgravity experiments on the photophoretic motion of microscopic particles show that such an optical particle-cloud trap is feasible. First tests of a two-dimensional trap were performed in the Bremen drop tower.     

Smooth solutions to a class of free boundary parabolic problems

We establish existence, uniqueness, and regularity results for solutions to a class of free boundary parabolic problems, including the free boundary heat equation which arises in the so-called ``focusing problem' in the mathematical theory of combustion. Such solutions are proved to be smooth with respect to time for positive , if the data are smooth.

     

Solubility of Lanthanide Chlorides ( Ln Cl3) in Alkali Metal Chlorides ( M Cl): Thermodynamics and Electrical Conductivity of the M 3 Ln Cl6 Compounds

Summary.  Several compounds may exist in LnCl₃–MCl mixtures. Those corresponding to the M ₂ LnCl₅ and MLn ₂Cl₇ stoichiometries are formed in a few systems only, with diverse stability strongly dependent on both the corresponding lanthanide and alkali metal. On the other hand, M ₃ LnCl₆ that occur in most systems have a far larger stability range and melt congruently. These latter compounds were investigated in the present work by differential scanning calorimetry and electrical conductivity measurements. The thermodynamic and transport properties were correlated to structural features and related to the mechanism of compound formation. Corresponding author. E-mail: Marcelle.Gaune-Escard@polytech.univ-mrs.fr Received October 2, 2002; accepted November 6, 2002 Published online April 24, 2003 RID="a" ID="a" This paper is dedicated to Professor H. Gamsj?ger on the occasion of his birthday     

On the nonexistence of finite time bubble trees in symmetric harmonic map heat flows from the disk to the 2-sphere

Let and be the unit disk and the unit sphere, and let be a radially symmetric harmonic map heat flow, whose singularities coincide with downward energy jumps. Then its finite time singularities are simple in the sense that precisely one harmonic sphere separates at a time.