An analysis of turbulent free convection about bodies of arbitrary geometrical configurations

A general solution method is suggested for the prediction of the turbulent free convection heat transfer from curved surfaces. The method which may be viewed as a generalized version of the Eckert-Jackson method for the isothermal plate, is designed to deal with bodies of arbitrary geometrical configurations. The surface wall temperature is also allowed to vary in the streamwise direction in an arbitrary fashion. For the illustrative purpose, the calculations are carried out for the turbulent free convection about the horizontal circular cylinder, and the results are compared with the existing empirical formula. The flow transition from laminar to turbulent is also predicted by matching the laminar and turbulent solutions.     

Dependence of sonochemical luminescence on various sound fields

To understand the effect of the sound field on sonochemical luminescence, the exact sound pressure must be determined in each field. In this study it was determined by the Shlieren method, which measures the sound pressure without mixing the sound fields. We compared the efficiency of the sonochemical luminescence in three different ways: changing the diameter of the transducer, combining two transducers to obtain crossed propagating directions and surrounding the sound field by a glass cylinder. In the last case cylinders with various sizes were studied. We found that (i) at the same sound pressure, the larger transducer induces stronger luminescence per unit volume, (ii) driving two transducers produces stronger luminescence than the sum of each transducer and (iii) a glass cylinder surrounding the sound field induces stronger luminescence.     

An arrayed-window microfluidic device for observation of mixed nanoparticles with an X-ray free-electron laser

Optical Review - A microfluidic device was developed for coherent diffraction imaging using an X-ray free-electron laser (XFEL-CDI). Liquid samples, which are separately packed in reservoirs of the...     

Chiral magnetic soliton lattice on a chiral helimagnet

Using Lorenz microscopy and small-angle electron diffraction, we directly present that the chiral magnetic soliton lattice (CSL) continuously evolves from a chiral helimagnetic structure in small magnetic fields in Cr(1/3)NbS2. An incommensurate CSL undergoes a phase transition to a commensurate ferromagnetic state at the critical field strength. The period of a CSL, which exerts an effective potential for itinerant spins, is tuned by simply changing the field strength. Chiral magnetic orders observed do not exhibit any structural dislocation, indicating their high stability and robustness in Cr(1/3)NbS2.     

Study on thermal stability of tertiary pyridine resin

The fundamental properties of tertiary pyridine resin (TPR) and its mixtures with methanol/HCl and HNO₃ were investigated in order to evaluate the thermal stability of TPR and to determine the conditions necessary to avoid runaway reactions. Based on experimental DSC results, it was found that TPR with HCl was thermally stable, but strong decomposition was possible with TPR in the presence of HNO₃. From the results of heating tests on the gram scale, TPR with HNO₃ reacted violently under high temperature regardless of HNO₃ concentration and presence or absence of methanol. However, it was considered that the violent exothermic reaction could be controlled by heating temperature.     

Rheology of SiO2/(acrylic polymer/epoxy) suspensions. I. Linear viscoelasticity

Linear viscoelastic properties of SiO₂/(AP/EP) suspension with various SiO₂ volume fractions (ϕ) in a blend of acrylic polymer (AP) and epoxy (EP) were investigated at various temperatures (T). The AP/EP contained 70 vol.% of EP. The SiO₂ particles were treated with epoxy silane coupling agent. The effects of the SiO₂ particles are more pronounced in the terminal zone: a transition from viscoelastic liquid (ϕ ≤ 30 vol.%) to viscoelastic solid (ϕ ≥ 40 vol.%) was observed which can be interpreted as a critical gelation occurring at a critical particle content and critical gel temperature. The SiO₂/(AP/EP) systems exhibited a critical gel behavior at ϕ ≅ 35 vol.% and T ≅ 100°C characterized with a power–law relationship between the storage and loss moduli (G ^′ and G ^″) and frequency (ω); G ^′ = G ^″/tan(nπ/2) ∝ ω ⁿ . The critical gel exponent (n) was estimated to be about 0.45. The gelation occurred with increasing T.     

Transient non-Darcy free convection between parallel vertical plates in a fluid saturated porous medium

Transient non-Darcy free convection between two parallel vertical plates in a fluid saturated porous medium is investigated using the generalized momentum equation proposed by Vafai and Tien. The effects of porous inertia and solid boundary are considered in addition to the Darcy flow resistance. Exact solutions are found for the asymptotic states at small and large times. The large time solutions reveal that the velocity profiles are rather sensitive to the Darcy number Da when Da<1. It has also been found that boundary friction alters the velocity distribution near the wall, considerably. Finite difference calculations have also been carried out to investigate the transient behaviour at the intermediate times in which no similarity solutions are possible. This analytical and numerical study reveals that the transient free convection between the parallel plates may well be described by matching the two distinct asymptotic solutions obtained at small and large times.Nomenclature C empirical constant for the Forchheimer term - f velocity function for the small time solution - F velocity function for the large time solution - g acceleration due to gravity - Gr* micro-scale Grashof number - H a half distance between two infinite plates - K permeability - Nu Nusselt number - Pr Prandtl number - t time - T temperature - u, v Darcian velocity components - x, y Cartesian coordinates - effective thermal diffusivity - coefficient of thermal expansion - porosity - dimensionless time - similarity variable - dimensionless temperature - viscosity - kinematic viscosity - density - the ratio of heat capacities     

Modeling strain hardening of polydisperse polystyrene melts by molecular stress function theory

The strain hardening of blends of polystyrene (PS) and ultra-high molecular weight polystyrene (UHMW-PS) in elongational flow is modeled by the molecular stress function (MSF) theory. Assuming that the ratios of strain energies stored in polydisperse and monodisperse polymers are identical for linear and nonlinear deformations, the value of the only non-linear parameter of the theory in extensional flows, the maximum molecular stress f_max, can be determined and is shown to be related to steady-state compliance J_e0. Using only linear-viscoelastic data, the elongational viscosity of PS/UHMW-PS blends is consistently predicted by the MSF theory.