Tube diameter effect on deflagration-to-detonation transition of propane–oxygen mixtures

An experimental study was conducted to study the tube diameter effect on deflagration- to-detonation run-up distance. The tube diameter effect is associated with the amplification factor, flame acceleration and heat loss. A simplified correlation of the run-up distance and tube diameter is proposed for the fuel-lean, stoichiometric and slight fuel-rich mixtures. The amplification factor, which is evaluated from the initial conditions of the propane–oxygen mixtures, might also be used to get a quick estimation of the run-up distance in tubes of larger diameter.

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Michrochip chromatography using an open‐tubular microchannel and a ternary water–ACN–ethyl acetate mixture carrier solution

A capillary chromatography system has been developed using a ternary mixed‐solvents solution, i.e. water–hydrophilic/hydrophobic organic solvent mixture as a carrier solution. Here, we tried to carry out the chromatographic system on a microchip incorporating the open‐tubular microchannels. A model analyte solution of isoluminol isothiocyanate (ILITC) and ILITC‐labeled biomolecule was injected to the double T‐junction part on the microchip. The analyte solution was delivered in the separation microchannel (40 μm deep, 100 μm wide, and 22 cm long) with the ternary water–ACN–ethyl acetate mixture carrier solution (3:8:4 volume ratio, the organic solvent rich or 15:3:2 volume ratio, the water‐rich). The analyte, free‐ILITC and labeled BSA mixture, was separated through the microchannel, where the carrier solvents were radially distributed in the separation channel generating inner and outer phases. The outer phase acts as a pseudo‐stationary phase under laminar flow conditions in the system. The ILITC and the labeled BSA were eluted and detected with chemiluminescence reaction.     

Asymptotic analysis of the non-linear behavior of long anisotropic tubes

An asymptotically correct beam model is obtained for a long, thin-walled, circular tube with circumferentially uniform stiffness (CUS) and made of generally anisotropic materials. By virtue of its special geometry certain small parameters cause unusual non-linear phenomena, such as the Brazier effect, to be exhibited. The model is constructed without ad hoc approximations from 3D elasticity by deriving its strain energy functional in terms of generalized 1D strains corresponding to extension, bending, and torsion. Large displacement and rotation are allowed but strain is assumed to be small. Closed-form expressions are provided for the 3D non-linear warping and stress fields, the 1D non-linear stiffness matrix and the bending moment–curvature relationship. In bending, failure could be caused by limit-moment instability, local buckling or material failure of a ply. A procedure to determine the failure load is provided based on the non-linear response, neglecting micro-mechanical failure modes, post-failure behavior, and hygrothermal effects. Asymptotic considerations lead to the neglect of local shell interlaminar and transverse shear stresses for the thin-walled configuration. Results of the theory are illustrated for a few symmetric, antisymmetric angle-ply and unsymmetric layups and show that some previously published theories are not asymptotically correct.     

Experimental and numerical investigation of turbulent cross-flow in a staggered tube bundle

This paper presents the results of measurements and numerical predictions of turbulent cross-flow in a staggered tube bundle. The bundle consists of transverse and longitudinal pitch-to-diameter ratios of 3.8 and 2.1, respectively. The experiments were conducted using a particle image velocimetry technique, in a flow of water in a channel at a Reynolds number of 9300 based on the inlet velocity and the tube diameter. A commercial CFD code, ANSYS CFX V10.0, is used to predict the turbulent flow in the bundle. The steady and isothermal Reynolds–Averaged Navier–Stokes (RANS) equations were used to predict the turbulent flow using each of the following four turbulence models: a k-epsilon, a standard k-omega, a k-omega-based shear stress transport, and an epsilon-based second moment closure. The epsilon-based models used a scalable wall function and the omega-based models used a wall treatment that switches automatically between low-Reynolds and standard wall function formulations.

The experimental results revealed extremely high levels of turbulence production by the normal stresses, as well as regions of negative turbulence production. The convective transport by mean flow and turbulent diffusion were observed to be significantly higher than in classical turbulent boundary layers. As a result, turbulence production is generally not in equilibrium with its dissipation rate. In spite of these characteristics, it was observed that the Reynolds normal stresses approximated from the k-based two-equation models were in a closer agreement with experiments than values obtained from the second moment closure. The results show that none of the turbulence models was able to consistently reproduce the mean and turbulent quantities reasonably well. The omega-based models predicted the mean velocities better in the developing region while the epsilon-based models gave better results in the region where the flow is becoming spatially periodic.     

Capillary chromatography based on tube radial distribution of aqueous-organic mixture carrier solvents

A capillary chromatography system was developed using open capillary tubes made of fused-silica, polyethylene, or poly(tetrafluoroethylene), and an aqueous-organic mixture (water-acetonitrile-ethyl acetate mixture) as a carrier solution. Model analyte mixture solutions, such as 2,6-naphthalenedisulfonic acid and 1-naphthol, Eosin Y and perylene, bis[N,N-bis(carboxymethyl)aminomethyl]fluorescein and 1,1’-bi-2-naphthol, and 2,7-naphthalenedisulfonic acid and p-nitroaniline, were injected into the capillary tube by a gravity method. The analyte solutions were subsequently delivered through the capillary tube with the carrier solution by a micro-syringe pump. The system worked under laminar flow conditions. The analytes were separated through the capillary tube and detected on-capillary by an absorption detector. For example, 2,6-naphthalenedisulfonic acid and 1-naphthol were detected in this order with a carrier solution of water-acetonitrile-ethyl acetate (volume ratio 15:3:2), while they were detected in the reverse order with a carrier solution of water-acetonitrile-ethyl acetate (volume ratio 2:9:4). The other analyte solutions were similarly separated by the system. The elution times of the analytes could be easily reversed by changing the component ratio of the solvents in the carrier solution.     

A mesoscopic tube model of polymer/layered silicate nanocomposites

Rheology of isothermal suspensions of completely exfoliated silicate lamellae in polymer melts is investigated. In order to express more faithfully the physics involved in low shear rates and low frequencies, we model the polymer molecules composing the melt as chains whose motion is confined to a tube formed by surrounding chains and lamellae. In the absence of lamellae, the model reduces to the mesoscopic model of reptating chains developed in Eslami and Grmela (Rheol Acta, 2008). If the chains are seen only as FENE-P dumbbells, the model reduces to the model developed in Eslami et al. (J Rheol 51:1189–1222, 2007). Responses to oscillatory, transient, and steady shear flows are calculated and compared with available experimental data. Particular attention is payed to the region of low shear rate and low frequency.     

Behaviour of a simple crystallisation model in tube and channel flow

A formulation describing the rheology of crystallising polymers is discussed. For some semi-crystalline polymers where spherulites form as part of the crystallisation process, the use of a suspension-type model is appropriate. Whilst it is possible to so describe simple shearing and elongational rheology during on-going crystallisation with such models, the flow through a capillary tube is much more complex and numerical solution is usually necessary. To give some insight into this complex flow, a ‘step function’ or ‘amorphous-frozen’ model of the viscosity changes due to crystallisation has been devised so that a semi-analytical approach is feasible. We use this simple model and compare the results with recently published experiments in tubes and channels at high (O(10³ s^− 1)) shear rates using poly(butene-1). A direct correlation between simple shear and tube flow crystallisation onset times is found.     

Optimal arrangement of structural and functional parts in a flat plate integrated collector storage solar water heater (ICSSWH)

Parameters that affect the efficiency of a flat plate integrated collector storage solar water heater (ICSSWH) are examined experimentally and numerically. This specific ICSSWH contains water that is not refreshed. The service water is heated indirectly through an immersed heat exchanger (HE) in contact with the front and back major surfaces. A forced convection mechanism consisting of a pump that brings the storage water into motion by recirculation is used for heat transfer intensification. The two major (front and back) flat plate surfaces need to be well interconnected so that they are not deformed by the weight of the contained water and the exerted high-pressure. Two main factors that influence the performance are optimized: the position and size of the recirculation ports and the arrangement and size of the interconnecting fins. Both factors are explored to maximize the velocity flow field of the recirculated storage water. Consequently, the heat transfer rate between the two water circuits is maintained at high levels. Various 3D computational fluid dynamics (CFD) models are developed using the FLUENT package. An experimental model, made by Plexiglas, is used for the visualization of the flow field. Flow velocities are measured using a laser doppler velocimetry (LDV) system. The optimal arrangement increases the mean storage water velocity by 65% and raises the outlet temperatures up to 8 °C.