Malcolm R. Mackley

Heat transfer and associated energy dissipation for oscillatory flow in baffled tubes

We report experimental data on the heat transfer performance of a periodically baffled tube subject to both steady (net) flow and oscillatory flow. The data show that, in particular, at a low net flow Reynolds number, significant heat transfer enhancement can be achieved with the superposition of fluid oscillations. A general correlation is derived for the measured Nusselt number as a function of both net flow and oscillatory Reynolds number. Dynamic pressure drop data for oscillatory flow are also reported, and estimates of energy efficiency for obtaining heat transfer enhancement made from these measurements are compared with smooth wall turbulent flow equations. For large amplitudes of oscillation (equivalent to half the tube diameter) the overall power dissipation follows the quasi-steady theory. At smaller amplitudes of oscillation the power dissipation was larger than predicted by the quasi-steady theory, indicating an increased eddy interaction.

Optical microstructure and viscosity enhancement for an epoxy resin matrix containing multiwall carbon nanotubes

This paper describes rheological measurements and associated optical microstructural observations of multiwall carbon nanotubes (MWCNTs) suspended in an epoxy resin matrix. The base epoxy resin was found to be essentially Newtonian, and the progressive incorporation of nanotubes enhanced the low shear rate viscosity of the suspension by nearly two decades. At higher shear rates, the suspension viscosity asymptotically thinned to the viscosity of the matrix alone. The low shear rate viscosity enhancement was correlated with the optical observations of interconnected aggregates of carbon nanotubes, which themselves were induced by the low shear conditions. Intermediate shear rates resulted in a reduction in the size of the aggregates. High shear rates appeared to cause near-complete dispersal of the aggregates. From these results it is conjectured that for this suspension, shear thinning is connected with the breaking of the interconnected networks between nanotubes and or aggregates of nanotubes, and not b...

Experimental observations on flow patterns and energy losses for oscillatory flow in ducts containing sharp edges

Abstract We report experimental observations on both flow patterns and energy losses for oscillatory flow in geometries that can contain sharp edges. A ‘U’ shaped manometer arrangement is chosen with either a rectangular or cylindrical cross section. Sharp edges are introduced either as right-angled bends or baffled inserts and fluid oscillation occurs as a periodically decaying amplitude from a preset starting height. Flow visualization observations show clearly that large scale eddy mixing can be generated in regions between sharp edges. Information from the measured surface height decay enables associated viscous and eddy dissipation energy losses to be determined.

In situ rheo-x-ray investigation of flow-induced orientation in layered silicate–syndiotactic polypropylene nanocomposite melt

This article describes experimental results for both the rheology and flow-induced orientation of a series of intercalated syndiotactic polypropylene nanocomposites which were prepared by melt intercalation in the presence or absence of an i-PP/maleic anhydride copolymer. The nanocomposites showed typical rheological signatures of well-dispersed interacalated nanocomposites such as a low frequency plateau in dynamic moduli and an apparent yield transition from very high viscosity at low shear stresses to low viscosity above a yield stress. In situ x-ray diffraction (XRD) measurements during shear provided direct evidence of rheology-microstructure links in these materials. It was found that the clay tactoids could be easily oriented by shear and that a high degree of orientation can be achieved after the yield transition. Further, the rheo-XRD apparatus allowed measurements of the relaxation of orientation upon the cessation of flow. The orientation relaxation time matched the characteristic relaxation times estimated from independent rheological measurements well.

Mixing and dispersion in a baffled tube for steady laminar and pulsatile flow

Abstract We report experimental observations on the dispersion of fluid in horizontal and vertical tubes where periodic baffles and fluid oscillation may be present. Local concentration profile measurements are made both at the centre and wall of the tube. Our observations show that small density differences between the tracer and bulk fluid can significantly modify the expected concentration profiles for unbaffled tubes. When baffles and oscillations are present excellent mixing is achieved across the tube and dispersion data are presented for this type of flow.

Mixing Through Oscillations and Pulsations—A Guide to Achieving Process Enhancements in the Chemical and Process Industries

In this article we review the concepts and key developments of mixing enhancement through pulsation and oscillation. We focus on more recent research using oscillations in baffled tubes or columns, which generate discrete vortices as distinct from the more random type of flow produced by the well-established pulsed plate and reciprocating plate column devices. The scope of this review ranges from the basic chemical engineering concepts and key findings from recent research projects, including heat/mass transfer and residence time distribution (RTD); to applications and case studies involving specific reactions, e.g. polymerization and process intensification. We hope that this review will enable the reader to identify additional potential and perhaps an unexpectedly wide range of applications for the oscillatory baffled flow technology.

Experimental residence time distribution measurements for unsteady flow in baffled tubes

Abstract Preliminary experimental measurementss are reported on residence time distributions obtained for unsteady flows in a baffled tube. A single baffled tube geometry is examined with a fixed net flow through the tube. An oscillatory motion is then superimped and it is found fluid oscillations can have a significant effect on the systems residence time distribution. Conditions have been found where the device can operate in a near plug mode, and in this situation flow visualisation observations show that efficient radial and axial eddy mixing has been achieved. Results are presented in terms of dimensionless residence time distribution and a single-parameter axial dispersion coefficient.

Experimental heat transfer measurements for pulsatile flow in baffled tubes

Abstract We report experimental heat transfer measurements for the flow of a lubricating oil on the tube side of a shell and tube heat exchanger. Results are reported for the case where there is a steady net flow through the smooth walled tube and where periodically spaced baffles have been inserted. Results are also reported when flow oscillations are superimposed on the net flow. A significant increase in the Nusselt number is reported for the system when both flow oscillation and baffles are present.

The rheological characterization of polymeric and colloidal fluids

Abstract The rheological characterization of a number of industrial and consumer fluids is considered. Experimental measurements of the fluids linear viscoelastic, non-linear viscoelastic and steady shear response are presented. A model originally developed for the description of polymer melts is then extended to test its applicability on an associative thickener, shampoo, a liquid crystalline polymer, tomato ketchup, an oil-based paint, and a kaolinite slurry. The oscillatory linear viscoelastic data are fitted to a discrete set of Maxwell elements and the non-linear step-strain data to a Wagner-type damping function. A factored time and strain dependent constitutive equation is then found in general to predict adequately the non-linear steady shear response. The rheological scheme has useful potential both for characterization and numerical prediction of engineering and processing flows.

Cross-flow cake filtration mechanisms and kinetics

An experimental investigation of the cake filtration behaviour of 125–180 μm polyethylene particles, suspended in a neutrally buoyant Newtonian fluid, has been carried out. Static cake filtration measurements of both flitrate volume out-flow and cake thickness kinetics show the familiar t12 time dependence. In addition, the hydraulic resistance of the cake was found to be pressure independent, indicating that incompressible cakes were formed under the pressure conditions examined. When cross-flow is applied, the filter cake tends towards a reduced limiting thickness but surprisingly the corresponding filtration rate or flux is observed to decrease. Direct in situ observations of the cake deposition process clearly reveal the mechanisms controlling particle capture at the surface and this effect, together with a particle deposition model where the packing within the filter cake is cross-flow dependent, is used to successfully describe the observed experimental behaviour.