Detection of entrapped moisture in honeycomb sandwich structures

Thermal neutron moisture detection system detects entrapped moisture in intercellular areas of bonded honeycomb sandwich structures. A radium/beryllium fast neutron source bombards a specimen. The emitted thermal neutrons from the target nucleus are detected and counted by a boron trifluoride thermal neutron detector

Investigating the shear rheology of molten instant coffee at elevated pressures using the Cambridge multipass rheometer

The processing of instant coffee may involve pumping the material in a melt phase through operations at elevated pressures. The shear rheology of this material was investigated using the Cambridge multipass rheometer, which allows for shear rheometric testing under conditions of independently controlled temperature and pressure. In this work the back pressure was set to dissolve any air that was present in the melt, so that the rheology of the single phase material could be tested. Data were collected over the accessible range of conditions; shear rates from 0.01 to 1000 s −1 , temperatures from 80 to 110 °C, and pressures from 0.01 to 300 bar. The melt exhibited thixotropic behaviour at low shear rates, and the data could be fitted to a non-dimensionalised Carreau fluid model with a temperature dependence which followed an Andrade relationship. Sample to sample variation was observed, which is attributed to differing water content. The results demonstrate how the rheology of complex food materials can be accessed under process conditions.This work was supported by Mondelēz International, Jacob Douwe Egberts, and the Engineering and Physical Sciences Research Council

Effect of bubble volume fraction on the shear and extensional rheology of bubbly liquids based on guar gum (a Giesekus fluid) as continuous phase

The effect of air bubble volume fraction, ϕ, on the steady shear and extensional rheology of aqueous guar gum solutions was studied at 0 ≤ ϕ ≤ 0.25 and gum concentrations of (i) 5° g/L and (ii) 10 g/L, corresponding to solutions in the (i) semi-dilute and (ii) entanglement regime. The rheological response of the fluids was largely independent of bubble size but strongly dependent on ϕ. The viscous and elastic moduli increased with increasing bubble volume fraction, with elastic dominance prevalent at the higher gum concentration. Extensional rheometry, investigated using filament stretching, revealed that the thinning dynamics of the liquid thread were affected by bubble size, but the filament rupture time was primarily dependent on ϕ. The rheological behaviour in both shear and extension could be modelled as a single mode Giesekus fluid, with a single set of parameters able to describe both the shear and extensional behaviour in the semi-dilute regime. In the entanglement regime the single mode Giesekus fluid could fit the shear data or the extensional data individually, but not both. The fitted Giesekus fluid model parameters exhibited a strong dependency on ϕ, offering a way to predict the flow behaviour of these complex food fluids.This is the author's accepted manuscript. The final version is available from Elsevier in the Journal of Food Engineering (http://www.sciencedirect.com/science/article/pii/S0260877414003744)

Effect of concentration on shear and extensional rheology of guar gum solutions

The steady shear and extensional rheology of aqueous guar gum solutions was studied for concentrations, C, ranging from 1 g/L to 20 g/L. Extensional rheometry measurements were made using the Cambridge Trimaster filament-stretching device. The steady shear tests indicated a transition between a semi-dilute regime, below 10 g/L, and an entangled regime at higher concentrations. The solutions were shear-thinning and obeyed the unmodified Cox–Merz rule in the dilute regime, but deviated from Cox–Merz and exhibited strongly viscoelastic behaviour at higher concentrations. The surface tension at higher concentration also deviated from the Szyszkowski model, exhibiting behaviour consistent with entanglement. The filament-thinning data did not fit the model for polymer solution behaviour presented by Entov and Hinch (1997), but gave a good fit to a modified form where time was normalised by the time for filament break-up. This scaling was independent of concentration effects, as reported by Chesterton, Meza, Moggridge, Sadd, and Wilson (2011) for cake batters. The modified model parameters approached asymptotic values for entangled solutions. The estimated apparent extensional viscosity exhibited a peak at unit strain followed by a constant value. The former increased as Cn, where n > 1, while the latter increased linearly with C.The authors acknowledge the financial support (POS-A/2012/116) from Xunta de Galicia’s Consellería de Cultura, Educación e Ordenación Universitaria of Spain and European Union’s European Social Fund.This is the accepted manuscript version. The final published version of the article is available from Elsevier at http://www.sciencedirect.com/science/article/pii/S0268005X14000605

The motion and shape of a bubble in highly viscous liquid flowing through an orifice

Experiments and theory concern the behaviour of a small bubble carried through an orifice by a very viscous liquid. The liquid was polybutene oil, of viscosity about 70 Pa s, i.e. 70,000 times that of water. The Reynolds number of the flow is substantially less than one, hence the flow pattern is approximately radial flowing into, and away from, the orifice. These flow patterns have profound effects on the shape of an entrained bubble. On the upstream side, the acceleration of the liquid, as it approaches the orifice, causes elongation of the bubble since the front of the bubble moves faster than the back. On the downstream side, the reverse occurs: the back of the bubble moves fast than the front. Thus the height of the bubble diminishes as it moves away from the orifice, leading to the formation of a ‘crescent-moon’ shape. The shape of these bubbles can be predicted by considering the motion of a droplet of the same liquid replacing the bubble: the resulting geometric theory gives good predictions of bubble deformation approaching the orifice and of ‘crescent-moon’ formation downstream of the orifice.The work was supported by EPSRC contract number EP/N00230X/1

Seasonal Abudance of Arthropod Populations on Selected Soybean Variteties Grown in Early Season Production Systems in Louisiana (Bulletin #860)

The data presented in this report were collected by entomologists to provide Louisiana soybean producers with information on insect management practices that may be required as they select the soybean maturity group that best fits their production systems.https://digitalcommons.lsu.edu/agcenter_bulletins/1044/thumbnail.jp

Experimental and simulation studies of the shape and motion of an air bubble contained in a highly viscous liquid flowing through an orifice constriction

This paper reports an experimental and computational study on the shape and motion of an air bubble, contained in a highly viscous Newtonian liquid, as it passes through a rectangular channel having a constriction orifice. The magnitude of the viscosity ratios, $\lambda$, and capillary numbers, CA, explored is high: 5.5 x 10$^{5}$ < $\lambda$ < 3.9 x 10$^{6}$ and 2.9 < Ca < 35.9 respectively. A multipass rheometer is used for the experimental work: air bubbles are suspended in 10 Pa s and 70 Pa s polybutene viscosity standards and passed through an orifice-plate geometry constructed within an optical flow-cell. High levels of bubble distortion are observed, including bubbles that resemble ‘crescent moons’. Simulation work is carried out using an implementation of the volume of fluid method in the freely-available finite-volume computational fluid dynamics code OpenFOAM. Quantitative data pertaining to the motion and shape of the bubble was extracted from both the experimental and simulation work. Initially, a good match between numerical simulation and experimental work could not be obtained: this problem was alleviated by changing the viscosity averaging method from an arithmetic mean to a logarithmically-weighted arithmetic mean. Medium- and high-resolution simulations using this new viscosity averaging method were able to match experimental data with coefficients of determination, R$^{2}$, typically 0.898 < R$^{2}$ < 0.985.Funding is gratefully acknowledged from the EPSRC, grant EP/N00230X/1

The distortion of a horizontal soap film due to the impact of a falling sphere

A horizontal soap film is established in vertical tube a few centimetres in diameter. A metal sphere, 1-2mm diameter, is dropped onto the film, whose distortion is observed by means of a high speed camera. The film wraps partly around the sphere, detaching at a circle which moves up the sphere as it falls. The shape of the film at successive radii, bigger than the radius of contact, was predicted from theory relying on the proposition that if both sides of the film are open to atmosphere, there can be no pressure difference across it. The pressure difference across a film is proportional to (surface tension) / (radius of curvature); hence it follows that the radii of curvature in two planes, perpendicular to each other and to the film surface, must be equal and opposite. This proposition gives equations predicting the shape, in reasonable agreement with experiment. This theory is compared with the theory of catenoids, first studied by Euler in 1744. Catenoid theory gives exactly the same results as the ‘radius of curvature’ theory presented here. A simple energy conservation argument shows that the two theories are compatible and agree with a published photograph of a soap film catenoid.The work was supported by EPSRC contract number EP/N00230X/1

A portable and affordable extensional rheometer for field testing

Extensional shear testing is often needed to characterise the behaviour of complex fluids found in industry and nature. Traditional extensional rheometers are typically expensive, fragile and heavy and are only suited to making measurements in a laboratory environment. For some applications, it is necessary to make in situ rheological measurements where, for example, fluid properties change rapidly over time or where laboratory facilities are unavailable. This paper reports the development and validation of an inexpensive, lightweight and robust 'open source' extensional rheometer, Seymour II. Validation was carried out experimentally and computationally. Measurements on a Newtonian fluid (492 mPa s Brookfield silicone oil) yielded results of 510  ±  51 mPa s; these are comfortably within the range of  ±10% which other authors have quoted for extensional techniques using laboratory rheometers. Comparison of the observed filament thinning dynamics to those obtained using computational fluid dynamics (CFD) gave good qualitative agreement. Use of Seymour II at the University of Cambridge Botanic Gardens revealed that the mucilage of the 'crane flower', $\textit{Strelitzia reginae}$, was a viscoelastic fluid whose extensional response could be described by a two-mode Giesekus equation. Engineering drawings and image analysis code for Seymour II are available for download at the project website, www.seymourII.org/.Support for a summer internship for NP from ENSTA, a PhD studentship for MPB from Sandvik Hyperion and Ceratizit, and a PhD studentship for OMM from Chemours