Modelling of the rheological behaviour of slurries used for cold transportation

National audienceSuspensions of solid crystals are used for cold transportation purposes with the aim of reducing the use of classical refrigerants. From a general point of view, the understanding and the mastering of the rheological properties of the crystal suspensions is essential for controlling the operating conditions. Water ice and Tetra-ButylAmmonium Bromide (TBAB) hydrate aqueous give rise to non-Newtonian flows. In particular Bingham-like behaviours are frequently observed. Two reasons at least can explain deviation from Newtonian characteristics: crystal agglomeration and particle

Rheological study of two-phase secondary fluids for refrigeration and air conditioning.

National audienceThe two phase fluids have promising application in refrigeration thanks to their large cooling capacity and their storage ability. However, the lack of information on their properties makes the selection of a proper fluid uneasy. An experimental set-up inspired from the scrapped surface heat exchanger technology is presented in this paper. It was developed both to generate and to characterise slurries in a rheological point of view. The large range of temperature envisaged here allows enlarging the field of application of the technology to cooler temperatures (freezer applications) and to positive ones (air conditioning systems). The principle of the viscosity measurements is described on solutions of ethyl alcohol; a hydrate is also presented as an example of compound showing a dissociation temperature in the range concerned by air conditioning applications

Rheological study of an hydrate slurry for air conditionning application

Fifth International Conference on Gas Hydrates (ICGH 5), Tromdheim, Norvège, 13 au 16 juin 2005International audienceUnder atmospheric pressure condition and tempertures between 0°C and +12°C, Tetra-n-ButylAmmonium bromide (TBAB) aqueous solutions crystallise into hydrate slurries. These slurries seem to be well appropriate for cold storage and transportation in the case of air-conditionning applications. We focus here on the crystallisation and the rheological properties of TBAB hydrates slurries. Once the crystallisation conditions described, we propose an experimental analysis of their flow behaviour. The experimental device is made up of a brushed surface heat exchanger in which the hydrates slurry is generated, and of a mesasurement loop. The flow behaviour of the slurry is characterised through flow rates and pressure drops measurements. We obtain flow curves of hydrates slurries depending on the volume fraction of hydrate solid particles. In the range of shear rate investigated, hydrate slurries behave as Bingham fluids. We propose a method of determining their apparent viscosities and yield shear stress versus the volume fraction hydrates

Crystallisation and rheology of an hydrate slurry as secondary two-phase refrigerant for air-conditioning application

8 pagesUnder atmospheric pressure condition and temperatures between 0°C and +12°C, Tetra-n- ButylAmmonium Bromide (TBAB) aqueous solutions crystallise into hydrate slurries. These slurries seems to be well appropriate for cold storage and transportation in the case of air conditioning applications. We focus here on the crystallisation and the rheological properties of TBAB hydrates slurries. Once the crystallisation conditions described, we propose an experimental analysis of their flow behaviour. The experimental device is made up of a brushed surface heat exchanger in which the hydrates slurry is generated, and of a measurement loop. The flow behaviour of the slurry is characterised through flow rates and pressure drops measurements. We obtain flow curves of hydrates slurries depending on the volume fraction of hydrate solid particles. In the range of shear rate investigated, hydrate slurries behave as Bingham fluids. We propose a method of determining their apparent viscosities and yield shear stress versus the volume fraction of hydrates

First trimester screening for trisomy 21 in gestational week 8-10 by ADAM12-S as a maternal serum marker

<p>Abstract</p> <p>Background</p> <p>A disintegrin and metalloprotease 12 (ADAM12-S) has previously been reported to be significantly reduced in maternal serum from women with fetal aneuploidy early in the first trimester and to significantly improve the quality of risk assessment for fetal trisomy 21 in prenatal screening. The aim of this study was to determine whether ADAM12-S is a useful serum marker for fetal trisomy 21 using the mixture model.</p> <p>Method</p> <p>In this case control study ADAM12-S was measured by KRYPTOR ADAM12-S immunoassay in maternal serum from gestational weeks 8 to 11 in 46 samples of fetal trisomy 21 and in 645 controls. Comparison of sensitivity and specificity of first trimester screening for fetal trisomy 21 with or without ADAM12-S included in the risk assessment using the mixture model.</p> <p>Results</p> <p>The concentration of ADAM12-S increased from week 8 to 11 and was negatively correlated with maternal weight. Log MoM ADAM12-S was positively correlated with log MoM PAPP-A (r = 0.39, P < 0.001), and with log MoM free beta hCG (r = 0.21, P < 0.001). The median ADAM12-S MoM in cases of fetal trisomy 21 in gestational week 8 was 0.66 increasing to approx. 0.9 MoM in week 9 and 10. The use of ADAM12-S along with biochemical markers from the combined test (PAPP-A, free beta hCG) with or without nuchal translucency measurement did not affect the detection rate or false positive rate of fetal aneuploidy as compared to routine screening using PAPP-A and free β-hCG with or without nuchal translucency.</p> <p>Conclusion</p> <p>The data show moderately decreased levels of ADAM12-S in cases of fetal aneuploidy in gestational weeks 8-11. However, including ADAM12-S in the routine risk does not improve the performance of first trimester screening for fetal trisomy 21.</p

Chord length distributions measurements during crystallization and agglomeration of gas hydrate in a water-in-oil emulsion: Simulation and experimentation

International audienceThe formation of gas hydrates from water-in-oil emulsion was investigated on two different flow loops: a laboratory scale flow loop (Archimede flow loop: 30 m long, and 1 cm diameter, St-Etienne School of Mines) and a pilot scale flow loop (Lyre flow loop: 150 m long, 5 cm diameter, IFP Solaize). Both flow loops are equipped with a focused beam reflectance measurement (FBRM) probe for in situ particle size analysis. These FBRM probes were used to monitor chord length distribution (CLD) during the crystallization process of water-in-oil emulsions into gas hydrate slurries. When water droplets crystallize into hydrate particles, an agglomeration phenomenon is evidenced by pressure drop measurements. This agglomeration phenomenon is also detected by the FBRM probe and is highlighted by a sharp change in the mean chord length and a spread of the CLD to larger chord length. In order to better interpret the chord length distribution measurements, a modelling work has been made. This paper gives a description of the algorithm used for building 3D fractal aggregates and simulating CLD measurements on them. Aggregates are constructed from a monodisperse spherical particle. The influence of different parameters (fractal dimension, number of particles in the aggregate, diameter of primary particles) on the simulated CLD is also discussed. Some comparisons between experimental and simulated CLD are finally used to describe the physical properties of aggregates during an experiment

Agglomeration of gas hydrate in a water-in-oil emulsion: Experimental and modeling studies

International audienceThe formation of gas hydrates in water-in-oil emulsion is investigated at the laboratory pilot scale on a flow loop. The Archimede flow loop (30 m long, and 1 cm diameter) has been built to reproduce the thermodynamic conditions encountered in deep-sea pipelines with a maximum flow rate equal to 3x10-5 m3.s-1. Recently, a Moineau pump has been added in order to maintain the flow at a constant rate, especially after the beginning of crystallization and independently of the rheological characteristics (the flow rate can be varied in the range 2x10-5 m3.s-1 to 14x10-5 m3.s-1). This work presents some preliminary experiments to characterize the flow properties. Also some crystallization experiments were realized in order to understand the coupling between crystallization and rheology by following the size of the agglomerates and the water conversion. When water droplets crystallize to form hydrate particles, an agglomeration phenomenon is evidenced by pressure drop measurements. The agglomeration phenomenon is also detected by a Focused Beam Reflectance Measurements (FBRM) probe and is highlighted by a sharp change in the mean chord length and a spread of the Chord Length Distribution (CLD) to larger chord length

The use of FBRM probe during hydrate particles agglomeration

National audienceGas hydrates formation from water in oil emulsion is of particular interest in the context of crude oil production. Once hydrates form in the pipeline, individual gas hydrate particles agglomerate together and form a plug preventing fluid flow. This work shows the main advantages of using a Focused Beam Reflectance Measurement (FBRM) probe for in situ chord lengths analysis during hydrate particles agglomeration for a better understanding of this process within the pipe. The formation of gas hydrate was studied in a flow loop. Experiments were carried out at 278K and 7.5 MPa. This paper provides a systematic study of the FBRM probe signal. It also underlines the links between the shape of the CLD and the morphology of agglomerates carried inside the flow. This is particularly useful to understand the agglomeration process

Identification of Pro-MMP-7 as a Serum Marker for Renal Cell Carcinoma by Use of Proteomic Analysis

International audienceBACKGROUND: No validated renal cell carcinoma (RCC) marker is known for detection of asymptomatic disease in selected populations or for prognostic purposes or treatment monitoring. We identified immunogenic proteins as tumor markers for RCC by combining conventional proteome analysis with serological screening, and we investigated the diagnostic clinical value of such markers in serum. METHODS: We studied the immunogenic protein expression profile of CAL 54, a human RCC cell line, by 2-dimensional electrophoresis combined with immunoblotting using sera from healthy donors compared with RCC patients. We developed a homogeneous, fluorescent, dual-monoclonal immunoassay for metalloproteinase 7 (MMP-7) and used it to measure MMP-7 in sera from 30 healthy donors, 30 RCC patients, and 40 control patients. RESULTS: Pro-MMP-7 (29 kDa; pI 7.7) in the CAL 54 cell line secretome was an immunogenic protein reactive with RCC patient sera but not with control sera. The concentrations of pro-MMP-7 were increased (P <0.0001) in sera of RCC patients (median 7.56 microg/L; range 3.12-30.5 microg/L) compared with healthy controls (median 2.13 microg/L; range 0.17-3.5 microg/L). Serum pro-MMP-7 had a sensitivity of 93% (95% CI 78%-99%) at a specificity of 75% (59%-87%) for RCC in the samples tested. CONCLUSION: Proteomics technology combined with serology led to the identification of serum pro-MMP-7 as a marker of RCC and represents a powerful tool in searching for candidate proteins as biomarkers

Etude rhéologique d'une suspension d'hydrates en tant que fluide frigoporteur diphasique. Résultats expérimentaux et modélisation

Secondary two-phase fluids are suspensions of solid crystals. Thanks to the melting latent heat, they present a great interest for cold transportation. Moreover, they are a mean of reducing the amount of classical refrigerant. In the refrigeration field, ice slurries are already used. The goal is now to extend this technology to other temperature ranges suitable for other applications like freezing or air-conditioning. For an air-conditioning application, a TBAB (Tetra-ButylAmmonium Bromide) aqueous solution is studied. Under atmospheric pressure and for positive temperatures, this solution crystallizes into ice-like compounds named “hydrates”. First, the physical properties of the aqueous solution and its crystallisation conditions were studied. Two different types of hydrates can appear.The goal of the experimental set-up is to study the rheological behaviour of two-phase fluids. Slurries are made in brushed-surface heat exchanger and pumped into pipes where flow rates and pressure drops are measured. The rheological behaviour of TBAB hydrates slurries can be described using a Bingham fluid model. We highlight that the two rheological parameters, which are the apparent viscosity and the yield shear stress, depend on the volume fraction of crystal of course, but also on the hydrate type, and on the initial concentration of the solution. The yield shear stress is interpreted as the consequence of the Van der Waals inter-particle interaction forces. Finally, possible stratification effects are modelled with a finite difference method. The principle is to calculate particle concentration and velocity profiles following the flow of the slurry. Calculations are validated with experimental velocity profiles published by P. Reghem (2002). This model underlines the influence of the particle distribution in the pipe on pressure drops.Les fluides frigoporteurs diphasiques sont des suspensions de cristaux solides. Exploitant l'énergie de changement de phase solide/liquide, ils sont intéressants d'un point de vue énergétique pour le transport du froid. De plus, leur utilisation est un moyen de réduire les quantités de réfrigérants classiques utilisés. Des coulis de glace sont actuellement mis en place dans le domaine de la réfrigération. Cette technologie peut être étendue vers d'autres domaines d'application, à d'autres domaines de températures : la congélation et la climatisation. Pour une application en climatisation, nous étudions une solution de TBAB (Bromure de Tetra-ButylAmmonium). A pression atmosphérique et pour des températures positives, cette solution cristallise pour former des composés similaires à la glace : des hydrates. Les propriétés physiques de la solution initiale et sa capacité à cristalliser ont tout d'abord été étudiées. Nous avons mis en évidence la possibilité de former deux types de cristaux de natures différentes.Un dispositif expérimental permettant la caractérisation rhéologique des fluides frigoporteurs diphasiques a été élaboré. Les suspensions sont formées dans un échangeur à surface brossée et caractérisées par des mesures de débit et pertes de charge en conduites cylindriques. Les coulis d'hydrates de TBAB peuvent être décrits par un modèle de type « fluide de Bingham ». Nous montrons que les paramètres rhéologiques (viscosité apparente et contrainte seuil) dépendent non seulement de la teneur en particules mais aussi du type d'hydrate en suspension et de la concentration initiale de la solution. La contrainte seuil est interprétée par les forces d'interactions entre particules de type Van der Waals. Enfin, d'éventuels effets de stratification sont modélisés par une méthode de différences finies. Le principe est de calculer les profils de vitesse et de concentration en particules au cours de l'écoulement d'une suspension de cristaux en conduite. Les calculs sont validés par les profils de vitesse obtenus expérimentalement par P. Reghem (2002). Ce modèle permet d'évaluer l'influence du profil de concentration en particules sur les pertes de charge