Etude des performances thermiques d'un chauffage ohmique pour la stérilisation UHT du lait - Définition d'un critère d'encrassement.

In : 6ième Colloque PROSETIA, Versailles – St Cyr, 19-21 Mars 2001.Etude des performances thermiques d'un chauffage ohmique pour la stérilisation UHT du lait - Définition d'un critère d'encrassement. . 6. Colloque Prosetia. Procédés de séparation et de transformation en industrie alimentair

Power requirement when mixing a shear-thickening fluid with a helical ribbon impeller type

International audienc

beta-lactoglobulin denaturation, aggregation, and fouling in a plate heat exchanger: Pilot-scale experiments and dimensional analysis

International audienceIn this work, we investigated the role of four independent process parameters, namely product temperature at the heat exchanger outlet, mean residence time, temperature increase between the heat exchanger inlet and outlet, and heat effectiveness, in the protein denaturation, aggregation, and fouling of a beta-lactoglobulin (beta-lg) concentrate that was chosen as model fluid for milk derivatives. A pilot scale plate heat exchanger in countercurrent configuration, supplied with a holder, was used in order to mimic industrial process conditions. The denaturation level and aggregates size of the heat treated beta-lg concentrate at the exchanger and holder outlets, along with the fouling mass in the plate heat exchanger were simultaneously determined. The results indicated that beta-lg denaturation, aggregation, and fouling reactions were mainly governed by the temperature profile in the investigated range of operating conditions, even though a small influence of residence time and healing rate was highlighted in the less denaturing conditions. A dimensional analysis was performed to identify the key dimensionless numbers governing beta-lg denaturation, aggregation, and fouling mechanisms in the heat treatment of a beta-lg concentrate. This allowed to emphasise the major influence of the Arrhenius exponential factor of beta-lg unfolding reaction, both related to temperature and beta-lg reactivity. The first Damkohler and Reynolds numbers, related to residence time and hydrodynamic conditions in the heat exchanger, as well as the heat exchange process parameters, linked to the heat effectiveness and the bulk-wall temperature differences, had also a small impact on beta-lg chemical behaviour. Moreover, empirical relationships based only on the Arrhenius exponential factor of beta-lg unfolding reaction permitted to describe the main trends observed in denaturation levels, aggregate sizes, and fouling masses, which underlined the predominant role of temperature and beta-lg reactivity in the investigated operating conditions. This study outlines finally that fast heat treatments permit to minimise fouling issues

Structure and rate of growth of whey protein deposit from in situ electrical conductivity during fouling in a plate heat exchanger

The influences of calcium concentrations , Reynolds number (2000–5000) and temperature () upon the deposit structure and the rate of growth deposition have been investigated in a plate heat exchanger. This was done from in situ measurements of the deposit electrical conductivity via implementation of stainless steel electrodes in channels combined with assessments of deposit thickness. Calcium ions affect structures of deposits and increase the rate of deposit growth upon heated surfaces. This was attributed to the formation of weaker size aggregates at higher calcium concentrations and a higher number of calcium bindings, which reinforce adhesion forces between protein aggregates. Structures and appearances of deposits also were affected by flow rates whatever the calcium concentrations. Deposit growth rate was enhanced by increasing flow rate below a critical Reynolds number comprised between 3200 and 5000. On the contrary, above the critical Reynolds number, a limitation of the deposit and/or an escape of the deposit from the fouled layer into the core fluid occurred, caused by the predominance of particle breakage on the deposit formation. Fouling tended to be reduced at higher flow rate. It was noteworthy that rates of growth decrease during fouling experiments which may be explained by an increase in local shear stresses leading to particle breakage

Antifouling stainless steel surface: Competition between roughness and surface energy

7. International Conference on Processing and Manufacturing of Advanced Materials Quebec City, Canada : AUG 01-05, 2011 Parts: 1-4International audienceTo increase the shelf-life qualities of dairy products, a heat treatment is usually done. However, heat treatments induce physico-chemical modifications of the products. Some of them lead to the expected product but an unwanted consequence of this process is the formation of a fouling deposit on the surfaces in contact with the processed fluid. To eliminate fouling, cleaning processes have to be done once a day. It increases the processing and maintenance costs. To control and to decrease the fouling are the main problems in food industries and an active research is carried out on efficient antifouling surface treatments. In the present study, a 316L 2B stainless steel was submitted to different surface treatments (Flame and plasma pre-treatments, Plasma Enhanced Chemical Vapour Deposition, hydrophobic coatings, mechanical polishing ...) to try to establish correlations between different surface parameters (roughness, hydrophobicity, nanostructuration, surface energy, ...) onto the fouling in heat exchangers. All the treated plates were then submitted to a fouling test using an aqueous solution of beta-lactoglobulin at 1% (p/p) with a final calcium concentration of 910 mg/L and compared to a bare steel plate. The results obtained imply different influences of each parameter depending on the surface roughness: the effect of a non organized micrometric roughness is preponderant compared to the surface energy: the fouling comes from a mechanical effect mainly due to rubbing. However, when the surface is nanostructured, fouling decreases. When the roughness reaches the nanometer scale (between 100 and 400 nm), it is the surface energy and the polar/apolar components which become preponderant compared to the roughness. Fouling is this time mainly due to the hydrophilicity of the surface and to the adsorption of the beta-lactoglobulin on acido-basic sites. Finally, when the roughness reaches less than 50 nm, polar/apolar components show no effect anymore, the preponderant parameter is the hydrophobicity of the surface

A CFD model as a tool to simulate beta-lactoglobulin heat-induced denaturation and aggregation in a plate heat exchanger

International audienceDuring the pasteurization process, the thermal treatment of milk and its derivatives in plate heat exchangers is limited by protein fouling. The deposition mechanism onto the heat transfer surface involves the denaturation and aggregation of B-lactoglobulin. In this work, a 2-D CFD analysis was conducted to simulate locally the heat-induced protein denaturation mechanisms. Firstly, we present various intermediate validations of the ability of the numerical model to capture the hydrodynamics, by showing the similarity of CFD results and experimental data. Finally, the close agreement between the denaturation level obtained by CFD and that obtained experimentally indicates the ability of the numerical model adopted to simulate the chemical reaction. The analysis of the species present in the plate heat exchanger is related to the deposit mass distribution along the heat exchanger using CFD data. It has been shown that the unfolded species are deposit precursors and that the distribution of the deposit is correlated to this source

Contrôle d'un encrassement laitier en procédé continu : comparaison de trois méthodes

National audienc

Effect of calcium content and flow regime on whey protein fouling and cleaning in a plate heat exchanger

Fouling and cleaning with a whey protein concentrate solution in a plate heat exchanger were investigatedwith a varying calcium concentration (from 70 to 87.5 mg L 1) and under a wide range of hydrodynamicconditions for a bulk fouling fluid temperature, ranging from 60 and 96 C.This work demonstrates that increasing the calcium concentration in whey protein concentrate contributesto the amount of fouling and affects the thermal conductivity of the deposit. It was also observedthat the fluid flow regime during fouling, impacts the deposit growth, modifies the structure of fouledlayers and has a significant consequence on cleaning behaviour.Finally, a dimensional analysis together with experimental measurements, allowed a relationship to beestablished enabling prediction of the amount of dry mass deposited locally as a function of the knowncalcium content, Reynolds number and bulk fluid temperatur

Relationship between β-lactoglobulin denaturation and fouling mass distribution in a plate heat exchanger

International audienceFew investigations have attempted to connect the mechanism of dairy fouling to the chemical reaction of denaturation (unfolding and aggregation) occurring in the bulk. The objective of this study is to contribute to this aspect in order to propose innovative controls to limit fouling deposit formation. Experimental investigations have been carried out to observe the relationship between the deposit mass distribution generated in a plate heat exchanger (PHE) by a whey protein isolate (WPI) mainly composed of β-lactoglobulin (β-Lg) and the ratio between the unfolding and aggregation rate constants. Data analysis showed that: i) β-Lg denaturation is highly dependent on the calcium content, ii) for each fouling solution, irrespective of the imposed temperature profile, the deposit mass in each channel vs the ratio of the unfolding and aggregation rate constants are well correlated. This study demonstrates that both the knowledge of the thermal profile and the β-Lg denaturation rate constants are required in order to predict accurately the deposit distribution along the PHE

Corrigendum to “Denaturation kinetics of whey protein isolate solutions and fouling mass distribution in a plate heat exchanger”

International audienc