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International audience; In the global context of process intensification, heat exchanger/reactors are promising apparatuses to implement exothermic chemical syntheses. However, unlike heat exchange processes, the implementation of chemical syntheses requires to control the residence time to complete the chemistry. A way to combine the laminar regime (i.e. enough residence time) with a plug flow and the intensification of both heat and mass transfers is the corrugation of the reaction path. In this work, the experimental set-up is based on plate heat exchanger/reactor technology. 7 milli channel corrugated geometries varying the corrugation angle, the curvature radius, the developed length, the hydraulic diameter and the aspect ratio have been designed and experimentally characterized (heat transfer, mixing times, pressure drops, RTD). The objectives were to assess their respective performances to derive some correlations depending on the channel design. The results confirmed the benefits of the reaction channel corrugation. Heat and mass transfers have been intensified while maintaining a plug flow behavior in the usually laminar flow regime. Moreover, whatever the meandering channel's curvature radius, the results highlighted the relevance of considering the Dean number as the scale-up parameter. This dimension less number, more than the Reynolds number, seems to govern the flow in the wavy channels.

International audience; When viscous fluids are involved, laminar hydraulic conditions and heat and mass transfer intensification are conflicting phenomena. A channel geometry based on Split-And-Recombine (SAR) patterns is experimentally investigated. The principle implements the Baker’s transformation and ‘chaotic’ structures are generated to promote heat and mass transfer. This work assesses the energy efficiency of different heat exchanger/reactors integrating these SAR patterns. The heat transfer capacity is assessed and compared with the energy consumption of each mock-up. It is sensitive to the cooling mode and to the number of SAR patterns per length unit as well. The continuous oxidation of sodium thiosulfate with hydrogen peroxide has been implemented. Conversions up to 99% are reached according to the utility fluid temperature and the residence time. Finally, the whole performances of the SAR geometries are compared to a plate-type heat exchanger/reactor with a corrugated pattern. The more viscous the fluid, the more the energy efficiency of the SAR design increases compared to the corrugated design because of the balance between advection and diffusion mechanisms. The interest in terms of energy efficiency in working with SAR heat exchanger/reactor appears from Reynolds numbers below 50.

International audience; Since the last ten years numerous studies have been carried out to develop micro-reactors or micro-structured reactors in order to improve scale of production, economics, safety and environmental impact of chemical production. Consequently Alfa Laval Vicarb has developed a new structured heat exchanger reactor. The design of the reactor is based on high performances heat plate exchanger in which small inserts allow a good mixing of the reactants and to improve the heat transfer phenomena or to increase the heat transfer coefficient. This new technology of heat plate exchange reactors has a modular structure where the exchange zones have two possible configurations: co- and counter counter-current. The structure of the reactor is also flexible, that makes possible to have multiple reactants injections and different local temperature control points. In order to have a rapid prediction of conversion and temperature profiles, a mathematical model conserving the same notion of the structure of the reactor has been developed. This mathematical model is a simple compartmental model which presents advantages in terms of flexibility, possible online simulations and rapid prediction simulations. The structure of the model has been determined with the help of tracer experiment and computational fluid dynamics simulations. Heat and mass transfer equations are written considering each cell and using experimental heat transfer data then chemical kinetics from literature are introduced to the model. A sub-compartmental model has been developed in order to predict the micro-mixing phenomena. Four reactions for which the kinetic laws of reactions are well known have been selected to test the model: alkaline hydrolysis of ethyl acetate, alkaline hydrolysis of ethylene glycol diacetate, oxidation of sodium thiosulphate by hydrogen peroxide and Bourne reactions. The results of comparison between simulations and experimental data in terms of yield, selectivity, temperature profiles and micro-mixing characteristics are in reasonable agreement.

The development of light and efficient Compact Heat Exchangers (CHE) for automotive or aerospace applications has motivated recent research for the energetic optimisation of these devices. Owing to their geometrical complexity, such a goal requires valuable knowledges on the more simple case of a single plate in a fluid flow. The purpose of this study is to present an experimental and numerical study of the heat transfer between an incompressible fluid and a blunt flat plate with constant wall temperature. An experimental test rig is built in which air flows around a constant temperature copper plate. The Reynolds number defined on the plate thickness is varied from 120 to 500. Flow measurements are achieved with laser anemometry and the temperature field is determined using the cold wire technique. For each experiment, the experimental data are compared to Direct Numerical Simulations. Classical features of the flow are observed, i.e. a recirculating vortex near the leading edge of the plate, which is followed by a boundary layer from which vortices are alternately shed from both faces of the plate. Unlike previous studies, a particular attention is paid to the longitudinal distribution of the heat transfer coefficient for low to moderate Reynolds numbers. It is shown that a Direct Numerical Simulation of the flow and heat transfer around a thick plate is an efficient tool of optimisation which could be used for the design of industrial CHE.

This paper presents an experimental study which demonstrates the potentiality of multifunctional heat exchangers (MHE) to carry out exothermal chemical reactions by the local control of the reactive environment temperature. Two highly exothermal chemical reactions with different kinetics (instantaneous and fast) have been investigated. The MHE is found to be very efficient in extracting the heat released by the chemical reactions. Due to its large heat transfer capacity, this process allows to increase considerably inlet reactant concentrations without thermal runaway and thus to enhance both chemical reaction conversion ratio and yield. This study also shows the limitations of the multifunctional heat exchanger for exothermal and instantaneous chemical reactions. (c) 2006 Elsevier Ltd. All rights reserved.

The iodide-iodate chemical probe method is modified by a novel adaptive procedure to investigate the mixing abilities of two compact curved-duct reactors. Both reactors have a rectangular cross section; the first has smooth curvature (called the wavy duct) and the second has sharper bends (zigzag duct). In the conventional procedure, this method is used to characterize local micro-mixing, and for all experiments (for different Reynolds numbers and injection points) the reagent initial concentrations are kept at the same values. Even with wall injection, the selectivity of the chemical system is generally improved by increasing the flow Reynolds number. Nevertheless, two limitation sencountered in using chemical probes (with the conventional protocol) tocharacterize the mixing abilities of the present reactors that prevent the conventional protocol of the chemical probe from discriminating between the mixing abilities of the two mockups. First, the duct walls are corrugated, so that the wall injection used to measure local micro-mixing is affected by the wall roughness, independently of the Reynolds number. Second, the flow Reynolds numbers are relatively low due to the small size of the duct sides, so that the measurements are inevitably hindered by meso-mixing effects. The challenge is thus to adapt the chemical method for characterizing the global mixing, by enlarging the measurement volumes o as to capture and take into account all mixing scales. In the new adaptive procedure, the kinetics of the second reaction are adjusted in such away as to impose the same reactive volume for different Reynolds numbers, leading to more relevant results for the segregation index XS. Experimental results reveal that the mixing performance of the zigzag channel as assessed by this method is slightly above that of the wavy one. Finally, these gregation indexin both reactor sisrelated to the mixing time tm by using a physical model in the literature. (C) 2011 ElsevierLtd. All rights reserved.

Toward a Competitive Process Intensification: A New Generation of Heat Exchanger-Reactors - Process Intensification (PI) in chemical production is a major concern of chemical manufacturers. Among the numerous options to intensify a process, the transposition from a batch reactor to a continuous plug flow reactor is a good alternative when the selectivity and the thermal exchange are an issue. In this context, the RAPIC R&D project aims to develop an innovative low-cost component (in the 10 kg/h range). This project deals with the design from the local to the global scale and with testing, from elementary mock-ups to pilot scale. The present paper gives a detailed description of this research project and presents the main results on specification and definition of the reaction channel and the first simple mock-ups.

Fischer-Tropsch synthesis (FTS), an exothermic reaction where hydrogen and carbon monoxide synthesis gas are converted to hydrocarbon products, has been under development since the 1930's. The interest in FTS depends on current and perceived future prices of crude oil but is increasingly viewed as an option for exploiting stranded natural gas. Other advantages of FTS hydrocarbons include the absence of sulphur, nitrogen, heavy metal contaminants, low aromatic content and the ability to produce high value middle distillates/fuels. Current interest is directed towards slurry bubble processes – comprising gas, liquid, and solid phases. Industrial slurry phase FTS reactors may range in size from 6 – 10 m in diameter and upwards of 30 m in height and include multiple internal heat transfer tubes. Such systems offer numerous advantages including high heat transfer rates, good mixing, and ease of online catalyst addition and withdrawal. However, one disadvantage is the complex hydrodynamics associated with slurry bubble columns, which make scale-up difficult. A literature review on heat transfer studies and correlations has been completed focusing on previous experimental setups, the synthesis of the key findings/parameters, and the identification of the necessary criteria required for reactor design and scale-up.The parameters having the most pronounced impact on heat transfer in slurry bubble columns and three-phase fluidized beds are the superficial gas velocity and liquid properties such as viscosity and surface tension, which significantly alter the bubble properties and the column hydrodynamics. The effect of particles is poorly understood and is a complex function of particle diameter and concentration. The experimental results and correlations reported here from the majority of studies are dependent upon the equipment and properties of the three phases studied – resulting in very limited applicability to other systems or for scale-up. Other concerns include the use of relatively low gas velocities, ambient temperature and pressure, relatively large particles, and relatively small columns employed in most studies, which are not relevant to industrial operating conditions. Furthermore, studies involving multiple internals were relatively few. Most columns were only equipped with a single tube or small heat flux probe thereby measuring only the local heat transfer and not taking into account the effect on column hydrodynamics of multiple internals. Of these studies only a few tubes were equipped with heaters (that did not run the entire tube length) and heat flux probes while the remaining probes were inactive.

International audience; The present probe is developed in order to accurately estimate in situ not only the convective exchange coefficient but also the fouling thickness of heat exchangers from a reliable transient state estimation method.The originality of the estimation method consists in considering a global response time of the system in fouling conditions to be compared to clean conditions. The sensitivity function is then built from the experimental signal without precise knowledge about the model or the absolute thermophysical properties. The reliability of the method is demonstrated in theoretical cases and with calibrated experiments.

International audience; The diagnosis of heat exchangers on duty with respect to flow mal-distributions needs the development of non-intrusive inlet–outlet experimental techniques in order to perform an online fault diagnosis. Tracer experiments are an example of such techniques. They can be applied to mono-phase heat exchangers but also to multi-phase ones. In this case, the tracer experiments are more difficult to perform. In order to check for the capabilities of tracer experiments to be used for the flow maldistribution diagnosis in the case of multi-phase heat exchangers, we present here a preliminary study on the simplest possible system: two-phase flows in a horizontal tube. 81mKr is used as gas tracer and properly collimated NaI (TI) crystal scintillators as detectors. The specific shape of the tracer response allows two-phase flow regimes to be characterized. Signal analysis allows the estimation of the gas phase real average velocity and consequently of the liquid phase real average velocity as well as of the volumetric void fraction. These results are compared successfully to those obtained with liquid phase tracer experiments previously presented by Oriol et al. 2007. Characterization of the two-phase flow regimes and liquid dispersion in horizontal and vertical tubes using coloured tracer and no intrusive optical detector. Chem. Eng. Sci. 63(1), 24–34, as well as to those given by correlations from literature.

International audience; The monitoring of heat exchangers on duty with respect to flow mal-distributions needs the development of inlet–outlet experimental techniques in order to perform a fault diagnosis. Within this framework and as a first attempt to solve this problem in the case of multi-phase heat exchangers, we propose to use a non-intrusive optical sensor associated to a liquid phase tracer experiment. In order to check the capabilities of this technique, we present here the results that we have obtained for the characterization of two phase flows in horizontal and vertical tubes. The difference between refractive index of the two phases allows estimating the void fraction on the section illuminated by the optical sensor and permits to characterize two-phase flow regime from the signal characteristics. Signal analysis and treatment of the absorbance variation due to the coloured tracer injected in the liquid phase permit to estimate the real liquid phase averaged velocity and consequently the real gas phase average velocity. We also calculated volumetric void fraction and compared it to usual correlations with a good agreement. Finally, the evolution of the experimental liquid phase Peclet number with the two-phase flow regime has been observed and qualitatively explained.

International audience; This article presents a study of heat transfer during condensation of n-hexane and isopropanol with a noncondensable gas in a new plate heat exchanger geometry. Nitrogen was used as the noncondensable gas and either n-hexane or isopropanol as the condensing vapour. Three test sections were installed on the test rig devoted to condensation of mixtures applications, either in reflux or cocurrent condensation configurations. For both condensation configurations, heat transfer measurements were performed. In single phase flow tests, experimental data reduced by log mean temperature difference were compared with new correlations on the gas side, adapted to the present specific plate geometry. Besides, correlations of the fanning factor were deduced from gas side pressure drop measurements on the two geometries tested. In two-phase flow tests, the log mean temperature difference method was assumed to be reasonable for a first analysis to compare the test sections. The condensation curve method was applied to the present results and cocurrent and reflux condensation configurations were compared in terms of experimental overall heat transfer coefficients. It is shown that for a condensing vapour Reynolds number higher than 2,000, heat transfer coefficients in reflux condensation become higher than those for cocurrent condensation. Flooding phenomenon was observed for specific experimental conditions in reflux condensation mode. The flooding experimental data are compared with three existing correlations (Wallis, English et al., McQuillan and Whalley and Zapke & Kröger)

Compact heat exchangers are well-known for their ability to transfer large amounts of heat while retaining low volume and weight. This paper studies the use of this device as a chemical reactor, generally called a heat exchanger reactor (HEX reactor). Indeed, the question arises: can these geometries combine heat transfer and mixing in the same device? Such a technology would offer many advantages, such as better reaction control (through the thermal aspect), improved selectivity (through intensified mixing, more isothermal operation and shorter residence time, and sharper residence-time distribution), byproduct reduction, and enhanced safety. Several geometries of compact heat exchanger based on turbulence generation are available. This paper focuses on two types: offset strip fins (OSFs) and metallic foams. Our main objective is to contribute to the estimation of micromixing generated by these geometries by using an experimental method based on a unique parallel-competing reaction scheme proposed by Villermaux et al. The micromixing time, estimated according to the incorporation model, lets us compare the micromixing levels generated by duct channel, OSFs and metallic foams at volume flow rates ranging from 1 to 350 1 h(-1). The metallic foam concept is found to be very efficient in micromixing enhancement. Furthermore, OSFs make it possible to generate micromixing levels ranging between the duct channel and metallic foam level. Moreover, the results show that the fin micromixing level increases with fin thickness and ligament diameter. Finally, in an HEX reactor application, the residence time of chemical reactants must be considered in order to choose the best geometry for intensifying mass and heat transfer. (c) 2006 Elsevier B.V. All rights reserved.

Compact heat exchangers are well known for their ability to transfer a large amount of heat while retaining low volume and weight. The purpose of this paper is to study the potential of using this device as a mixer as well as a chemical reactor, generally called a multifunctional heat exchanger (MHE). Indeed, the question arises: can these geometries combine heat transfer and mixing in the same device? Such a technology would offer many potential advantages, such as better reaction control (through the thermal aspect [S. Ferrouillat, P. Tochon, H. Peerhossaini, D. Della Valle, Open-loop thermal control of exothermal chemical reactions in multifunctional heat exchangers, Int. J. Heat Mass Transfer, in press]), improved selectivity (through intensified mixing, more isothermal operation and shorter residence time, and sharper residence time distribution (RTD)), byproduct reduction, and enhanced safety. Several geometries of compact heat exchanger based on turbulence generation are available. This paper focuses on one type: vortex generators. The main objective is to contribute to the determination of turbulent flow inside various geometries by computational fluid dynamics methods. These enhanced industrial geometries are studied in terms of their thermal-hydraulic performance and macro-/micro-mixing ability [S. Ferrouillat, P. Tochon, H. Peerhossaini, Micromixing enhancement by turbulence: application to multifunctional heat exchangers, Chem. Eng. Process., in press]. The longitudinal vortices they generate in a channel flow turn the flow perpendicular to the main flow direction and enhance mixing between the fluid close to the fin and that in the middle of the channel. Two kinds of vortex generators are considered: a delta winglet pair and a rectangular winglet pair. For both, good agreement is obtained between numerical results and data in the literature. The vortex generator concept is found to be very efficient in terms of heat-transfer enhancement and macro-mixing. Nevertheless, the micro-mixing level is poor due to strong inhomogeneities: the vortex generator must be used as a heat-transfer enhancement device or as a static mixer for macro- and meso-mixing. (c) 2006 Elsevier Ltd. All rights reserved.