Intensification of heat-transfer and mixing in multifunctional heat exchangers by artificially generated streamwise vorticity

Abstract

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-/micromixing 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 heattransfer enhancement device or as a static mixer for macro-and meso-mixing.

Enhancing Heat Transfer of Drag-Reducing Surfactant Solution by an HEV Static Mixer with Low Pressure Drop

“…Counter-rotating vortices behind the tabs were shown both by experiments and simulations [46][47][48]. An HEV static mixer enhanced heat transfer and mixing in chemical reactions in integrated chemical reactor-heat exchangers [46,49,50].…”

Effect of concave rectangular winglet vortex generator on convection coefficient of heat transfer

“…The increase in heat transfer is because of the mixing in the channel. This fluid mixing rate caused by VG investigated by Ferrouillat et al [16]. This mixing rate was stated by the mixing efficiency.…”

Heat exchanger/reactors (HEX reactors): Concepts, technologies: State-of-the-art

“…In their works [47], Ferrouillat et al studied two forms of vortex generators: rectangular winglet pairs and delta winglet pairs as shown in Fig. 13.…”

“…Moreover heat transfer does not increase for angles of attack (ˇ) larger than 65 • . Ferrouillat et al [47] pursued these works in order to characterize the mixing properties of vortex generators. This was made thanks to numerical simulations and they showed that the rectangular winglet pair significantly increases the mixing efficiency as shown in Fig.…”