Jean-Luc Harion

Numerical analysis of the fin spacing effect on the horseshoe vortex system evolution in a two-rows finned-tube heat exchanger

Purpose – In finned-tube heat exchangers, the array of tubes generates three-dimensional vortices at fin-tube junctions. Theses vortices known as horseshoe vortex (HSV) system are responsible of flow mixing and heat transfer increase. The purpose of this paper is to focus on the effect of the fin spacing on the formation, the spatial evolution and dissipation of the HSV system at fin-tube junctions in a two-rows finned-tube heat exchanger. The global characterisation of the heat exchanger performance is also presented. Design/methodology/approach – The flow structure is numerically analysed through the use of computational fluid dynamics tools. The different vortices of the HSV system are highlighted and quantitatively analysed at each fin-tube junction with vorticity, wall shear stress analysis and two-dimensional streamline plots around tubes. Findings – The results show that the primary and secondary vortices of the HSV system have antagonistic behaviors with respect to the azimuthal angle variation. T...

Development of turbulent boundary layer with large density gradients

Abstract A hot-wire/film and flow visualization study has been carried out in a turbulent boundary layer. Density differences were generated by injecting different gas mixtures parallel to the wall. Measurements show that the effects of the density ratio S on the mean velocity field are small. On the contrary, dilution of helium injected into an air-helium mixture (density ratio S = 4 ) is very rapid compared to the case with small density differences ( S = 0.88 ). The friction coefficient is little affected by S, whereas the heat exchange is considerably increased by helium injection in the initial region.