Heat and mass transfer of free-flow arrangements with corresponding pressure drop

Plate heat exchangers in free flow arrangement consist of channels with curved concave and convex surfaces, Fig. 1, which are employed for the enhancement of heat and mass transfer. This geometry is used in food technology for the heat treatment of juices and mashes with fibers. For the optimization of compact heat and mass transferring equipment accurate information is necessary on the local heat and mass transfer regarding its homogeneity, pressure losses, flow field and mixing behaviour and residence time characteristics for the specific analyzed geometry. In channel flows, the hydraulic diameter fails to correlate the local or integral heat and mass transfer for different channel geometries. So each specific geometry has to be analyzed theoretically or in complex surface structures experimentally. In the concave part of the wavy ducts in free-flow arrangement for small spacings a flow instability can be observed experimentally, leading to longitudinal vortices comparable to the Goertler instability at concave walls or the Dean instability in tube flows. This influences the spanwise heat transfer homogeneity and is investigated for its effect on heat and mass transfer as well as pressure drop.