Heat and/or mass transfer intensification in helical pipes: Optimal helix geometries and comparison with alternative enhancement techniques

•Intensification performance of heat/mass transfer enhancement strategies is addressed.•Evaluation criteria accounting for specific surface area effects are proposed.•Particular helical pipe designs allow impressive intensification performances.•They allow energy-efficient volume reduction of heat/mass exchangers and reactors.•Comparison with alternative enhancement techniques is carried out. Maximizing the transfer performances of heat and mass exchangers is a major target for process intensification purposes. Basically, flux enhancement can be achieved through increased specific surface area and/or increased transfer coefficients (e.g. Dean vortices generation in curved pipes), but this has to be balanced to energy requirement. In this study, novel performance criteria taking into account both specific surface area effects and the associated friction losses are proposed and applied to helical pipe exchangers covering a broad range of geometries. It is shown that most helical pipe geometries exhibit poor efficiencies in terms of volumetric transfer rates. Nevertheless, some very particular helix designs are shown to offer a huge potentiality for intensified heat/mass transfer performances. Surprisingly, a major volume reduction is indeed shown to be achievable together with a decreased energy requirement (pumping power). The performances of these novel designs are finally critically compared to alternative process intensification techniques.