Simulation of heat transfer enhancement by longitudinal vortex generators in dimple heat exchangers

A three-dimensional DDF-MRT-LBE (double distribution function multi-relaxation-time lattice Boltzmann equation) is presented to study the flow and heat transfer in dimple heat exchangers. Results are obtained for periodically fully-developed laminar flow in parallel-plate channels with spherical dimples symmetrically opposing onto both walls. Both the heat transfer and flow resistance are discussed. Furthermore, to enhance the heat transfer with low pressure penalty, a small crescent-shape protrusion was added as a LVG (longitudinal vortex generator). And a grooved LVG was developed to reduce the drop loss caused by the crescent-shape protrusion. The streamline contours, isotherms, Nusselt numbers and friction coefficients at various Reynolds numbers are presented. The results show that the thermal performance of the LVG cases is higher than that of the dimple cases with similar flow characteristics. Moreover, from the viewpoint of energy saving, LVG cases perform better than the dimple cases.