Study on the influence of geometrical parameters to enhance heat transfer in a finned cylindrical segment, incorporating vortex generators.

Abstract

The present work addresses the simulation of geometries considering forced convection of turbulent flow for the thermal optimization of a generator of a water-ammonia absorption refrigeration system, for which purpose, several simulations were carried out on ANSYS Fluent, varying the geometric parameters in order to define the optimal design for the generator. In the first part, a geometrical analysis of the previously geometry proposed for the construction of the generator is presented, evaluating those geometrical factors that enhance the heat transfer. The results obtained from the simulations are used to calculate the global heat transfer coefficient by convection, as well as the average Nusselt number. High heat transfer coefficients were found where geometries shows specific arrangements that modify the evolution of the flow, those changes in the flow contributes to the higher mixed and to the heat transfer. The second part of the thesis analyze the modification of arrangement and evaluate the introduction of different types of fin geometries. Realistic and manufacturable geometries were considered for maximization of thermal heat transfer coefficient and also the minimization of friction forces. In order to compare these various geometries, a set of standard conditions were required. Finally, the thesis contemplates the incorporation of Vortex Generators (VG) to enhance the heat transfer along the generator. Vortex generators is one of the passive methods to generate streamwise vortices that create high turbulence in fluid flow over heat transfer surfaces. VG have shown to be an effective way to increase the heat transfer coefficient, decreasing the thermal resistance of the sublayer adjacent to the wall immediately where the viscous effects of the sublayer are dominant. The increase of turbulence of the fluid flow in the main stream have shown positive effects on the heat transfer. The thesis evaluates the present research of VG and contemplate the simulation of the incorporation of an array of VG over the surface of a previously finned- cylindrical geometry of generator, contrasting the immersion of the VG's to baseline geometry, the effects on the pressure drop are also studied. Subsequently, the incorporation of a modified annular winglet vortex generator over the generator surface was also evaluated. The results were compared to the no VG fin type geometry. The results show that the heat transfer increases considerably, but an increase on the pressure drop is also observed.