The effect of turbulator holes diameter on heat transfer optimization of a geothermal heat exchanger by using nanofluid

This paper numerically investigates the effect of using some turbulators in a geothermal heat exchanger with the optimal arrangement. The geothermal heat exchanger includes a constant-temperature tube through which the nanofluid flow with Cu nanoparticles passes. In the geothermal heat exchanger, five conical turbulators are used on which there are some holes. By changing the radius of holes on turbulators, turbulator spacing, and length of each turbulator, the outlet nanofluid temperature, the nanofluid temperature in the tube, heat transfer coefficient, mean transverse kinetic energy, velocity contours, and nanofluid temperature in the geothermal heat exchanger are studied. Simulations are conducted using the finite element method, and the nanofluid flow is considered two-phase. Also, artificial intelligence is used to conduct a sensitivity analysis and optimization of results. Results of this study indicate that decreasing the turbulator spacing and decreasing the radius of turbulator holes, and arranging turbulators at moderate distances from each other increase the heat transfer coefficient by up to 27.9%. Increasing the turbulator spacing and diameter of holes leads to mean transverse kinetic energy reduction. The highest and lowest values of maximum nanofluid temperature in the tube are 309.77 K and 303.34 K. The outlet nanofluid temperature varies from 302.42 K to 306.57 K, and the most significant effect on the outlet nanofluid temperature is related to changing the radius of turbulator holes.