Numerical investigations of the impact of a novel turbulator configuration on the performances enhancement of heat exchangers. (February 2022) - Salhi, Jamal-Eddine
Highlights: Proposition of a heat exchanger configuration using small helical baffle turbulators. The numerical simulations were performed by using a three dimensional CFD computer code. The average deviation between the numerical and experimental data is between 4 and 8%. The improvements in heat transfer (ηTPF ) can reach 2.71 for a pitch distance of 48 mm. For high Re numbers a tube with a configuration A3 is the optimal choice with an air inlet-outlet temperature difference of 39.91 °K in comparison to the smooth tube. The variation of Nu/Nusmooth shows that the case (D3 ) is the best choice for high Re numbers with 4.41. Abstract: This paper presents an numerical simulation of the thermo-fluid characteristics for a heat exchanger with smooth concentric double tube equipped by Turbulators operating in the turbulent regime with Reynolds numbers from 3000 to 17, 000. This heat exchanger is designed to provide a tubular heat energy exchange from a primary fluid (hot air) to a secondary fluid (cold water) in order to ensure efficient heat transfer with less heat loss. The main focus of this work is the development of a novel configuration for the exchangers with the insertion of a small baffle turbulators on it. These tabulators act as a turbulence promoters for enhancing the thermal performance of the heat exchanger system. Besides, the optimization of these turbulators is assessed by evaluating different baffles configuration and the influence of the pitch distance between them on the thermos-hydrodynamic behavior of the coolant flow. To evaluate the performance of the proposed configuration we evaluated a bench of thermal parameters, mainly Nusselt number, the friction factor, the thermal performance factor, the turbulent viscosity, the temperature field and the velocity field among others. After that, correlations between the Reynolds and Nusselt numbers and Reynolds and the friction factor were conducted for the whole configurations. Results show that the structure of the flow is strongly influenced by the shape and dimensions of inserted baffles. The Nusselt number and the friction factor increase when the inter-Turbulator distance is reduced. Also, the separating of the tube by the insert of the turbulators induces a vortex flow which leads to the improvement of the forced convection. The improvements in heat transfer (ηTPF ) is also evaluated using turbulators with different pitches (260; 108.57; 67.27 and 48 mm). These configurations leads to an increase of ηTPF with 2.36; 2.42; 2.53 and 2.71 in respect to the pitches mentioned above. Besides, the outlet temperatures are respectively equal to: 358.79, 340.15, 337.39, 333.09 and 329.72 ° K. This reflects a difference in the overall inlet-outlet air temperature of: 14.21 ° K for the smooth case; 32.85 ° K (case (A1 ); 35.61 ° K case (A2 ); 39.91 ° ​​K case (A3 ) and 43.28 ° K case (A4 ).