No abstract

In the present paper, the effects of a new baffle design on the efficiency of a tubular heat exchanger are numerically investigated. It concerns butterfly baffles inserted in a cylindrical tube heat exchanger. We focus on the influence of the shape of baffles, the space between baffles (pitch ratio, PR) and the baffle size (i.e. the blockage ratio, BR) on the heat transfer and flow characteristics. Three geometrical configurations with different PRs are realized (PR = 1, 2 and 4) and five others with different blockage ratios (BR = 0.1, 0.2, 0.3, 0.4 and 0.5). The investigations are achieved for Reynolds numbers ranging from 3000 to 8000. All analyses are realized with the help of the CFD Fluent software. The numerical results are compared with available experimental data and a satisfactory agreement is found. The obtained results showed that the butterfly baffle with PR = 4 and BR = 0.1 is the best design that ensures the best flow mixing and increases the thermal enhancement factor by about 1.7 time with a moderate pressure drop.

The forced convective heat transfer behavior of a turbulent air flow, steady and Newtonian over a fin and oval-tube heat exchanger has been examined numerically. Where, the effect of the tube tilt angle (α) on the heat transfer coefficient and the friction factor was tested. The inclination angle of the oval-tubes going from 0° (Baseline case) to 90° with a step of 10°. The fluid flows and heat transfer characteristics are presented for Reynolds numbers ranging from 3.000 to 12.000. All investigations are carried out with the help of the CFD ANSYS Fluent. Heat transfer coefficient results in the term of the Nusselt number are validated with the available experimental data and a maximum deviation of 9 % is observed. Reasonable agreement is found. The obtained results show that the tube's inclination angle of 20° is the best design which significantly removes the hot spots behind the tubes, thus giving an increase in the heat transfer coefficient of 13 % compared to the baseline case. In addition, useful correlations are developed to predict Nusselt number and friction factor in the fin and oval-tube heat exchanger.