Investigation Of Flow And Heat Transfer Of Fluid Mixing In A Tee Junction With Or Without Porous Media

Tee junction is easily suffered from temperature fluctuation resulting in thermal fatigue in the piping system of petroleum, chemistry, energy, and power. Velocity and temperature fluctuations of the mixing of hot and cold fluids are the essence to induce thermal fatigue of the tee junction. Flow and heat transfer model was established with the sub-grid scale model of Smagorinsky-Lilly. Large-eddy simulation (LES) of the mixing was compeleted to capture the information of velocity and temperature. Mean and root mean square value of velocity and temperature were analyzed. The object of the present work was to reveal the mechanism of flow and heat transfer of the hot and cold fluids mixing in the tee junction. Furthermore, it was proposed that porous media was packed in the tee junction to weaken the velocity and temperature fluctuations of the mixing. The main work was conducted as following:(1) Validation of LES of hot and cold fluids mixing in the tee junction. Comparisons of normalized mean velocity and normalized root mean square velocity of LES to their corresponding in the previous reference were analyzed.(2) Based on the validation of LES, the influences of the Reynolds number, Re, and Richardson number, Ri, which reflect inertial force and buoyancy force, respectively, to the hot and cold fluids mixing in the tee junction were investigated and analyzed for the case without porous media.(3) Characteristics of flow and heat transfer of the cases with or without porous media in the tee junction were compared and analyzed.Throught above investigation, the main conclusions were drawn as following:(1) The numerical results have somewhat agreentment with the experimental results, which describles that LES could effectively predict the flow and heat transfer of the hot and cold fluids mixing in the tee junction.(2) For the case without porous media, altought there is some difference of normalized mean and root mean square velocity and temperature between symmetrical planes, as a whole, the results showed good symmetry; The normalized root mean square velocity and temperature near the mixing center of the downstream of the main duct were greater than those far from the mixing center, which explains that the mixing of hot and cold fluids near the mxing center of the downstream of the mian duct was stonger than that far from the mixing center.(3) For the case without porous media, influences of different momentum ratios of main duct to brach duct without temperature difference between maind duct and brach duct, namely, different Reynolds number, Re, on the mixing were discussed and analyzed. Typacial impinging jet, deflecting jet, and wall jet were obtained. Greater momentum ratio was, uniformer the distribution of mean velocity along the z/db direction was, smaller the root mean square velocity was, which implys that the vertical momentum of the brach duct has less influence on the horizontal momentum of the main duct.(4) For the case without porous media, influences of temperature difference between main duct and brach duct, namely, different Richardson number, Ri, on the mixing were discussed and analyzed. Greater temperature difference between cold fluid of brach duct and hot fluid of main duct was, greater buoyance force was, unevener the distributions of the normalized mean velocity and temperature were, greater the normalized root mean square velocity and temperature were.(5) Comparisons of the parameters such as normalized mean velocity and temperature, normalized root mean square velocity and temperature, and power spectrum density between the cases with porous media and without porous media were completed. The analysis reveals that the porous media could cause the mixing uniformer resulting in the distributions of normalized mean velocity and temperature uniformer and the normalized root mean square velocity and temperature smaller. It was concluded that porous media could effectively reduce the velocity and temperature fluctuations of the hot and cold fluids mixing in the tee junction. In the present work the mechanism of flow and heat transfer inducing the thermal fatigue of the tee junction was revealed. The porous media could effectively weaken the fluctuation of velocity and temperature of the mixing in the tee junction. The present results have somehow significance for the design, optimization, safty, and lifecycle evaluation of the tee junction.