Thermal mixing of flows in horizontal T-junctions with low branch velocities

With a constant mass flow rate ratio (main/branch) of 4:1, thermal mixing tests were carried out at temperature differences (ΔT) between the mixing fluids of 65 °C (Case 1) and 143 °C (Case 2), respectively. Two distinct flow trends were identified in the mixing region: (i) an unstable stratified flow being subjected to extreme oscillations in case 1 and (ii) a stable stratified flow being subjected to significant buoyancy effects in case 2. Near-wall thermal fluctuations (a factor in thermal fatigue analysis) with highest amplitudes were recorded by the thermocouples located in the vicinity of the stratification layer in both the cases. Frequency analyses of thermal fluctuations using the power spectral density (PSD) method indicates no dominant frequency (spectral peak) in the frequency range identified to be of relevance for HCTF (0.1-10 Hz). Instead, the energy of thermal fluctuations were mainly contained in the frequency range of 0.1-2 Hz. LES predictions of parameters, viz., mean temperature, thermal fluctuations and its frequency distribution showed good agreement with measurement data.