The mixing process of pre-evaporated afterburner fuel at different positions upstream of the mixers and airflow was numerically simulated in a straight channel, with semicircular mixer, rectangular mixer, triangular mixer and chevron mixer respectively. The effects of vortices generated by mixers on fuel distribution and mixing characteristics were studied. The results show that: (1) The scale, strength and breaking speed of the streamwise vortex and the development speed of normal vortex are different downstream of the four mixers, which accelerate the mixing process of fuel and airflow. (2) The fuel distribution at the outlet of mixers, downstream of straight section and downstream of the crest and trough is mainly affected by secondary flow, the streamwise vortex and the normal vortex respectively. (3) The fuel mixing uniformity downstream of the four mixers is increased by about 80% compared with no mixer. In the limited distance, the mixing performance of chevron mixer is the best, while the triangular mixer is the worst Rectangular mixer has the fastest mixing speed and superior comprehensive performance. In addition, the effect of the channel wall on the mixing process downstream of mixers cannot be ignored.

Supercritical water (scW) is important for various engineering applications. The structure and distribution of scW is key to dominate the related processes and phenomena. Here, scW is investigated using molecular dynamics (MD) simulation with controlled pressure and temperature. Density oscillation is observed to occur in a 1 nm thickness bin, indicating mass exchange of particles across the bin interface. We show that the low density scW behaves strong heterogeneity. Quantitative analysis of system density fluctuations is performed by square root error and maximum structure factor, demonstrating the agreement between the two methods. The scW molecules are tightly gathered to form “liquid island” locally, but are very sparse in other regions, which are similar to the gas-liquid mixture in subcritical pressure. A target molecule is tracked to plot 3D displacements and rotating angles, with the former indicating large amplitude ballistic (diffusing) motion and small amplitude oscillation, and the latter displaying two scales of angle jumping. Both translation and rotating motion are related to hydrogen bond break up and reorganization. The low density scW behaves isolated molecules with few combinations of hydrogen bonds between molecules, while the high density scW behaves more combinations of molecules via hydrogen bonds. The two scales motion is expected to influence thermal/chemical process in supercritical state, deepening the fundamental understanding of scW structure.

In order to study the variation of brake torque, vibration, pressure fluctuation, exterior noise and internal flow for a hydraulic retarder with different inclination angles and liquid-filled amount, a bench-scale hydraulic retarder was built. The INV3020 data collection system was used for the synchronous acquisition of brake torque, vibration, pressure fluctuation and exterior noise signals. Experiments were performed with different inclination angles (90° and 75°) and six liquid-filled amount (50 vol%, 60 vol%, 70 vol%, 80 vol%, 90 vol% and 100 vol%). The torque-volume ratio was proposed to accurately analyze the influence of inclination angle on the liquid volume in stator and rotor and the brake performance. Mixture multiphase flow model was employed to capture the volume and velocity distribution. The research shows that the brake performance improves and the vibration increases with the decrease of inclination angle and the increase of liquid-filled amount. The pressure fluctuation increases as the liquid-filled amount increases, while the lower inclination angle effectively lowers the pressure fluctuation amplitude. The sound pressure level trends upward with increasing liquid-filled amount, and the lower inclination angle can effectively reduce the noise. The volume distribution of the liquid phase under different liquid-filled amount is basically consistent. The lower inclination angle can induce more vortexes.

Condensation is a phase-change heat-transfer phenomenon crucial in many industries involving latent heat release and mass transfer. Shell-and-tube condensers are essential contributors to the condensation process, and their tube bundles serve as a substrate. Here, the thermal-hydraulic characteristics of condensation in a longitudinal-flow shell-and-tube condenser were investigated numerically. The shell-side longitudinal-flow condensation on the horizontal tube bundles was studied considering inlet flow rate, overheating temperature, and non-condensable gases. Related pressure drops and heat transfer coefficients were subdivided into several components to provide further insights. Two-phase interface behavior analyses were conducted to demonstrate the outcomes with respect to the non-condensable gas layer, vapor quality, and non-condensable gas type. Based on the thorough quantitative analyses outlined above, the thermal resistance of the condensation on the horizontal tube bundle was investigated. The thermal resistance outside the tube was found to dominate the condensation process. Finally, hexagon clamping baffles (HCBs) were introduced as a novel solution to impair condensate boundary layers and provide perturbations to intensify condensation heat transfer. The results revealed that the HCBs enhanced the total heat transfer coefficients by 8.1%–40.7% while reducing the critical overheating temperature and the threshold ratio between sensible and latent heat.

The thermal-hydrologic-mechanical (THM) coupled processes in water-based enhanced geothermal system (EGS) greatly influence the heat extraction performance of EGS. Many THM models have been proposed, however, there is a lack of detailed analysis of water storage, which is caused by the increments of reservoir porosity and water density, and the influence of water storage on the heat extraction performance needs to be uncovered. In this paper, a 3D THM model is established to simulate the water storage amount and heat extraction rate for a water-based EGS. The 3D THM model is verified against an analytical solution. Then, the influences of water storage are investigated, and comparisons between the THM and thermal-hydrologic (TH) processes are made for different initial reservoir porosities. The results show that the increment of reservoir porosity has a larger influence on water storage than that of water density. If ignoring water storage, the injection flow rate would be underestimated, while the production flow rate and heat extraction rate would be overestimated, and the reservoir would be cooled a little slower. Compared with the TH processes, the THM processes show larger cumulative water storage amount, higher steady-state heat extraction rate and higher cooling rate of reservoir, indicating that mechanical process has important influences on EGS performances. For higher initial reservoir porosity, the cumulative water storage amount is larger. It can be inferred that the water storage amount is related to the cooling rate of reservoir. The results of this paper show that water storage has a certain influence on the heat extraction rate, and that the mechanical process and initial reservoir porosity have important effects on the water storage amount, which should be simulated based on a THM model.