Numerical analysis of NOx reduction for compact design in marine urea-SCR system

ABSTRACTIn order to design a compact urea selective catalytic reduction system, numerical simulation was conducted by computational fluid dynamics tool. A swirl type static mixer and a mixing chamber were considered as mixing units in the system. It had great influence on flow characteristics and urea decomposition into ammonia. The mixer caused flow recirculation and high level of turbulence intensity, and the chamber increased residence time of urea- water-solution injected. Because of those effects, reaction rates of urea decomposition were enhanced in the region. When those mixing units were combined, it showed the maximum because the recirculation zone was significantly developed. NH3 conversion was maximized in the zone due to widely distributed turbulence intensity and high value of uniformity index. It caused improvement of NOx reduction efficiency of the system. It was possible to reduce 55% length of the chamber and connecting pipe without decrease of NOx reduction efficiency

Prediction of Refrigerant Leakage for Discharge Valve System in A Rolling Piston Rotary Compressor

The flow coefficient of a discharge valve system with lift height was functionalized by experiments and Computational Fluid Dynamics(CFD) simulation to predict the mass flow rate through a discharge valve system in a rolling piston compressor with different compressor frequency and operating conditions. The flow coefficients of the discharge valve system were determined by both experiments and CFD simulation for specifically configured condition with varying discharge port diameter, valve lift height and valve shape to consider operating and geometric conditions. The experiment and CFD simulation were conducted under the incompressible flow and steady state. Ambient air was used as a working fluid. In order to verify the reliability of CFD simulation, the computational results were compared with those of experiment. The flow coefficient maps for each discharge valve system could be obtained from the computational results. The functional flow coefficient model was derived from the maps. It was applied to compressor performance simulation to calculate mass flow rate at the discharge valve system as a function of diameter of discharge port and lift height of the valve. Energy Efficiency Ratio(EER) obtained from the functional flow coefficient model with varying compressor frequency showed good agreement with experimental data. The Functionalization of flow coefficient may improve the precision of compressor performance simulation

Prediction of Leakage Flow of Radial Clearance in a Rolling Piston Rotary Compressor

The functional formula of the flow coefficients for the radial clearance in a rolling piston rotary compressor was developed by the experiments and Computational Fluid Dynamics (CFD) to improve the accuracy of a compressor simulation program. The experiments and CFD simulation were conducted to obtain the flow coefficients at the radial clearance under the assumptions of incompressible flow and steady state. The experiments were carried out with the variation of pressure ratio (0.1 to 0.9, step 0.2) and upstream pressure using the nitrogen as a working fluid. The CFD simulation was adopted to calculate the flow coefficients at the radial clearance with change of the area of radial clearance. The results of CFD calculation were compared with the experimental results for verifying the reliability of CFD simulation. The functional formula obtained from the results of the CFD calculation was applied to compressor simulation for calculating the leakage flow through the radial clearance. The results of compressor simulation with the functional formula showed good agreement with the experimental data of the compressor calorimeter like EER (Energy Efficiency Ratio). Thus, the function of the flow coefficients may be acceptable for prediction of leakage through the radial clearance under the various conditions