Heat Transfer Characteristics outside the Condenser of a Rotating Heat Pipe Grinding Wheel with a Lateral Air Impinging Jet

This study numerically analyzed the heat transfer characteristics outside the condenser of a rotating heat pipe grinding wheel(RHP-GW).The goal of this investigation is to determine the optimal structure and parameters for the condenser section of RHP-GW.Different fin height(f=0-7 mm),rotational Reynolds number(Rer=1602-6408)and jet Reynolds number(Rej=42379-108302)were analyzed under input heat flux of 4000 W/m2.A fully developed flow was imposed at the outlet of the nozzles.Results showed that the optimal heat transfer rate was obtained for fin height of 5 mm,which improved the average Nusselt number by 84%compared to the structure without fins.A critical Rej for each Rer that the impinging jet can reach the condenser section was found.The critical Rej value increases with Rer,which is in the range from 42379 to 61215 and 61215 to 80050 for Rer=6408 and Rer=9610,respectively.

Particulate matter emission by an isolated rotating wheel

Particulate matter emission from rotating wheels, which imparts a force to the contact surface and causes strong air currents, is one of the important pollutant sources on the road. This study investigates the particulate matter emission by measuring mass and size distributions of particulate matter near an isolated rotating wheel in a deliberately designed setup. Five rotating speeds from 0.7 m/s to 1.5 m/s are conducted to test its impact on the emission of particulate matter. Mass of particulate matter is measured at twenty-six sampling points around the rotating wheel under different experimental conditions. Experimental results show that the farther away from the wheel, the less of particulate matters deposited on the sampling points in general. Moreover, the emission factor increases from 0.12 g/vkt to 0.24 g/vkt when the rotating speed of the wheel increases from 0.7 m/s to 1.5 m/s. The number and proportion of PM2.5 and PM10 on different sampling points are also measured. The results show that the position of the highest number of PM2.5 and PM10 tends to move to a further and higher sampling point with the increasing of the speed. Moreover, the number proportions of PM2.5 and PM10 on the sampling points range from 19% to 97% and 61% to 100% at different speeds, respectively. This study is believed to be helpful to estimate particulate matter emission and make effective control strategies on targeted pollution.

Influence of ground effect on flow field structure and aerodynamic noise of high-speed trains

The simulation of the ground effect has always been a technical difficulty in wind tunnel tests of high-speed trains.In this paper,large eddy simulation and the curl acoustic integral equation were used to simulate the flow-acoustic field results of high-speed trains under four ground simulation systems(GSSs):“moving ground+rotating wheel”,“stationary ground+rotating wheel”,“moving ground+stationary wheel”,and“stationary ground+stationary wheel”.By comparing the fluid-acoustic field results of the four GSSs,the influence laws of different GSSs on the flow field structure,aero-acoustic source,and far-field radiation noise characteristics were investigated,providing guidance for the acoustic wind tunnel testing of high-speed trains.The calculation results of the aerodynamic noise of a 350 km/h high-speed train show that the moving ground and rotating wheel affect mainly the aero-acoustic performance under the train bottom.The influence of the rotating wheel on the equivalent sound source power of the whole vehicle was not more than 5%,but that of the moving ground slip was more than 15%.The average influence of the rotating wheel on the sound pressure level radiated by the whole vehicle was 0.3 dBA,while that of the moving ground was 1.8 dBA.