In the framework of this research, the principle focus is to analyze the effects of fluid Prandtl number (Pr) on natural convection heat transfer in a volumetrically heated molten pool. As a part of the work, numerica...In the framework of this research, the principle focus is to analyze the effects of fluid Prandtl number (Pr) on natural convection heat transfer in a volumetrically heated molten pool. As a part of the work, numerical analysis is performed for hemispherical 3-D vessel slice to investigate the physics of the effect of Pr number on convective heat transfer characteristics in the melt pool. The investigation is based on ANSYS FLUET, where natural convection heat transfer effect is taken into consideration by Phase-change Effective Convectivity Model (PECM), which is implemented with FLUENT CFD as User Defined Function (UDF), programed by the user. The PECM is tested first by a benchmark test against CFD to gain confidence in its applicability as an analysis tool. Different simulant materials are used with their thermo-physical properties representing different Pr number as input for modelling for both single and double layer melt pool configuration. The selected modelling approach is validated against RASPLAV experimental result with respect to the inner temperature distribution that qualifies our model to run in the proceeding calculation. It is ensured that an isothermal boundary condition (343 K) is applied along vessel outer wall throughout the series of simulation cases. The corresponding Rayleigh number (Ra) ranges from 1014 - 1015 and Prandtl number (Pr) 3 - 5. It is found that the fluid Pr number has small effects on the averaged Nu numbers in the convection-dominated regions. The decrease in the Pr number may cause a decrease in the Nu numbers on the top and sidewalls of cavities. In the conduction dominated regions (stably stratified bottom parts of enclosure), the effect of fluid Pr number on heat transfer is more significant and it grows with increasing Ra number.展开更多
The electric double layer with the transmission of particles was presented based on the principle of electrochemistry.In accordance with this theory,the cavitation catalysis removal mechanism of ultrasonic-pulse elect...The electric double layer with the transmission of particles was presented based on the principle of electrochemistry.In accordance with this theory,the cavitation catalysis removal mechanism of ultrasonic-pulse electrochemical compound machining(UPECM) based on particles was proposed.The removal mechanism was a particular focus and was thus validated by experiments.The principles and experiments of UPECM were introduced,and the removal model of the UPECM based on the principles of UPECM was established.Furthermore,the effects of the material removal rate for the main processing parameters,including the particles size,the ultrasonic vibration amplitude,the pulse voltage and the minimum machining gap between the tool and the workpiece,were also studied through UPECM.The results show that the particles promote ultrasonic-pulse electrochemical compound machining and thus act as the catalyzer of UPECM.The results also indicate that the processing speed,machining accuracy and surface quality can be improved under UPECM compound machining.展开更多
文摘In the framework of this research, the principle focus is to analyze the effects of fluid Prandtl number (Pr) on natural convection heat transfer in a volumetrically heated molten pool. As a part of the work, numerical analysis is performed for hemispherical 3-D vessel slice to investigate the physics of the effect of Pr number on convective heat transfer characteristics in the melt pool. The investigation is based on ANSYS FLUET, where natural convection heat transfer effect is taken into consideration by Phase-change Effective Convectivity Model (PECM), which is implemented with FLUENT CFD as User Defined Function (UDF), programed by the user. The PECM is tested first by a benchmark test against CFD to gain confidence in its applicability as an analysis tool. Different simulant materials are used with their thermo-physical properties representing different Pr number as input for modelling for both single and double layer melt pool configuration. The selected modelling approach is validated against RASPLAV experimental result with respect to the inner temperature distribution that qualifies our model to run in the proceeding calculation. It is ensured that an isothermal boundary condition (343 K) is applied along vessel outer wall throughout the series of simulation cases. The corresponding Rayleigh number (Ra) ranges from 1014 - 1015 and Prandtl number (Pr) 3 - 5. It is found that the fluid Pr number has small effects on the averaged Nu numbers in the convection-dominated regions. The decrease in the Pr number may cause a decrease in the Nu numbers on the top and sidewalls of cavities. In the conduction dominated regions (stably stratified bottom parts of enclosure), the effect of fluid Pr number on heat transfer is more significant and it grows with increasing Ra number.
基金Project(51275116)supported by the National Natural Science Foundation of ChinaProject(2012ZE77010)supported by the Aero Science Foundation of ChinaProject(LBH-Q11090)supported by the Postdoctoral Science Research Development Foundation of Heilongjiang Province,China
文摘The electric double layer with the transmission of particles was presented based on the principle of electrochemistry.In accordance with this theory,the cavitation catalysis removal mechanism of ultrasonic-pulse electrochemical compound machining(UPECM) based on particles was proposed.The removal mechanism was a particular focus and was thus validated by experiments.The principles and experiments of UPECM were introduced,and the removal model of the UPECM based on the principles of UPECM was established.Furthermore,the effects of the material removal rate for the main processing parameters,including the particles size,the ultrasonic vibration amplitude,the pulse voltage and the minimum machining gap between the tool and the workpiece,were also studied through UPECM.The results show that the particles promote ultrasonic-pulse electrochemical compound machining and thus act as the catalyzer of UPECM.The results also indicate that the processing speed,machining accuracy and surface quality can be improved under UPECM compound machining.
