Precessing vortex breakdown and energy separation in a Ranque–Hilsch vortex tube

Significance 

Ranque–Hilsch vortex tube is a mechanical device that separates a compressed gas into hot and cold streams. This vortex tube is popular due to the fact that it’s among the few eco-friendly thermal devices. As a result, it has been widely applied in thermal dynamic systems and in oil and gas industries. Unfortunately, the development of this device has been bottle-necked by its empirical design method and relatively low thermal efficiency which tend to affect its energy separation performance. From the existing plethora of literature, it is crystal clear that the structure of this vortex tube if far from the desired clear flow structure. In addition, when considering external conditions, it has become extremely difficult to predict the trend of changes in the flow structure due to lack of a theoretical model. As a resolve, studying the flow structure and energy separation with vortex breakdown in the Ranque–Hilsch vortex tube would be a possible solution. Despite the awareness of such knowledge, no work has been reported on the same.

To this note, researchers professor Bo Zhang and his PhD Student Xiangji Guo from the School of Energy and Power at Dalian University of Technology in China proposed a study where the main objective was to advance the 3D computational simulation in order to analyze the effect of different external conditions on the flow structure based on the vortex breakdown theory. In addition, the two scholars also intended to comprehend how cold mass fraction behaves as an external condition that affects the vortex breakdown, and how the large-scale vortex flow structure influences the flow field, and subsequently the energy separation performance within the Ranque–Hilsch vortex tube. Their work is published in the research journal, International journal of refrigeration.

The two researchers commenced the empirical procedure by computationally investigating the flow structure and energy separation when considering the effect of cold mass fraction in a Ranque–Hilsch vortex tube. Next, they adopted a quasi-cylindrical approximation to predict the size of the vortex core size by considering the pressure gradient. Eventually, a novel analysis was conducted on the energy separation mechanism after which the type of vortex breakdown witnessed was assessed.

The authors observed that by an increase in the cold mass fraction in a vortex tube resulted in the enhancement of the adverse pressure gradient along the same axis. The axial pressure gradient was seen to significantly affect the vortex breakdown structure. Moreover, it was seen that an increment in the vortex core size caused expansion of the area of the reverse flow boundary.

Zhang and Guo study has presented a detailed computational investigation of precessing vortex breakdown and energy separation in a Ranque–Hilsch vortex tube. This study has thoroughly elucidated on the process by which changes in an external condition affect the final energy separation performance.  It has been seen that for the vortex tube used, the vortex breakdown phenomenon occurs in the strong swirling flow. Altogether, this paper has presented a novel idea on the manner in which external factors influence the large-scale vortex structure and on the subsequent energy separation performance.

About the author

Bo Zhang

He is a professor of school of energy and power, Dalian University of Technology. He obtained his B.S. degree at Xi’an Jiaotong University and Ph.D. degree at Dalian University of Technology. He has focused on study on the complex fluid flow structure and heat/mass transfer. And he realized the industrialization of large and efficient ejector refrigeration/heat pump system with Freons for the first time in China.

About the author

Xiangji Guo

She is a doctoral student at school of energy and power, Dalian University of Technology. She investigates the heat and mass transfer processes in a Ranque-Hilsch vortex tube by numerical simulation and non-intrusive laser measurements with PIV and LDV. She also focuses on the explanation and optimization of energy separation performance in vortex tube and published several papers.

Reference

Xiangji Guo, Bo Zhang. Computational investigation of precessing vortex breakdown and energy separation in a Ranque–Hilsch vortex tube. International journal of refrigeration, volume 85 (2018) pages 42–57.

 

Go To International journal of refrigeration

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