The working principle of a vortex tube

• A novel explanation for the temperature separation in a vortex tube.
• Experimental validation of the proposed flow behaviour.
• Analytical validation of the proposed hypothesis.
• Successful application in explaining the geometrical effects.

The generation of cold and hot streams from a single injection in a vortex tube has been investigated by many researchers, aiming to define the primary reasons for the separation. This paper reports a detailed description of the flow behaviour inside a vortex tube and addresses the mechanism for the generation of cold and hot streams in a vortex tube, which is confirmed by different experimental methodologies, including visualization of the flow structure in a water-operated vortex tube, and measurement of velocity profiles in both water- and air-operated vortex tubes. Estimation of the theoretical temperature drop based on the pressure gradient of a forced vortex flow is addressed in this paper, and good agreement with the experimental results was observed. Exergy analysis of the flow properties in an air-operated vortex tube indicates that there is no outward energy transfer in the hot region of the vortex tube. Furthermore, the governing factor for the temperature rise is attributed to the stagnation and mixture of the flow structure. Based on the proposed mechanism, the predicted performance of the vortex tube with variable geometrical parameters, were congruent with the experimental results, underpinning the validity of the proposed mechanism.