Although the mechanism of the energy separation in a vortex tube still remains debatable, it is well agreed that the geometrical parameters have significant impacts on its thermal performance. The present parametric experimental investigation sheds new light upon the temperature variation and energy separation in a novel convergent valveless vortex tube, whereas the performance of a straight vortex tube is additionally measured for comparison. The temperature variation and energy separation of the convergent vortex tube were observed in all the tested configurations and the convergent valveless vortex tube was found to have a better working performance with some configurations comparing with the conventional straight vortex tube. It achieved a maximum increase of 25 degrees in the temperature variation and 32% in the coefficient of performance (COP). This implies that it is possible to reduce the cost of a vortex tube and achieve a better performance in the meantime.