ORIGINAL Nozzle parameters affecting vortex tube energy separation performance Mohammad O. Hamdan • Basel Alsayyed • Emad Elnajjar Received: 16 December 2011 / Accepted: 27 November 2012 Ó Springer-Verlag Berlin Heidelberg 2012 Abstract This experimental study reports the effect of nozzle parameters on the energy separation of the vortex tube. The results indicate that maximum energy separation is achieved with tangential nozzle orientation while the symmetry/asymmetry of nozzles has a minimal effect on the performance of the energy separation. For current selected conditions and parameters, the study shows that the optimum number of nozzles for maximum energy separation is around 4 nozzles. List of symbols COP Coefficient of performance C p Specific heat constant (kJ/kg K) D Vortex tube inner diameter (m) P in Inlet pressure (bar) _ m h Hot mass flow rate (kg/s) _ m c Cold mass flow rate (kg/s) _ m in Inlet mass flow rate (kg/s) RHVT Ranque-Hilsch vortex tube r Radial coordinate T h Hot outlet temperature (°C) T c Cold outlet temperature (°C) T in Inlet temperature (°C) DT h Temperature difference between the inlet and the hot outlet, DT h = T h - T in DT c Temperature difference between the inlet and the cold outlet, DT c = T in - T c z Axial coordinate Z Dimensionless axial coordinate representing the distance between the vortex generator and the vortex stopper, Z = z/D Greek symbols e Cold mass fraction e = m c /m in h Tangential coordinate / Tangent nozzle orientation angle Subscripts HP Heat pump R Refrigerator 1 Introduction The vortex tube is a thermal static tube that separates compressed gas flow to two streams; one stream colder than the inlet flow while the other stream is hotter than the inlet flow. The vortex tube does not have any moving parts and the separation occurs due to vortex flow generation without requiring any external mechanical work or heat transfer. The vortex tube was first discovered by Ranque [1, 2] who was granted a French patent for the device in 1932, and a United States patent in 1934. Ranque encountered the vortex tube phenomenon while he was experimentally working with vortex tube pump in 1928. In 1945, Rudolf Hilsch [3] conducted an experiment on vortex tube that focused on the thermal performance with different inlet pressure and different geometrical parameters. In the recent years it was known that vortex tube is a low cost and an effective solution for many spot cooling problems. The separation mechanism inside the vortex tube remains until today not completely understood [4]. The ability to obtain either hot or cold flow streams using compressed gas, allowed the use of vortex tube in many M. O. Hamdan (&)  B. Alsayyed  E. Elnajjar Department of Mechanical Engineering, United Arab Emirates University (UAE), P.O. Box 17555, Al-Ain, United Arab Emirates e-mail: MohammadH@uaeu.ac.ae 123 Heat Mass Transfer DOI 10.1007/s00231-012-1099-2