Nozzle parameters affecting vortex tube energy separation performance

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.     

Temperature separation and friction losses in vortex tube

The process of energy separation and friction losses in a vortex tube is studied in detail. The hot and cold exit air temperatures were measured. Experiments have been conducted at inlet pressure of 3.5, 5, 7.5 and 9 bar, at inlet temperature of 292.15 and 298.15 K and at cold air mass ratio from 0 to1. The results demonstrate that the hot air temperature reaches its maximum value at a cold air mass ratio of nearly 0.82, while the minimum value of cold air temperature is found at a cold air mass ratio of 0.3. Based on energy and mass balances as well as on the definition of internal energy and on experimental results a new model for the determination of hot and cold exit gas temperature has been developed. The model includes the relevant primary parameters and predicts the experimental results as well as the data published in the literature sufficiently accurate for engineering purposes.A cross-section area m³ - D diameter of the pipe m - F model parameter - f friction factor - L length of the tube m - m mass flow rate kg/s - y cold air mass ratio - P static pressure Pa - T temperature K - t thickness of the orifice m - R gas constant J/kg K - v velocity of fluid m/s - density of the fluid kg/m³ - friction factor for pipe - friction factor for orifice and tee junction - 1 inlet of compressed gas - 2 exit of hot gas - 3 exit of cold gas - atm atmospheric pressure - c cold exit gas - f friction - h hot exit gas - o orifice plate - T tee junction     

Flow and thermodynamic characteristics of energy separation in a double-circuit vortex tube - An experimental investigation

Experimental investigations were made into the vortex energy separation effect of gas flux in tubes known as the Ranque effect. Technical applications of the results are considered. Unlike traditional energy separation tubes, so-called double-circuit vortex tubes were chosen that allowed the creation of a refrigeration device with high thermodynamic efficiency. Different thermodynamic and gas dynamical aspects of the processes taking place in the scheme developed are discussed taking into account the modern vortex interaction hypothesis. The possibility of constructing a double-circuit vortex tube refrigeration machine as efficient as a gas expansion system is demonstrated.     

Effect of the conical-shape on the performance of vortex tube

The present study focuses on the effect of conical shape in the cold side of the Ranque-Hilsch vortex tube which is shown to have a considerable influence on the system performance. A vortex tube is a simple circular tube with no moving parts which is capable to divide a high pressure flow into two relatively lower pressure flows with temperatures higher and lower than the incoming flow. A three-dimensional computational fluid dynamic model is used to analyse the mechanisms of flow inside a vortex tube. The SST turbulence model is used to predict the turbulent flow behaviour inside the vortex tube. The geometry of a vortex tube with circumferential inlet slots as well as axial cold and hot outlet is considered. Performance curves temperature separation versus cold outlet mass fraction are calculated for a given inlet mass flow rate and varying outlet mass flow rates.     

Effect of pressure on the exchange of energy in a vortex tube

Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 4, pp. 72–74, July–August, 1989.     

Comparison of heat transfer performance of tube bank fin with mounted vortex generators to tube bank fin with punched vortex generators

The results obtained from naphthalene sublimation heat/mass analogy experiments in selecting the optimum geometrical parameters of tube bank fin heat exchanger with fins mounted with vortex generators are compared with the results obtained from the condensing experiments of the real heat exchangers with vortex generators punched out on the fins. The results declare that VGs pouched or mounted on fin surfaces have only limited effects on heat transfer performance in the studied configurations; naphthalene sublimation method can be used to select fin patterns with reasonable reliability.     

Experimental investigation of the flow characteristics within a vortex tube with different configurations

The energy separation in a vortex tube is a combined result of different factors and its explanation remains debatable. As a classical fluid mechanics phenomenon, understanding of the complex helical flow mechanism within a vortex tube is a necessary foundation. The small scale of an industrial vortex tube and the extremely complex flow conditions are the two main challenges in obtaining the internal flow properties. This paper reports the results of an experimental investigation on the flow behaviour within a confined cylindrical system having different configurations corresponding to the actual flow field in a vortex tube at different conditions. Transparent devices were used to enable flow visualisation and Particle Image Velocimetry (PIV) measurement. The results of the flow visualisation and PIV experiments show that a precessing vortex core is significant only in a specific range of swirling strength. A good agreement between the observed flow characteristics and previously published results was observed.     

Experimental study on thermal performance of filled-type evacuated tube with U-tube

The filled-type evacuated tube with U-tube, in which the filled layer is used to transfer energy absorbed by working fluid in the U-tube, is proposed to eliminate the effect of thermal resistance between the absorber tube and copper fin of the conventional solar collector. In this paper, the thermal performance of the filled-type evacuated tube was researched by means of experimental study. In order to avoid the effect of some uncertain factors, the single collector tube was considered as investigated objective. The test setup of the thermal performance of the filled-type evacuated tube with U-tube was established. The results show that the filled-type evacuated tube with U-tube has a favorable thermal performance compared with the evacuated tube with copper fin. The heat efficiency of filled-type evacuated tube is higher than that of copper fin evacuated tube by 12%. The useful energy gain of filled-type evacuated tube is 22% higher than that of copper fin evacuated tube at the practical irradiance received I _T?=?800?W/m² and flow rate M _f?=?0.005 L/s. In addition, the exergy efficiency of the filled-type evacuated tube is higher than that of copper fin evacuated tube.     

Numerical simulation of secondary vortex chamber effect on the cooling capacity enhancement of vortex tube

A vortex tube with additional chamber is investigated by computational fluid mechanics techniques to realize the effects of additional chamber in Ranque–Hilsch vortex tube and to understand optimal length for placing the second chamber in order to have maximum cooling effect. Results show that by increasing the distance between two chambers, both minimum cold and maximum hot temperatures increase and maximum cooling effect occurs at Z/L = 0.047 (dimensionless distance).     

Experimental study of the airside performance of tube row spacing in finned tube heat exchangers

Almost all of the studies in dehumidifying coils are experimental studies. In this study, effect of tube regulation space on heat and mass transfer and friction factor for heat exchangers made from aluminum fins and cooper tubes are identified experimentally. External surface heat transfer coefficient, Colburn factor and friction factor was calculated by the help of the computer program by using experimental values done. After the diagrams investigated, with the decreasing of tube row spacing the external surface heat transfer in the dry surface and friction factor increased. If wet and dry surfaces are compared, Colburn and friction factor in wet surfaces is larger than Colburn and friction factor in dry surfaces.     

Experimental analysis of the precessing vortex core in a free swirling jet

An experimental analysis of the precessing vortex core (PVC) instability in a free swirling jet of air at ambient pressure and temperature is performed by means of laser Doppler velocimetry (LDV) and particle image velocimetry (PIV). Two parametric studies are considered, varying the swirl parameter and the Reynolds number. The range of parameters considered allowed to study conditions of strong precession as well as the inception and settlement of the instability. Mean velocity and standard deviation profiles, power spectral density functions and probability density functions for the axial and tangential velocity components are presented. Average as well as instantaneous PIV maps are considered in the characterization of the flowfield structure and detection of the instantaneous position of the vortex center. Joint analysis of velocity PDFs and power spectra shows that the PVC contribution to the global statistics of the velocity field can be properly separated from the contribution of the true flow turbulence, giving additional insight to the physics of the precession phenomenon. The results obtained in the explored range of conditions indicate that the true turbulence intensity is not dependent on the swirl parameter. An erratum to this article can be found at     

Visualization of the flow structure in a vortex tube

The temperature separation in a vortex tube has been investigated for the purpose of exploring the phenomenon and improving the tube performance. Different explanations for the temperature separation have been proposed. However, there has not been a consensus in the hypothesis.This paper reports on a study in progress exploring the flow structure in a vortex tube. Flow visualization, using water as a working fluid, is used to reveal the existence of multiple circulation regions within the vortex tube and a new hypothesis describes the temperature separation mechanism. This research contributes to the understanding of the flow behavior in a vortex tube and supports the previous works that show the generation of the cold component of the flow is the result of the expansion near the cold nozzle and the hot component is produced due to the friction between the layers of flow.     

Experimental investigation of vortex rings impinging on inclined surfaces

Vortex–ring interactions with oblique boundaries were studied experimentally to determine the effects of plate angle on the generation of secondary vorticity, the evolution of the primary vorticity and secondary vorticity as they interact near the boundary, and the associated energy dissipation. Vortex rings were generated using a mechanical piston-cylinder vortex ring generator at jet Reynolds numbers 2,000–4,000 and stroke length to piston diameter ratios (L/D) in the range 0.75–2.0. The plate angle relative to the initial axis of the vortex ring ranged from 3 to 60°. Flow analysis was performed using planar laser-induced fluorescence (PLIF), digital particle image velocimetry (DPIV), and defocusing digital particle tracking velocimetry (DDPTV). Results showed the generation of secondary vorticity at the plate and its subsequent ejection into the fluid. The trajectories of the centers of circulation showed a maximum ejection angle of the secondary vorticity occurring for an angle of incidence of 10°. At lower incidence angles (<20°), the lower portion of the ring, which interacted with the plate first, played an important role in generation of the secondary vorticity and is a key reason for the maximum ejection angle for the secondary vorticity occurring at an incidence angle of 10°. Higher Reynolds number vortex rings resulted in more rapid destabilization of the flow. The three-dimensional DDPTV results showed an arc of secondary vorticity and secondary flow along the sides of the primary vortex ring as it collided with the boundary. Computation of the moments and products of kinetic energy and vorticity magnitude about the centroid of each vortex ring showed increasing asymmetry in the flow as the vortex interaction with the boundary evolved and more rapid dissipation of kinetic energy for higher incidence angles.     

The evolution of starting vortex and secondary separation on an elliptic cylinder

Flow visualization was used to investigate experimentally the evolution process from symmetrical shedding to staggered shedding of the starting vortex and the phenomenon of secondary separation on an elliptic cylinder at moderate Reynolds numbers. The vortex structure of the flow separation was studied. The temporal variation of separation angle and length of wake vortex were given. The photographs and experimental results provided basis for further investigation of the complicated feature of the starting process of unsteady separated flows around an elliptic cylinder. The project supported by the National Natural Science Foundation of China.     

Thin‐tube vortex simulations for sinusoidal instability in a counter‐rotating vortex pair

A thin‐tube vortex method is developed to investigate the intrinsic instability within a counter‐rotating vortex pair system and the effects from the core size and the wavenumbers (or wavelengths). The numerical accuracy and the advantages of the scheme are theoretically estimated. A nearest‐neighbour‐image method is employed in this three‐dimensional vortex simulation. Agreement with Crow's instability analysis has been achieved numerically for the long‐wave cases. A short‐wave instability for the zeroth radial mode of bending instability has also been found using the thin‐tube vortex simulations. Then, the combinations of long‐ and short‐wave instability are investigated to elucidate the non‐linear effects due to the interactions of two different modes. It is shown that instability is enhanced if both long‐ and short‐wave instabilities occur simultaneously. Although the method used in the paper is not capable of including effects such as axial flow, vortex core deformation and other complicated viscous effects, it effectively predicts and clarifies the first‐order factor that dominates the sinusoidal instability behaviour in a vortex pair. Copyright © 2002 John Wiley & Sons, Ltd.     

Modeling and preliminary analysis of piezoelectric energy harvester based on cylindrical tube conveying fluctuating fluid

In this contribution, a novel type of piezoelectric tubular energy harvester based on fluctuating fluid pressure is investigated. Analytic model of the proposed energy harvester is built under the assumption of axisymmetric radial vibration. Exact solution of the piezoelectric vibrating tube is obtained with its output performances formulated. A series of numerical simulations are conducted to investigate the influences of geometrical parameters, input mechanical load parameters and output electrical load parameters upon the output performances of the proposed piezoelectric tubular energy harvester. The model and simulation results indicate the potential of the proposed piezoelectric tubular energy harvester. It is expected that the energy harvester be useful in powering wireless sensor network for the health monitoring of hydraulic systems, where fluid conveying pipe vibration is omnipresent.