Search

A test facility was constructed to investigate the flow characteristics of lateral synthetic jets generated by an actuator composed of a cavity, an orifice and a vibrating piezoelectric disc. Subsequently, 3D unsteady numerical simulations were conducted to analyze the formation of the synthetic jets and their dependence on the height of the orifice exit from the outer surface of the cavity. The time-averaged axial velocity was measured and used to validate the numerical results, and the maximum velocity reached approximately 8 m/s. In this work, it was found that the interaction of the vortex tube generated at the edge of the orifice exit and the outer surface of the cavity has a significant impact on the axial velocity distribution and characteristics of the lateral synthetic jets. Based on the experimental data and the numerical results, an attempt has been made to understand the formation of the synthetic jets and their interaction with the outer surface. [ABSTRACT FROM AUTHOR]

We numerically study a distorted version of the Euler and Navier–Stokes equations, which are obtained by depleting the advection term systematically. It is known that in the inviscid case some solutions blow up in finite time when advection is totally discarded, Constantin (1986 Commun. Math. Phys. 104 311–26). Taking a pair of orthogonally offset vortex tubes and the Taylor–Green vortex as initial data, we show the following. (1) Blowup persists even with viscosity when advection is discarded, and (2) for small viscosity, the time of blowup increases logarithmically as we reinstate advection using a continuous parameter, which would be consistent with the regularity of the Navier–Stokes equations. A tiny mismatch in the coefficient of the advection term, as minute as parts per trillion, throws the system out of compactness and leads to blowup. [ABSTRACT FROM AUTHOR]

In hydro turbines, the draft tube vortex rope is one of the most crucial impact factors causing pressure pulsation and vibration. It is affected by operating conditions due to differences in the flow rate and state and can be symmetric or asymmetric along the rotational direction. It may influence the stability of draft tube flow. To achieve a better understanding, in this work, dynamic mode decomposition is used in a draft tube case study of a simplification of a vortex rope. As the flow rate increases, the shape of the vortex rope becomes clear, and the flow rotation becomes more significant as the inlet flow rate increases. Dynamic mode decomposition was used to determine the relative frequencies, which were 0 (averaged), 0.7 times, and 1.4 times the features of the reference frequency. As the inlet flow rate increases, the order of high-energy modes and their influence on the vortex rope gradually increase, and this characteristic is exhibited further downstream of the draft tube. When the inlet flow rate is low, the impact of mode noise is greater. As the flow velocity increases, the noise weakens and the rotation mode becomes more apparent. Identifying the mode of the vortex flow helps extract characteristics of the vortex rope flow under different operating conditions, providing a richer data-driven basis for an in-depth analysis of the impact of operating conditions on the flow stability of a draft tube. [ABSTRACT FROM AUTHOR]

With the widespread application of vortex tube in various fields, it becomes essential to quantitatively explore the separation effect of different fluids (natural fluids, hydrocarbons, etc.) within the vortex tube and to promote its utilization. A new approach has been developed in this study to establish quantitative models for predicting the thermal effects of different fluids in a vortex tube. These models are based on both the macro properties of the working fluid and micro molecular descriptor through a molecular scale. A dataset of 11 numerical simulation results of hydrocarbons and hydrofluorocarbons refrigerants is employed. Three operating conditions, 10 property parameters, and 115 molecular descriptors are screened and identified using random forest feature analysis. Two types of models (micro and macro) have been developed by employing artificial neural network (ANN) modeling techniques. In the result, four key influencing fluid property parameters (the specific heat ratio γ, the multiplication of heat capacity and the molar weight cp·M, the kinematic viscosity ν, and the thermal conductivity λ) and nine molecular descriptors in affecting the thermal effect are identified and respectively chosen as the input in the macro and the micro ANN model establishment. Both types of developed models show a high correlation coefficient (R >.999) and a comparatively low mean square error (MSE). When R600 is employed in the validation, most of the relative error is less than 10%, suggesting both types of models can work effectively in predicting the thermal effect for other fluid. The findings contribute to a deeper understanding of the thermodynamic effect of vortex tubes and provide a valuable tool for selecting and optimizing working fluids in various applications. [ABSTRACT FROM AUTHOR]

In hydrogen refueling stations, a hydrogen pre-cooling system is essential to protect the onboard hydrogen storage cylinder from high-temperature damage during refueling. To address the high power consumption of existing systems, this study proposes an integrated vortex tube hydrogen pre-cooling system. This system combines the vortex tube with a two-stage compression refrigeration cycle to create a new refrigeration device. The vortex tube component is numerically simulated using the standard k-ε turbulence model. Comparative analysis of power consumption and coefficient of performance (COP) is conducted between the new system, single-stage, and two-stage hydrogen pre-cooling systems. The results indicate that the vortex tube, as the pressure ratio increases from 1.5 to 20, reduces power consumption by 26.37%–41.52% compared to the single-stage system. Additionally, it improves the COP by 30.9%–53.8% compared to the single-stage system. Furthermore, compared to the two-stage system, the vortex tube achieves power savings of 4.08%–10.44% and COP improvements of 4.3%–11.7%. [Display omitted] • Propose an integrated vortex tube hydrogen pre-cooling system. • Evaluate the integrated Vortex Tube system using numerical simulation. • Investigate the impact of pressure ratio variations on the integrated system during the hydrogenation process. • Conduct exergy loss analysis of the integrated vortex tube system. • Demonstrate that the vortex tube system achieves energy savings and enhanced coefficient of performance while achieving the same cooling effect. [ABSTRACT FROM AUTHOR]

A wavelet-based machine learning method is proposed for predicting the time evolution of homogeneous isotropic turbulence where vortex tubes are preserved. Three-dimensional convolutional neural networks and long short-term memory are trained with a time series of direct numerical simulation (DNS) data of homogeneous isotropic turbulence at the Taylor microscale Reynolds number 92. The predicted results are assessed by using the flow visualization of vorticity and statistics, e.g., probability density functions of vorticity and enstrophy spectra. It is found that the predicted results are in good agreement with DNS results. The small-scale flow topology considering the second and the third invariants of the velocity gradient tensor likewise shows an approximate match. Furthermore, we apply the pre-trained neural networks to coarse-grained vorticity data using super-resolution. It is shown that the super-resolved flow field well agrees with the reference DNS field, and thus small-scale information and vortex tubes are well regenerated. [ABSTRACT FROM AUTHOR]

Draft tube vortex rope is considered a special cavitation flow phenomenon in tubular turbine units. Cavitation vortex rope is one of the most detrimental factors affecting the safety of hydraulic turbines. In this study, ANSYS CFX software was utilized to numerically simulate the internal cavitation flow of a hydraulic turbine draft tube. The evolution of the cavitation vortex core was characterized by vortex line distribution and vorticity transport equation. The shape and number of blades influenced the revolving direction and distribution characteristics of the vortex close to the runner cone, which formed a counterclockwise-clockwise-counterclockwise distribution pattern. Simultaneously, there were many secondary flows in the draft tube. Mutual cancellation and dissipation between the flows was one of the reasons for reduction in vorticity. When the cross-sectional shape of the draft tube was changed, the vorticity was distributed from the center of the vortex rope to all parts of the cross-sectional draft tube, with extreme values at the center and at the walls. The vortex stretching and dilatation terms played a major role in the change in vorticity, with the baroclinic torque having an effect at the center of the vortex rope, this study is helpful to understand the flow of water in the draft tube and guide the design and optimization of the draft tube in engineering application [ABSTRACT FROM AUTHOR]

Using hydrogen fuel cell electric vehicles equipped with proton exchange membrane fuel cells could reduce greenhouse gas emissions from the transportation sector. Heating is necessary for a safe cold start-up process, but current methods consume a lot of electrical energy. In this research, it is proposed to heat the hydrogen by using vortex tubes to separate the compressed hydrogen into a low and a high enthalpy streams and by using a heat exchanger to pump heat from the ambient into the cold stream. This system uses only the excess pressure available from the hydrogen tank as the motive power. A real gas thermodynamic model coupled with a genetic algorithm is used to maximize the hydrogen inlet temperature to the fuel cell for three different configurations of vortex tubes and heat exchangers for a 4-passenger 100 kW fuel cell electric vehicle while minimizing the heat exchanger conductance and area product. For hydrogen stored at −30 °C, vortex tubes can increase the hydrogen feeding temperature from −1.6 °C (Joule-Thompson heating in an isenthalpic throttling valve) to up to 18.3 °C, which corresponds to a heating power of 622 W. • Vortex tubes are proposed to preheat hydrogen for improved cold start of vehicles. • Vortex tube use the high storage pressure to pump heat from the ambient air. • A thermodynamic model is used to optimize vortex tubes and heat exchangers. • The temperature increases from −30 °C to values well above the freezing point. • Maximum heating power range from 325 W to 630 W for a 100 kW fuel cell. [ABSTRACT FROM AUTHOR]

Tip-leakage cavitating flow around hydrofoils has attracted much research interest, but the complex structures of tip separation vortex (TSV) and tip-leakage vortex (TLV) have not been clearly resolved and discussed with the effects of tip clearance and skew angle yet. In the present work, large eddy simulation (LES) with multi-level octree grid refinement is used to investigate the tip-leakage flows around a series of twisted hydrofoils with various skew angle and tip clearance. High resolution is guaranteed by the normalized grid sizes of y + < 1 , Δ x + ∼ 50 and Δ z + ∼ 10 , through which the predicted flow meets the criterion that at least 80% of the turbulent kinetic energy is resolved. The TSVs are identified to grow from the entire lower edge of the tip and twine with the TLV into a primary vortex tube, which leads to counter-rotating induced vortices (IV) strongly twisted around the primary vortex in the case of medium tip clearance but weakened for small one. Cavitation effect significantly accelerates the roll-up process of the vortices so that the primary vortex is formed earlier. The tip-leakage flow turns from wake-like to jet-like when the clearance is reduced, but the jet velocity diminishes markedly for extremely small clearance. The hydrofoil skewness barely makes a lift on the vortex tube, distinctive from the effect of tip clearance variation. The adverse pressure gradient induced by the skew angle has significant effect on the laminar–turbulent​ transition of the flow. The tip vortex flow induces strongly characterized laminar ant turbulent flow regions on the suction side, which continuously changes with the variation of the skewness. • LES with multilevel octree grid refinement is used to clearly resolve flow details. • High-resolution TSV grows from entire tip edge and twines with TLV into vortex tube. • Cavitation has significant acceleration effect on the roll-up process of vortices. • Induced vortex is twisted around lifting primary vortex as tip clearance is reduced. • Adverse pressure gradient caused by skew angle makes laminar–turbulent flow pattern. [ABSTRACT FROM AUTHOR]

A method has been proposed that allows calculating the parameters of a vortex cooling system for aircraft equipment as functions of flying conditions. The optimum configuration and the dimensions of basic elements of the vortex tube have been determined. By the numerical-modeling method, the operating parameters of the vortex system have been obtained. The adequacy of a computational model has been checked. [ABSTRACT FROM AUTHOR]

The underwater vehicle is subjected to complex hydrodynamic loads during water-exit process, which seriously affect the structural strength and water-exit stability of the vehicle. This paper investigates the effect of high-pressure venting conditions on the dynamic evolution characteristics of the cavity during the completely free water-exit of a vehicle based on self-designed experiments. Some novel phenomena are found in the experiment, and the hypothesis of constant acceleration is established to explain the formation mechanism. The results reveal that the reentrant jet is the main factor influencing the pattern of cavity development and causes great differences between the partial and supercavity states. The balance between the initial cavity volume increase and the gas leakage rate results in the fact that increasing the launch Froude number in the partial cavity state does not cause significant changes in the cavity size. There is a stable interval between 0.0038 and 0.03 for the effect of gas entrainment coefficient on the development of the cavity. The influence of the launch Froude number on the cavity morphology varies within different gas entrainment coefficient ranges. Besides, six patterns of cavity closure are found for free water-exit conditions. The coupling closure pattern of reentrant jet and interaction vortex tube is the most stable during the water-exit process. The stable development intervals of cavity closure pattern and cavity morphology are roughly the same. The present study aims to provide a reference for the active venting flow control of the vehicle during water-exit. [ABSTRACT FROM AUTHOR]

We address the sources and dynamics of vorticity and helicity and their relations in transitions to turbulence arising due to Kelvin–Helmholtz instability (KHI) "Tube" and "Knot" (T&K) events. Such events are common in the atmosphere and oceans, and initial numerical simulations reveal that T&K dynamics significantly accelerate turbulence transitions and enhance KHI peak and mean energy dissipation rates. KHI T&K events arise where emerging KH billows exhibit varying wavelengths, phases, amplitudes, and/or discontinuities along their axes. As the KH billows intensify, these regions evolve roughly orthogonal billow cores and induced vortex tubes in close proximity. Their mutual advection as they intensify induces large-amplitude Kelvin vortex waves, or "twist waves", that arise where locally uniform vortices are distorted by axial or radial advection. The twist waves propagate along, and fragment, the vortex tubes and billow cores, thus accounting for the emergence of helicity and the down-scale energy, enstrophy, and helicity fluxes within the turbulence inertial range. We describe the results of four direct numerical simulations (DNS) addressing KHI T&K dynamics in large and idealized small domains. The large-domain vorticity fields reveal the character and diversity of KHI T&K dynamics, the emergence of twist waves at larger and smaller scales, and their driving of turbulence transitions. Two small-domain DNS exhibit idealized KHI T&K events arising from KH billows that are mis-aligned and that exhibit phase variability along their axes. A third examines the interactions of two vortex tubes in close proximity. These reveal that twist waves drive the character and evolutions of the vorticity and helicity fields. [ABSTRACT FROM AUTHOR]

The calculations of thermohydrodynamic parameters using a mathematical model of a plane swirling flow are compared with experimental data obtained in a vortex chamber and a Ranque vortex tube. It is shown that the proposed generalized solution is in good agreement with experiment and describes a stable flow core in the plane of the vortex cross section. In terms of application, the proposed solution can serve as the basis for engineering methods for the preliminary calculation of vortex apparatuses. [ABSTRACT FROM AUTHOR]

Using the methods of computational fluid dynamics, an investigation has been conducted into convective heat transfer by a bundle of tubes with heat transfer enhancers in the form of a system of spherical dimples made on their outer surface. The presence of enhancers changes the structure of the flow and turbulizes it in the vicinity of dimples, which can lead to a reduction in the length of the wake behind the tube bundle and to a decrease in hydraulic losses due to this. Prospects are shown for the use of enhancers to raise the thermal and aerodynamic efficiency of tube bundles at their various arrangements. [ABSTRACT FROM AUTHOR]

The thermal management of the batteries in electrical and hybrid vehicles is a major concern for operation safety, battery life, and performance. In the current research, the temperature of the battery is tracked for 10,000 s of operation while using a Ranque–Hilsch vortex tube (RHVT) for the thermal management of the battery. An analytical model is developed and validated to study the impact of the heat generated per unit volume from the battery, the mass ratio for the cold air at the outlet to the total air at the inlet (x), entered air pressure, temperature, and mass flow rate. The peak temperature of the battery can be reduced by increasing the pressure and mass flow rate of the air at the inlet, decreasing the temperature of the air at the inlet, and using four RHVTs instead of a single RHVT. The proposed system significantly decreased the maximum temperature of the battery to 48.12 °C, compared to the battery thermal management method of using direct air, which resulted in a temperature of 75.73 °C. Furthermore, employing four RHVTs to cool the battery further reduced the maximum temperature from 48.12 to 11.23 °C, demonstrating a substantial improvement compared to utilizing a single RHVT. Utilizing the RHVT provides a good solution for the battery thermal management problem because it is cheap, small, and reduces the temperature of the air rapidly. [ABSTRACT FROM AUTHOR]

The maldistribution of working fluid is one of the issues in heat exchangers that causes a reduction in performance of not only the heat exchanger but also the entire HVAC system. One of the methods to reduce such maldistribution is to improve manifold design to evenly distribute the flow. In the present work, an advanced maldistribution reduction manifold, which was based on a preliminary maldistribution reduction manifold, was designed to further improve the flow distribution in the heat exchanger. In the design, spiral baffles are used to create vortices in the tubes to regulate the flow in each tube. The design also keeps the tubes away from the manifold inlet to avoid direct flow from the inlet. Due to the complexity, the design of the advanced maldistribution reduction manifold is for AM only, which cannot be fabricated by traditional manufacturing. To evaluate the design, a computational fluid dynamic model is developed to study flow distribution in heat exchanger manifolds. The simulation results reveal that the relative standard deviation of the tubes in the advanced maldistribution reduction design is half of the preliminary maldistribution reduction design and about 1/20 of the reference design. [ABSTRACT FROM AUTHOR]

Increasing the J-factor for atomized flow is expected to reduce porosity in high-pressure die casting (HPDC) products. Casting experiments were conducted to confirm changes in the amount of porosity in two parts of a piston and a wheel with increasing J-factor. As a result, the amount of porosity was reduced in the piston, but increased in the wheel under high J-factor conditions. To clarify the mechanism, a multiphase flow analysis system was developed to calculate turbulent flow using large eddy simulation. The developed system visualizes the state of small voids and vortex structures in molten metal during HPDC. In the piston, the formation of vortex tubes from the thick parts to the overflow promoted void discharge and reduced the number of voids in the thick parts. In the wheel, voids formed by the vortices in the hub part were transferred to the rim part, which is the final filling area, resulting in an increase in voids. From these results, it was possible to clarify the process from the generation to discharge of voids in molten metal flow by analyzing the microscopic state of atomized flow in the die cavity. [ABSTRACT FROM AUTHOR]

With the wide application of unmanned aerial vehicles, interest in multirotor configurations has increased. The unique features of multirotor configuration have been intensely investigated, including aerodynamic interference, which is particularly important because it influences the vibration, noise, and handling quality of rotorcraft. Most previous studies have used high-fidelity approaches, such as computational fluid dynamics to identify such interference. However, such an approach is inappropriate for real-time flight simulations. In this study, an improved aerodynamic interference analysis based on a dynamic vortex tube was established for performance prediction in real-time flight simulation. A simple and effective formulation is proposed for integration with rotor aerodynamics to evaluate the interference of multirotor configurations. The present analysis is validated on various multirotor configurations. An investigation of interference in a multirotor unmanned aerial vehicle (UAV) is then presented. The analysis results exhibit good agreement with experimental results and high-fidelity predictions. Although the accuracy of the proposed analysis is lower than that of experimental studies and high-fidelity analyses, it is sufficient for capturing interference trends. The proposed analysis can account for aerodynamic interference in the flight simulation of a multirotor UAV. [ABSTRACT FROM AUTHOR]

Polyglycolic acid (PGA) nanoparticles show promise in biomedical applications due to their exceptional biocompatibility and biodegradability. These nanoparticles can be readily modified, facilitating targeted drug delivery and promoting specific interactions with diseased tissues or cells, including imaging agents and theranostic approaches. Their potential to advance precision medicine and personalized treatments is evident. However, conventional methods such as emulsification solvent evaporation via batch synthesis or tubular reactors via flow chemistry have limitations in terms of nanoparticle properties, productivity, and scalability. To overcome these limitations, this study focuses on the design and development of a 3D-printed vortex tube reactor for the continuous synthesis of PGA nanoparticles using flow chemistry. Computer-aided design (CAD) and the design of experiments (DoE) optimize the reactor design, and computational fluid dynamics simulations (CFD) evaluate the mixing index (MI) and Reynolds (Re) expression. The optimized reactor design was fabricated using fused deposition modeling (FDM) with polypropylene (PP) as the polymer. Dispersion experiments validate the optimization process and investigate the impact of input flow parameters. PGA nanoparticles were synthesized and characterized for size and polydispersity index (PDI). The results demonstrate the feasibility of using a 3D-printed vortex tube reactor for the continuous synthesis of PGA nanoparticles through flow chemistry and highlight the importance of reactor design in nanoparticle production. The CFD results of the optimized reactor design showed homogeneous mixing across a wide range of flow rates with increasing Reynolds expression. The residence time distribution (RTD) results confirmed that increasing the flow rate in the 3D-printed vortex tube reactor system reduced the dispersion variance in the tracer. Both experiments demonstrated improved mixing efficiency and productivity compared to traditional tubular reactors. The study also revealed that the total flow rate had a significant impact on the size and polydispersity index of the formulated PGA nanoparticle, with the optimal total flow rate at 104.46 mL/min, leading to smaller nanoparticles and a lower polydispersity index. Additionally, increasing the aqueous-to-organic volumetric ratio had a significant effect on the reduced particle size of the PGA nanoparticles. Overall, this study provides insights into the use of 3D-printed vortex tube reactors for the continuous synthesis of PGA nanoparticles and underscores the importance of reactor design and flow parameters in PGA nanoparticle formulation. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) flow reconstruction over a 6:1 prolate spheroid using scanning stereoscopic particle image velocimetry has been conducted in a towing-tank facility. Forces, moments, surface pressure and reconstructed 3D vortical-flow structures are acquired in order to characterize the separated flow within the subcritical regime at three Reynolds numbers ( Re = 0.5 × 10 6 , 1.0 × 10 6 and 1.5 × 10 6 ), and at four incidence angles ( α = 5 ∘ , 10 ∘ , 15 ∘ and 20 ∘ ). Key flow features are evaluated through the reconstructed 3D flowfield data. In particular, the interaction of the crossflow vortices and the surface-pressure distribution is discussed. It is shown that the crossflow vortices consist of helical vortex tubes as the dominant coherent structures, which are more distinct at large α . For α ≥ 15 ∘ , four high-vorticity regions were observed. A pair of upper vortex tubes originate on the windward side of the model, while a lower vortex tube is formed on the strong curvature region on the leeward side of the model. The vortex dynamics are further characterized through stretching and tilting terms via the vorticity-transport equation. Larger incidence angles α lead to a stronger alignment of the crossflow vortices with the mean flow direction, which is reflected in the tilting terms. A weak Re dependency of the loads and flow structures within the range 1.0 × 10 6 ≤ Re ≤ 1.5 × 10 6 is reported, while a significantly different result was captured for separation at Re = 0.5 × 10 6 . An increase in separation size at Re = 0.5 × 10 6 at 20 ∘ results in an additional flow structure; a pair of secondary vortices is formed, leading to a change in the pressure distribution on the model surface when compared to higher Re. [ABSTRACT FROM AUTHOR]

The multi-bypass structure established a radial gas channel between the regenerator and the pulse tube in the pulse tube refrigeration. Numerical results of the flow field were obtained in two dimensions by the finite element method. Afterward, the position and thermal state of selected gas parcels were tracked with the tracking algorithms. The multi-bypass structure generates vortices at the pulse tube, and the existence of these vortices inhibits the capacity of the gas parcels to take heat away from the cold end. Placing porous material near the multi-bypass structure, it could effectively reduce the vortices in the pulse tube. [ABSTRACT FROM AUTHOR]

• Energy, exergy and multi-objective optimization are performed for vortex tube integrated single-stage vapour compression refrigeration cycle (VTC). • The parametric investigation is done to assess the thermodynamic performance of VTC. • The cooling capacity of VTC is found to be 13.19% – 49.73% higher than that of VCR. • The maximum COP and exergetic efficiency of VTC are higher than those of VCR. • The evaporator temperature is the most influential input parameter in multi-objective optimization. This paper evaluates the thermodynamic performance of a vortex tube integrated single-stage vapour compression refrigeration cycle (VTC) in a subcritical region. The thermodynamic evaluation consists of an energy and exergy analyses for VTC in order to determine the effect of various design and operating parameters on its performance. Moreover, the results of VTC are compared with those of a simple vapour compression refrigeration cycle (i.e., VCR) for the considered range of evaporator and condenser temperatures using R1234yf as a refrigerant. The analysis reveals that the cooling capacity of VTC is 14.53% – 49.73% higher than that of VCR for the considered range of condenser temperature. Also, the maximum COP of VTC is 5.59% – 27.32% higher than that of VCR. The exergetic efficiency of VTC is 5.62% – 27.33% higher than that of VCR. A multi-objective optimization using a genetic algorithm has been conducted, which suggests that the evaporator temperature is the major decisive parameter to find the suitability of various applications of the system based on VTC. [ABSTRACT FROM AUTHOR]

This article intends to examine the cooling capacity enhancement for the Ranque-Hilsch vortex tube when two inlet sections are introduced compared to a single inlet section along with the optimum distance between the intake sections by computational fluid dynamics (CFD) approach. Air is taken as working fluid in a steady-state, 3-D, axisymmetric, Ranque-Hilsch vortex tube. ANSYS FLUENT software has been used to simulate flow using standard k-ɛ turbulent model. The numerical analysis is accomplished with variable intake pressure and validated with the experimental results. The numerical investigation shows that using the two inlet sections decreases the fluid temperature at the cold outlet as compared to single inlet section, but the cold and hot exit fluid temperature increases by increasing the distance between the two sections. The optimum cold outlet temperature value occurs at a dimensionless distance between intake sections of ζ/L = 0.075 and a temperature difference of 19.27 K at cold exit between single and double inlet section of vortex tube has been found from the present study. A correlation has been developed for the hot temperature gradient (ΔTh) and cold temperature gradient (ΔTc) by considering the operating parameters such as mass fraction and inlet pressure. [ABSTRACT FROM AUTHOR]

With the large-scale application of polymer flooding technology, the polymer concentration in produced water is increasing, which leads to incomplete regeneration of filter media by gravity field hydraulic backwashing technology only. In this study, the high-gravity backwashing technology is constructed by coupling gravity field and swirl field, which promotes the development of the oilfield. Based on the cascade theory, this paper establishes a mathematical expression of radial collision force in the high-gravity backwashing process in the vortex tube and solves a mathematical equation of high-gravity backwashing velocity gradient G based on the efficient zone of collision force action. Meanwhile, based on the discrete element method and computational fluid dynamics theory, the inter-particle collision regulation of the high-gravity backwashing process is simulated by the coupled FLUENT-EDEM method, and the high-efficiency zone of the backwashing process is verified. In this high-efficiency zone, the theoretical and simulated values of velocity gradient G for different high-gravity values match well, with differences ranging from –5.8 % to +7.1 %, indicating that the theoretical model of high-gravity backwashing is correct. When the high-gravity value is 210–240 g, the total impulse of the filter bed per unit time reaches a great value, and the backwashing velocity gradient G is 3047.1 s−1, which is much larger than the G value of combined air-water backwashing. The high-gravity backwashing technology breaks through the technical bottleneck of low efficiency in the action of the gravity field. It enriches and develops the gravity field hydraulic backwashing technology of the filter bed. • A new method of high-gravity backwashing is proposed, and a theoretical model of high-gravity backwashing is constructed. • The mathematical equations particle impact force and velocity gradient in high efficiency area of high-gravity backwashing are established. • The coupling method of FLUENT-EDEM is used to study the backwashing process, which provides a new idea for the backwashing of traditional water treatment filter bed. [ABSTRACT FROM AUTHOR]

This paper discusses a numerical model study for the simulation of flow characteristics and critical submergence for a laterally placed horizontal circular bottom intake under uniform flow. The proposed model simulates the free surface using the volume of fluid model to check the vortex formation at critical submergence. A new combined approach using phase volume fraction and swirl strength-based vortex identification mechanism is used to compute the critical submergence. The swirl strength-based vortex identification mechanism can show the vortex tube in approach flow with swirl generated at the free surface due to the axial flow withdrawal through side bottom intake at critical submergence. The computational fluid dynamics (CFD) model results were validated using experimental data, which showed a maximum error of less than ±10% in the prediction of the critical submergence. The effect of significant parameters like intake and approach flow Froude number and sill height of intake on the critical submergence is discussed. The results of this study help practitioners to adopt CFD-based numerical modelling for the design of water intakes instead of entirely relying on physical model studies, which require more finance and time. [ABSTRACT FROM AUTHOR]

Machining is a manufacturing process that can be used to produce precision machine parts and has many advantages. The first is the ability to achieve superior surface quality. Tool wear is an inevitable phenomenon that occurs during machining. It is affected by many machining conditions; therefore, this process needs to be monitored and controlled. In this study, tool wear and surface roughness tests were carried out on AISI 4462 duplex stainless-steel materials, known to be a hard-to-cut material. For this purpose, tool wear and surface roughness analyses were implemented by using the environmentally friendly vortex tube cooling system in addition to wet turning conditions for the first time. For both methods, experiments were conducted at a 1 mm depth of cut, 120 m/min cutting speed, and 0.1 mm/rev feed with a 90 mm cutting length for each pass. Both tool wear and surface roughness were examined at the end of each pass. The analysis showed that wet turning gave better results in terms of tool life (19.8 minutes of tool life) compared to 11.1 minutes of tool life in vortex turning. In contrast, the surface roughness values differed up to two times in some experiments, and the vortex tube experiments gave better surface roughness values in all passes. In addition, the vortex tube experiments showed less built-up-edge (BUE) formation than the wet-turning experiments. [ABSTRACT FROM AUTHOR]

The working principle for the energy separation observed in a Ranque–Hilsch Vortex Tube (RHVT) is a matter that is widely debated and unsettled. It is, however, indisputable that modifications to the tube geometry can substantially affect the performance of the tube. In this paper, a three-dimensional computational fluid dynamic study is performed to investigate the enhanced performance of a geometrically modified vortex tube by studying the flow structure, heat transfer, and energy separation. The novel vortex tube is modeled in ANSYS FLUENT, similar to the original device: 3D Steady-state flow analysis using the standard k- ϵ turbulence model on a hybrid mesh. The results acquired are compared and found to demonstrate the increase in the observed energy separation in the novel geometry. The total increase in thermal separation for the novel design is observed to be 15.1 K at 0.9 Cold Mass Fraction, with an increase of 10 W in overall energy transfer. Compared to the nominal design, a maximum of 13.74 percent improvement in thermal separation. Furthermore, the flow structures are compared to understand the reason behind the increased performance. It is found that the factors responsible for the extent of separation of energy in the tube are: Higher Radial Pressure Gradient, Higher Circumferential, and Axial Shear Work, and Conductive Heat Transfer. Finally, an energy balance is carried out on the peripheral hot control volume to study the fundamental modes of energy transfer. The energy balance verifies that these factors are the prominent factors responsible for the observed increase in separation. • Effect of right-angled ribs on energy separation in an RHVT was analyzed in detail. • Recirculation zones promote the transfer of energy through shearing. • Net radial potential difference plays a governing role in the final flow structure. • An improvement in thermal separation was achieved in the presence of ribs. [ABSTRACT FROM AUTHOR]

This work proposes an innovative method for adjusting the natural gas from the grid to the consumer pipeline requirements in a full-scale pressure reduction station. The use of two counterflow vortex tubes instead of the traditional boiler to preheat the gas before throttling is demonstrated as a powerful alternative. Thus, a reduction of fossil fuel consumption is reached, which amounts to 7.1 % less CO 2 emitted. To ensure the optimal configuration, the vortex tube was thoroughly characterized in laboratory facilities using nitrogen as the working fluid. Various operating conditions were tested to determine the most efficient setup. Computational Fluid Dynamics (CFD) simulations were conducted with nitrogen to validate the behavior of the vortex tube. Subsequently, the working fluid was switched to methane to assess the performance differences between the two gases. Finally, the vortex tubes were deployed at a full-scale installation and tested under real consumption demand. The results obtained from this study offer promising insights into the practical implementation of the proposed method for adjusting the natural gas flow, highlighting its potential for reducing fossil fuel consumption and minimizing CO 2 emissions. Further improvements and refinements can be made based on these findings. [ABSTRACT FROM AUTHOR]

This paper gives a survey on recent results about the existence of knotted vortex structures in incompressible fluids. This includes the proof of Lord Kelvin's conjecture on the existence of knotted vortex tubes in steady Euler flows and a new probabilistic approach to address Arnold's speculation that typical Beltrami fields should exhibit vortex lines of arbitrary topological complexity. We review the key tools to establish these results: the global approximation properties of Beltrami fields, the inverse localization principle in spectral theory, and the theory of Gaussian random Beltrami fields, which permits the introduction of probabilistic considerations in the picture. Finally, we include some applications of these techniques to other problems, such as the existence of vortex reconnections for smooth solutions of the 3D Navier–Stokes equation and the evolution of local hot spots under the heat equation. [ABSTRACT FROM AUTHOR]

In order to solve the problem of fluid accumulation in horizontal gas wells and improve the fluid-carrying capacity and recovery efficiency of gas wells, this paper simulates three internal vortex tools using the commercial software ANSYS FLUENT, and analyzes the drainage recovery efficiency of the three vortex structures and the vortex characteristics of the downstream section vortex field. The results show that the axial velocity of the three-bladed spiral tube in the cyclonic field rotates quasi-periodically with the flow field compared with the internal vortex tube and the rifled tube, and the axial velocity, tangential velocity and vortex intensity of the three-bladed vortex tube guided flow field are the highest; meanwhile, the axial velocity, tangential velocity and vortex intensity of the three-bladed spiral tube guided flow field decay the fastest, and the line rifled tube decays the slowest. The liquid phase in the cyclonic field exhibits obvious spiral motion and maintains a long-distance cyclonic flow state under the action of cyclonic flow. The enhancement of the vortex intensity easily leads to the increase of liquid volume fraction and liquid film thickness at the tube wall. Through the analysis of the energy efficiency of the three structures, it is found that the three-leaf spiral tube is more suitable for the initial phase of drainage transport, while the internal vortex tube is more favorable for the stable phase of transport. The study of the gas-liquid swirl flow of the three swirl tools demonstrated the feasibility of the internal swirl tool for application in horizontal wells. It can provide theoretical guidance and practical basis for effective liquid filling with internal vortex tools in the future. [ABSTRACT FROM AUTHOR]

An experimental investigation was conducted to study the effect of various materials on the performance of vortex tube. Beforehand, the recent progresses in the improvements on the performance of vortex tube (VT) and its efficiency, a literature survey has been discussed. The present work reports vortex tube performance augmentation considering four different materials vortex tubes and their orifice. The thermophysical properties of the material was considered to analyse the performance of vortex tubes for various materials. It was found that the aluminium vortex tube and its orifice achieved the highest performance among all the rest of the materials. The highest cold and hot temperature separation magnitude for Al VT and Al Vortex generator is 24 °C and 50 °C at an inlet pressure of 5 bar. The vortex tube of various materials had exact dimensions and specifications for an "apple to apple" comparison. Results show that the specific heat, thermal diffusivity, and thermal conductivity were the significant properties that affect the thermal performance of the VT. Furthermore, exergy analysis was done for the Al vortex tube and its orifice to predict the quality of available energy. It shows that high exergy destruction is found in hot regions for a high cold mass fraction. [ABSTRACT FROM AUTHOR]

• The performance of counter-flow Ranque-Hilsch Vortex Tube (RHVT) was modelled with respect to pressure, working fluid and nozzle specifications. • Linear Regression (LR), Support Vector Machines (SVM), Gaussian Process Regression (GPR), Regression Trees (RT) and Ensembles of Trees (ET) prediction methods were used. • Optimizing the performance of counter-flow RHVT, it is aimed to fill the gap in the literature by using LR, SVM, GPR, RT and ET methods among the machine learning methods. This study planned to model a counter-flow Ranque-Hilsch Vortex Tube (RHVT) using compressed air and oxygen gas by machine learning to separate the thermal temperature. From within machine learning models, Linear Regression (LR), Support Vector Machines (SVM), Gaussian Process Regression (GPR), Regression Trees (RT), and Ensemble of Trees (ET) were preferred. By leaving the outlet control valve on the hot fluid side fully open, data were received for each material and nozzle at RHVT with inlet pressure starting from 150 kPa and up to 700 kPa at 50 kPa intervals. In the counter flow RHVT, the lack in the literature has been tried to be eliminated by modeling the RHVT by finding the difference (ΔT) between the temperature of the cold flow exiting (T c) and the temperature of the leaving hot flow (T h). When analyzing each of the machine learning models in the study, 80% of all data was used as training data, 20% of all data was used for the test, 70% of all data was used as training data, and 30% of all data was used for the test. As a result of the analysis, when both air and oxygen fluids were used, the GPR method gave the best result with 0.99 among the machine learning models in two different test intervals of 70%–30% and 80%–20%. The success of other machine learning models differed according to the fluid and model used. [ABSTRACT FROM AUTHOR]

The turbulent/non-turbulent layer (TNTL) in a turbulent Boussinesq plume is analyzed using direct numerical simulations. The Reynolds number (Re) used in the simulation, based on the scales defined at the bottom hot patch, is 2000, and the Reynolds number (R e λ ) based on the Taylor microscale (λ) is 114.4 in the self-similar region. The flow is sufficiently resolved till the Kolmogorov scale. The outer edge of the TNTL is detected using the vorticity magnitude. Conditional statistics of various quantities are calculated with reference to the outer edge of the TNTL, which is referred to as the irrotational boundary (IB). The profiles of conditional vorticity magnitude are used to identify the TNTL and determine its thickness. The presence of viscous superlayer (VSL) and turbulent sublayer (TSL) within the TNTL is revealed by exploring the conditional profiles of the enstrophy transport equation. The baroclinic torque, which is a source of vorticity, has been shown to be inconsequential in determining the width of the VSL. The widths of the TNTL and the VSL are determined to be δ TNTL ≈ 15 η and δ VSL ≈ 3.12 η , respectively, where η is the Kolmogorov length scale. This gives the width of the TSL as δ TSL = δ TNTL − δ VSL ≈ 13.88 η. The invariants of the velocity gradient tensor have been analyzed across the TNTL. The joint probability density function of the invariants Q and R shows a teardrop shape within the turbulent core. The teardrop shape is not fully developed within the TNTL. The TNTL and the turbulent core have a mixed tendency for irrotational dissipation, vortex sheets, and vortex tubes. When normalized by Kolmogorov length and velocity scales, the conditional statistics of the TNTL of the plume are similar to other turbulent flow types, and hence, this provides additional evidence for the universality of small-scale motion within/around the TNTL of various turbulent flows. [ABSTRACT FROM AUTHOR]

A three-dimensional compressible large eddy simulation (LES) method was performed to explore the flow and heat transfer characteristics in the hole and mixing zone of a crossflow film cooling model. A traditional cylindrical hole and diffusion slot hole were selected as the cases for the film hole. The characteristics of the crossflow film flow-field and the influence of the internal crossflow on the film cooling of the diffusion slot hole were explained by the vortex flow in the hole and the instantaneous/time-averaged jet mixing. The results showed that helical motion is easily induced in the holes under the influence of crossflow. Asymmetric outlet flow behavior is the main reason for the asymmetric characteristics downstream of the hole. The difference in the blowing ratio results in the difference in the strength of the spiral vortex and the central vortex tube inside the hole. For the diffusion slot hole, the high-speed zone caused by the crossflow effect at the hole-inlet gradually evolves into strip shapes under the combined action of axial extrusion and spanwise diffusion. With the disappearance of the helical structure, the high-speed areas gradually converge on both sides of the hole exit in the span direction, and the streamline at the exit develops relatively smoothly. The inlet crossflow and the crossflow Reynolds number have little effect on the film cooling effectiveness of the diffusion slot hole. With an increase in the blowing ratio, the lateral diffusion capacity of the film is gradually enhanced. Furthermore, compared with the cylindrical hole, the instantaneous film fluctuation region of the diffusion slot hole case is smaller in range and more symmetrical in distribution. These findings advance the understanding of the film cooling of diffusion slot holes. [ABSTRACT FROM AUTHOR]

In this paper, a transcritical carbon dioxide power generation system based on a vortex tube is studied, which has the advantage of the self-condensation of carbon dioxide. The thermodynamic performance of the system was investigated by establishing a mathematical model. The results showed that under fundamental working conditions, the system could output a net power of 271.72 kW, and the thermal efficiency as well as the exergy efficiency of the system could reach 7.38% and 27.09%, respectively. Exergy analysis showed that the turbine had the greatest exergy loss among the system's components, followed by the vortex tube, pump, heater and cooler. Parameter analysis showed that increasing the outlet pressure and inlet temperature of the vortex tube can improve the thermal efficiency and exergy efficiency of the system. In addition, the improvement in the turbine component's efficiency is the most beneficial to the system's performance, among which the turbine's efficiency has the greatest impact. Carbon dioxide can be effectively liquified by expanding it in the vortex tube, and its liquefaction ratio increases with the decrease in the vortex tube's inlet temperature and the increase in the vortex tube's inlet pressure. [ABSTRACT FROM AUTHOR]

The temperature separation effects of vortex tubes have been widely studied in open systems, using mainly air or N2 as the working fluid. When a vortex tube is employed in a closed thermal system, more fluid choices, such as refrigerants, could be considered. Different to air, refrigerants have quite varied thermal-physical properties, and research of the thermal-physical properties' influence on the temperature separation effect is rather limited. Based on CFD simulated temperature separation effect of eight refrigerants (R152a, R290, R134a, R600a, R143a, R245fa, R227ea, and R218), this study attempts to gain a better insight into how their properties could be related to compare their temperature separation performance. The analysis shows for small mass-flow ratios at the cold end, the cooling effect can be assessed by the relative values of their isentropic expansion exponent. The results also suggest that a large thermal diffusivity and kinematic viscosity, and a small vapour density and Joule-Thomson coefficient would lead to better heating effects. [ABSTRACT FROM AUTHOR]

The development of the Ranque-Hilsch vortex tube has stagnated since the 1950s, when Hilsch improved the vortex tube proposed by Ranque. Consequently, the performance of vortex tubes has remained constant for the past 70 years. In addition to the unclear flow structure and energy separation mechanism of vortex tubes, the lack of a mature design method for vortex tubes has also limited its widespread adoption for industrial applications. The inlet nozzle and main tube parameters have been studied extensively, and matching the inlet with the main tube is considered an important step in the design of a vortex tube; however, this process has not been studied extensively. In addition, although the temperature drop at the cold exit is a commonly adopted performance benchmark, it is not possible to establish a close relationship between this parameter and the geometric parameters of a vortex tube. This study investigates the relationship between the cooling performance and the area ratio of a vortex tube. The results indicate that the inlet mass flowrate per unit area has a positive correlation with the cooling performance, and its influence on the performance of a vortex tube is higher than that of the distribution of the reverse flow boundary. Therefore, the inlet mass flowrate per unit area can potentially be a geometric performance benchmark. However, further studies are required to develop better guidelines for optimizing the design and to obtain a deeper understanding of the energy separation mechanism of vortex tubes. [ABSTRACT FROM AUTHOR]

Turbulent/turbulent interfacial (TTI) layers are investigated with direct numerical simulation of temporally evolving grid turbulence. The present study considers a temporally evolving wake of two parallel-bar grids with different mesh sizes, which generate homogeneous isotropic turbulent regions with large and small turbulent kinetic energies (TKE). A shearless mixing layer of turbulence forms between the large- and small-TKE regions. The TTI layer bounded by the large- or small-TKE region is identified with a passive scalar field, and the flow statistics are evaluated as functions of a position with respect to the TTI layer. Statistics of a velocity gradient tensor suggest that the center and edges of the TTI layer are dominated by vortex sheets and vortex tubes, respectively. Because of the configuration of these vortical structures, the flow toward the TTI layer in the layer-normal direction generates a compressive strain, which is important to sustain the thin layer structure. The mean velocity jump due to the compressive strain is about 3 u η and is observed over a length of about 20 η , where u η and η are the Kolmogorov velocity and length scales, respectively. The thickness of the TTI layer is about 12 η , which hardly depends on time. The TTI layer has a large surface area when it is bounded by the large-TKE region. Consequently, the shearless mixing layer tends to entrain more amount of fluid from the large-TKE region than from the small-TKE region although the entrainment rate per unit surface area normalized by the Kolmogorov velocity is similar for both regions. [ABSTRACT FROM AUTHOR]

Understanding the interactions between hydrogen flame and turbulent vortices is important for developing the next-generation carbon neutral combustion systems. In the present work, we perform several direct numerical simulation cases to study the dynamics of a hydrogen diffusion flame embedded in the Taylor–Green Vortex (TGV). The evolution of flame and vortex is investigated for a range of initial Reynolds numbers up to 3200 with different mass diffusion models. We show that the vortices dissipate rapidly in cases at low Reynolds numbers, while the consistent stretching, splitting, and twisting of vortex tubes are observed in cases with evident turbulence transition at high Reynolds numbers. Regarding the interactions between the flame and vortex, it is demonstrated that the heat release generated by the flame has suppression effects on the turbulence intensity and its development of the TGV. Meanwhile, the intense turbulence provides abundant kinetic energy, accelerating the mixing of the diffusion flame with a contribution to a higher strain rate and larger curvatures of the flame. Considering the effects of the non-unity-Lewis number, it is revealed that the flame strength is more intense in the cases with the mixture-averaged model. However, this effect is relatively suppressed under the impacts of the intense turbulence. [ABSTRACT FROM AUTHOR]

Gravity-driven horizontal falling-film flow phenomenon is a ground-breaking technology that has been actively used in a wide range of industrial applications, including desalination, petroleum refineries, food processing industries, and refrigeration, among others. A series of experiments and a 2-D two-phase model were developed to investigate falling-film flow regimes, microscopic flow mechanism, and finer flow parameter details. The experiments focused primarily on axial inter-tube flow modes, and circumferential flow parameters were evaluated using numerical simulations. A high-speed digital photographic device was used to capture and visualize the flow pattern. The VOF method is used to capture the liquid–gas interface. The Reynolds number ranged from 41 to 1000, the tube spacing was 10/20/30/40 mm, and the contact angle was 0°. According to the findings, droplet flow has three important phases, detached spherical flow pattern, discrete spherical flow pattern, full neck formation by linked droplets, and droplet flow before reaching column flow. The Reynolds numbers 166, 208, and 250 have departure-site spacing values of approximately 23.84 mm, 18.16 mm, and 14.52 mm, respectively. The flow parameters such as radial film thickness and vortices beneath the tube increase with increasing Reynolds number. As Reynolds number increases, the departure-site spacing and liquid film inter-tube propagation time decrease. The thinnest film zone appeared between 90°and 140°. The velocity magnitude of the liquid film over the test tube is greater than that of the stabilizing tube, despite being close to the distributor. Furthermore, the film velocity on the lower half of the tube wall is slightly higher than that on the upper half of the tube wall. [ABSTRACT FROM AUTHOR]

Pumped storage hydropower (PSH) can be focused on the transient stability in the field of energy sources in the world. A great challenge can be the hydraulic instability characteristics of PSH units in the anti-S instability zone. The PSH units are prone to enter the anti-S instability zone during low head start, leading to the failure of the grid connection. There was a serious threat to the safe and stable operation of the units. The severe pressure pulsations can be caused by the complex flow evolution in the dynamic characteristics of the unit. In this study, a computational fluid dynamics (CFD) numerical simulation was introduced to explore the start-up process of a pump turbine at low-head in PSH. Experimental verification was also made on the accuracy of the numerical simulation. A dynamic mesh was used to realize the dynamic opening of the guide vanes. A proportional-integral-differentiation (PID) regulation was also introduced. A closed-loop feedback model was established to regulate the opening of the guide vane using rotational speed fluctuations, in order to realize the simulation of the low-head star-up process of a PSH whole flow system. The numerical simulation was focused on the pressure pulsation characteristics in the area of the guide vane and draft tube. The results show that the numerical simulation was in an excellent agreement with the experimental, and the maximum error does not exceed 10%. The PID regulation model was added to simulate the variation pattern of the active guide vane opening. The strong dynamic and static interaction was caused by the speed of the unit. There were the significant mean pressure changes in the vaneless zone, followed by the speed of the unit. The stator-rotor interaction was dominated the variation of the time-averaged pressure dimensionless amplitude and pulsating pressure dimensionless amplitude in the vaneless zone. By contrast, there were the effects of dynamic and static interference on the pulsation amplitude of the pressure in the upstream. The pressure pulsation signal was evenly distributed over the circumference in the area between the stay vane and the guide vane, whereas, there was the uneven distribution along the circumference in the vaneless area. The vortex near the rotor area first appeared in the center of the blade, and then progressed upstream, eventually forming a stable vortex ring structure at the mid-plane position in the vaneless zone. There were the different fluctuation characteristics in the pressure pulsation in the straight cone section of the draft tube in different stages of the start-up process. The pressure fluctuation was more significant in the PID regulation. The comparison of internal flow revealed that the guide vane opening was caused some changes in the distribution and fluctuations of the velocity in the vaneless zone. Significant large-scale vortices were found in the runner inlet and the vaneless zone at the small guide vane opening. The stator-rotor interaction was combined to be responsible for the high amplitude of the time-averaged pressure and pulsation pressure fluctuations in the vaneless zone. The draft tube vortex rope was ever changing from a side strip vortex rope to a spiral vortex rope, and then to a curtain vortex rope during the start-up process. The persistence and dynamics of the vortex rope were induced the uneven pressure radial distribution. The main reasons were attributed to the drastic pressure fluctuations. The findings can provide a strong reference to improve the success rate of the starting pump-turbine at the low head and connecting to the grid. [ABSTRACT FROM AUTHOR]

Structure parameters have an important influence on the refrigeration performance of pulse tube refrigerators. In this paper, a method combining the Kriging metamodel and Non-Dominated Sorting Genetic Algorithm II (NSGA II) is proposed to optimize the structure of regenerators and pulse tubes to obtain better cooling capacity. Firstly, the Kriging metamodel of the original pulse tube refrigerator CFD model is established to improve the iterative solution efficiency. On this basis, NSGA II was applied to the optimization iteration process to obtain the optimal and worst Pareto front solutions for cooling performance, the heat and mass transfer characteristics of which were further analyzed comparatively to reveal the influence mechanism of the structural parameters. The results show that the Kriging metamodel presents a prediction error of about 2.5%. A 31.24% drop in the minimum cooling temperature and a 31.7% increase in cooling capacity at 120 K are achieved after optimization, and the pressure drop loss at the regenerator and the vortex in the pulse tube caused by the structure parameter changes are the main factors influencing the whole cooling performance of the pulse tube refrigerators. The current study provides a scientific and efficient design method for miniature cryogenic refrigerators. [ABSTRACT FROM AUTHOR]