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Abstract This study investigates the flow dynamics and energy losses of Tesla turbines using Computational Fluid Dynamics with OpenFOAM. Our goal is to identify the main sources of energy loss. Four main sources of energy loss were identified. The most significant loss occurred during the conversion of pressure energy to kinetic energy, estimated to range from 88 % to 64 % of the total energy. Energy losses due to leaks between the rotor and the casing were also quantified, ranging from 4.97 % to 7.95 % of the kinetic energy at peak efficiency points. Design modifications, such as incorporating a nozzle at the entrance of the turbine, can improve efficiency. These findings highlight specific areas for efficiency improvement, offering opportunities for improved turbine design and integration into energy‐generation systems.

Although research interest in pressure gain combustion remains high, information on the deflagration-to-detonation transition (DDT) process in actual multiple-cycle pulse detonation combustors is sparse, especially in terms of initial pressure studies, a crucial parameter in design and operation of such combustors. To develop microscale detonation combustion technology and gain a better understanding of the impact of initial pressure, an experimental study on flame acceleration of hydrogen-oxygen premixed gas is conducted using a micro spiral channel with a Tesla turbine at the outlet, which can realize precise initial pressure regulation in an open-ended pulse detonation combustor. The initial pressure consists of turbine wind pressure (p T) and intake residual pressure (p ir). p T increases the back pressure at combustor's outlet, and p ir is derived from the channel static pressure and flow velocity during the gas intake phase by bringing the ignition timing close to the moment when the solenoid valve closes. The flames are recorded by high-speed photography and the flame propagation characteristics under different initial pressures are compared. Results demonstrate that different combinations of p ir and p T yield three distinct DDT modes (Mode1: low p ir ∩ low p T ; Mode2: low p ir ∩ high p T ; Mode3: high p ir ∩ any p T), with p ir significantly outperforming p T in shortening DDT distance (L DDT , Mode3＜Mode2＜Mode1) and mitigating the detonation wave velocity deficit (DWVD, Mode3＜Mode2≤Mode1). High-pressure intake and timely ignition after valve closure (to trigger Mode3) is a very efficient way to generate detonation waves, which could be an ideal operation method for microscale pulse-detonation-based devices with hydrogen energy. [Display omitted] • DDT distance for 2H 2 –O 2 mixtures in a millimeter-scale spiral channel is investigated. • Initial pressure regulation in an open-ended pulse detonation combustor is realized. • The impact of initial pressure and initial flow field is compared. • Intake process flow field can promote DDT and reduce detonation velocity deficits. • Generating detonation waves within a coin-sized space. [ABSTRACT FROM AUTHOR]

This study investigates the flow dynamics and energy losses of Tesla turbines using Computational Fluid Dynamics with OpenFOAM. Our goal is to identify the main sources of energy loss. Four main sources of energy loss were identified. The most significant loss occurred during the conversion of pressure energy to kinetic energy, estimated to range from 88% to 64% of the total energy. Energy losses due to leaks between the rotor and the casing were also quantified, ranging from 4.97% to 7.95% of the kinetic energy at peak efficiency points. Design modifications, such as incorporating a nozzle at the entrance of the turbine, can improve efficiency. These findings highlight specific areas for efficiency improvement, offering opportunities for improved turbine design and integration into energy‐generation systems. [ABSTRACT FROM AUTHOR]

Momentum diffusion and kinetic energy transfer in turbomachinery have always been significant issues, with a considerable impact on the performance of the bladeless Tesla turbine. This radial turbine shows high potential for various energy applications, such as Organic Rankine Cycle or combined heat and power systems. Analyzing the flow inside the gap between the corotating disks of the Tesla turbine presents challenges due to several factors, including submillimeter length scales, variations in flow cross-section, interactions of body forces arising from rotation with turbulence, interactions between the turbine's inlet nozzles and rotor, and moving walls. General design parameters, e.g., number of nozzles, also pose a challenge in order to achieve the full potential of this turbine. In this research, two different variants of the supply system are considered with six and forty nozzles. To minimize computational expenses, a portion of the entire domain is considered. The flow in each domain, consisting of one inlet nozzle and a segment of one gap between the disks, is examined to reveal the complexity of flow structures and their impact on the Tesla turbine performance. Large Eddy Simulation (LES) with the Smagorinsky subgrid-scale model is used to verify the results of the k-ω Shear-Stress Transport (SST) turbulence model in the first case study with six nozzles. Analyzing the results indicates that the k-ω SST model provides valuable insights with appropriate accuracy. The second case study, with forty nozzles, is simulated using the k-ω SST turbulence model. The research compares flow structure, flow parameters, and their impact on the system's performance. From the comparison between the k-ω SST turbulence model and LES simulation, it was observed that although the k-ω SST model slightly overestimates the general parameters and damps fluctuations, it still provides valuable insights for assessing flow structures. Additionally, the mesh strategy is described, as the LES requirements make this simulation computationally expensive and time-consuming. The overall benefits of this method are discussed. [ABSTRACT FROM AUTHOR]

The so-called ORC (Organic Rankine Cycle) heat recovery technology has attracted much attention with regard to medium and low temperature waste heat recovery. In the present study, it is applied to a Tesla turbine. At the same time, the effects of the disc speed, diameter and inter-disc gap on the internal flow field and output power of the turbine are also investigated by means of CFD (Computational Fluid Dynamics) numerical simulation, by which the pressure, velocity, and output efficiency of the internal flow field are obtained under different internal and external conditions. The highest efficiency (66.4%) is obtained for a number of nozzles equal to 4, a disk thickness of 1 mm, and a gap of 1 mm between the disks. The results of the study serve as a theoretical basis for the structural design and optimization of Tesla turbines. [ABSTRACT FROM AUTHOR]

This study describes direct numerical simulation (DNS) of radially inward spiralling corotating disk flow with a narrow disk spacing, using the open source solver Nek5000 and the supercomputer SuperMUC-NG at Leibniz Supercomputing Centre. Knowledge about laminar and turbulent regime boundaries in this flow scenario is important for modelling and performance prediction of friction turbines. Simulations are performed in differently sized sections of the flat annulus that is formed by two opposing corotating disk surfaces. Three sets of operating conditions are covered, from the laminar, transitional and turbulent region of a previously determined stability chart respectively. Directly downstream of the inlet boundary, the flow is artificially perturbed with a random body force acting normal to the disk surfaces. Fourier analysis of the DNS flow field reveals that the artificial perturbation is dampened across all wavenumbers for the laminar conditions, while at the transitional conditions a small range of modes is weakly amplified towards the outlet. The identified unstable modes were previously correctly predicted by linear stability analysis. Comparison to experimental velocity profile measurements from a previous study at the same transitional operating conditions suggests strongly perturbed flow during the experiment. For inflow conditions leading to turbulent flow, average velocity profiles from DNS coincide with those from experiment and from commercial fluid simulation software with turbulence modelling (ANSYS CFX). Close to the walls, turbulent dissipation and turbulent kinetic energy distributions do not agree with the ANSYS CFX results. Friction Reynolds number settles at about 118 after turbulent flow has developed from the initial perturbation. Two point correlations and corresponding energy spectra are presented. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Engineering for Thermal Energy & Power / Reneng Dongli Gongcheng is the property of Journal of Engineering for Thermal Energy & Power and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Due to the rapid growth in small-scale energy systems, the scientific community has rekindled its interest in developing a more efficient Tesla turbine owing to its simple design, low cost and efficient operation at these scales. This article is a combined effort of numerical and experimental investigation to improve a Tesla turbine’s overall performance using several inlet and outlet configurations. After achieving good accuracy (≈ 6% difference between the results) with the experimental result, we continue the numerical investigation for three different circular-to-slit type nozzle configurations at a total pressure and temperature difference of 2 bar and 50 ∘ C, respectively. Results from the numerical simulation indicate that nozzle 3 delivers the highest peak Mach no and uniformity across the slits. The maximum disparity in peak Mach no across the slits reduced from 12 to 25%. Furthermore, we experimentally investigate the turbine in bi and uni-axial outlet configurations with compressed air at 6 bar for nozzle 1. We observe a maximum RPM of ≈ 11,000 for bi-axial outlet configuration, whereas the RPM crossed for ≈ 13,300 for uni-axial outlet configuration. These observations suggest that we can improve the maximum turbine power output by ≈ 38% for uni-axial outlet configuration. Finally, we measure the electrical power generated by the turbine in a bi-directional outlet configuration by coupling the turbine with a generator. In combination, these observations would help optimize both inlet and outlet configurations suitable for the later versions of the Tesla turbine. [ABSTRACT FROM AUTHOR]

The design, numerical simulation, manufacturing, and physical experimentation of Tesla's bladeless centripetal turbine for electrical power production are the topics of this research project. The turbine generates rotational motion in the discs by directing pressurized air and water tangentially across parallel smooth disc surfaces. The fluid speed parameter at the nozzle inlet determines the power generated. To ensure optimal mechanical design parameters, SolidWorks design software, fluid dynamics concepts, and machine element design were employed. The numerical simulation software ANSYS CFX was used. The numerical and qualitative findings of the models and physical experiments coincided well. The study revealed that the power production and turbine efficiency were regulated by the input sources and blade size. Variations in the fluid composition between the discs may additionally have an impact on the outcomes. The researchers investigated the connection between input fluid pressure and turbine efficiency, as well as the number of discs and turbine power. The prototype could generate 76.52 W of electricity at 50 bar pressure and 1.01e+05 Reynolds number. The operation was efficiently simulated using CFD, with only a 9.3% difference between experimental and simulated results. Overall, this research provides an in-depth assessment of Tesla's bladeless centripetal turbine. It verifies the design and numerical simulation methodologies used, as well as identifies the essential aspects impacting turbine performance and efficiency. The findings contribute to a better understanding of the turbine's behavior and give ideas for improving its performance.

Microfluidics has earned a reputation for providing numerous transformative but disconnected devices and techniques. Active research seeks to address this challenge by integrating microfluidic components, including embedded miniature pumps. However, a significant portion of existing microfluidic integration relies on the time-consuming manual fabrication that introduces device variations. We put forward a framework for solving this disconnect by combining new pumping mechanics and 3D printing to demonstrate several novel, integrated and wirelessly driven microfluidics. First, we characterized the simplicity and performance of printed microfluidics with a minimum feature size of 100 µm. Next, we integrated a microtesla (µTesla) pump to provide non-pulsatile flow with reduced shear stress on beta cells cultured on-chip. Lastly, the integration of radio frequency (RF) device and a hobby-grade brushless motor completed a self-enclosed platform that can be remotely controlled without wires. Our study shows how new physics and 3D printing approaches not only provide better integration but also enable novel cell-based studies to advance microfluidic research. [ABSTRACT FROM AUTHOR]

Globally, the most popular upper-limb prostheses are powered by the human body. For body-powered (BP) upper-limb prostheses, control is provided by changing the tension of (Bowden) cables to open or close the terminal device. This technology has been around for centuries, and very few BP alternatives have been presented since. This paper introduces a new BP paradigm that can overcome certain limitations of the current cabled systems, such as a restricted operation space and user discomfort caused by the harness to which the cables are attached. A new breathing-powered system is introduced to give the user full control of the hand motion anywhere in space. Users can regulate their breathing, and this controllable airflow is then used to power a small Tesla turbine that can accurately control the prosthetic finger movements. The breathing-powered device provides a novel prosthetic option that can be used without limiting any of the user’s body movements. Here we prove that it is feasible to produce a functional breathing-powered prosthetic hand and show the models behind it along with a preliminary demonstration. This work creates a step-change in the potential BP options available to patients in the future.

Copyright of Eastern-European Journal of Enterprise Technologies is the property of PC TECHNOLOGY CENTER and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Globally, the most popular upper-limb prostheses are powered by the human body. For body-powered (BP) upper-limb prostheses, control is provided by changing the tension of (Bowden) cables to open or close the terminal device. This technology has been around for centuries, and very few BP alternatives have been presented since. This paper introduces a new BP paradigm that can overcome certain limitations of the current cabled systems, such as a restricted operation space and user discomfort caused by the harness to which the cables are attached. A new breathing-powered system is introduced to give the user full control of the hand motion anywhere in space. Users can regulate their breathing, and this controllable airflow is then used to power a small Tesla turbine that can accurately control the prosthetic finger movements. The breathing-powered device provides a novel prosthetic option that can be used without limiting any of the user's body movements. Here we prove that it is feasible to produce a functional breathing-powered prosthetic hand and show the models behind it along with a preliminary demonstration. This work creates a step-change in the potential BP options available to patients in the future. [ABSTRACT FROM AUTHOR]

Consideration of roughness effects in the flow in a minichannel has been a major scientific problem for many decades. Roughness can alter the momentum diffusion, heat transfer conditions or laminar-turbulent transition. These effects are even more pronounced in minichannel flows where the roughness can occupy a large part of the cross-section. Modelling methods applied so far usually fall short in internal flows with high relative roughness. The presented paper pertains to the analytical flow model in Tesla turbine components with consideration of roughness on the rotor walls. The model uses the equivalent sand grain approach to modify dynamic viscosity in the governing equations to achieve a desired downward shift of the dimensionless velocity profile. The model solves two-dimensional equations of continuity, momentum and energy. The semi-empirical function was derived to consider the change in the shape of the radial velocity. The applied model incorporates Euler's turbomachinery equation to determine the influence of roughness on the turbine performance under varied operating conditions. Roughness shortens the streamlines inside the rotor, but the overall turbine's performance is improved. The roughness equal to 10−5 m increased the power generated and isentropic efficiency by factors of 3 and 2.5, respectively, compared to the smooth rotor. • Modification of fluid viscosity is used to account for roughness in the Tesla turbine. • Blockage effect of roughness elements in microchannels is considered. • Semi-empirical function for velocity profile is used to improve modelling accuracy. • Roughness can increase power three-fold and efficiency two-fold. [ABSTRACT FROM AUTHOR]

The heat pump system has been widely used in residential and commercial applications due to its attractive advantages of high energy efficiency, reliability, and environmental impact. The massive exergy loss during the isenthalpic process in the expansion valve is a major drawback of the heat pump system. Therefore, the Tesla turbine exergy analysis in terms of transiting exergy efficiency is investigated and integrated with the transcritical heat pump system. The aim is to investigate the factors that reduce exergy losses and increase the coefficient of performance and exergy efficiency. The contribution of this paper is twofold. First, a three-dimensional numerical analysis of the supercritical CO2 flow simulation in the Tesla turbine in three different geometries is carried out. Second, the effect of the Tesla turbine on the coefficient of performance and exergy efficiency of the heat pump system is investigated. The effect of the rotor speed and disk spacing on the Tesla turbine power, exergy loss, and transiting exergy efficiency is investigated. The results showed that at a lower disk spacing, the turbine produces higher specific power and transiting exergy efficiency. In addition, the coefficient of performance (COP) and exergy efficiency improvement in the heat pump system combined with the Tesla turbine are 9.8% and 28.9% higher than in the conventional transcritical heat pump system, respectively. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Engineering for Thermal Energy & Power / Reneng Dongli Gongcheng is the property of Journal of Engineering for Thermal Energy & Power and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

• Topology optimization formulation for designing Tesla-type turbine devices. • Use of MINI elements for modeling fluid flow, instead of the more computationally expensive Taylor-Hood elements. • Extra term proposed to the power function in order to better match the traditional energy dissipation definition. Tesla-type turbine devices are turbine devices which convert fluid motion into the rotating motion of a rotor, but without the need of any blades. This is possible due to the interaction of the boundary layer with the rotating fluid motion. In order to successfully optimize this type of fluid flow device through the topology optimization method, some relevant aspects need to be considered. The first one is due to its unique configuration, meaning that the 2D swirl flow model may be considered, which is much less computationally expensive than considering a "full" 3D model. Moreover, since higher mesh resolutions may be necessary in the design of Tesla-type turbines from to the possible appearence of smaller disk-like structures, this may increase the overall optimization cost if the traditional Taylor-Hood elements (quadratic finite elements for the velocity) are considered. This additional computational cost may be reduced by considering MINI elements (linear finite elements with bubble enrichment for the velocity) instead. Another modification that may be useful in its design is augmenting the traditional Brinkman model used in topology optimization with an additional inertial term (Brinkman-Forchheimer model), which may lead to better optimized Tesla turbine designs. Another factor to be considered is the multi-objective function, which may be defined to minimize the relative energy dissipation and maximize the power transferred from the fluid. In such case, the power objective function may be augmented with an additional porosity (material model) term. Numerical examples are presented, taking into account some aspects of the design of Tesla-type turbine devices. [ABSTRACT FROM AUTHOR]

Microfluidics has earned a reputation for providing numerous transformative but disconnected devices and techniques. Active research seeks to address this challenge by integrating microfluidic components, including embedded miniature pumps. However, a significant portion of existing microfluidic integration relies on the time-consuming manual fabrication that introduces device variations. We put forward a framework for solving this disconnect by combining new pumping mechanics and 3D printing to demonstrate several novel, integrated and wirelessly driven microfluidics. First, we characterized the simplicity and performance of printed microfluidics with a minimum feature size of 100 µm. Next, we integrated a microtesla (µTesla) pump to provide non-pulsatile flow with reduced shear stress on beta cells cultured on-chip. Lastly, the integration of radio frequency (RF) device and a hobby-grade brushless motor completed a self-enclosed platform that can be remotely controlled without wires. Our study shows how new physics and 3D printing approaches not only provide better integration but also enable novel cell-based studies to advance microfluidic research.

In order to identify transitional flow, the linear stability of inward flow in a narrow gap between co-rotating disks is studied. Two methods are developed. The local approach assumes periodic nature of the flow in radial and circumferential direction, whereas the computationally more expensive biglobal variant only requires periodicity in circumferential direction. Stability maps are provided for a single set of operating conditions spanning a range of Reynolds numbers at fixed rotor geometry and rotational speed. The theoretical findings are compared to a set of experimental velocity profiles that includes the transitional region according to profile shapes. Apart from some explainable inconsistencies, the determined stability limits agree with each other and with results from previous studies. [ABSTRACT FROM AUTHOR]

The paper presents a comprehensive numerical and experimental analysis of the Tesla turbine. The turbine rotor had 5 discs with 160 mm in diameter and inter-disc gap equal to 0.75 mm. The nozzle apparatus consisted of 4 diverging nozzles with 2.85 mm in height of minimal cross-section. The investigations were carried out on air in subsonic flow regime for three pressure ratios: 1.4, 1.6 and 1.88. Maximal generated power was equal to 126 W and all power characteristics were in good agreement with numerical calculations. For each pressure ratio, maximal efficiency was approximately the same in the experiment, although numerical methods proved that efficiency slightly dropped with the increase of pressure ratio. Measurements included pressure distribution in the plenum chamber and tip clearance and temperature drop between the turbine’s inlet and the outlet. For each pressure ratio, the lowest value of the total temperature marked the highest efficiency of the turbine, although the lowest static temperature was shifted towards higher rotational speeds. The turbine efficiency could surpass 20% assuming the elimination of the impact of the lateral gaps between the discs and the casing. The presented data can be used as a benchmark for the validation of analytical and numerical models.

The inward flow between two parallel, co-rotating disks undergoes a thorough examination by analytical, experimental and numerical means. The analytical approach utilizes the asymptotical truncated series solution provided by Batista (2011) and extends it by a correction for an arbitrary mean tangential velocity at the rotor inlet. Taylor series expansions of the analytical results provide an estimate for the orders of magnitude of velocity components and the polynomial order of their profile shapes. The common assumption of parabolic velocity distributions is only appropriate in the radial direction. In parallel, a unique test rig provides the experimental counterpart of the velocity profiles inside a rotor gap, that is suitably narrow for turbomachinery applications. The optical flow measurements are based on a novel calibration technique and volumetric particle tracking evaluation. Both laminar and turbulent operating conditions are examined. Finally, numerical studies using commercial CFD software provide insight into the flow field inside the test rig rotor where experimental methods fall short and provide an additional means to investigate the effects of the approximations made in the derivation of the analytical results. The velocity distributions acquired by analytical, numerical and experimental means agree well, the asymptotical nature of the analytical solution by Batista (2011) can be observed. The comparison of experimental and numerical results of a turbulent case suggests that the Shear Stress Transport turbulence model reproduces turbulent flow inside the rotor gap appropriately. [ABSTRACT FROM AUTHOR]

The aerodynamic performance and flow characteristics of a multichannel nozzled Tesla turbine were investigated numerically with different nozzle and outlet geometries at different rotational speeds. Two kinds of nozzle geometries were proposed: one nozzle channel to one disc channel (named as one-to-one turbine) and one nozzle channel to several disc channels (named as one-to-many turbine). Simplified radial outlet and real axial outlet geometries of the Tesla turbines were adopted to research the influence of outlet geometries. The results show that compared with the one-to-many turbine, the isentropic efficiency of the one-to-one turbine is much higher; while the flow coefficient is much lower. In addition, in the middle disc channels (DC1 and DC2) of which two walls are rotating disc walls, the flow fields are almost the same, but different from that in the side channel (DC3) of which one wall is a rotating wall and the other one is a stationary casing wall. DC1 and DC2 generate more torque with less working fluid, thus the disc spacing distance of DC3 should be narrower than that of DC1 and DC2. Compared to the one-to-many turbine, the working fluid flowing through DC1 and DC2 of the one-to-one turbine is much less, and the flow path lines are much longer. The results of different turbine outlet geometries show that compared with the turbines with radial outlet, the isentropic efficiency of the one-to-many turbine with axial outlet is a little higher, while that of the one-to-one turbine with axial outlet is lower. This is due to the larger torque on the disc hole walls, despite a lot more total pressure loss in the exhaust vent of the one-to-many turbine. Therefore, the contribution of disc hole walls to torque cannot be neglected in numerical simulations. [ABSTRACT FROM AUTHOR]

Abstract Tesla expander is a bladeless turbine suited to low power range applications. In this article, a comparison between the performance prediction, as well as the assessment of the main flow characteristics, of a Tesla turbine working with organic fluids obtained through an in-house 2D code developed in EES environment and a simulation run with a computational fluid dynamics commercial software was done. Three working fluids (R404a, R134a and R245fa) were analysed in order to determine the related performance parameters. Various computations were carried out at several speeds of revolution, both with the laminar model and the Langtry-Menter transitional shear stress transport model for turbulence processing. High rotor efficiency was predicted for a small-scale prototype working with all analysed fluids (69% at 3000 rpm). The results obtained by the CFD simulations and by the in-house code showed an excellent matching. Finally, absolute and relative flow path lines were computed in order to determine fluid dynamics inside the channel and to analyse the fundamental flow phenomena. Highlights • In-house 2D model and CFD simulations with organic fluids match well. • High Tesla turbine rotor efficiency are achievable (69% with R404a and R134a). • Flow reversal condition and flow stream lines were computed and depicted. • Home built model allows quick design of Tesla expanders. [ABSTRACT FROM AUTHOR]

A countless amount of energy has been wasted in all kinds of expansion valves (EV) in industries. In fact, EVs, including regulators, throttling valves, capillary tubes, etc., have been used to intentionally reduce the potential of carrier fluid. City gate stations (CGS) have been recognized as one of the important points with high potential for energy harvesting due to its function for regulating natural gas (NG) pressure by EV. In this study, Tesla turbine (TT) is introduced as a new candidate for substitution of EV, particularly those that have been employed in CGS on high-pressure NG pipelines, as well as those applications in which high-potential fluid must be reduced to a low-potential state to form a complete thermodynamic cycle or to be used at end-user equipment. Although harvesting energy is one of the hottest fields of science and engineering, there are few traces of research on using a TT as an alternative for EVs, even for the industries possessing high-pressure lines. This numerical experiment intends to show the capability of TT as a robust candidate for substituting regulation valves through investigating thermohydrodynamic characteristics of the turbulent high-pressure compressible NG flow through a TT under different operation conditions. This study, with the objective of managing the exploitation of resources, can be considered as one step forward toward reinforcing economic and environmental pillars of sustainable development. It is also found that the generated power by TT can support the 285 7W LED simultaneously, or it is equivalent to 84.4 m2 area of the solar panel (150 W, 15.42% efficiency) for the climate condition of Toronto, Canada.

Tesla turbines are a kind of unconventional bladeless turbines, which utilize the viscosity of working fluid to rotate the rotor and realize energy conversion. They offer an attractive substitution for small and micro conventional bladed turbines due to two major advantages. In this study, the effects of two influential geometrical parameters, disc thickness and disc spacing distance, on the aerodynamic performance and flow characteristics for two kinds of multichannel Tesla turbines (one-to-one turbine and one-to-many turbine) were investigated and analyzed numerically. The results show that, with increasing disc thickness, the isentropic efficiency of the one-to-one turbine decreases a little and that of the one-to-many turbine reduces significantly. For example, for turbine cases with 0.5 mm disc spacing distance, the former drops less than 7% and the latter decreases by about 45% of their original values as disc thickness increases from 1 mm to 2 mm. With increasing disc spacing distance, the isentropic efficiency of both kinds of turbines increases first and then decreases, and an optimal value and a high efficiency range exist to make the isentropic efficiency reach its maximum and maintain at a high level, respectively. The optimal disc spacing distance for the one-to-one turbine is less than that for the one-to-many turbine (0.5 mm and 1 mm, respectively, for turbine cases with disc thickness of 1 mm). To sum up, for designing a multichannel Tesla turbine, the disc spacing distance should be among its high efficiency range, and the determination of disc thickness should be balanced between its impacts on the aerodynamic performance and mechanical stress. [ABSTRACT FROM AUTHOR]

Highlights • A small-scale waste heat recovery system by virtue of Tesla turbine is proposed. • Computational fluid dynamics simulations on Tesla turbine are performed to calculate flow and pressure field. • A performance experiment of Tesla turbine is conducted to validate simulation results. • Tesla turbine clearly improves total power and thermal efficiency over a low rotation-speed range. • Working-fluid property and number of nozzles impact Tesla turbine performance. Abstract Waste heat recovery is significant to improve energy utilization. Expander is one of the most important components in waste heat recovery. Tesla turbine offers an attractive option for the expander if an efficient design can be well achieved. Faced the theoretical and computational challenges associated with the feasibility of Tesla turbine in a small-scale waste heat recovery system, this paper formulates a systematic design methodology to seek optimal parameters and geometric model of the Tesla turbine which is applied to a coolant waste heat recovery system of an automobile engine. To achieve this goal, a detailed investigation into the performance of Tesla turbine, which incorporates experimental and computational fluid dynamics analysis manifests that Tesla turbine achieves higher performance at lower rotation-speed. Performance analysis on the waste heat recovery system under various operating conditions is conducted based on a comprehensive thermodynamic model. Results show that the total power and overall thermal efficiency of the waste heat recovery system are clearly increased over a low rotation-speed range, furtherly, which can be improved by selecting appropriate viscosity of the working fluid and number of nozzles. It is desirable and significative to effectively improve power output and thermal efficiency for an automobile engine at a lower expense of volume and cost. [ABSTRACT FROM AUTHOR]

The Tesla turbine seems to offer several points of attractiveness when applied to low-power applications. Indeed, it is a simple, reliable, and low cost machine. The principle of operation of the turbine relies on the exchange of momentum due to the shear forces originated by the flow of the fluid through a tight gap among closely stacked disks. This turbine was firstly developed by Tesla at the beginning of the 20th century, but it did not stir up much attention due to the strong drive towards large centralized power plants, on the other hand, in recent years, as micro power generation gained attention on the energy market place, this original expander raised renewed interest. The mathematical model of the Tesla turbine rotor is revised, and adapted to real gas operation. The model is first validated by comparison with other assessed literature models. The optimal configuration of the rotor geometry is then investigated running a parametric analysis of the fundamental design parameters. High values of efficiency (isolated rotor) were obtained for the optimal configuration of the turbine, which appears interesting for small-scale power generation. The rotor efficiency depends on the configuration of the disks, particularly on the gap and on the outlet diameter, which determines largely the kinetic energy at discharge. [ABSTRACT FROM AUTHOR]

The Tesla turbine operation is based on the use of tangential stresses arising from the fluid viscosity and turbulence and from the phenomenon of the fluid adhesion to the surface it flows past. The paper presents a description and testing of the Tesla turbine model, pointing to the impact of the applied turbulence models on the prediction of the Tesla turbine operating conditions. Non-stationary simulations are performed using the Ansys CFX 18 commercial code. The following turbulence models are analysed: the RNG k-ε, the k-ω SST and the SST-SAS in two variants of time and space discretization. The flow field structures and the flow unsteadiness occurring in the gaps between the rotor discs are described. The distribution of power unit arising on the discs is determined and the predictions as to the power generated by the turbine coming from numerical analysis and preliminary experimental investigations are compared. A comparison of efficiency estimation is made using different methods. [ABSTRACT FROM AUTHOR]

The article establishes the physics of the complex interaction of discrete multiple inflows with the stationary shroud and the rotating channel of a Tesla disc turbine. Using a large number (150) of separate, fully three-dimensional computational fluid dynamic simulations, we demonstrate the (sometimes dramatic) role of four important input parameters, namely the number of nozzles (Nnozzle), rotational speed of the discs (Ω), radial clearance between the rotor and the shroud (Δrc), and disc thickness (dt), in the fluid dynamics and performance of a Tesla turbine. An increase in Nnozzle or Δrc assists in the attainment of axisymmetric condition at rotor inlet. Ω influences significantly the distribution of radial velocity including the fundamental shape of its z-profile (parabolic, flat or W-shaped). The paper demonstrates the existence of an optimum Δrc for which the efficiency of the rotor (η) is maximized. Present computational fluid dynamics simulations for many combinations of Nnozzle and Ω establish that the η versus Ω curves, for each fixed value of Nnozzle, are of the shape of an inverted bucket. With increasing Nnozzle, the operable range of Ω decreases, the buckets become more peaky and the maximum possible η increases substantially (by a factor of 2 in the example calculation shown). The present systematic work thus demonstrates quantitatively, for the first time, that an axisymmetric rotor inflow condition represents the best possible design for the rotor. It is further shown that, as the disc thickness is increased, the efficiency may decrease substantially (even dramatically) and its maxima occur at lower rotational speeds. Chamfering of the disc edge or partial admission decreases the turbine efficiency. Thus, small disc thickness, flat disc edge, full nozzle opening, optimum radial clearance, and inlet condition as close to axisymmetry as is possible are recommended for the design of an efficient Tesla disc turbine. [ABSTRACT FROM AUTHOR]

In recent years, small-micro power generation was appointed as one of the proper solutions to tackle the increasing energy consumption, while opening the way to distributed energy systems and micro grids. The most interesting solution for small-micro power generation is the ORC technology, however, it still needs further developments especially regarding the design of small and micro expanders. A possible solution for micro-expanders is the Tesla turbine, which is a viscous bladeless turbine. This concept was developed by Nikola Tesla at the beginning of the 20th century, but it went through a long period of indifference due to the run towards large size centralized power plants. Only recently it found a renewed appeal, as its features make it suitable for utilization in small and micro size systems, like ORC applications, where low cost components become very attractive for the exploitation of residual pressure drop. The present study develops a design procedure of a Tesla turbine for ORC applications. A throughout optimization method was performed by evaluating the losses of each component and by introducing an innovative rotor model. Three turbine configurations with different expander size were assessed, in order to show the performance potential of the Tesla turbine, which achieved 64% total-to-static efficiency when working with N-hexane fluid. [ABSTRACT FROM AUTHOR]

The Tesla turbine is an original expander working on the principle of torque transmission by wall shear stress. The principle – demonstrated for air expanders at lab scale - has attractive features when applied to ORC expanders: it is suitable for handling limited flow rates (as is the case for machines in the range from 500 W to 5 kW), it can be developed to a reasonable size (rotor diameters between 0.1 and 0.3 m), with limited rotational speeds (from 1000 to 12000 rpm). The original concept is revisited, improving the stator layout (which is the main responsible for poor performance) and developing a modular design allowing to cover a wide power range, as well as to realize a perfectly sealed operation and including other fluid dynamics improvements. The flow model assumes complete real fluid behaviour, and includes several new concepts such as bladed channels for the stator and a detailed treatment of losses. Preliminary design sketches are presented and results discussed and evaluated. Several working fluids are considered, from refrigerants (R245fa, R134a, SES36) to hydrocarbons (n-Hexane, n-Pentane). [ABSTRACT FROM AUTHOR]

As a competitive small-scale turbomachinery option, Tesla turbines have wide potential in various fields, such as renewable energy generation systems and small power equipment. This paper investigates the influence of disc tip geometry, including its profile and relative height, on the aerodynamic performance and flow characteristics of one-to-one and one-to-many multichannel Tesla turbines. The results indicate that compared to the turbine with blunt tips, the isentropic efficiency of the one-to-one turbine with sharp tips has a little decrease, which is because the relative tangential velocity gradient near the rotational disc walls decreases a little and additional vortices are generated at the rotor inlet, while that of the one-to-many turbine with sharp tips increases significantly, resulting from an increase in the relative tangential velocity in the disc channels and a decrease in the low Mach number and vortex area; for instance the turbine efficiency for the former relatively decreases by 3.6% and that for the latter increases by 13.5% at 30,000 r/min. In addition, the isentropic efficiency of the one-to-many turbine with sharp tips goes up with increasing relative height due to increasing improvement of flow status, and its increment rate slows down. A circular or elliptic tip performs better with lower relative height and a triangular tip behaves better with higher relative height. To sum up, a blunt disc tip is recommended for the one-to-one turbine, and a sharp disc tip is for the one-to-many turbine. The relative height and tip profile of the one-to-many turbine should be determined according to their effects on turbine performance, manufacturing difficulty and mechanical deformation.

This article presents a systematic and comprehensive computational fluid dynamic study for co-rotating discs and, Tesla turbines, in which the full benefit of similitude and scaling is extracted by expressing the results and analyses in terms of carefully formulated non-dimensional numbers—five input parameters and three output parameters. The work formulates a systematic design methodology for the optimum selection of input parameters for the rotor of a Tesla disc turbine that would satisfy practical constraints and deliver high values of power and efficiency. Many subtle flow physics (e.g. the identification of dynamic similarity number, inlet tangential speed ratio and inlet flow angle as the three most important non-dimensional input parameters, the secondary role of aspect ratio as a separate quantity independent of dynamic similarity number, and, the variation in the four fundamental components of the radial pressure difference) are critically explained. The present study establishes, for the first time, that unlike the flow in a conventional turbomachine in which fluid friction plays only a detrimental role, fluid friction plays a dual role in a Tesla disc turbine—a detrimental role in increasing the radial pressure drop (thus tending to decrease the efficiency) and a beneficial role by providing the sole mechanism for power production. This dual role is comprehensively analyzed and quantified in this work. The balance between this dual role of fluid friction gives rise to the optimum values of dynamic similarity number and inlet tangential speed ratio that maximize efficiency. [ABSTRACT FROM AUTHOR]

The TESLA turbine is an original expander working on the principle of torque transmission by wall shear stress. The principle – demonstrated for air expanders at lab scale - has some attractive features when applied to ORC expanders: it is suitable for handling limited flow rates (as is the case for machines in the range from 500W to 5 kW), it can be developed to a reasonable size (rotor of 0.1 to 0.3 m diameters), with possible rotational speeds (which range from 1000 to 12000 rpm). The original concept was revisited, improving the stator layout (which is the main responsible for poor performance) and developing a modular design allowing to cover a wide power range, as well as a perfectly sealed operation and other fluid dynamics improvements. The flow model was developed using complete real fluid assumptions, and includes several new concepts such as bladed channels for the stator and detailed treatment of losses. Preliminary design sketches are presented and results discussed and evaluated. [ABSTRACT FROM AUTHOR]

This paper summarises the numerical and theoretical studies of the incompressible, laminar airflow through a single flow passage of a blade-less radial turbine. Furthermore, it yields the numerical validation of the simplified theoretical model for incompressible rotor flows without the consideration of mechanical losses. It exposes the accuracy of the simplified, analytical performance prediction and flow field for a given geometry, which is based on an optimisation of performance by solving the simplified and incompressible Navier-Stokes-Equations in cylindrical coordinates. The influences of the dimensionless machine parameters on performance and efficiency are obtained from a theoretical analysis. The stream-lines of the bulk flow are derived by analytical means. The inflow conditions for maximum performance and efficiency are theoretically determined and later compared to laminar CFD. In order to quantify the error of the simplified theoretical analysis, different inflow conditions and their influences on shaft power and flow behavior are examined by means of CFD. The development of the axial velocity distribution at the inlet zone is compared to the one from the theoretical inflow assumption. The influences of Reynolds number and revolution speed on the velocity profiles are investigated. In addition to that, a compressible flow model is introduced. Numerical results are obtained and compared to the incompressible solution. Moreover, compressibility effects on turbine performance are derived. [ABSTRACT FROM AUTHOR]

Tesla turbine and its applications in power generation and fluid flow were demonstrated by Nicholas Tesla in 1913. However, its real-world implementations were limited by the difficulty to maintain laminar flow between rotor disks, transient efficiencies during rotor acceleration, and the lack of other applications that fully utilize the continuous flow outputs. All of the aforementioned limits of Tesla turbines can be addressed by scaling to the microfluidic flow regime. Demonstrated here is a microscale Tesla pump designed and fabricated using a Digital Light Processing (DLP) based 3D printer with 43 μm lateral and 30 μm thickness resolutions. The miniaturized pump is characterized by low Reynolds number of 1000 and a flow rate of up to 12.6 mL/min at 1200 rpm, unloaded. It is capable of driving a mixer network to generate microfluidic gradient. The continuous, laminar flow from Tesla turbines is well-suited to the needs of flow-sensitive microfluidics, where the integrated pump will enable numerous compact lab-on-a-chip applications. [ABSTRACT FROM AUTHOR]

The objective of the present research is to examines the potential benefits of Tesla Disk Turbine (TDT), a harmless mean of energy conversion from high pressure non-polluting fluid (compressed air, water & steam) to a form of energy e. g. electricity, mechanical power which can be used in various applications. A prototype model of TDT was designed and different experiments were performed with various pressure ranges of compressed air. Theoretical sound (boundary layer theory, adhesion, and viscosity), design, material selection, fabrication, efficiency, power output, advantages, limitations, its applications have been discussed. This model canal ternatively be used in different applications of power generation as replacement of batteries & generators. Steam, water and other medium can also be part of this technology by adapting this turbine for large scale energy production. The result obtained from the current research could be utilized as a guide for the further design and operation of the industrial system. [ABSTRACT FROM AUTHOR]

• A one-dimensional model of Tesla turbine for wet working fluids is proposed. • Thermodynamic performance of five wet working fluids in Tesla turbine is analyzed. • Tesla turbine using R22 has the highest efficiency at low rotor speed conditions. • Tesla turbine with R417a has the maximum output power in most operating conditions. • Optimum rotor speed and rotor gap distance exist for each working fluid. In the field of clean energy, Organic Rankine Cycle (ORC) is considered a vital method to utilize low-grade waste heat effectively. Due to certain application advantages in low power level ORC systems, the Tesla turbine is considered one of the essential choices for the core components of ORC systems. Given the inadequacy of the current research on the performance of the Tesla turbine under two-phase flow conditions, a one-dimensional model of the Tesla turbine was constructed in this paper to make it equally applicable to the two-phase flow conditions of wet working fluids. A model of the Tesla turbine and ORC system was constructed from the thermodynamic point of view, and five typical wet working fluids (R22, R417a, R134a, R152a, and R290) were selected to study the effects of the five wet working fluids on the thermal performance of Tesla turbine and ORC system. The effects of the changes in key structural parameters of the Tesla turbine on the performance of the Tesla turbine and the ORC system were further analyzed when different wet working fluids were used in the ORC system. The results showed that the highest turbine efficiency of 42.0 % was achieved when the Tesla turbine used R22 as the working fluid under the design conditions, while the highest turbine output power and the highest system thermal efficiency of 1.19 kW and 3.96 % were achieved when R417a was used as the working fluid. The analysis of the key structural parameters of the system showed that for the five different wet working fluids, the turbine efficiency, turbine output power, and system thermal efficiency increased monotonically with increasing rotor inlet radius. For each of the five wet working fluids, an optimum rotor speed, rotor outlet radius, and rotor gap distance exist, resulting in optimal turbine efficiency and system performance. The related work provides an important reference for the optimal design of Tesla turbines with wet working fluids. [ABSTRACT FROM AUTHOR]

Tesla turbines can be employed as small-scale turbines to recover waste energy in several industrial applications. However, there is no consensus on the turbine efficiency as experimental studies show significantly lower values than those obtained by analytical and CFD approaches. The present work addresses that question by performing a systematic literature review (SLR) on Tesla turbines, comparing the efficiency values reported by experimental and simulation works. To validate the SLR findings an experimental small-scale air driven Tesla turbine was built. The Design of Experiments (DoE) methodology was applied to understand the effects of selected independent variables on the turbine output power and mechanical efficiency. Inlet air pressure, temperature, and rotational speed were chosen as controllable factors of a Central Composite Design applied to the prototype of < 1 kW output power. The results indicate a 5% efficiency increase when inlet pressure increases 1 bar, on average. In the SLR, the average efficiency of 40%–60% was reported by simulation works, while experimental articles reported maximum efficiencies of 20%, on average. The experimental turbine analyzed in this paper presented a maximum efficiency of 14.2% ± 0.4% at 3 barg and 4,000 rpm, agreeing with other experimental studies. • Literature review shows a lack of consensus regarding the TT maximum efficiency. • The designed TT is limited to efficiencies below 20%. • From SLR, higher experimental efficiencies are found for output power ≤1 kW and forward into sub-Watt scale. • Is still to be proven that TT performance can be competitive concerning other turbine technologies. [ABSTRACT FROM AUTHOR]

This article presents the strength and modal analysis of the rotor model of the Tesla microturbine. The calculations were made in order to verify the design of multi-disc turbine's rotor before production process. Two commercial solvers were used independently, which are capable to deal with problems of solid state physics - Abaqus and Ansys Mechanical with Workbench software. The comparison of results from two applications aimed at checking solvers' applicability in the present case. Preliminary analysis was carried out in Abaqus software. The calculations were performed assuming perfect bearing stiffness for different rotation speeds. A more detailed analysis was made in Ansys Mechanical software using structure analysis modules to determine the stresses in the structure which arise as a consequence of rotor's rotational motion. Subsequently, it was followed up with modal analysis results. Additionally the parameters of selected bearings were determined and modal analysis took into account the stiffness corresponding to individual rolling bearings. [ABSTRACT FROM AUTHOR]

As the demand for optical glasses has increased, precision requirements for specific shapes, forms, surface textures, and sizes (miniaturization) have also increased. The standards and surface finishes applied to the reference mirrors used in measuring appliances are crucial. Hence, enhancements in figuring and surface finishing are indispensable to manufacturing industries. In this article, a novel self-propelled multi-jet abrasive fluid polishing technique is proposed for an ultra-precision polishing process in which a blade-less Tesla turbine was used as a prime mover. The turbine was characterized by high swirling velocity at the outlet; therefore, high levels of kinetic energy moving away from the turbine were used as polishing energy. Computational fluid dynamics (CFD) was also used to simulate the flow on the turbine blades. With a newly designed and manufactured polishing tool, the optimal polishing parameters for improving the surface roughness of crown optical glasses (N-BK7) were investigated. Taguchi's experimental approach, an L18orthogonal array, was employed to obtain the optimal process parameters. An analysis of variance (ANOVA) was also conducted to determine the significant factors. The surface roughness has been improved by approximately 94.44% from (Ra) 0.36 μm to (Ra) 0.02 μm. This study also presents a discussion on the influence of significant factors on improving surface roughness. [ABSTRACT FROM AUTHOR]