Radial Flow Turbine Research Articles

Performance analysis of high-speed cryogenic turbo-expander at cooling process based on numerical and experimental study

Abstract In order to make a detailed understanding of the cryogenic turbo-expander off-design performance at cool-down procedure, an extensive experimental and numerical program have been carried out on a mixed and inward flow radial turbine. According to the design and cooling process condition, just like pressure at stator inlet or brake power of the turbo-expander, a series of CFD simulations were carried out in order to guide design and off-design iterations towards achieving a matched flow capacity for each situation. The analyses also include the study of the effect of different gas models on the CFD calculations. Through the results analysis it was concluded that the direct use of the Hepak database for the real gas properties in the CFD solver improve the prediction of the thermodynamic properties and so the performance of the turbo-expander. With experimental comparison, the cryogenic turbo-expander off-design performance at cooling process can be better known.

The Effect of Using Baffles on the Rate of Mass Transfer of a Cylindrical Stirred Tank Reactor

Owing to the high mixing capacity, the stirred tank reactor is the key class of reactors in the chemical process industry and pharmaceutical industry. The mass transport nature of a batch stirred tank reactor with a fixed copper wall with a cylinder form was studied using copper dissolution in acidified dichromate which is controlled by diffusion. Variables analyzed included the speed of rotation of the impeller, the shape of the impeller and the physical specifications of the solution and the existence of baffles. The data were correlated for the conditions 3667.323 < Re < 34993.18 and 960 < Sc < 1364, for radial flow by the equation: Sh =0.3453 *Sc1/3*Re0.66 but for axial flow by the equation: Sh =0.5866 *Sc1/3*Re0.59. Through speed of rotation of the impeller increases,it allows the rate of mass transfer from the fixed bed to the solution to rise. The radial-flow turbine is more effective than the axial-flow turbine in increasing the rate of mass transfer. The usage of baffles plays a significant role in rising the rate of mass transfer. Using baffles; the correlation will be Sh =0.0769 *Sc1/3*Re0.84 for radial flow and Sh =0.1157 *Sc1/3*Re0.78 for axial flow. The purpose of this research is to estimate the rate of mass transport that can be required in corrosive reactions, and also to maximize the mass transfer rate that can be achieved in other processes, such as electroplating in presence of baffles.

Radial turbine optimization under unsteady flow using nature-inspired algorithms

This paper investigated the performance of a radial flow turbine by coupling metaheuristic algorithms with Computational Fluid Dynamics. We performed the optimization of the casing and wheel of the turbine simultaneously. The computer codes of four metaheuristic algorithms, namely the Genetic Algorithm, Flower Pollination Algorithm, Grey Wolf Optimizer, and the Grasshopper Optimization Algorithm were developed using MATLAB. The optimization results indicated that Grey Wolf Optimizer is the most powerful algorithm to achieve a higher temperature drop in comparison with other algorithms. Revealed by the study, choosing the best angle at the blade inlet is the most influential factor for efficiency improvement. Besides, casing optimization has a positive effect on the pressure recovery of the turbine by eliminating swirling flow. A comparison of the physics of fluid in the optimized and base wheel showed that the flow is more attached to the optimized blade since the backward-facing step produces a favorable pressure gradient mainly in the recirculating bubble. Employing pulsating flow confirmed that the efficiency of the optimized turbine has a significant increase in comparison to the base turbine by more than 2% in high mass flow rates.

Scaling a radial flow turbine from air to multiple compressible fluids and performance evaluation using computational fluid dynamics

Many new turbine designs may take large timelines to prove their worth. For getting duty condition at optimum efficiency, one can always scale speed, diameter, if a very efficient benchmark is available. This paper examines the similarity-based scaling strategy to develop radial inflow turbines for different compressible fluids from a well-established NASA radial flow turbine designed and experimentally tested with air as the working fluid. The NASA 1730 air turbine experimental data have been used as the benchmark here and adopted multiple fluids to understand scaling. The considered fluids are supercritical carbon dioxide for the Brayton cycle, helium for the cryogenic liquefaction cycle, and R143a for the organic Rankine cycle. The uniqueness here is to have three types of cycles, viz. closed-loop Brayton cycle, organic Rankine cycle, and cryogenic helium liquefaction cycle, which employ different working fluids, adapting the same NASA turbine geometry. This paper has described the scaling methodology and presented the simulated turbine performance of SCO2, helium, and R143a using computational fluid dynamics. The dimensionless curves for these fluids are plotted on the corresponding experimental characteristics of the NASA turbine. Out of the three fluids, SCO2 showed the perfect Mach number matching for the flow and torque coefficient curves. The Mach number deviations in the case of helium were small, and the variations were slightly higher for R143a. The efficiencies were the highest for R143a, followed by SCO2 and helium. Thus, the scaling was found to be effective in all cases. Thus, the standard turbomachinery space developed for air as fluid can be used effectively for the development of turboexpanders for various cycles with different working fluids without redesigning the entire shape using similarity-based scaling. The benchmark NASA 1730 turbine has proven this in three special cases. This paper is not against designing new machines but is only trying to say that when such good benchmark machines like NASA 1730 turbine is available; designers must use the power of similitude to adapt it to match new fluids and new conditions.

Optimization of a Radial Turbine for Pulsating Flows

Abstract A turbocharger turbine is exposed to pulsating flow conditions when it is connected to an engine exhaust system due to the opening and closing of the exhaust valves. However, many radial turbines are designed and tested under steady-state conditions without taking into account these unsteady exhaust flows. In order to seek the optimal aerodynamic design of a radial flow turbine (RFT) under pulsating flow conditions, the present research utilizes a numerical simulation approach to optimize the blade shape of a small-scale mixed flow turbine (MFT) under 50 Hz pulses. This corresponds to a four-stroke, three-cylinder engine rotating at 2000 rpm. In order to understand how a less computationally intensive, steady-state optimization compares, the blade shape was also optimized using the peak power point of the pulse. Three turbine features were modified during the optimization process, including blade cone angle, blade axial location, and blade camber angles. The optimization was carried out using a computational fluid dynamics (CFD)–genetic algorithm (GA) coupled approach, targeting at maximizing both energy-weighted efficiency and energy output during a predefined pulse period. To ensure that the new design maintains a similar matching to the engine, the maximum deviation of turbine swallowing capacity is controlled to within ±5% of the baseline for all new blade designs. The design that achieves the maximum pulse cycle-averaged efficiency was produced from unsteady optimization, with a performance benefit of 0.66%. The unsteady optimization also produced a blade shape that delivers the maximum energy output, with an improvement of 5.42%.

Transient performance of the mixed flow and radial flow variable geometry turbines for an automotive turbocharger

In our previous paper, the steady-state test results of a mixed flow turbine with variable nozzle vanes for a turbocharger are reported. In this paper, the transient response of the same mixed flow turbine along with that of a similarly sized radial flow turbine is presented. The turbine size is suitable for handling the flow capacity of the diesel engines with swept volume up to 1.5 L. The previous experimental test set up is modified by adding a quick-release valve – actuation system before the turbine inlet to obtain a transient response. The radial and mixed flow turbines are tested for different turbine inlet pressures and for various opening positions of the nozzle vanes while matching the turbine mass flow parameters between radial and mixed flow turbines. Typically at nozzle vane openings corresponding to 50% mass flow parameter and 1.5 bar (abs) pressure at the inlet to the turbine, the transient response time for the turbine with mixed flow variable nozzle vanes configuration is about 0.770 s, as compared to 0.858 s for the turbine with radial flow variable nozzle vanes configuration.

Experimental study of a low-temperature micro-scale organic Rankine cycle system with the multi-stage radial-flow turbine for domestic applications

The paper presents an experimental evaluation of the efficiency of a small-scale low-temperature organic Rankine cycle (ORC) as an mCHP (micro Combined Heat and Power) system. Ultimately, the cogeneration system is dedicated to individual households and should be able to supply them with electricity and heat. A high-speed four-stage radial-flow microturbine with a nominal power of 2.5 kWe was used as an expansion machine. The low-boiling medium under the trade name of HFE7100 was used as a working medium in the system. Experimental tests of the ORC system were performed with various loads and under various operating conditions. The main purpose of the work was to achieve the maximum power of the microturbine at maximum possible efficiency of the ORC system. For this purpose, the supply system of the microturbine was improved by using an additional hole through which the blade system is fed. After the improvement, the microturbine produced about 3.9% more electric energy; this was due to the increase in the rotational speed (by approx. 7.2%) as compared to earlier measurement results. The maximum electric power generated by the microturbine was 2.12 kWe and was achieved at a rotational speed of about 22,440 rpm. The maximum thermal efficiency of the ORC was about 6.5%. The cycle had the maximum isentropic efficiency of the microturbine at 71% and it was lower by 1% than the value obtained using a numerical model. The improvement of the microturbine’s supply system enhanced the exergetic efficiency of the ORC system and its maximum value was about 21.5%.

Investigation on propagation characteristics of rotating detonation wave in a radial-flow turbine engine combustor model

In this experiment, the propagation characteristics of rotating detonation waves in a radial-flow turbine engine combustor model were investigated. An annular combustor, with an inner diameter of 94 mm and an outer diameter of 106 mm was used as the rotating detonation combustor, and the H2 and air were separately injected into the combustor. The stability of the detonation wave propagation with and without a guide vane at the exit of the combustor was analyzed. The velocity of the detonation wave for the guide vane tests is higher than that of no guide vane tests, and the guide vane has a significant effect on the oscillating pressure. For the no guide vane tests, only the two-wave collision mode of detonation wave is obtained for all the equivalence ratios, and there is an unstable phenomenon of the collision point displacement. For the guide vane tests, the detonation-wave gradually stabilizes with the increase of the equivalence ratio, and then the stability gradually weakens. The phenomenon of the low-frequency pressure fluctuation occurs with the equivalence ratio larger than 1, and the fluctuation frequency is lower than 400 Hz.

Experimental Investigation on Performance of an Organic Rankine Cycle System Integrated with a Radial Flow Turbine

An experimental method is used to investigate the performance of a small-scale organic Rankine cycle (ORC) system which is integrated with a radial flow turbine, using 90 °C hot water as a heat source. The considered working fluids are R245fa and R123. The relationship between cycle performance and the operation parameters is obtained. With constant condensing pressure (temperature), the outlet temperature of the hot water, the mass flow rate of the hot water and the evaporator heat transfer rate increase with increasing evaporating pressure. Turbine isentropic efficiency decreases and transmission-generation efficiency increases with rising evaporating pressure. In the considered conditions, the maximum specific energy is 1.28 kJ/kg, with optimal fluid of R245fa and an optimal evaporating temperature of 69.2 °C. When the evaporating pressure (temperature) is constant, the outlet temperature of the cooling water increases, and the mass flow rate of the cooling water decreases with increasing condensing pressure. Turbine isentropic efficiency increases and transmission-generation efficiency decreases with the rise of condensing pressure. In the considered conditions, the maximum specific energy is 0.89 kJ/kg, with optimal fluid of R245fa and an optimal condensing temperature of 29.1 °C. Turbine efficiency is impacted by the working fluid type, operation parameters and nozzle type.

A comparative study of the performance of the mixed flow and radial flow variable geometry turbines for an automotive turbocharger

A new design of a mixed flow variable geometry turbine is developed for the turbocharger used in diesel engines having the cylinder capacity from 1.0 to 1.5 L. An equivalent size radial flow variable geometry turbine is considered as the reference for the purpose of bench-marking. For both the radial and mixed flow turbines, turbocharger components are manufactured and a test rig is developed with them to carry out performance analysis. Steady-state turbine experiments are conducted with various openings of the nozzle vanes, turbine speeds, and expansion ratios. Typical performance parameters like turbine mass flow parameter, combined turbine efficiency, velocity ratio, and specific speed are compared for both mixed flow variable geometry turbine and radial flow variable geometry turbine. The typical value of combined turbine efficiency (defined as the product of isentropic efficiency and the mechanical efficiency) of the mixed flow variable geometry turbine is found to be about 25% higher than the radial flow variable geometry turbine at the same mass flow parameter of 1425 kg/s √K/bar m2 at an expansion ratio of 1.5. The velocity ratios at which the maximum combined turbine efficiency occurs are 0.78 and 0.825 for the mixed flow variable geometry turbine and radial flow variable geometry turbine, respectively. The values of turbine specific speed for the mixed flow variable geometry turbine and radial flow variable geometry turbine respectively are 0.88 and 0.73.

Thermo-economic performance analyses and comparison of two turbine layouts for organic Rankine cycles with dual-pressure evaporation

Multi-pressure evaporation organic Rankine cycle involves two or more evaporation processes with different pressures. Compared to the conventional single-pressure evaporation type, the multi-pressure evaporation type can significantly reduce the exergy loss in the endothermic process, and its widely used in the heat–work conversion of low and medium temperature (<350 °C) thermal energy is promising. The turbine layout of the multi-pressure evaporation type has two typical forms: the separate turbine layout and induction turbine layout. Turbines in two layouts may exhibit considerable differences in the geometric and operating parameters. Selecting a suitable turbine layout is crucial to improve the system thermo-economic performance. While, the thermo-economic performance variations and comparison of two turbine layouts remain indeterminate for various operating conditions. This study was based on the one-dimensional efficiency model and purchased equipment cost model of the radial-flow turbine. The thermo-economic performance of two turbine layouts was analyzed and compared for nine pure organic fluids. Effects of two-stage evaporation pressures on the thermo-economic performance of two turbine layouts were also studied. Results show that the total power output of the induction turbine layout can increase by 0.3–5.4%, and its specific investment cost is lower for most of operating conditions and the maximum decrement is 34.2%, compared to the separate turbine layout. The decrement in the specific investment cost decreases as the high-stage evaporation pressure increases, and it generally increases as the low-stage evaporation pressure increases. Moreover, the total power output is larger, the thermo-economic advantage of the induction turbine layout is generally greater.

EFFECT OF TIP CLEARANCE ON THE FLOW FIELD OF THE MIXED FLOW TURBOCHARGER TURBINE

Turbocharger is a device comprising mainly of a turbine and a compressor. The demand of turbocharger in the automotive industry increases as it significantly enhances the output power of an Internal Combustion Engine and reduces emission. The use of mixed flow turbine to replace the conventional radial turbine gives better impact since the turbine transient response increases and operates more efficiently at low velocity ratio. The flow behaviour inside the turbine affects the torque generation by the turbine. It is necessary for the turbine to have a specified clearance between the rotor tip and the casing of the turbomachine. This undoubtedly will contribute to clearance loss and mixing of leaked flow which produce disturbance to the exhaust flow. In order to investigate this effect, the validated Computational Fluid Dynamics method is chosen in order to replicate the flow field inside the mixed flow turbine. The simulation is carried out at the optimum operating condition which is at turbine total-to-static efficiency of 79% with inlet mass flow rate of 0.5kg/s. The flow inside the passage is plotted into pressure and velocity contours which are compared at 50% (30000rpm) and 80% (48000rpm) of the turbine design speed. The comparison between having 0% (no leakage) and 3% shroud tip clearance are then compared. Through the analysis, it is suggested that clearance leakage and flow separation cause disruption to the desirable uniform flow inside the turbine passage. The presence of Coriolis effect that resists the clearance leakage flow only at near leading edge of the rotor is observed. Furthermore, a low pressure region is perceived at rotor hub which absent in the radial flow turbine. These factors eventually reduce the performances of the actual turbine.

Numerical and experimental study of the performance effects of varying vaneless space in high-speed micro turbine stators

In order to make direct performance comparisons of varying the vaneless space in high-speed micro turbomachinery, an extensive experimental and numerical program have been carried out on a 22mm leading-edge diameter mixed and inward flow radial turbine using a variety of stator designs. The stator was designed using commercial design software, having 9 vanes and the radial clearance (vaneless space) between stator and rotor was 0.5mm single side, that means the ratio of the stator trailing edge radius to the rotor leading edge radius Rte/rle is 1.0455. Two additional stators (Rte/rle is 1.0182 and 1.0727) were also designed and manufactured. According to the design condition, just like pressure at stator inlet or mass flow rate for all passages, a series of CFD simulations were carried out in order to guide design iterations towards achieving a matched flow capacity for each stator. In this way the variations in the measured stage efficiency could be attributed to the stator passages only, thus allowing direct comparisons to be made. The losses for different radial clearances have been quantified and the variations in the measured and computed efficiency were used to recommend optimum values of Rte/rle.

Influence of Angle of Slope of Blades on Operation of Centrifugal Turbine

The velocity of a fluid in the impeller of a centrifugal (radial-flow) turbine and the energy of the fluid flow which it absorbs are analyzed as a function of the angle of slope of the blade (which is assumed to be constant). The blades of the impeller absorb the kinetic energy of the flow, which is expended in rotation of the impeller and is determined by Euler’s equation. One-half the energy of the fluid is expended in rotation of the impeller and in varying the direction of the fluid, while the other half is expended in overcoming the action of centrifugal force, which reduces the rate of flow of the fluid through the impeller. The maximal flow rate of the fluid is achieved with an angle of slope of the blades of 45° while the maximal power transmitted by the fluid to rotate the turbine is attained at an angle of 60°.

Mass and heat transfer behaviour of catalytic and electrochemical stirred tank reactors employing metallic screens lining as a reaction surface

AbstractLiquid‐solid mass transfer behaviour of a rectangular stirred tank reactor lined with single screens and stacks of closely packed screens was studied in relation to catalytic and electrochemical reactor design by the electrochemical technique. Variables studied were impeller rotation speed, mesh number, and wire diameter of the screen, as well as physical properties of the solution, number of screens per stack, and impeller geometry. The rate of mass transfer increased with increasing impeller rotation speed and decreased with increasing screen mesh number and number of screens per stack. Radial flow turbine impellers produced higher rates of mass transfer than axial flow impellers. The data were correlated by dimensionless mass transfer equations. A comparison between the volumetric mass transfer coefficient at a stirred single‐screen electrode and at a stirred flat plate electrode shows that the volumetric mass transfer coefficient at the single screen is higher than that at the flat plate by a factor ranging from 7.3–22.5, depending on the operating conditions. For screen stacks, the ratio between the stack volumetric mass transfer coefficient and the flat plate value ranges from 2–46 depending on the operating conditions.The importance of the present results in the design and operation of catalytic and electrochemical reactors used to conduct diffusion‐controlled reactions was highlighted. The possibility of using screens as turbulence promoters to enhance the rate of heat transfer between the reactor wall and the surrounding cooling jacket was noted.

Investigations on the Aerodynamic Characteristics and Blade Excitations of the Radial Turbine with Pulsating Inlet Flow

AbstractThe aerodynamic performance, detailed unsteady flow and time-based excitations acting on blade surfaces of a radial flow turbine have been investigated with pulsation flow condition. The results show that the turbine instantaneous performance under pulsation flow condition deviates from the quasi-steady value significantly and forms obvious hysteretic loops around the quasi-steady conditions. The detailed analysis of unsteady flow shows that the characteristic of pulsation flow field in radial turbine is highly influenced by the pulsation inlet condition. The blade torque, power and loading fluctuate with the inlet pulsation wave in a pulse period. For the blade excitations, the maximum and the minimum blade excitations conform to the wave crest and wave trough of the inlet pulsation, respectively, in time-based scale. And toward blade chord direction, the maximum loading distributes along the blade leading edge until 20% chord position and decreases from the leading to trailing edge.

A Miniature Radial-Flow Wind Turbine Using Piezoelectric Transducers and Magnetic Excitation

This paper presents a miniature radial-flow piezoelectric wind turbine for harvesting airflow energy. The turbine's transduction is achieved by magnetic “plucking”of a piezoelectric beam by the passing rotor. The magnetic coupling is formed by two magnets on the beam's free end and on the rotor plate. Frequency up-conversion is realized by the magnetic excitation, allowing the rotor to rotate at any low frequency while the beam can vibrate at its resonant frequency after each plucking. The operating range of the device is, therefore, expanded by this mechanism. Two arrangements of magnetic orientation have been investigated, showing that the repulsive arrangement has higher output power. The influence of the vertical gap between magnets was also examined, providing guidance for the final design. A prototype was built and tested in a wind tunnel. A peak power output of 159 μW was obtained with a 270 kΩ load at 2.7 m/s airflow speed. The device started working at 3.5 m/s and kept operating when the airflow speed fell to 1.84 m/s.

Forced responses on a radial turbine with nozzle guide vanes

Radial turbines with nozzle guide vanes are widely used in various size turbochargers. However, due to the interferences with guide vanes, the blades of impellers are exposed to intense unsteady aerodynamic excitations, which cause blade vibrations and lead to high cycle failures (HCF). Moreover, the harmonic resonance in some frequency regions are unavoidable due to the wide operation conditions. Aiming to achieve a detail insight into vibration characteristics of radial flow turbine, a numerical method based on fluid structure interaction (FSI) is presented. Firstly, the unsteady aerodynamic loads are determined by computational fluid dynamics (CFD). And the fluctuating pressures are transformed from time domain to frequency domain by fast Fourier-transform (FFT). Then, the entire rotor model is adopted to analyze frequencies and mode shapes considering mistuning in finite element (FE) method. Meanwhile, harmonic analyses, applying the pressure fluctuation from CFD, are conducted to investigate the impeller vibration behavior and blade forced response in frequency domain. The prediction of the vibration dynamic stress shows acceptable agreement to the blade actual damage in consistent tendency.

Steady State Engine Test Demonstration of Performance Improvement With an Advanced Turbocharger

Heavy EGR required on diesel engines for future emission regulation compliance has posed a big challenge to conventional turbocharger technology for high efficiency and wide operation range. This study, as part of the U.S. Department of Energy sponsored research program, is focused on advanced turbocharger technologies that can improve turbocharger efficiency on customer driving cycles while extending the operation range significantly, compared to a production turbocharger. The production turbocharger for a medium-duty truck application was selected as a donor turbo. Design optimizations were focused on the compressor impeller and turbine wheel. On the compressor side, advanced impeller design with arbitrary surface can improve the efficiency and surge margin at the low end while extending the flow capacity, while a so-called active casing treatment can provide additional operation range extension without compromising compressor efficiency. On the turbine side, mixed flow turbine technology was revisited with renewed interest due to its performance characteristics, i.e., high efficiency at low-speed ratio, relative to the base conventional radial flow turbine, which is relevant to heavy EGR operation for future diesel applications. The engine dynamometer test shows that the advanced turbocharger technology enables over 3% BSFC improvement at part-load as well as full-load condition, in addition to an increase in rated power. The performance improvement demonstrated on an engine dynamometer seems to be more than what would typically be translated from the turbocharger flow bench data, indicating that mixed flow turbine may provide additional performance benefits under pulsed exhaust flow on an internal combustion engine and in the low-speed ratio areas that are typically not covered by steady state flow bench tests.

Investigation of Horizontal Velocity Fields in Stirred Vessels with Helical Coils by PIV

Horizontal velocity flow fields were measured by particle image velocimetry for a stirred vessel with baffles and two helical coils for enlargement of heat transfer area. The investigation was carried out in a cylindrical vessel with flat base and two different stirrers (radial-flow Rushton turbine and axial-flow propeller stirrer). Combined velocity plots for flow fields at different locations are presented. It was found that helical coils change the flow pattern significantly. Measurements for the axial-flow Rushton turbine showed a strong deflection by the coils, leading to a mainly tangential flow pattern. Behind baffles large areas of unused heat transfer area were found. First results for the axial-flow propeller reveal an extensive absence of fluid movement in the horizontal plane. Improved design considerations for enhanced heat transfer by more compatible equipment compilation are proposed.