Design of an efficient space constrained diffuser for supercritical CO<sub>2</sub> turbines

Keep, Joshua A.; Head, Adam J.; Jahn, Ingo

doi:10.1088/1742-6596/821/1/012026

Cited by 8 publications

(11 citation statements)

References 4 publications

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“…As research into improving industry operations and equipment continues, high density, low viscosity fluids, such as supercritical carbon dioxide (Keep et al, 2017;Heshmat et al, 2018), become more prominent and desirable for efficient operation. As these new designs are operating within a higher Taylor number regime, extensions to existing heat transfer correlations, backed by new high-quality experimental data, are essential to produce robust and efficient thermal management systems.…”

Section: Introductionmentioning

confidence: 99%

Taylor-Couette-Poiseuille flow heat transfer in a high Taylor number test rig

Swann

Russell

Jahn

2021

J. Glob. Power Propuls. Soc.

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As technology advances, rotating machinery are operating at higher rotational speeds and increased pressures with greater heat concentration (i.e. smaller and hotter). This combination of factors increases structural stresses, while increasing the risk of exceeding temperature limits of components. To reduce stresses and protect components, it is necessary to have accurately designed thermal management systems with well-understood heat transfer characteristics. Currently, available heat transfer correlations operating within high Taylor number (above 1×10^10) flow regimes are lacking. In this work, the design of a high Taylor number flow experimental test rig is presented. A non-invasive methodology, used to capture the instantaneous heat flux of the rotating body, is also presented. Capability of the test rig, in conjunction with the use of high-density fluids, increases the maximum Taylor number beyond that of previous works. Data of two experiments are presented. The first, using air, with an operating Taylor number of 8.8± 0.8 ×10^7 and an effective Reynolds number of 4.2± 0.5 ×10^3, corresponds to a measured heat transfer coefficient of 1.67 ± 0.9 ×10^2 W/m2K and Nusselt number of 5.4± 1.5×10^1. The second, using supercritical carbon dioxide, demonstrates Taylor numbers achievable within the test rig of 1.32±0.8×10^12. A new correlation using air, with operating Taylor numbers between 7.4×10^6 and 8.9×10^8 is provided, comparing favourably with existing correlations within this operating range. A unique and systematic approach for evaluating the uncertainties is also presented, using the Monte-Carlo method.

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Section: Introductionmentioning

confidence: 99%

Taylor-Couette-Poiseuille flow heat transfer in a high Taylor number test rig

Swann

Russell

Jahn

2021

J. Glob. Power Propuls. Soc.

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“…As seen in Figure 1.2, the efficiency is closely linked to turbine inlet temperature. Turbine inlet temperatures from 450 • C up to 750 • C) and pressures of 20 to 30 MPa appear to be the range of interest in much of literature [43], [44]. These temperatures result in significant reductions in allowable stress as per the ASME Boiler and Pressure Vessel code.…”

Section: Thermal Management Systems and Strategiesmentioning

confidence: 99%

“…A forward and backward facing arrangement for the candidate turbine is shown schematically with typical temperatures and pressures of interest in Figure 3.1. From a sealing and cooling system operational standpoint, a backward facing rotor is advantageous as it reduces the static pressure and temperature at the seal positioned between the turbine exit and bearings [43]. For the current analysis, it is assured that the flow enters the turbine at fluid conditions of 500 to 600 • C and 20 MPa and exits at conditions of 400 to 500 • C and 7 to 8 MPa, which is typical for sCO 2 turbines studied in literature.…”

Section: Candidate Geometrymentioning

confidence: 99%

Investigation into Taylor-Couette-Poiseuille flow heat transfer for supercritical carbon dioxide turbomachinery

Swann¹

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In recent years there has been significant research in the area of supercritical carbon dioxide (sCO 2 ) closed-loop Brayton cycles as a possible alternative to conventional steam Rankine cycles due to their many advantages. These advantages include, a simpler cycle configuration, higher thermal efficiency, smaller component size and strong compatibility with renewable heat sources such as concentrated solar thermal. In order to make sCO 2 power cycles commercially available, a number of design challenges remain which must be addressed.Several design challenges arise in the sCO 2 turbine component due to its reduction in relative size.This decreases the relative distance between the rotor and temperature sensitive components, such as seals and bearings. An effective thermal management zone between the rotor and these components is required to appropriately manage the temperature of the shaft. This has been done in the past by removing heat over a long shaft, managing the temperature and mitigating thermal stresses. However, as the turbine reduces in size, the shaft speed must increase in order to maintain turbine efficiency.

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“…A review of geometric characteristics and prior geometries in Section 7.2 reveals that a short diffuser inlet is desired in order to limit the adverse impact of boundary layer growth on performance when turning the flow. The review of ideal pressure recovery characteristics in Section 7.1, and past geometries [118,119] reveals that it is desirable to maintain constant passage area on the inlet bend. In the radial section of the diffuser, parallel walls are desirable, with radial section spacing scaled according to the inlet.…”

Section: Diffuser Designmentioning

confidence: 99%

“…A hybrid annular-radial geometry combining the above characteristics was considered for the present application in a preliminary study [119], with geometry schematically shown in Figure 7.3. A fixed radial section spacing was used, and variations on annular inlet and bend were analysed with steady state CFD calculations for the diffuser in isolation to the stage.…”

Section: Introductionmentioning

confidence: 99%

On the design of small to medium scale radial inflow turbines for supercritical CO2 power cycles

Keep¹

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In rural Australia, concentrating solar power at sub 10 MWe scale is a candidate technology to displace current fossil fuel based technologies [1]. For concentrating solar power to be competitive for this application, coupling with an advanced power cycle is essential. A candidate is the supercritical CO 2 Brayton cycle, which is suitable for higher turbine inlet temperature operation, and has the potential to exceed the efficiency of the steam Rankine cycle. Furthermore, due to lower volumetric flow variation over the cycle, simpler turbomachinery may be used, which enables the cycle to be downscaled while maintaining turbomachinery and cycle efficiency. Of the constituent components in the cycle, turbine efficiency has the greatest impact on cycle efficiency [2]. Radial turbomachinery is a key technology for energy conversion in the supercritical CO 2 Brayton cycle at small scales (i.e. below 30 MW shaft power). While the design of efficient turbines for the supercritical CO 2 Brayton cycle is critical to realising efficient concentrating solar power plants, only a limited number of prototypes have been tested, and none at representative inlet conditions. Radial inflow supercritical CO 2 turbines are characterised by small dimensional scale and high shaft speeds. Prototype turbine designs are characterised by low expansion ratio and medium specific speed to accommodate mechanical restrictions on shaft speed. Medium specific speed designs are selected for prototypes designs due to their implied optimal efficiency. Demonstration test facilities have utilised multiple stages, or lower expansion ratio cycles in order to accommodate designs of this specific speed without exceeding mechanical limits. Increasing inlet conditions to representative cycle conditions for concentrating solar power applications will require higher shaft speeds, or additional stages if specific speed of the stage is to be maintained. Alternatively, the use of single stage low specific speed designs may pose a feasible alternative, however these designs are generally disregarded owing to the implied efficiency penalties shown on gas turbine derived architecture selection charts. Better understanding of loss characteristics of low specific speed supercritical CO 2 turbomachinery is required in order to make an assessment on the feasibility of single stage expansions. Further to sizing of the stator and rotor, stage design also includes components upstream and downstream of the rotor. The broadest challenge for supercritical CO 2 turbomachinery is designing components within a system for high pressure, high density, high temperature, and high shaft speed operation. These constraints may have significant impact on the geometry of these hot gas path features. Details of these features are not clearly detailed in published prototype designs. Considering the knowledge gap for supercritical CO 2 turbines, one key aim of this thesis is to quantify the performance of low specific speed radial inflow turbines using numerical methods. A further aim is t...

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Design of an efficient space constrained diffuser for supercritical CO₂ turbines

Cited by 8 publications

References 4 publications

Taylor-Couette-Poiseuille flow heat transfer in a high Taylor number test rig

Taylor-Couette-Poiseuille flow heat transfer in a high Taylor number test rig

Investigation into Taylor-Couette-Poiseuille flow heat transfer for supercritical carbon dioxide turbomachinery

On the design of small to medium scale radial inflow turbines for supercritical CO2 power cycles

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Design of an efficient space constrained diffuser for supercritical CO2 turbines

Cited by 8 publications

References 4 publications

Taylor-Couette-Poiseuille flow heat transfer in a high Taylor number test rig

Taylor-Couette-Poiseuille flow heat transfer in a high Taylor number test rig

Investigation into Taylor-Couette-Poiseuille flow heat transfer for supercritical carbon dioxide turbomachinery

On the design of small to medium scale radial inflow turbines for supercritical CO2 power cycles

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Design of an efficient space constrained diffuser for supercritical CO₂ turbines