The Influence of Condensation on the Performance Map of a Fuel Cell Turbocharger Turbine

2021 ◽  
Author(s):  
Tim Wittmann ◽  
Sebastian Lück ◽  
Tim Hertwig ◽  
Christoph Bode ◽  
Jens Friedrichs
Keyword(s):  
Fuel Cell ◽  
Pressure Ratio ◽  
Nucleation Theory ◽  
Classical Nucleation Theory ◽  
Droplet Growth ◽  
Pressure Potential ◽  
Automotive Fuel ◽  
Performance Map ◽  
A Minor ◽  
Gas Expansion

Abstract Exhaust gas of an automotive fuel cell is enriched with water vapour and has a pressure potential which can be utilized by a turbine. The gas expansion in the turbine leads to droplet nucleation and condensation. This results in a release of latent heat and a decrease of the gaseous mass flow which has a considerable influence on the turbine performance. This study aims to numerically investigate the influence of these phenomena on the performance map of the radial turbine of an automotive fuel cell turbocharger. For this purpose, the classical nucleation theory and Young’s droplet growth law are integrated into an Euler-Lagrange approach. The results show an almost linear relation between the pressure ratio and the condensation while the specific aerodynamics of an operating point has only a minor influence. At 80 % relative humidity of the inflow, the investigated turbine showed condensation above a total-to-static pressure ratio of 1.8. Condensation leads to thermal throttling of the turbine and to a temperature increase of the rotor outflow of up to 50 K. Increasing humidity of the inflow increases the power output, but condensation losses reduce the efficiency.

scholarly journals Modelling the Condensation Phenomena within the Radial Turbine of a Fuel Cell Turbocharger

2021 ◽  
Vol 6 (3) ◽  
pp. 23
Author(s):  
Tim Wittmann ◽  
Sebastian Lück ◽  
Christoph Bode ◽  
Jens Friedrichs
Keyword(s):  
Fuel Cell ◽  
Latent Heat ◽  
Nucleation Theory ◽  
Classical Nucleation Theory ◽  
Outlet Temperature ◽  
Full Resolution ◽  
Blade Tip ◽  
Gas Expansion ◽  
Individual Droplet ◽  
Radial Turbines

Radial turbines used in automotive fuel cell turbochargers operate with humid air. The gas expansion in the turbine causes droplets to form, which then grow through condensation. The associated release of latent heat and decrease in the gaseous mass flow strongly influence the thermodynamics of the turbine. This study aims to investigate these phenomena. For this purpose, the classical nucleation theory and Young’s growth law are integrated into a Euler–Lagrange approach. The main advantages of this approach are the calculation of individual droplet trajectories and a full resolution of the droplet spectrum. The results indicate an onset of nucleation at the blade tip and in the tip gap, followed by nucleation over the entire blade span, depending on the humidity at the turbine inlet. With a saturated turbine inflow, condensation causes the outlet temperature to rise to almost the same level as at the inlet. In addition, condensation losses reduce the efficiency and the latent heat released by condensation leads to significant thermal throttling.

The Feasibility of an Euler-Lagrange Approach for the Modelling of Wet Steam

2020 ◽  
Author(s):  
Tim Wittmann ◽  
Christoph Bode ◽  
Jens Friedrichs
Keyword(s):  
Optimal Parameter ◽  
Nucleation Theory ◽  
Classical Nucleation Theory ◽  
Droplet Growth ◽  
Wet Steam ◽  
Discrete Phase Model ◽  
Ansys Fluent ◽  
Validation Data ◽  
Numerical Validation ◽  
Lagrange Approach

Abstract This study investigates the applicability of an Euler-Lagrange approach for the calculation of nucleation and condensation of steam flows. Supersonic nozzles are used as generic validation cases, as their high expansion rates replicate the flow conditions in real turbines. Experimental and numerical validation data for these nozzles are provided by the International Wet Steam Modelling Project of Starzmann et al. (2018). In contrast to most participants of that project, an Euler-Lagrange approach is utilized for this study. Therefore, the classical nucleation theory with corrections and different droplet growth laws is incorporated into the Discrete Phase Model of ANSYS Fluent. Suggestions for an efficient implementation are presented. The Euler-Lagrange results show a good agreement with the experimental and numerical validation data. The sensitivities of the Euler-Lagrange approach to modelling parameters are analysed. Finally, an optimal parameter set for the calculation of nucleation and condensation is proposed.

The Feasibility of an Euler–Lagrange Approach for the Modeling of Wet Steam

2021 ◽  
Vol 143 (4) ◽  
Author(s):  
Tim Wittmann ◽  
Christoph Bode ◽  
Jens Friedrichs
Keyword(s):  
Optimal Parameter ◽  
Nucleation Theory ◽  
Classical Nucleation Theory ◽  
Droplet Growth ◽  
Wet Steam ◽  
Discrete Phase Model ◽  
Validation Data ◽  
Numerical Validation ◽  
Discrete Phase ◽  
Lagrange Approach

Abstract This study investigates the applicability of an Euler–Lagrange approach for the calculation of nucleation and condensation of steam flows. Supersonic nozzles are used as generic validation cases, as their high expansion rates replicate the flow conditions in real turbines. Experimental and numerical validation data for these nozzles are provided by the International Wet Steam Modeling Project of Starzmann et al. (2018, “Results of the International Wet Steam Modeling Project,” Proc. Inst. Mech. Eng. A, 232(5), pp. 550–570). In contrast to most participants of that project, an Euler–Lagrange approach is utilized for this study. Therefore, the classical nucleation theory with corrections and different droplet growth laws is incorporated into the discrete phase model of ansysfluent. Suggestions for an efficient implementation are presented. The Euler–Lagrange results show a good agreement with the experimental and numerical validation data. The sensitivities of the Euler–Lagrange approach to modeling parameters are analyzed. Finally, an optimal parameter set for the calculation of nucleation and condensation is proposed.

Asymptotic solution of shock tube flows with homogeneous condensation

1995 ◽  
Vol 287 ◽  
pp. 93-118 ◽  
Author(s):  
Can F. Delale ◽  
Günter H. Schnerr ◽  
Jürgen Zierep
Keyword(s):  
Shock Wave ◽  
Asymptotic Solution ◽  
Shock Tube ◽  
Complete Solution ◽  
Nucleation Theory ◽  
Classical Nucleation Theory ◽  
Droplet Growth ◽  
Homogeneous Condensation ◽  
Shock Fitting ◽  
Supercritical Flows

The asymptotic solution of shock tube flows with homogeneous condensation is presented for both smooth, or subcritical, flows and flows with an embedded shock wave, or supercritical flows. For subcritical flows an analytical expression, independent of the particular theory of homogeneous condensation to be employed, that determines the condensation wave front in the rarefaction wave is obtained by the asymptotic analysis of the rate equation along pathlines. The complete solution is computed by an algorithm which utilizes the classical nucleation theory and the Hertz–Knudsen droplet growth law. For supercritical flows four distinct flow regimes are distinguished along pathlines intersecting the embedded shock wave analogous to supercritical nozzle flows. The complete global solution for supercritical flows is discussed only qualitatively owing to the lack of a shock fitting technique for embedded shock waves. The results of the computations obtained by the subcritical algorithm show that most of the experimental data available exhibit supercritical flow behaviour and thereby the predicted onset conditions in general show deviations from the measured values. The causes of these deviations are reasoned by utilizing the qualitative global asymptotic solution of supercritical flows.

Instabilities and bifurcation of non-equilibrium two-phase flows

1997 ◽  
Vol 348 ◽  
pp. 1-28 ◽  
Author(s):  
STEPHAN ADAM ◽  
GÜNTER H. SCHNERR
Keyword(s):  
Equilibrium Phase ◽  
Practical Interest ◽  
Nucleation Theory ◽  
Classical Nucleation Theory ◽  
Droplet Growth ◽  
Sudden Increase ◽  
Pressure Amplitude ◽  
Two Phase ◽  
Supersonic Wind Tunnel ◽  
Non Equilibrium

New instabilites of unsteady transonic flows with non-equilibrium phase transition are presented including unsymmetric flow patterns with moving oblique shock systems in supersonic nozzles with perfectly symmetric shapes. The phenomena were first detected when performing experiments in our supersonic wind tunnel with atmospheric supply and could be perfectly reproduced by numerical simulations based on the Euler equations, i.e. neglecting the viscosity of the fluid. The formation of the liquid phase is modelled using the classical nucleation theory for the steady state together with the Hertz–Knudsen droplet growth law and yields qualitatively and quantitatively excellent agreement with experiments in the unsteady flow regime with high-frequency oscillations including the unstable transient change of the structure from symmetric to unsymmetric flow.For engineering applications the sudden increase or decrease of the frequency by a factor 2 or more and of the pressure amplitude at the bifurcation limits is of immediate practical interest, e.g. for flutter excitation of turbomachinery blading.

Classical Nucleation Theory and Its Application to Condensing Steam Flow Calculations

2005 ◽  
Vol 219 (12) ◽  
pp. 1315-1333 ◽  
Author(s):  
F Bakhtar ◽  
J B Young ◽  
A J White ◽  
D A Simpson
Keyword(s):  
Predictive Accuracy ◽  
Nucleation Theory ◽  
Classical Nucleation Theory ◽  
Droplet Radius ◽  
Droplet Growth ◽  
Wide Range ◽  
Recent Developments ◽  
Judicious Choice ◽  
The Many ◽  
Low Pressures

The paper discusses the classical theory of the homogeneous nucleation of water droplets from supersaturated vapour and its application in predicting condensation in steam nozzles. The first part consists of a review of classical nucleation theory, focusing on the many modifications made to the original Becker-Döring theory and providing some new insights into recent developments. It is concluded that the predictive accuracy required for engineering calculations is not yet attainable with a theory derived from first principles. The areas that require most attention relate to the properties of small molecular clusters and the energy transfer processes in the non-isothermal theory. Experiments in converging-diverging nozzles provide the best means for validation at the very high nucleation rates of interest, but measurements of pressure distribution and the Sauter mean droplet radius are insufficient to provide independent checks on the separate theories of nucleation and droplet growth. Nevertheless, a judicious choice for the nucleation rate equation, in combination with a standard droplet growth model and a suitable equation of state for steam, can provide accurate predictions over a wide range of conditions. The exception is at very low pressures where there is evidence that the droplet growth rate in the nucleation zone is underestimated.

Molecular Dynamics Simulation of Nanocluster Formation in a Supersonic Nano Nozzle Fabricated by Anodizing the Aluminum

2013 ◽  
Vol 829 ◽  
pp. 813-817
Author(s):  
Mohammad Hossein Tanhai ◽  
Shahyar Saramad ◽  
Peyman Nayebi
Keyword(s):  
Molecular Dynamics ◽  
Nucleation Theory ◽  
Dynamics Simulation ◽  
Classical Nucleation Theory ◽  
Magic Numbers ◽  
Gas Flows ◽  
Macro Scale ◽  
Novel Method ◽  
Gas Expansion ◽  
Small Clusters

A molecular dynamics method has been developed and applied for simulation of a supersonic Ne gas expansion through a convergingdiverging nozzle. Although the classical nucleation theory is able to explain some physics of the nucleation processes, however, due to the physical inaccuracy of the classical nucleation theory for small clusters, molecular dynamic method is more usable for studying gas flows having clusters. Pressure, flow velocity, temperature were parameters that extracted by MD method along the central x-axis. The nucleation and condensation of the clusters and their transient and equilibrium behavior are other parameters that are investigated in this simulation. The results show that although with suitable conditions the formation of clusters in a nanonozzle is possible, but the size of clusters is much smaller than its counterpart in macro scale and clusters with especial magic numbers are formed. The proposed novel method for fabrication this kind of nanonozzle is multi-step anodizing of the aluminum. This nanonozzle which can be fabricated experimentally can be used in Ionized Cluster Beam Deposition (ICBD) method.

Design of a Centrifugal Compressor With Low Specific Speed for Automotive Fuel Cell

2008 ◽  
Author(s):  
Xinqian Zheng ◽  
Yangjun Zhang ◽  
Hong He ◽  
Zhiling Qiu
Keyword(s):  
Fuel Cell ◽  
Centrifugal Compressor ◽  
Electric Motor ◽  
High Speed ◽  
High Efficiency ◽  
Pressure Ratio ◽  
System A ◽  
Automotive Fuel ◽  
Low Specific Speed ◽  
Specific Speed

Centrifugal compressors driven by electric motor are the promising type for fuel cell pressurization system. A low specific speed centrifugal compressor powered by an ordinary high-speed (about 25,000rpm) electric motor has been designed at Tsinghua University for automotive fuel cell engines. The experimental results indicate that the designed low specific speed centrifugal compressor has comparatively high efficiency and wide operating range. In the condition of designed speed (24,000rpm), the highest efficiency and pressure ratio of the centrifugal compressor is up to 70% and 1.6, respectively. The designed low specific speed centrifugal compressor can meet the requirement of air systems of automotive fuel cell engines preliminarily. Moreover, the low specific speed centrifugal compressor avoids difficulties of usage of ultra-high-speed electric motors (about 60,000rpm) in high specific speed compressor. Based on the preliminary results of this centrifugal compressor, a new low specific speed centrifugal compressor with higher performances is being developed.

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