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Research Papers: Gas Turbines: Heat Transfer

Numerical Analysis of Energy Flow Paths in Exhaust Gas Turbochargers by Means of Conjugate Heat Transfer

[+] Author and Article Information
Bjoern Hoepke

Institute for Combustion Engines,
RWTH Aachen University,
Forckenbeckstraße 4,
Aachen 52074, Germany
e-mail: hoepke@vka.rwth-aachen.de

Maximilian Vieweg

Institute for Combustion Engines,
RWTH Aachen University,
Forckenbeckstraße 4,
Aachen 52074, Germany
e-mail: Maximilian.Vieweg@rwth-aachen.de

Stefan Pischinger

Institute for Combustion Engines,
RWTH Aachen University,
Forckenbeckstraße 4,
Aachen 52074, Germany
e-mail: pischinger@vka.rwth-aachen.de

Contributed by the Heat Transfer Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received June 13, 2016; final manuscript received September 27, 2016; published online January 18, 2017. Assoc. Editor: Riccardo Da Soghe.

J. Eng. Gas Turbines Power 139(6), 061901 (Jan 18, 2017) (9 pages) Paper No: GTP-16-1213; doi: 10.1115/1.4035229 History: Received June 13, 2016; Revised September 27, 2016

Heat transfer effects play a significant role in assessing the performance of automotive turbochargers. Thermal effects are becoming increasingly relevant due to reduced machine sizes and increased exhaust gas temperatures. In this work, a study of the individual energy flows is conducted by simulation of a complete turbocharger comprising compressor (dC = 51 mm), turbine, and bearing housing using conjugate heat transfer. Special focus is given to the analysis of the various heat flows occurring in the machine aiming to identify the major heat transfer paths and their sensitivity with respect to varying operating conditions. Cooling of the bearing housing is shown to be a powerful thermal isolator mitigating the heat transferred to the compressor by up to 60%. Moreover, the rotating speed largely dictates the amount of heat transfer in the compressor and the direction of the heat flow: Whereas at low speeds (22% of max. speed), 117 W are introduced into the fluid and 338 W are being discharged from the fluid at maximum speed. At high speed operation, the heat transfer is shown to be insignificant compared to the aerodynamic work. At low speeds, however, it can reach up to 35% of the aerodynamic work. While the turbine inlet temperature largely governs the overall heat that is lost from the exhaust gas passing the turbine (from 630 W at 300 °C up to 3.72 kW at 1050 °C), only a minor effect on the compressor heat transfer is detected.

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References

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Figures

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Fig. 1

Cross section of the overall CHT turbocharger model

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Fig. 2

Iterative method to control the shaft power equilibrium in the steady-state CHT simulation

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Fig. 3

Simulated operating points plotted in the overall compressor flow capacity map

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Fig. 4

Comparison of simulated and measured overall turbocharger efficiencies for variation of turbocharger speed

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Fig. 5

Comparison of simulated and measured temperature difference across the compressor stage for varying turbocharger speed

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Fig. 6

Comparison of simulated and measured temperature difference across the turbine stage for varying turbocharger speed

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Fig. 7

Energy flow chart of the turbocharger at low rotational speed with cooling water (nTC = 44,000 1/min; Tt3 = 600 °C; TCW = 30 °C); enthalpies referenced to Tref = 0 °C

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Fig. 8

Analysis of heat transfer paths between turbine and bearing housing

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Fig. 9

Energy flow chart of the turbocharger at low rotational speed w/o cooling water (nTC = 44,000 1/min; Tt3 = 600 °C); enthalpies referenced to Tref = 0 °C

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Fig. 10

Main heat flows in the TC as a function of TC speed (Tt3 = 600 °C; TCW = 90 °C)

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Fig. 11

Comparison of different compressor efficiencies as a function of TC speed (Tt3 = 600 °C; TCW = 90 °C)

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Fig. 12

Main heat flows in the TC for varying turbine inlet temperatures (TCW = 90 °C)

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