Turbochargers make an essential contribution to the development of efficient combustion engines by increasing the boost pressure. In recent years, there has been a trend towards enhanced turbine inlet temperatures, which cause heat fluxes within the turbocharger. Due to the high rotational speed, the centrifugal force and thermal stress of the turbine components rise inevitably. In addition to the enhanced temperature level, due to the variation of the load and speed of the engine in cold start, acceleration and deceleration periods, the turbine inlet temperature is changing permanently, which leads to higher thermal loads. The flow state and thus the heat transfer in the turbocharger are constantly changing within a single cycle. This induces an unsteady temperature profile, which is essential for the thermal stress and thus the prediction of the component life cycle. The present study reports about the results of the experimental steady state and transient heat transfer investigations of a turbocharger which are conducted at a hot gas test rig. The investigations are performed transiently between different steady state operating points. In order to simulate the real driving conditions, the turbine inlet temperature is changed between a high and low temperature level abruptly (thermal shock) or cyclically at an approximately constant mass flow. The flow parameters at the inlet and outlet of the turbine as well as material and surface temperatures of the turbine wheel and casing are recorded. Additionally the compressor as well as the bearing housing inlet and outlet conditions are measured. The heat flux between the components is analyzed by means of the measured data.

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Due to increasing demands on the efficiency of modern Otto and Diesel engines, turbochargers are subjected to higher temperatures. In consequence rotor speed and temperature gradients in transient operations are more severe and therefore thermal and centrifugal stresses increase. To determine the life cycle of turbochargers more precisely, the exact knowledge of the transient temperature distribution in the turbine wheel is essential. To assess these temperature distributions, experimental and numerical investigations on a turbocharger of a commercial vehicle were performed. For this purpose, four thermocouples were applied on the shaft and the turbine wheel. The measured temperatures are used to determine the boundary conditions for the numerical calculations and to validate the results. In the numerical investigations three methods are used to determine and to analyse the transient solid body temperature distribution in respect of the fluid. The methods are compared and evaluated using the measured data. Based on the calculations the transient temperature field is discussed and conclusions concerning to the thermal stresses are drawn.

Increasing the efficiency of steam power plants is important to reduce their CO2 emissions and can be achieved by increasing steam temperatures beyond 700 °C. Within the present study, the thermal behavior of a steam by-pass valve subject to cyclic operation with 700 °C steam is investigated experimentally and numerically. An innovative numerical approach was applied to predict the valve’s thermal behavior during cyclic operation, which is essential for fatigue life assessment of such a component. Validation of the applied numerical approach has shown good agreement with measurement results, indicating the potential of its application for the valve design process.

Increasing the efficiency of steam cycle power plants is extremely important for the reduction of their CO2 emissions. Today’s best steam cycle power plants have a net plant efficiency of 46 %. Since the worldwide average efficiency is still in the range of 30 %, there exists a great potential in reduction of CO2 emissions by replacing old power stations with new ones. A further great potential lies in achieving even higher efficiencies by increasing live steam temperatures to more than 700 °C, so that the efficiency of steam power plants is pushed over the 50 % mark. Within a research project funded by the German government the challenges associated with material’s behaviour under elevated temperatures are investigated. In this project, a bypass-valve was installed in an experimental set-up in a real power station and is supplied with over 700 °C steam and investigated under long-term cyclic operation. Thermocouple measurements on reference points on the valve body and thermo graphic camera measurements deliver information about the real transient thermal behaviour of the valve. Numerical investigations aim to accurately model the transient thermal behaviour of the valve during cyclic operation and calculate corresponding three-dimensional temperature distributions, which are essential for conducting reliable mechanical integrity analysis for the applied Nickel-base material. Applying standard FEM thermal analyses that are based on heat transfer boundary conditions is often related with uncertainties regarding the convective heat transfer and corresponding coefficients. The application of a hybrid stepwise frozen conjugate heat transfer calculation approach aims to make use of the advantage of the conjugate heat transfer approach with respect to high accuracy in heat transfer calculation and reduce the calculation effort by freezing the fluid domain at different steps along the loading cycle and coupling it to the transient thermal load calculation in the solid domain. Both the standard FEM thermal analysis method and the hybrid stepwise frozen conjugate heat transfer calculation approach have been applied to calculate the transient thermal load in the valve. A validation of the numerical results has been performed for the reference points on the valve body and shows that the hybrid approach has better accuracy than the standard approach and shows very good agreement with the experimental results.