Thermomechanical Analysis of Transient Temperatures in a Radial Turbine Wheel

2017 ◽  
Vol 139 (9) ◽  
Author(s):  
Mathias Diefenthal ◽  
Piotr Łuczyński ◽  
Christian Rakut ◽  
Manfred Wirsum ◽  
Tom Heuer
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Thermal Stresses ◽  
Cooling Process ◽  
Transfer Coefficients ◽  
Transient Heating ◽  
Turbine Wheel ◽  
Heat Transfer Coefficients ◽  
Radial Turbine ◽  
Speed Up

In turbomachinery design, the accurate prediction of the life cycle is one of the most challenging issues. Traditionally, life cycle calculations for radial turbine wheels of turbochargers focus on mechanical loads such as centrifugal and vibration forces. Due to the increase of exhaust gas temperatures in the last years, thermomechanical fatigue in the turbine wheel came more into focus. In order to account for the thermally induced stresses in the turbine wheel as a part of the standard design process, a fast method is required for predicting metal temperatures. In order to develop a suitable method, the mechanisms that cause the thermal stresses have to be understood. Thus, in a first step, a detailed analysis of the temperature fields is conducted in the present paper. Extensive numerical simulations of a thermal shock process are carried out and validated by experimental data from a test rig. Based on the results, the main heat transfer mechanisms are identified, which are crucial for the critical thermal stresses in transient operation. It is shown that these critical stresses mainly depend on local 3D flow structures. With this understanding, two fast methods to calculate the transient temperatures in a radial turbine were developed. The first method is based on a standard method for transient fluid/solid heat transfer. In this standard method, heat transfer coefficients are derived from steady-state computational fluid dynamics (CFD)/conjugate heat transfer (CHT) calculations and are linearly interpolated over the duration of the transient heating or cooling process. In the new method, this interpolation procedure was modified to achieve an exponential behavior of the heat transfer coefficients over the transient process in order to enable a sufficient accuracy. Additionally, a second method was developed. In this method, the specific heat capacity of the solid state is reduced by a “speed up factor” to shorten the duration of the transient heating or cooling process. With the shortened processes, the computing times can be reduced significantly. After the calculations, the resulting times are transferred into realistic heating or cooling times by multiplying them with the speed up factor. The results of both methods are evaluated against experimental data and against the results of a numerical method known from literature. The methods show a good agreement with those data.

Thermomechanical Analysis of Transient Temperatures in a Radial Turbine Wheel

2016 ◽  
Author(s):  
Mathias Diefenthal ◽  
Michael Hopfinger ◽  
Christian Rakut ◽  
Manfred Wirsum ◽  
Tom Heuer
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Life Cycle ◽  
Standard Method ◽  
Thermal Stresses ◽  
Temperature Fields ◽  
Fast Method ◽  
Turbine Wheel ◽  
Radial Turbine ◽  
Standard Design

In turbomachinery design the accurate prediction of the life cycle is one of the most challenging issues. Traditionally, life cycle calculations for radial turbine wheels of turbochargers focus on mechanical loads such as centrifugal and vibration forces. Due to the increase in exhaust gas temperatures in the last years, thermomechanical fatigue in the turbine wheel came more into focus. In order to account for the thermally induced stresses in the turbine wheel as a part of the standard design process, a fast method is required for predicting metal temperatures. In order to develop a suitable method, the mechanisms have to be understood that cause the thermal stresses. Thus, in a first step a detailed analysis of the temperature fields is conducted in the present paper. Extensive numerical simulations of a thermal shock process are carried out and validated by experimental data from a test rig. Based on the results the main heat transfer mechanisms are identified, that are crucial for the critical thermal stresses in transient operation. It is shown that these critical stresses mainly depend on local 3D flow structures. With this understanding, a fast method to calculate the transient temperatures in a radial turbine was developed. It is based on a standard method for transient fluid/solid heat transfer. This standard method was modified in order to achieve a sufficient accuracy in the calculation of the investigated heat transfer processes. The results show a good agreement with experimental data and with the results of the extensive numerical calculations.

Analysis of Heat Transfer in a Radial Turbine Wheel of Turbochargers and Prediction of Heat Transfer Coefficients With an Empirical Method

2016 ◽  
Author(s):  
Christian Rakut ◽  
Mathias Diefenthal ◽  
Manfred Wirsum ◽  
Tom Heuer
Keyword(s):  
Heat Transfer ◽  
Thermal Stress ◽  
Steady State ◽  
Empirical Method ◽  
Transfer Coefficients ◽  
Turbine Wheel ◽  
Heat Transfer Coefficients ◽  
Radial Turbine ◽  
Operating Points ◽  
Good Agreement

The accurate prediction of the life cycle is one of the most challenging issues in turbomachinery design. Nowadays life cycle calculations for radial turbines focus on mechanical loads such as centrifugal and vibration forces. Because of enhanced turbine inlet temperatures with inevitably increasing thermal stress, the requirements in the design process of turbine wheels become higher. Therefore, it is desirable to know the temperature profile and thus the thermal stress in the turbine wheel as early as possible in the design process for steady state operating points and transient operation. This paper reports the development of a fast empirical method to calculate the heat transfer coefficients on the surface of a radial turbine wheel for steady state operating points. In order to do this, steady state Conjugate Heat Transfer (CHT) investigations of a turbocharger turbine wheel for commercial application were performed to model the heat transfer between the fluid and the solid state. These investigations provide a basis for the analysis and characterization of the heat transfer distribution at the turbine wheel and the flow phenomena that cause these. The empirical method for determining heat transfer coefficients of a turbine wheel is developed based on the numerical results. To model the local different heat transfer coefficients the turbine wheel is divided in several surface segments which correspond to the geometry of a radial turbine wheel. To validate the method the heat transfer coefficients from the empirical model are used as boundary conditions for a subsequent Finite Element Analysis (FEA). The calculated temperatures of the FEA results are compared to those of the CHT simulation and to the experimental data. For operating points with a circumferential velocity of u ≤ 0.75 u0 a good agreement are reached. The deviations increase for higher circumferential velocities. Furthermore the number of surface segments is varied to show the influence of the segmentation level to the temperature profile. It is also possible to reach a good agreement for operating points of u ≥ 0.75 u0 if the blade is segmented over its height. With the presented method a fast prediction of the heat transfer coefficients and the steady state temperature field of the turbine wheel are possible for steady state operating points.

Study on Forced Convective Heat Transfer of FC-72 in Vertical Small Tubes

2020 ◽  
Vol 12 (6) ◽  
Author(s):  
Yantao Li ◽  
Yulong Ji ◽  
Katsuya Fukuda ◽  
Qiusheng Liu
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Convection Heat Transfer ◽  
Bulk Liquid ◽  
Transfer Coefficients ◽  
Forced Convective Heat Transfer ◽  
Heat Transfer Coefficients ◽  
Convective Heat Transfer Coefficients

Abstract This paper presents an experimental investigation of the forced convective heat transfer of FC-72 in vertical tubes at various velocities, inlet temperatures, and tube sizes. Exponentially escalating heat inputs were supplied to the small tubes with inner diameters of 1, 1.8, and 2.8 mm and effective heated lengths between 30.1 and 50.2 mm. The exponential periods of heat input range from 6.4 to 15.5 s. The experimental data suggest that the convective heat transfer coefficients increase with an increase in flow velocity and µ/µw (refers to the viscosity evaluated at the bulk liquid temperature over the liquid viscosity estimated at the tube inner surface temperature). When tube diameter and the ratio of effective heated length to inner diameter decrease, the convective heat transfer coefficients increase as well. The experimental data were nondimensionalized to explore the effect of Reynolds number (Re) on forced convection heat transfer coefficient. It was found that the Nusselt numbers (Nu) are influenced by the Re for d = 2.8 mm in the same pattern as the conventional correlations. However, the dependences of Nu on Re for d = 1 and 1.8 mm show different trends. It means that the conventional heat transfer correlations are inadequate to predict the forced convective heat transfer in minichannels. The experimental data for tubes with diameters of 1, 1.8, and 2.8 mm were well correlated separately. And, the data agree with the proposed correlations within ±15%.

Calibration of External Heat Transfer Coefficients During Cooling of a Partially-Filled Water Tank Using Measured Temperature-Time Data

2018 ◽  
Author(s):  
Vishal Ramesh ◽  
Sandip Mazumder ◽  
Gurpreet Matharu ◽  
Dhaval Vaishnav ◽  
Syed Ali ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Measured Temperature ◽  
Water Tank ◽  
Time Data ◽  
Transfer Coefficients ◽  
Ansys Fluent ◽  
Heat Transfer Coefficients ◽  
Computational Fluid Dynamics Cfd ◽  
Temperature Time

A combined Computational Fluid Dynamics (CFD) and experimental approach is presented to determine (calibrate) the external convective heat transfer coefficients (h) around a partially-filled water tank cooled in a climactic chamber. A CFD analysis that includes natural convection in both phases (water and air) was performed using a 2D-axisymmetric tank model with three prescribed average heat transfer coefficients for the top, side and bottom walls of the tank. The commercial CFD code ANSYS-Fluent™, along with User-Defined Functions (UDFs), were utilized to compute and extract temperature vs. time curves at five different thermocouple locations within the tank. The prescribed h values were then altered to match experimentally obtained temperature-time data at the same locations. The calibration was deemed successful when results from the simulations exhibited match with experimental data within ±2°C for all thermocouples. The calibrated h values were finally used in full-scale 3D simulations and compared to the experimental data to test their accuracy. Predicted 3D results were found to agree with experimental results within the error of the calibration, thereby lending credibility to the overall approach.

Heat Transfer in Rotating Multi-Pass Rectangular Smooth Channel With and Without a Turning Vane in Hub Region

2013 ◽  
Author(s):  
Jiang Lei ◽  
Shiou-Jiuan Li ◽  
Je-Chin Han ◽  
Luzeng Zhang ◽  
Hee-Koo Moon
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Reynolds Number ◽  
Density Ratio ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
The Third ◽  
Rotation Numbers ◽  
Smooth Channel ◽  
Turn Region

This paper experimentally investigates the effect of a turning vane on hub region heat transfer in a multi-pass rectangular smooth channel at high rotation numbers. The experimental data were taken in the second and the third passages (Aspect Ratio = 2:1) connected by an 180° U-bend. The flow was radial inward in the second passage and was radial outward after the 180° U-bend in the third passage. The Reynolds number ranged 10,000 to 40,000 while the rotation number ranged 0 to 0.42. The density ratio was a constant of 0.12. Results showed that rotation increases heat transfer on leading surface but decreases it on the trailing surface in the second passage. In the third passage, the effect of rotation is reversed. Without a turning vane, rotation reduces heat transfer substantially on all surfaces in the hub 180° turn region. After adding a half-circle-shaped turning vane, heat transfer coefficients do not change in the second passage (before turn) while they are quite different in the turn region and the third passage (after turn). Regional heat transfer coefficients are correlated with rotation numbers for multi-pass rectangular smooth channel with and without a turning vane.

On the Influence of the Thickness and Thermal Properties of Heating Walls on the Heat Transfer Coefficients in Nucleate Pool Boiling

1975 ◽  
Vol 97 (2) ◽  
pp. 173-178 ◽  
Author(s):  
U. Magrini ◽  
E. Nannei
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Atmospheric Pressure ◽  
Metal Layer ◽  
Pool Boiling ◽  
Transfer Coefficients ◽  
Heating Wall ◽  
Heat Transfer Coefficients ◽  
The Heat Transfer Coefficient ◽  
Zinc Nickel

An experimental investigation was conducted under conditions of saturated pool boiling of water at atmospheric pressure on thin, horizontal, cylindrical walls of different metals and thicknesses, electrically heated. The heating walls, ranging in thickness from 5 to 250 μm, were obtained by plating copper, silver, zinc, nickel, and tin on nonmetallic rods. Experiments showed that the heat transfer coefficient can be affected, in particular conditions, by the heating wall thickness. In particular, it resulted that the smaller the thermal conductivity of the metal layer, the higher the influence of the thickness. A semiempirical correlation of the form ΔT = (q/A)nf(κd, √κρc) suitable to correlate the experimental data within ±15 percent in the whole range of variables here investigated is proposed.

A New Correlation for Heat Transfer Coefficient Prediction of Supercritical Pressure Water Flowing in Vertical Upward Tubes

2016 ◽  
Author(s):  
Xiangfei Kong ◽  
Huixiong Li ◽  
Changjiang Liao ◽  
Xianliang Lei ◽  
Qian Zhang
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Supercritical Pressure ◽  
Good Prediction ◽  
Empirical Correlations ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
New Correlation ◽  
Pressure Water ◽  
Supercritical Pressure Water

Supercritical pressure water has been widely used in many industrial fields, such as fossil-fired power plants and nuclear reactors because mainly of its high thermal efficiencies. Although many empirical correlations for heat transfer coefficients of supercritical pressure water have been proposed by different authors based on different experimental data base, there exist remarkable discrepancies between the predicted heat transfer coefficients of different correlations under even the same condition. Heat transfer correlations with good prediction performance are of considerable significance for developing supercritical (ultra-supercritical) pressure boilers and SCWRs. In this paper, the experimental data (about 7389 experimental data points) and 30 existing empirical correlations for heat transfer of supercritical pressure water (SCW) flowing in vertical upward tubes are collected from the open literatures. Evaluations of the prediction performance of the existing correlations are conducted based on the collected experimental data, and a detailed multi-collinearity analysis has been made on different correction factors involved in the existing correlations, and then based on the collected experimental data, a new heat transfer correlation is developed for the supercritical pressure water flowing in vertical upward tubes under normal and enhanced heat transfer mode. Compared with the existing correlations, the new correlation exhibits good prediction accuracy, with a mean absolute deviation (MAD) of 9.63%.

scholarly journals Cooling Temperature and Heat Transfer Coefficients in Cylindrical Heat Exchangers

2021 ◽  
Vol 15 ◽  
pp. 254-259
Author(s):  
Enrique Torres Tamayo ◽  
José W. Morales ◽  
Mauro D. Albarracín ◽  
Héctor L. Laurencio ◽  
Israel P. Pachacama ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Mass Flow ◽  
Outlet Temperature ◽  
Cooling Zone ◽  
Cooling Process ◽  
Transfer Coefficients ◽  
Cooling Temperature ◽  
Heat Transfer Coefficients ◽  
Temperature Heat ◽  
Temperature Water

The parameters behavior that characterize the process was carried out through an experimental investigation to obtain the cooling temperature, heat transfer coefficients and the heat flow in mineral coolers. The values of water temperature, water flow and mineral temperature were recorded at the inlet and outlet of the cylindrical cooler. Experiments were carried out with five values of the mass flow, keeping the cylinder revolutions constant. The calculation procedure for the system was obtained, in the mineral coolers the heat transfer by conduction, convection and evaporation predominates as a function of the cooling zone. A reduction in temperature is shown with increasing length, the lowest temperature values were obtained for a mass flow of 8 kg/s. The mineral outlet temperature should not exceed 200 oC, therefore it is recommended to work with the mass flow less than 10 kg/s that guarantees the cooling process.

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