103 Numerical simulation of temperature fluctuation at a T-junction pipe toward the development of sophisticated evaluation method for thermal fatigue

2012 ◽  
Vol 2012.25 (0) ◽  
pp. 698-700
Author(s):  
Akira NAKAMURA ◽  
Yoichi UTANOHARA ◽  
Koji MIYOSHI ◽  
Naoto KASAHARA
Keyword(s):  
Numerical Simulation ◽  
Thermal Fatigue ◽  
Temperature Fluctuation ◽  
Evaluation Method

Spectra Thermal Fatigue Tests Under Frequency Controlled Fluid Temperature Variation: Development of Test Equipment and Preliminary Tests

2004 ◽  
Author(s):  
Naoto Kasahara ◽  
Shinichi Hasebe ◽  
Sumio Kobaysashi ◽  
Masanori Ando ◽  
Nobuchika Kawasaki ◽  
...  
Keyword(s):  
Temperature Variation ◽  
Thermal Fatigue ◽  
Temperature Fluctuation ◽  
Evaluation Method ◽  
Mechanical Valve ◽  
Test Equipment ◽  
Frequency Effect ◽  
Measured Temperature ◽  
Fluid Temperature ◽  
Constant Flow Rate

High cycle thermal fatigue induced by fluid temperature fluctuation is one of the important issues in nuclear plants. JNC has proposed a fatigue evaluation method paying attention to temperature attenuation related with frequency of fluctuation. In order to clarify the frequency effect of fluid temperature fluctuation on the crack initiation and propagation, a sodium temperature controlled thermal fatigue test equipment (SPECTRA) was developed. This equipment is capable of preciously controlling sodium temperature variation under various frequencies with a constant flow rate. This performance was achieved by the control of electromagnetic pumps without mechanical valve operations. Specimens are long straight pipes where temperature fluctuation ranges gradually reduce from upstream to downstream. As preliminary tests, temperature measurement and fatigue experiments were conducted. Measured temperature was preciously controlled under various frequencies. Cracks were observed in upstream area of a specimen. From above results, capability of frequency controlled test by SPECTRA facility was confirmed.

Development of High Cycle Thermal Fatigue Evaluation Method Based on Time Interval of Peak-to-Peak of Fluid Temperature

2010 ◽  
Author(s):  
Nobuyuki Kimura ◽  
Jun Kobayashi ◽  
Hideki Kamide
Keyword(s):  
Thermal Stress ◽  
Thermal Fatigue ◽  
Temperature Fluctuation ◽  
Evaluation Method ◽  
Frequency Characteristics ◽  
Time Interval ◽  
Fluid Temperature ◽  
Cycle Number ◽  
The Core ◽  
High Cycle Thermal Fatigue

Hot and cold fluids are mixed at the core outlet of sodium cooled fast reactors. The temperature fluctuation causes high cycle thermal fatigue in structural components. The temperature fluctuation at the core outlet region does not have always a sinusoidal waveform but a sharp edged waveform. The temperature shows intermittent and sudden decrease and recovery like a spike form. It is necessary to take into account the spiky waveform of temperature fluctuation for the construction of an evaluation method of the high cycle thermal fatigue. The conventional method uses the amplitude and cycle number of waves without reference to the frequency of temperature fluctuation. In this study, the time interval of each wave based on the rainflow method was applied to consider frequency characteristics against the conversion from fluid temperature to thermal stress in structure. The thermal stress obtained from the new method was compared to the results of FEM analysis. It was found that the consideration of frequency characteristics of waves could evaluate the fatigue damage in structure. Furthermore, the frequency characteristics of waves in this method were expressed as the unified curve independent of the velocity. Hereby the new evaluation method could evaluate the thermal fatigue in the reactor.

Numerical Evaluation of Wall Temperature Measurement Methods Developed to Investigate Thermal Fatigue at T-Junction Pipe

2012 ◽  
Author(s):  
Koji Miyoshi ◽  
Akira Nakamura ◽  
Nobuyuki Takenaka
Keyword(s):  
Numerical Simulation ◽  
Thermal Fatigue ◽  
Temperature Fluctuation ◽  
Fatigue Cracking ◽  
Temperature Fluctuations ◽  
Measured Data ◽  
Inner Surface ◽  
Simulation Results ◽  
The Difference ◽  
Sinusoidal Temperature

Thermal fatigue cracking may initiate at a T-junction pipe where high and low temperature fluids flow in from different directions and mix. Thermal stress is caused by a temperature gradient in a structure and its variation. The accurate simulation of the temperature distribution in structures is, therefore, important for estimating thermal fatigue. In this study, an experimental method using a T-junction pipe with thermocouples was developed. Wall temperatures in the experiment have to be obtained at the inner surface of the pipe to validate numerical simulation results. The difference of position between the inner surface and the measurement point where using thermocouples may, however, have an effect on temperature data. The numerical simulation results showed that the amplitude of temperature fluctuations was reduced to 54% and the difference of phase was 0.91 radians when the sinusoidal temperature fluctuation of 5Hz was applied from the inner surface to the thermocouple measurement points. These results showed that wall temperatures at the inner surface should be estimated from measured data obtained by the thermocouples. A transfer function was, therefore, obtained to calculate wall temperatures at the inner surface from measured data. In addition, the numerical simulation results showed that the amplitude and the phase of temperature fluctuations differed depending on existence of voids around thermocouples. Respective differences of it in the amplitude and the phase were about 5% and 3% when the sinusoidal temperature fluctuation of 5Hz was applied at the inner surface. These results showed that thermocouples should be installed in pipes without voids to measure accurate temperature fluctuations. A mock-up test showed that voids stayed behind the thermocouples when the thermocouples were brazed into the pipe wall at atmospheric pressure, but the voids disappeared when thermocouples were brazed in a vacuum atmosphere into the inner surface of the pipe.

Direct Damage Evaluation Method for Thermal Fatigue Based on Power Spectrum Density Functions

2007 ◽  
Author(s):  
Shinsuke Sakai ◽  
Kei Honda ◽  
Satoshi Okajima ◽  
Satoshi Izumi ◽  
Naoto Kasahara
Keyword(s):  
Power Spectrum ◽  
Fatigue Damage ◽  
Thermal Fatigue ◽  
Temperature Fluctuation ◽  
Evaluation Method ◽  
Safety Margin ◽  
Amplitude Distribution ◽  
Power Spectrum Density ◽  
Damage Evaluation ◽  
Spectrum Density

At an incomplete mixing area of high and low temperature fluids, fluid temperature fluctuation often occurs. It induces cyclic thermal stresses in the wall, which may result in fatigue crack initiation. Kasahara et. al. proposed the thermal fatigue evaluation method based on power spectrum density (PSD) in PVP05. This method generalizes the evaluation procedure by preparing PSD charts of fluid and frequency transfer functions of stress for various kinds of plant components. From design point of view, however, this method is too complicated due to the inverse Fourier transform and wave decomposition procedures named Rain Flow Cycle Counting (RFC). In this paper, simplified damage evaluation method for thermal fatigue is proposed by directly evaluating fatigue damage from PSD of stress. Since analytical treatment for evaluation of fatigue amplitude distribution based on PSD is difficult due to complicated procedure of RFC, direct evaluation method for RFC amplitude distribution from PSD is newly proposed. This method gives fatigue damage evaluation with safety margin. This paper shows the dependency of safety margin on geometry of PSD. Finally, application to design for thermal fatigue will be shown. Since PSD of stress in the wall near temperature fluctuation can be easily evaluated using Kasahara’s method, the proposed method will make thermal fatigue damage evaluation far easier.

Fundamental Study of Turbulence-Radiation Interaction in Turbulent Channel Flow Using Direct Numerical Simulation

2011 ◽  
Author(s):  
Atsushi Sakurai ◽  
Koji Matsubara ◽  
Shigenao Maruyama
Keyword(s):  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Channel Flow ◽  
Temperature Fluctuation ◽  
Turbulent Channel Flow ◽  
Gas Absorption ◽  
Fundamental Aspect ◽  
Turbulent Fluctuation ◽  
Fundamental Study ◽  
Turbulent Flow Structure

Importance of turbulence and radiation interaction (TRI) has been investigated in a turbulent channel flow by using direct numerical simulation (DNS) to clarify detailed turbulent flow structure and heat transfer mechanisms. To investigate the effect of correlation functions between gas absorption and temperature fluctuation, the two cases of correlation are tested. Consequently, the TRI effect can be clearly observed when the correlation is positive. This fact provides the evidence that radiative intensity is enhanced by the turbulent fluctuation. The DNS results suggest the significance in the fundamental aspect of TRI. Furthermore, effects of frictional Reynolds number, Reτ, are investigated. Comparing with the case of Reτ = 150, the location of the enhancement peaks of Reτ = 300 shifts toward the walls. It is found that the relative importance of the TRI correspond to the structure of temperature fluctuation intensity originated from the differences of the Reτ.

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