Stress Response Functions to Multi-Dimensional Spatial Fluctuations of Fluid Temperature

2002 ◽  
Author(s):  
Naoto Kasahara ◽  
Hideki Takasho
Keyword(s):  
Thermal Stress ◽  
Temperature Fluctuation ◽  
Thermal Stratification ◽  
Thermal Stresses ◽  
Fluid Mixing ◽  
Cold Spot ◽  
Fluid Temperature ◽  
Response Functions ◽  
Spatial Fluctuations ◽  
Stress Functions

Temperature fluctuation from incomplete fluid mixing induces fatigue damages on structures of nuclear components, which should be prevented. For rational analyses of this phenomenon, the authors have developed a frequency response function of thermal stress and extended to multi-dimensional spatial fluctuations of fluid temperature. This function is formulated by a product of the effective heat transfer and the effective thermal stress functions, and enables us to quickly calculate the thermal stresses induced by both local and global temperature distributions in structures. Furthermore, it can evaluate sensitivities of thermal stress to frequencies of temperature fluctuation, Biot number and constraint conditions of structures. Applicability of this function was verified for multi-dimensional problems such as thermal stratification problems and hot/cold spot ones.

Experimental Study on Fluid Mixing for Evaluation of Thermal Striping in T-Pipe Junction

2002 ◽  
Author(s):  
Minoru Igarashi ◽  
Masaaki Tanaka ◽  
Shigeyo Kawashima ◽  
Hideki Kamide
Keyword(s):  
Temperature Fluctuation ◽  
Velocity Ratio ◽  
Impinging Jet ◽  
Fluid Mixing ◽  
Cold Spot ◽  
Wall Jet ◽  
Fluid Temperature ◽  
Thermochromic Liquid Crystal ◽  
Inflow Condition ◽  
Thermal Striping

A water experiment is performed to investigate thermal striping phenomena in a T-pipe junction which is a typical geometry of fluid mixing. The flow velocity ratio and temperature difference were experimental parameters. The jet form was classified into four patterns; (1) impinging jet, (2) deflecting jet, (3) re-attachment jet and (4) wall jet according to the inflow condition. The parameter experiments showed that the jet form could be predicted by a momentum ratio between the two pipes. The thermochromic liquid crystal sheet showed that a cold spot was formed at the wall surface in the main pipe in the cases of the impinging jet and the wall jet. From the temperature measurement in the fluid, temperature fluctuation intensity was high along the edge of the jet exiting from branch piping. A database of temperature fluctuation and frequency characteristics was established for an evaluation rule of thermal striping in a T-pipe junction.

Numerical Estimation of Flow Penetrating Depth Into Stagnant Branch Pipes for Thermal Fatigue Prediction

2014 ◽  
Author(s):  
Yoshihiro Ishikawa ◽  
Yukihiko Okuda ◽  
Naoto Kasahara
Keyword(s):  
Thermal Stress ◽  
High Temperature ◽  
Temperature Fluctuation ◽  
Thermal Stratification ◽  
Branch Pipe ◽  
Large Temperature ◽  
Bend Pipe ◽  
Main Pipe ◽  
High Temperature Water ◽  
Temperature Water

In the nuclear power plants, there are many branch pipes with closed-end which are attached vertically to the main pipe. We consider a situation in which the high temperature water is transported in the main pipe, the branch pipe is filled with stagnant water which has lower temperature than the main flow, and the end of the branch pipe is closed. At the branch connection part, it is known that a cavity flow is induced by the shear force of the boundary layer which separates from the leading edge of the branch pipe along the main pipe wall. In cases where the high temperature water penetrates into the branch pipe, there is a possibility that a steep and large temperature gradient field, called “thermal stratification layer” is formed at the boundary between high and low temperature water in the branch pipe. If the thermal stratification layer is formed in a bend pipe, which is used for connecting the vertical branch pipe and to a horizontal pipe, at the same time, the temperature fluctuation by the thermal stratification layer motion occurs, there may cause the thermal stress in the piping material. Furthermore, keeping the piping material under the thermal stress, there might be a possibility of a crack on the surface of the bend pipe. For this reason, the evaluation of the position where the thermal stratification layer reaches is very important during early piping design process. And, deeply understanding regarding the phenomena, is also important. However, because of the complexities of the phenomena, it is difficult to immediately clarify the whole mechanisms of the thermal stress arising due to the temperature fluctuation by the thermal stratification layer change. The complete prediction method for the position of the thermal stratification layer based on the mechanisms that is able to be applied to any piping system, any temperature and any velocity conditions, is also difficult. Therefore, a practical approach is required. The authors attempt to develop the practical estimation method for the thermal stratification layer position using the three-dimensional Navier-Stokes simulation which was based on the Reynolds-average in order to reduce the computational costs. In this paper, three different configurations of the piping were simulated and the simulation results were compared with the experimental results obtained by the other research group.

Thermal Fatigue Evaluation Method Based on Power Spectrum Density Functions Against Fluid Temperature Fluctuation

2005 ◽  
Author(s):  
Naoto Kasahara ◽  
Nobuyuki Kimura ◽  
Hideki Kamide
Keyword(s):  
Thermal Stress ◽  
Power Spectrum ◽  
High Frequency ◽  
Thermal Stresses ◽  
Evaluation Method ◽  
Power Spectrum Density ◽  
Temperature Gradients ◽  
Fluid Temperature ◽  
Spectrum Density ◽  
Fatigue Evaluation

Fluid temperature fluctuates at an incomplete mixing area of high and low temperature fluids in nuclear components. It induces random variations of local temperature gradients in structural walls, which lead to cyclic thermal stresses. When thermal stresses and cycle numbers are large, there are possibilities of fatigue crack initiations and propagations. It is recognized that there are attenuation factors depending on fluctuation frequency in the transfer process from fluid temperature to thermal stresses. If a frequency of fluctuation is very low, whole temperature of the wall can respond to fluid temperature, because thermal diffusivity homogenizes structural temperature. Therefore, low frequency fluctuations do not induce large thermal stress due to temperature gradients in structures. On the other hand, a wall surface cannot respond to very high frequency fluctuation, since a structure has a time constant of thermal response. High frequency fluctuations do not lead to large thermal stress. Paying attention to its attenuation mechanism, Japan Nuclear Cycle Development Institute (JNC) has proposed a fatigue evaluation method related to frequencies. The first step of this method is an evaluation of Power Spectrum Density (PSD) on fluid, from design specifications such as flow rates, diameters of pipes and materials. In the next step, the PSD of fluid is converted to PSD of thermal stress by the frequency transfer function. Finally, the PSD of thermal stress is transformed to time history of stress under an assumption of random phase. Fatigue damage factors can be evaluated from stress ranges and cycles obtained by the rain flow wave count method. Proposed method was applied to evaluate fatigue damage of piping junction model tests conducted at Oarai Engineering Center. Through comparison with direct evaluation from measurements and predictions by conventional methods, the accuracy of the proposed method was validated.

Solution of Thermal Stress Problems in Tube Sheets by the Boundary Point Least Squares Method

1970 ◽  
Vol 92 (2) ◽  
pp. 339-349 ◽  
Author(s):  
L. E. Hulbert
Keyword(s):  
Thermal Stress ◽  
Least Squares ◽  
Boundary Point ◽  
Thermal Stresses ◽  
Least Squares Method ◽  
Tube Sheet ◽  
Point Matching ◽  
Stress Functions ◽  
Plane Stress Analysis ◽  
Least Squares Approach

This paper describes the application of the boundary point least squares approach to the plane stress analysis of tube sheets with either mechanical or thermal loads. The paper includes a derivation of appropriate stress functions, a discussion of the point matching and boundary point least squares methods, and a description of the application of the method to the analysis of different hole configurations in tube sheets. It concludes with numerical results obtained from the analysis of the thermal stresses near the divider lane of a tube sheet from a two-pass heat exchanger.

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.

Study on the Frequency Response Characteristics of Thermal Stress Induced by Multidimensional Fluid Temperature Fluctuation

2012 ◽  
Author(s):  
Cristian Santiago Perez T. ◽  
Naoto Kasahara
Keyword(s):  
Heat Transfer ◽  
Thermal Stress ◽  
Frequency Response ◽  
Temperature Fluctuation ◽  
Hot Spot ◽  
Heat Diffusion ◽  
Fluid Temperature ◽  
Dimensional Approach ◽  
One Dimensional ◽  
The Impact

A simplified one dimensional approach for predicting the thermal stress in structures subject to near wall fluid temperature fluctuations has been previously developed and published by the author Kasahara. The method predicted the thermal stress by calculating the frequency response, formulated by the product of the effective heat transfer and the effective thermal stress related to one-dimensional temperature gradient developed through the wall thickness of the structure. Although, currently adopted by the Japanese Society of Mechanical Engineers (JSME) guideline for calculating the thermal fatigue damage in structures, recent studies have highlighted the limitations of the one dimensional approach by showing the presences of multidimensional fluid temperature fluctuation in plane direction, increasing the need to extend the current analysis to more detailed multidimensional guideline. The aim of this research is to advance the theoretical knowledge and understanding of complex multidimensional phenomenon related to local thermal fluctuations within small localized area at the surface of the structure, referred to as “Hot Spot” which is observed to have important effects on the thermal stress phenomenon. Furthermore, the understanding of heat transfer processes in the structure, especially heat diffusion that is known to produce a thermal gradient and, therefore, thermal stress. Understanding the behavior of each heat transfer process in the Hot Spot and the relationship to the response in frequency has formed the bases for extending the current one-dimensional model. This paper presents the analytical results of the study and proposes an extended multidimensional model to understand the thermal stress in tee-junction due to fluid temperature fluctuation and the close relation with the frequency. The model is derived from the understanding of the phenomenon which has leaded to quantify the effect by introducing certain multidimensional factors to explain the impact of the multidimensional fluid temperature fluctuation.

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