Classification of Flow Patterns in Angled T-Junctions for the Evaluation of High Cycle Thermal Fatigue

2014 ◽  
Vol 137 (2) ◽  
Author(s):  
Shaoxiang Qian ◽  
James Frith ◽  
Naoto Kasahara
Keyword(s):  
Flow Pattern ◽  
Thermal Fatigue ◽  
Velocity Ratio ◽  
Branch Pipe ◽  
General Characteristic ◽  
Flow Patterns ◽  
Characteristic Equations ◽  
Piping Systems ◽  
Fatigue Evaluation ◽  
High Cycle Thermal Fatigue

Temperature fluctuations caused by the mixing of hot and cold streams at tee junctions may lead to high cycle thermal fatigue (HCTF) failure. It is necessary to evaluate the integrity of structures where the HCTF may occur. Therefore, the Japan Society of Mechanical Engineers (JSME) published “Guideline for Evaluation of High Cycle Thermal Fatigue of a Pipe (JSME S017),” in 2003, which provides the procedures and methods for evaluating the integrity of structures with the potential for HCTF. In JSME S017, one of the important procedures of thermal fatigue evaluation is to classify the flow patterns at tee junctions, because the degree of thermal fatigue damage is closely related to the flow pattern downstream of the mixing junction. The conventional characteristic equations for classifying flow patterns are only applicable to 90-deg tee junctions (T-junctions). However, angled tee junctions other than 90 deg (Y-junctions) are also used in chemical plants and refineries for reducing the pressure drop in the mixing zone and for weakening the force of the impingement of the branch pipe stream against the main pipe. The aim of this paper is to develop general characteristic equations applicable to both T- and Y-junctions. In this paper, general characteristic equations have been proposed based on the momentum ratio for all angles of tee junctions. Further, the validity of the proposed characteristic equations and their applicability to all angles of tee junctions have been confirmed using computational fluid dynamics (CFD) simulations. The results have also highlighted that the angle of the branch pipe has a significant effect on increasing the velocity ratio range for less damaging deflecting jet flow pattern, which is an important finding that could be used to extend the current design options for piping systems where HCTF may be a concern. In addition, categorization 3 is recommended as a more proper method for classifying flow patterns at tee junctions when evaluating the potential for thermal fatigue.

Classification of Flow Patterns in Angled T-Junctions for the Evaluation of High Cycle Thermal Fatigue

2010 ◽  
Author(s):  
Shaoxiang Qian ◽  
James Frith ◽  
Naoto Kasahara
Keyword(s):  
Pressure Drop ◽  
Thermal Fatigue ◽  
Pipe Flow ◽  
Velocity Ratio ◽  
Branch Pipe ◽  
Flow Patterns ◽  
Minor Role ◽  
Characteristic Equations ◽  
Main Pipe ◽  
High Cycle Thermal Fatigue

Temperature fluctuations generated by the mixing of hot and cold streams at T-junctions can cause high cycle thermal fatigue failure. One of the important parameters for determining the degree of thermal fatigue damage is related to the flow patterns downstream of the mixing junction. Many papers have been published identifying the characteristic equations for classifying the flow patterns at the T-junctions, which have been shown to be related to the momentum ratios between the main pipe flow and the branch pipe flow. The flow patterns and governing equations studied in the past are only applicable to 90-degree tee junctions (T-junctions). The intention of this paper is to extend the work of others to include angled tee junctions other than 90 degrees (Y-junctions). Y-junctions especially with 45-degree angle are also used in the chemical and refinery plants of our concern for lowering the pressure drop in the mixing zone and weakening the impingement of the branch pipe stream against the main pipe. This paper presents the proposal for a set of extended characteristic equations for classifying the flow patterns in mixing tees which can be applied to all angles of tee junctions. The modified characteristic equations have been verified using computational fluid dynamics (CFD) simulations. Models with branch angles other than 90 degrees have been used to confirm the robustness and validity of the modified equations. The effect of the pressure drop caused by the varying opening sizes has been shown to play only a minor role in determining the overall flow patterns, with the key variables being the velocity ratio and the interaction area between the flow in the main pipe and the jet exiting from the branch pipe. The results have also highlighted that the angle of the branch pipe has significant impact on increasing the velocity ratio range for the less damaging deflecting jet flow pattern, which is an important finding that could be used to extend the current design options for piping systems where high cycle thermal fatigue may be a concern.

Thermal Fatigue Evaluation Method of Pipes by Equivalent Stress Amplitude

2012 ◽  
Author(s):  
Takafumi Suzuki ◽  
Naoto Kasahara
Keyword(s):  
Fatigue Damage ◽  
Thermal Fatigue ◽  
Evaluation Method ◽  
Stress Amplitude ◽  
Equivalent Stress ◽  
Safety Margin ◽  
Evaluation Procedure ◽  
Fatigue Evaluation ◽  
High Cycle Thermal Fatigue ◽  
Equivalent Stress Amplitude

In recent years, reports have increased which are about failure cases caused by high cycle thermal fatigue both at light water reactors and fast breeder reactors. One of the biggest reasons of the cases is a turbulent mixing at a Tee-junction, where hot and cold temperature fluids are mixed, in a coolant system. In order to prevent thermal fatigue failures at Tee-junctions, The Japan Society of Mechanical Engineers (JSME) published the guideline S017-2003 (or JSME guideline) which is an evaluation method of high cycle thermal fatigue damage at a nuclear piping. It has some limitations in terms of its inconstant safety margin and its complexity in evaluation procedure, however. In order to solve these limitations, this paper proposes a new evaluation method of thermal fatigue damage with use of the “equivalent stress amplitude” which represents random temperature fluctuation effects on thermal fatigue damage. Because this new method makes methodology of evaluation clear and concise, it will contribute to improving the guideline for thermal fatigue evaluation.

Experimental Investigation of Flow Field Structure in Non-Isothermal Mixing Tee

2007 ◽  
Author(s):  
Seyed Mohammad Hosseini ◽  
Kazuhisa Yuki ◽  
Hidetoshi Hashizume
Keyword(s):  
Thermal Fatigue ◽  
Velocity Fluctuation ◽  
Temperature Fluctuation ◽  
Pipe Wall ◽  
Branch Pipe ◽  
Main Flow ◽  
Turbulent Jet ◽  
Junction Area ◽  
Main Pipe ◽  
High Cycle Thermal Fatigue

T-junction is one of familiar components in the cooling system of power plants with enormous capability to high-cycle thermal fatigue. This research tries to investigate fluid mixing mechanism in non-isothermal T-junction area with 90-degree bend upstream. Classification of turbulent jet and effects of 90-degree bend were evaluated previously and re-attached jet was selected as complicated mixing structure with highest velocity fluctuation [4]. For considering the mixing mechanism of re-attached jet, T-junction area is visualized in various lateral and longitudinal sections. The measuring data show the flow of branch pipe acts as turbulent jet in finite space and interaction between the jet and main flow can create various eddies and develops high velocity fluctuation area near the main pipe wall as well as temperature fluctuation. Three regions are more affected by maximum velocity fluctuation in T-junction area near the main pipe wall; the region close to the jet surface (fluctuation mostly is caused by Kelvin-Helmholtz instability), the region above the jet and along the main flow (fluctuation mostly is caused by Karman vortex) and re-attached area (fluctuation mostly is caused by moving the jet body with pressure gradient). Finally, the re-attached area is selected as region with strongest possibility to high cycle thermal fatigue with effective velocity fluctuation on the main pipe wall above the branch nozzle as well as temperature fluctuation.

Flows in T-junction Piping Systems : Flow Patterns and Characteristics of Vortex formed by Branch Pipe Flow

2002 ◽  
Vol 2002 (0) ◽  
pp. 45-46
Author(s):  
Hideki HIBARA ◽  
Toshiharu MURAMATSU ◽  
Naoki HIRATA ◽  
Kozo SUDO
Keyword(s):  
Pipe Flow ◽  
Branch Pipe ◽  
Flow Patterns ◽  
Piping Systems

scholarly journals Flow Pattern Map of Flow Boiling in a Rectangular Channel Filled with Porous Media

Energies ◽  
2021 ◽  
Vol 14 (9) ◽  
pp. 2440
Author(s):  
Youngwoo Kim ◽  
Dae Yeon Kim ◽  
Kyung Chun Kim
Keyword(s):  
Porous Media ◽  
Flow Pattern ◽  
Flow Regime ◽  
Annular Flow ◽  
Flow Boiling ◽  
Rectangular Channel ◽  
Flow Patterns ◽  
Flow Pattern Map ◽  
Mist Flow ◽  
Churn Flow

A flow visualization study was carried out for flow boiling in a rectangular channel filled with and without metallic random porous media. Four main flow patterns are observed as intermittent slug-churn flow, churn-annular flow, annular-mist flow, and mist flow regimes. These flow patterns are clearly classified based on the high-speed images of the channel flow. The results of the flow pattern map according to the mass flow rate were presented using saturation temperatures and the materials of porous media as variables. As the saturation temperatures increased, the annular-mist flow regime occupied a larger area than the lower saturation temperatures condition. Therefore, the churn flow regime is narrower, and the slug flow more quickly turns to annular flow with the increasing vapor quality. The pattern map is not significantly affected by the materials of porous media.

Two-Phase Flow and Heat Transfer in Rectangular Micro-Channels

2003 ◽  
Author(s):  
Weilin Qu ◽  
Seok-Mann Yoon ◽  
Issam Mudawar
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Flow Pattern ◽  
Two Phase Flow ◽  
Flow Patterns ◽  
Heat Sinks ◽  
Phase Flow ◽  
Micro Channel ◽  
Two Phase ◽  
Micro Channels

Knowledge of flow pattern and flow pattern transitions is essential to the development of reliable predictive tools for pressure drop and heat transfer in two-phase micro-channel heat sinks. In the present study, experiments were conducted with adiabatic nitrogen-water two-phase flow in a rectangular micro-channel having a 0.406 × 2.032 mm cross-section. Superficial velocities of nitrogen and water ranged from 0.08 to 81.92 m/s and 0.04 to 10.24 m/s, respectively. Flow patterns were first identified using high-speed video imaging, and still photos were then taken for representative patterns. Results reveal that the dominant flow patterns are slug and annular, with bubbly flow occurring only occasionally; stratified and churn flow were never observed. A flow pattern map was constructed and compared with previous maps and predictions of flow pattern transition models. Annual flow is identified as the dominant flow pattern for conditions relevant to two-phase micro-channel heat sinks, and forms the basis for development of a theoretical model for both pressure drop and heat transfer in micro-channels. Features unique to two-phase micro-channel flow, such as laminar liquid and gas flows, smooth liquid-gas interface, and strong entrainment and deposition effects are incorporated into the model. The model shows good agreement with experimental data for water-cooled heat sinks.

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