Study on Characteristics of Wall Temperature Fluctuation at a Mixing Tee With an Upstream Elbow

2018 ◽  
Author(s):  
Koji Miyoshi ◽  
Akira Nakamura
Keyword(s):  
Wall Temperature ◽  
Temperature Fluctuation ◽  
Hot Spot ◽  
Branch Pipe ◽  
Circumferential Direction ◽  
Wall Jet ◽  
Main Pipe ◽  
Inner Surface ◽  
Fluctuation Range ◽  
Dominant Frequencies

The characteristics of wall temperature fluctuation at the mixing tee with an upstream elbow were investigated and compared to those of the case without the elbow. The elbow of 90 degrees was installed in the inlet of the horizontal main pipe. The inlet flow velocities in the main and branch pipes were set to about 1.0 m/s and 0.7 m/s, respectively, to produce a wall jet pattern where the jet from the branch pipe was bent by the main pipe flow and made to flow along the pipe wall. A total of 148 thermocouples were installed near the pipe inner surface to measure the temperature distribution in the mixing tee. The upstream elbow decreased the temperature fluctuation intensity and the temperature fluctuation range at the inner surface. On the other hand, the distribution profiles and the dominant frequencies of temperature fluctuations were similar. The temperature fluctuation was also caused by the movement of a hot spot in the circumferential direction for both cases with and without the upstream elbow. The reduction of the movement of the hot spot in the circumferential direction decreased the temperature fluctuation for the case with the upstream elbow.

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.

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.

Experimental Study on Temperature Fluctuation Phenomena in a Closed Branch Pipe Connecting to High Velocity and High Temperature Flow in a Main Pipe

2010 ◽  
Author(s):  
N. Takenaka ◽  
S. Hosokawa ◽  
A. Saito ◽  
T. Oumaya ◽  
A. Nakamura ◽  
...  
Keyword(s):  
High Temperature ◽  
Flow Velocity ◽  
Wall Temperature ◽  
High Velocity ◽  
Branch Pipe ◽  
Temperature Fluctuations ◽  
Liquid Temperature ◽  
Spiral Flow ◽  
Main Pipe ◽  
Stagnant Point

Flow structures and temperature fluctuations in a closed branch pipe connected to a high velocity and high temperature flow in a main pipe were investigated experimentally. A straight pipe and a pipe with a bend were tested for uniform and non-uniform temperature conditions. Visualization of the flow patterns, measurement of the flow velocity and measurement of the liquid and wall temperature distributions were conducted. The flow pattern near the stagnant point in the branch pipe was a spiral flow. The time averaged velocity distributions were linear and the structure of the spiral flow was a simple forced vortex with a vertical circulation. The spiral flow velocity was fluctuated with a long period of several tens seconds. It was shown that large liquid temperature fluctuations were initiated when the spiral flow penetrated into a thermal stratified layer in the bend. The liquid temperature fluctuations caused the wall temperature fluctuations and two types of the wall temperature fluctuations were observed.

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.

Root Cause Analysis of SI Nozzle Thermal Sleeve Breakaway Failures Occurring at PWR Plants

2008 ◽  
Vol 131 (1) ◽  
Author(s):  
Jong Chull Jo ◽  
Myung Jo Jhung ◽  
Seon Oh Yu ◽  
Hho Jung Kim ◽  
Young Gill Yune
Keyword(s):  
Cold Water ◽  
Operation Mode ◽  
Branch Pipe ◽  
Thin Wall ◽  
Reactor Operation ◽  
Support Condition ◽  
Primary Coolant ◽  
Root Cause ◽  
Main Pipe ◽  
Flow Situation

At conventional pressurized water reactors (PWRs), cold water stored in the refueling water tank of emergency core cooling system is injected into the primary coolant system through a safety injection (SI) line, which is connected to each cold leg pipe between the main coolant pump and the reactor vessel during the SI operation, which begins on the receipt of a loss of coolant accident signal. In normal reactor power operation mode, the wall of SI line nozzle maintains at high temperature because it is the junction part connected to the cold leg pipe through which the hot main coolant flows. To prevent and relieve excessive transient thermal stress in the nozzle wall, which may be caused by the direct contact of cold water in the SI operation mode, a thermal sleeve in the shape of thin wall cylinder is set in the nozzle part of each SI line. Recently, mechanical failures that the sleeves are separated from the SI branch pipe and fall into the connected cold leg main pipe occurred in sequence at some typical PWR plants in Korea. To find out the root cause of thermal sleeve breakaway failures, the flow situation in the junction of primary coolant main pipe-SI branch pipe and the vibration modal characteristics of the thermal sleeve are investigated in detail by using both computational fluid dynamics code and structure analysis finite element code. As a result, the transient response in fluid pressure exerting on the local part of thermal sleeve wall surface to the primary coolant flow through the pipe junction area during the normal reactor operation mode shows oscillatory characteristics with the frequencies ranging from 15Hzto18Hz. These frequencies coincide with the lower mode natural frequencies of thermal sleeve, which has a pinned support condition on the outer surface with the circumferential prominence set into the circumferential groove on the inner surface of SI nozzle at the midheight of thermal sleeve. In addition, the variation of pressure on the thermal sleeve surface yields alternating forces and torques in the directions of two rectangular axes perpendicular to the longitudinal axis of cylindrical thermal sleeve, which causes both rolling and pitching motions of the thermal sleeve. Consequently, it is seen that this flow situation surrounding the thermal sleeve during the normal reactor operation can induce resonant vibrations accompanying the shaking motion of the thermal sleeve at the pinned support condition, which finally leads to the failures of thermal sleeve breakaway from the SI nozzle.

Impingement of an unsteady two-phase jet on unheated and heated flat plates

1993 ◽  
Vol 252 ◽  
pp. 499-523 ◽  
Author(s):  
İ. Bedii Özdemir ◽  
J. H. Whitelaw
Keyword(s):  
Wall Temperature ◽  
High Speed ◽  
Continuous Phase ◽  
Size Class ◽  
Wall Jet ◽  
Flat Plates ◽  
Two Phase ◽  
Secondary Atomization ◽  
Wall Jet Flow ◽  
The Impact

This paper is concerned with an experimental investigation of the oblique impingement of an unsteady, axisymmetric two-phase jet on heated surfaces. Size and velocity were measured simultaneously with a phase-Doppler velocimeter, and the spatial distributions over the wall jet were found to be correlated with the interfacial activities as inferred from vertical velocity measurements in the vicinity of the wall. These results are discussed together with size measurements by a laser-diffraction technique to quantify the effect of the approach conditions of the inflowing jet droplet field and wall temperature in relation to mechanisms of secondary atomization.Two mechanisms of secondary atomization were identified; the first did not involve direct wall contact and was due to the strain acting on the droplets by the continuous phase within the impingement region and was enhanced by thermal effects from the wall to cause breakup. The approaching velocity of the inflowing droplets to the plate was important to this process so that higher velocities increased the rate of strain within the impingement region and, consequently, the wall temperature promoting the secondary atomization shifted towards lower values. The second mechanism required direct wall contact and involved atomization of the film deposited on the wall by the impingement of the inflowing two-phase jet. With the penetration of high-speed inflowing droplets into the film, liquid mass was raised into the two-phase medium due to splashes from the film so that a new size class with larger droplets was generated. The resulting large droplets tended to stay close to the wall within the impingement region with small vertical velocitiesIn between the injections, the suspended droplet field above the film oscillated normal to the plate as a cloud so that the impact of large droplets on the film resulted in coalescence with the film and the ejection of smaller numbers of small droplets. The unsteady wall jet flow, caused by the arrival of the spray at the plate, swept the vertically oscillating droplet cloud radially outwards so that the resulting radial transport caused the dynamics of the unsteady film to be correlated with the size characteristics of the unsteady wall jet. Based on this phenomenological description, a radial droplet transport equation is derived.The correlation suggests that the secondary atomization with direct wall contact is the dominant process for the generation of a new size class within the wall flow and initiates the mutual interaction between the unsteady film and wall jet droplet field.

Root Cause Analysis of SI Nozzle Thermal Sleeve Breakaway Failures Occurred at PWR Plants

2006 ◽  
Author(s):  
Jong Chull Jo ◽  
Myung Jo Jhung ◽  
Seon Oh Yu ◽  
Hho Jung Kim ◽  
Young Gill Yune
Keyword(s):  
Branch Pipe ◽  
Hot Water ◽  
Thin Wall ◽  
Reactor Operation ◽  
Support Condition ◽  
Primary Coolant ◽  
Lower Mode ◽  
Root Cause ◽  
Main Pipe ◽  
Flow Situation

Thermal sleeves in the shape of thin wall cylinder seated inside the nozzle part of each safety injection (SI) line at pressurized water reactors (PWRs) have such functions as prevention and relief of potential excessive transient thermal stress in the wall of SI line nozzle part which is initially heated up with hot water flowing in the primary coolant piping system when cold water is injected into the system through the SI nozzles during the SI operation. Recently, mechanical failures that the sleeves are separated from the SI branch pipe and fall into the connected cold leg main pipe occurred in sequence at some typical PWR plants in Korea. To find out the root cause of thermal sleeve breakaway failures, the flow situation in the in the junction of primary coolant main pipe and SI branch pipe and the vibration modal characteristics of the thermal sleeve are investigated in details by using both computational fluid dynamic (CFD) code and structure analysis finite element code. As the results, the transient response in fluid pressure exerting on the local part of thermal sleeve wall surface to the primary coolant flow through the pipe junction area during the normal reactor operation mode shows oscillatory characteristics with the frequencies ranging from 15 to 18, which coincide with the lower mode natural frequencies of thermal sleeve having a pinned support condition on the circumferential prominence on the outer surface of thermal sleeve which is put into the circumferential groove on the inner surface of SI nozzle at the mid-height of thermal sleeve. In addition, the variation of pressure on the thermal sleeve surface yield alternating forces and torques in the directions of two rectangular axes perpendicular to the longitudinal axis of cylindrical thermal sleeve, which causes both rolling and pitching motions of the thermal sleeve. Consequently, it is seen that this flow situation surrounding the thermal sleeve during the normal reactor operation can induce resonant vibrations accompanying the shaking motion of the thermal sleeve at the pinned support condition, which finally leads to the failures of thermal sleeve breakaway from the SI nozzle.

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