nan Deendarlianto

Image-Processing-Based Study of the Interfacial Behavior of the Countercurrent Gas-Liquid Two-Phase Flow in a Hot Leg of a PWR

The interfacial behavior during countercurrent two-phase flow of air-water and steam-water in a model of a PWR hot leg was studied quantitatively using digital image processing of a subsequent recorded video images of the experimental series obtained from the TOPFLOW facility, Helmholtz-Zentrum Dresden-Rossendorf e.V. (HZDR), Dresden, Germany. The developed image processing technique provides the transient data of water level inside the hot leg channel up to flooding condition. In this technique, the filters such as median and Gaussian were used to eliminate the drops and the bubbles from the interface and the wall of the test section. A Statistical treatment (average, standard deviation, and probability distribution function (PDF)) of the obtained water level data was carried out also to identify the flow behaviors. The obtained data are characterized by a high resolution in space and time, which makes them suitable for the development and validation of CFD-grade closure models, for example, for two-fluid model. This information is essential also for the development of mechanistic modeling on the relating phenomenon. It was clarified that the local water level at the crest of the hydraulic jump is strongly affected by the liquid properties.

Air/Water Counter-Current Flow Experiments in a Model of the Hot Leg of a Pressurized Water Reactor

Different scenarios of small break loss of coolant accident for pressurized water reactors (PWRs) lead to the reflux-condenser mode in which steam enters the hot leg from the reactor pressure vessel (RPV) and condenses in the steam generator. A limitation of the condensate backflow toward the RPV by the steam flowing in counter current could affect the core cooling and must be prevented. The simulation of counter-current flow limitation conditions, which is dominated by 3D effects, requires the use of a computational fluid dynamics (CFD) approach. These numerical methods are not yet mature, so dedicated experimental data are needed for validation purposes. In order to investigate the two-phase flow behavior in a complex reactor-typical geometry and to supply suitable data for CFD code validation, the “hot leg model” was built at Forschungszentrum Dresden-Rossendorf (FZD). This setup is devoted to optical measurement techniques, and therefore, a flat test-section design was chosen with a width of 50 mm. The test section outlines represent the hot leg of a German Konvoi PWR at a scale of 1:3 (i.e., 250 mm channel height). The test section is mounted between two separators, one simulating the RPV and the other is connected to the steam generator inlet chamber. The hot leg model is operated under pressure equilibrium in the pressure vessel of the TOPFLOW facility of FZD. The air/water experiments presented in this article focus on the flow structure observed in the region of the riser and of the steam generator inlet chamber at room temperature and pressures up to 3 bar. The performed high-speed observations show the evolution of the stratified interface and the distribution of the two-phase mixture (droplets and bubbles). The counter-current flow limitation was quantified using the variation in the water levels measured in the separators. A confrontation with the images indicates that the initiation of flooding coincides with the reversal of the flow in the horizontal part of the hot leg. Afterward, bigger waves are generated, which develop to slugs. Furthermore, the flooding points obtained from the experiments were compared with empirical correlations available in literature. A good overall agreement was obtained, while the zero penetration was found at lower values of the gaseous Wallis parameter compared with previous work. This deviation can be attributed to the rectangular cross section of the hot leg model.

Experimental investigation on the interfacial characteristics of stratified air-water two-phase flow in a horizontal pipe

The interfacial wave characteristics of stratified air-water two-phase flow in a horizontal pipe were experimentally investigated by using the flush-mounted constant electric current method (CECM) sensors. The experiments were conducted in a horizontal two-phase flow loop 9.5u2005m long (L) consisting of transparent acrylic pipe of 26u2005mm i.d. (D). To obtain the stratified flow pattern, the superficial gas and liquid velocities were set to 1.02 – 3.77u2005m/s and 0.016 – 0.92u2005m/s, respectively. Several interfacial wave patterns as described by several investigators were identified. The common parameters such as liquid hold-up, probability distribution function, wave velocity and wave frequency were investigated as the function of the liquid and gas flow rates. The interfacial curvature was calculated on the basis of the liquid hold-up data from the CECM sensors and the liquid film thickness data from the image processing technique in the previous work. As a result, it was found that the mean liquid hold-up decreas...

Image processing analysis on the air-water slug two-phase flow in a horizontal pipe

Slug flow is a part of intermittent flow which is avoided in industrial application because of its irregularity and high pressure fluctuation. Those characteristics cause some problems such as internal corrosion and the damage of the pipeline construction. In order to understand the slug characteristics, some of the measurement techniques can be applied such as wire-mesh sensors, CECM, and high speed camera. The present study was aimed to determine slug characteristics by using image processing techniques. Experiment has been carried out in 26u2005mm i.d. acrylic horizontal pipe with 9u2005m long. Air-water flow was recorded 5u2005m from the air-water mixer using high speed video camera. Each of image sequence was processed using MATLAB. There are some steps including image complement, background subtraction, and image filtering that used in this algorithm to produce binary images. Special treatments also were applied to reduce the disturbance effect of dispersed bubble around the bubble. Furthermore, binary images w...

An improved algorithm of image processing technique for film thickness measurement in a horizontal stratified gas-liquid two-phase flow

Due to the importance of the two-phase flow researches for the industrial safety analysis, many researchers developed various methods and techniques to study the two-phase flow phenomena on the industrial cases, such as in the chemical, petroleum and nuclear industries cases. One of the developing methods and techniques is image processing technique. This technique is widely used in the two-phase flow researches due to the non-intrusive capability to process a lot of visualization data which are contain many complexities. Moreover, this technique allows to capture direct-visual information data of the flow which are difficult to be captured by other methods and techniques. The main objective of this paper is to present an improved algorithm of image processing technique from the preceding algorithm for the stratified flow cases. The present algorithm can measure the film thickness (hL) of stratified flow as well as the geometrical properties of the interfacial waves with lower processing time and random-a...

Counter Current Flow Limitation of Gas-Liquid Two-Phase Flow in Nearly Horizontal Pipe

Experimental work about counter current two-phase flow of air and gas in nearly horizontal pipe has been performed. The work was performed in a 1.1u2009m long circular transparent acrylic pipe with 50u2009mm inner diameter, in two inclination angle settings (20° and 10° from horizontal). The smooth liquid and air inlet was used. Porous liquid inlet and a nozzle connected with calm section were used as liquid and gas inlet. The effect of liquid properties is examined by using five different working fluids (Water, two different concentration of butanol and glycerin aqua solutions). As for results. (1) CCFL causes a drastic change in the delivered liquid to the lower plenum. (2) The effect of inclination angle is significantly observed. The flooding gas superficial velocity decreases with inclination angle. (3) The liquid viscosity affects the flooding phenomena.

Experimental investigation on the phenomena around the onset nucleate boiling during the impacting of a droplet on the hot surface

Onset of nucleate boiling of a droplet when impacted onto hot surface was investigated. Three kinds of surfaces, normal stainless steel (NSS), stainless steel with TiO2 coating (UVN), and stainless steel with TiO2 coating and radiated by ultraviolet ray were employed to examine the effect of wettability. The droplet size was 2.4u2005mm diameter, and dropped under different We number. The image is generated by high speed camera with the frame speed of 1000 fps. The boiling conditions are identified as natural convection, nucleate boiling, critical heat flux, transition, and film boiling. In the present report, the discussion will be focused on the beginning of nucleate boiling on the droplet. Nucleate boiling occurs when bubbles are generated. These bubbles are probably caused by nucleation on the impurities within the liquid rather than at nucleation sites on the heated surface because the bubbles appear to be in the bulk of the liquid instead of at the liquid-solid interface. In addition, the smaller the con...

Experimental investigation on liquid film asymmetry in air-water horizontal annular flow

The asymmetry of circumferential liquid film thickness distribution in an air-water horizontal annular flow has been experimentally investigated using superficial gas and liquid velocity of 10 – 40u2005m/s and 0.025 to 0.4u2005m/s, respectively. In general, the film at the bottom of the pipe will be thicker than that of the side and the top. The asymmetry parameter could be expressed in the ratio of average film thickness to the bottom film thickness or the ratio of the top-to-bottom film thickness. Measurement using compact multiple probe instrument shows that the circumferential film thickness distribution is strongly affected by superficial gas velocity. The higher gas velocity results in the more uniform liquid film circumferential distribution. In comparison to the existing correlations, the asymmetry parameter resulted from the experiment shows a good agreement. It is also shown from the experiment that a less symmetry of film thickness distribution is resulted when the gravity force is dominant. A more sym...

Experimental study on the effect of surface temperature and Weber number to spreading ratio of multiple droplets on a horizontal surface

In this study, the phenomena of multiple droplet impingement on a horizontal stainless steel hot surface are investigated and discussed. Visualization process is used to study the dynamic characteristics of droplet impingement. Image processing technique is used to capture and analyze the sequential images from a high-speed camera. The effects of the surface temperature and Weber number to the spreading ratio are investigated. The results of this study show that Weber number has a strong correlation with the droplet form for droplet impinging on the horizontal surface. On a lower Weber number, the form of multiple droplets are shaped better than higher Weber number. It is also found that, the pattern is formed more clearly at lower Weber numbers. Spreading and recoiling are shaped better at lower Weber numbers. The results also show that higher Weber numbers result in wider droplet spreading.

Determining Contact Angle and Spreading Velocity of a Droplet Impacted Hot Solid Surface

Spray cooling is a method to lower the solid surface temperature by splashing droplets. The evaporation of droplet will take the heat from solid surface. One of the factors that contributes to the evaporation rate and droplet spreads on the surface is the wettability of fluid on surface. Contact angle is a parameter in categorizing the wettability of fluid at a solid surface. Many methods have been developed to measure the contact angle on solid surface. This paper will explain how to measure the contact angle by analyzing the image taken when droplet fluid attached to a surface. The method use MATLAB codes as tools for processing image and compute the result. There are four steps in processing an image of droplet on a surface: convert image to binary image, detect the boundary of the surface, determine the correlation of x-y pixel, and take the tangent of a line at the outer point of contact between fluid and surface. Validation is taken by comparing the result with “standard image” with various resolutions. This method also explains droplet dynamics when impacting a hot surface.