Nuclear Engineering and Design 240 (2010) 2215–2224 Contents lists available at ScienceDirect Nuclear Engineering and Design journal homepage: www.elsevier.com/locate/nucengdes PIV measurements of turbulent jet and pool mixing produced by a steam jet discharge in a subcooled water pool Yeon Jun Choo, Chul-Hwa Song ∗ Korea Atomic Energy Research Institute, Daeduk-daero 1045, Yuseong-gu, Daejeon 305-353, Republic of Korea a r t i c l e i n f o Article history: Received 5 February 2009 Received in revised form 14 September 2009 Accepted 15 September 2009 a b s t r a c t This experimental research is on the ﬂuid-dynamic features produced by a steam injection into a subcooled water pool. The relevant phenomena could often be encountered in water cooled nuclear power plants. Two major topics, a turbulent jet and the internal circulation produced by a steam injection, were investigated separately using a particle image velocimetry (PIV) as a non-intrusive optical measurement technique. Physical domains of both experiments have a two-dimensional axi-symmetric geometry of which the boundary and initial conditions can be readily and well deﬁned. The turbulent jet experiments with the upward discharging conﬁguration provide the parametric values for quantitatively describing a turbulent jet such as the self-similar velocity proﬁle, central velocity decay, spreading rate, etc. And in the internal circulation experiments with the downward discharging conﬁguration, typical ﬂow patterns in a whole pool region are measured in detail, which reveals both the local and macroscopic characteristics of the mixing behavior in a pool. This quantitative data on the condensing jet-induced mixing behavior in a pool could be utilized as benchmarking for a CFD simulation of relevant phenomena. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Direct Contact Condensation (DCC) between steam and water may be regarded as an inevitably occurring phenomenon in water cooled nuclear power plants. In the design of the APR 1400, an in-containment refueling water storage tank (IRWST) is installed to play the role of a primary heat sink and the collector of the steam discharged from the reactor coolant system (RCS) during a feed-and-bleed operation and a rapid depressurization of the RCS (Song et al., 2007). In this discharge process, a heat and mass transfer through the DCC between steam and subcooled water occurs very effectively. Different scales of experiments to investigate the thermo-hydraulic characteristics in this DCC process have been conducted (e.g., Weimer et al., 1973; Kim et al., 1997; Cho et al., 1998; Song et al., 1998, 2007). These studies, however, have mostly focused on steam jet shapes, condensation regimes and a condensational heat transfer. In addition, most of these works have been interested in the internal characteristics of a steam jet. General characteristics of free shear single phase jets are explained well in many textbooks (e.g., Abramovich, 1963; Pope, 2000) and other open literatures. However, information on the steam jet-induced turbulent jet and the resultant internal circulation in a conﬁned pool cannot be found in previous researches. ∗ Corresponding author at: Thermal Hydraulics Safety Research Division. Tel.: +82 42 868 8876; fax: +82 42 868 8362. E-mail address: [email protected] (C.-H. Song). 0029-5493/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.nucengdes.2009.11.028 The turbulent jet produced by a steam injection could be one of the important topics because the effectiveness of a thermal mixing in a pool and the safety concerns relevant to the IRWST design are closely related to the overall features of this steam-induced turbulent jet. Kim and Youn (2008) measured the velocity distribution of a condensing jet discharged by a single hole sparger using a point-wise Pitot tube and compared the measured velocity proﬁles with theoretical models. Even though their results have provided information about the mixing characteristics of a steam injection, their usefulness is rather limited due to adopting a local measuring technique. Recently Van Wissen et al. (2005) presented the characteristics of a turbulent jet discharged from a ring-shaped oriﬁce using PIV measurements and presented detailed information on the jet. However, their results are only valid for their speciﬁc type of oriﬁce. There are few efforts to simulate the overall mixing phenomena caused by a large steam discharge in a pool using a CFD tool such as Gamble et al. (2001) and Kang and Song (2008). In spite of the convenience and usefulness of the CFD analysis approach, it is strongly recommended to validate the computed results against reliable experimental data. However, there is a lack of proper experimental data for a steam jet-induced turbulent jet and the resultant mixing phenomena in a pool. Systematic efforts via experimental and numerical studies on steam jet-induced pool mixing phenomena were recently made by KAERI’s thermal-hydraulic research group (Song et al., 2007). Local measurements of the pool temperature distribution in a large quench tank were compared with the CFD analysis results 2216 Y.J. Choo, C.-H. Song / Nuclear Engineering and Design 240 (2010) 2215–2224 Fig. 1. JICO experimental facility. which were determined based on the so-called condensation region model, which provides the inlet boundary conditions to the whole calculation domain, as a simpliﬁed analytical model to describe a steam jet region. This local information was insufﬁcient to be compared directly between experimental and numerical results and, consequently, more precise information on the steam jet-induced turbulent jet and the resultant global pool mixing is needed to reasonably describe the macroscopic behavior in a pool. Based on the above background, the quantitative and qualitative experimental data adequate to validate the results of a numerical simulation of the relevant problems are presented in this study. Numerical simulation, which directly compare with these experimental results, is on-going in parallel with this study. This paper, dealing with only experimental part, is divided into two kinds of topics: the steam jet-induced turbulent jet and the overall mixing produced by a steam jet discharge in a pool, and Fig. 2. Steam nozzle (all unit is in millimeter). Y.J. Choo, C.-H. Song / Nuclear Engineering and Design 240 (2010) 2215–2224 2217 Table 1 Test matrix for the turbulent jet and pool mixing experiments. Experiments Test I.D. Mass ﬂux (kg/m2 s) Steam temperature (◦ C) Nozzle pressure (kPa) Pool temperature (◦ C) Turbulent jet M300T30 M300T60 M450T30 M450T40 M450T50 M450T60 M650T30 M650T60 300.28 300.06 450.89 450.72 450.05 451.45 648.39 647.42 137.64 137.52 151.92 151.96 151.96 151.85 166.98 166.75 307.00 305.46 457.98 457.92 458.64 458.05 675.88 673.34 30.09 60.01 30.10 40.14 50.14 59.97 30.33 60.04 Pool mixing M300T45 M450T45 M650T45 300.81 449.22 650.77 135.95 151.88 165.12 305.45 458.53 673.19 45.10 45.67 44.96 provides a set of benchmarking data which will be useful in validating the results of a numerical simulation of the relevant problems. 2. Experimental facility The experimental facility, JICO (Jet Injection and Condensation), used in this work is shown schematically in Fig. 1. The JICO was designed so as to realize various conﬁgurations of the jets and pool mixing phenomena, such as a condensing steam jet, single or two-phase jet, plunging jet and a pool mixing driven by these jets. The transparent side wall, made of acrylic material, is optically accessible so that non-intrusive optical measurement techniques can be easily applicable. Moreover, the capability of having an alternative choice of an upward or downward injection of a jet allows us to perform a variety of experimental simulations in this facility. The JICO facility consists of a test section and an electric boiler to supply saturated steam. The test section consists of two open tanks, an inner cylinder (an inner diameter of 0.78 m and a height of 2 m) as a mixing pool of our interest and an outer square tank (a square cross section of 1 m × 1 m and a height of 1.8 m), and a replaceable injection nozzle. Two overﬂow lines (Ø = 50 mm) are installed to maintain a constant water level in the inner cylinder at a height of 1825 mm. The outer square tank is installed to eliminate an optical distortion and also to minimize the heat loss through the inner cylinder wall. Three thermocouples are installed inside the inner cylinder to measure the pool water temperature. Electric boiler consists of a feed water storage tank with a capacity of about 0.5 m3 and an immersion electrical heater of 12 kW, and it can provide a maximum 0.023 kg/s of saturated steam under an operating pressure of a maximum 10 bar. Before the water in the storage tank is fed into the boiler, it is pre-heated for a degassing. In the case of the turbulent jet experiment, the steam discharging nozzle is installed at the bottom of the inner cylinder for a vertical upward injection of the steam. On the other hand, in the pool mixing experiment, the nozzle is installed at the upper part of the pool with a downward-facing injection direction. The detailed dimensions and shape of the nozzle are shown in Fig. 2. In order to avoid a complexity in the simulation of a discharging nozzle, the steam nozzle has a single hole with a sharp edge and a straight ﬂow channel. In order to minimize the pressure drop and to ensure a developed velocity proﬁle at the nozzle exit, a gradually converged shape of a ﬂow channel is adopted in the nozzle. In addition, the thermal insulation tube enveloped on the outer surface of the nozzle makes it possible to minimize the heat loss though the submerged part of the nozzle wall. Steam temperature and pressure to be discharged are measured at an upstream part of the discharging nozzle exit. 3. Experimental methods 3.1. Turbulent jet experiment From a practical viewpoint of validating a CFD analysis tool against rather complicated thermal-hydraulic phenomena, it is recommended to choose a simple domain of interest. The present subject, therefore, is on the assumption of a two-dimensional axi-symmetric ﬂow spatially and a steady-state ﬂow temporally. Fig. 3a schematically shows the geometrical conditions of the target domain in the case of the turbulent jet experiment. The nozzle is installed vertically at the bottom plate of the tank so that the jet axis is in-line with the axi-symmetric line of the target domain. For the sake of convenience, the wall condition can be assumed to be adiabatic due to the adoption of the water-ﬁlled outer tank; the Fig. 3. Geometrical description of the experiment (turbulent jet and pool mixing). 2218 Y.J. Choo, C.-H. Song / Nuclear Engineering and Design 240 (2010) 2215–2224 Fig. 4. Schematic representation of the PIV measurement: (a) turbulent jet experiment, (b) pool mixing experiment. heat loss through both the wall and free surface of the pool was actually estimated to be negligible during the test. Free surface in the pool is constantly maintained to be a 1825 mm height by an overﬂow hole. The radius of the inner tank from the jet axis to the wall boundary is 390 mm, i.e. the ratio of the inner cylinder diameter to the nozzle exit diameter (D/d) is 156, so that we can assume it to be an unconﬁned jetting condition. The initial velocity proﬁle at the nozzle exit can be regarded as fully developed by ensuring the nozzle length is L/d = 20. Since the supplied steam mass ﬂux is small compared with the total amount of the pool water and the disturbance by the ﬂow through an overﬂow hole at the free surface is weak, so the inﬂuence of the free surface movement on the nature of the turbulent jet itself could be neglected. The test matrix for the turbulent jet experiments is shown in Table 1. 3.2. Pool mixing experiment During the process of a blowdown from the RCS, steam or highenergy liquid is discharged into the IRWST pool and consequently a strong thermal-hydraulic mixing process is generated in the pool. In a real pool, the radial injection through multi-holed spargers makes the ﬂow characteristics asymmetric and transient in general; it means that it is difﬁcult to simulate or measure a real situation in a practical manner. Moreover, even for some possible cases, the real complex situation would increase the uncertainties of the measurements and numerical simulation. For these reasons, pool mixing experiments in this work were carried out in simple ﬂow conﬁgurations just like in the turbulent jet experiments. Differences of the pool mixing experiments from the turbulent jet experiments lie only in the jet injection direction and the level of the free surface. A vertical-downward injection is more advantageous when compared with an upward one for inducing a strong internal circulating ﬂow in a pool just like in an impinging jet case. The level of free surface is 850 mm in height from the bottom plate and the steam discharge nozzle is immersed at about 60 mm below the free surface, as shown in Fig. 3b. Visual observation shows that the free surface is quiescent in this condition. The test matrix for the pool mixing experiments is also shown in Table 1. 4. Measurement techniques and the uncertainties 4.1. PIV technique In the present work, the PIV technique is used to measure the velocity ﬁeld of a turbulent jet and a pool mixing driven by a steam injection. In recent years, the PIV measurement technique has shown very promising results in ﬂuid ﬂow researches and has been used very extensively for velocity ﬁeld measurements in particular due to its non-intrusive capability. A typical PIV system consisting of two functions, i.e., image capture and image analysis, was used. In the image capture system, the light source is a doublehead Nd–YAG laser (Continuum) operated at a frequency of 10 Hz and a power of 200 mJ per pulse at = 532 nm. MegaPlus ES1.0 PIV camera (1018 × 1008 pixels) operating in a triggered double exposure mode is coupled with 60 mm Nikon microlens. With this system, two paired-instantaneous particle images are stored in a synchronized PIV processor (PIV 2100, Dantec Inc.) and transferred to a PC. Small non-condensable bubbles (typically 10–100 m in size) could be incidentally used as tracer particles. In the condensation process of a steam jet, the production of non-condensable gas bubbles is almost unavoidable due to a possible existence of dissolved gas in the feed water in the boiler and also due to the interaction of the pool water with air at the free surface. Nevertheless, it was thought that these bubbles are small enough to follow a jet ﬂow with a high momentum. However, since local zones with a small momentum may exist in a pool where even the small bubbles cannot follow the liquid motion, this non-condensable gas bubble could not be used as a tracer in the pool mixing experiment. Therefore, ﬂuorescent solid tracer particles (Dantec Inc. FPP-RhB35, 20–50 m) are dispersed into the pool in the case of the pool mixing experiments, unlike the turbulent jet experiment. The signals scattered from the ﬂuorescent particles can be imaged through a narrow band-pass ﬁlter attached to a lens. Y.J. Choo, C.-H. Song / Nuclear Engineering and Design 240 (2010) 2215–2224 2219 Fig. 5. Typical PIV images: (a) turbulent jet experiment, (b) pool mixing experiment. In the process of the image analysis, we have used the Adoptive Cross-Correlation (ACC) algorithm, which would be rather useful in the case of measuring the velocity for the free shear layer, where a larger velocity gradient inside an observation area may exist and possibly introduce an erroneous calculation and/or underestimation. For this reason, two steps of an ACC are adopted in this work. The initial interrogation widow is 64 × 64 pixels and then the reﬁnement process is conducted at 32 × 32 pixels over the 2 steps. The measuring strategies of both experiments are schematically shown in Fig. 4. The measuring ﬁeld-of-view in the PIV camera for the turbulent jet and pool mixing experiments are 100 mm × 100 mm and 400 mm × 400 mm, respectively. In the turbulent jet experiment, one camera scans the target area along the axial direction of the jet from the nozzle exit to a far-ﬁeld region (z/d ≈ 0–100) over 6 intervals. In the pool mixing experiment, two horizontally mounted cameras simultaneously capture the particles image over the whole test section. In the region of a steam jet and the dense non-condensable gases at the near ﬁeld of the nozzle exit (over 70–90 mm from the nozzle exit), i.e., at the lower right part of region-1 in Fig. 4a and the upper left part in Fig. 4b, a measurement of the velocity is difﬁcult or its result would be unreliable even in the possible cases. Fig. 5 shows some typical images captured in both experiments. As shown in the image of region-1, a separate particle’s signal cannot be observed. Along the downstream, the moderate density of the bubble scattering allows for an efﬁcient vector calculation. In the case of the pool mixing experiment, two cameras cover the entire internal region of the test section as shown in Fig. 5b. 4.2. Error analysis Uncertainties of the velocity measurements by PIV and the other experimental parameters are presented below by estimating them according to the ISO GUM Guide. 4.2.1. Temperature Three K-type thermocouples (WATLOW Inc.) are employed for the pool temperature at three vertical places and one K-type thermocouple for the steam temperature at the nozzle exit. The type-B uncertainties of each error source are estimated as follows: 0.8 ◦ C for the K-type thermocouple; 1.1 ◦ C for the compensation cable; 1.0 ◦ C for the digital multi-meter. The overall uncertainty of the temperature measurement was estimated to be ±1.910 ◦ C at a 95% conﬁdence level (k-factor 1.96). 2220 Y.J. Choo, C.-H. Song / Nuclear Engineering and Design 240 (2010) 2215–2224 Fig. 6. Typical instantaneous and average velocity vectors and contours of their magnitudes. 4.2.2. Mass ﬂux Steam mass ﬂux injected by a nozzle is measured by a Vortex type ﬂowmeter (OVAL, EX DELTA) which has an accuracy of a ±1% reading value. Including the uncertainties of the digital multi-meter (0.0035% of a reading and 0.0005% of a span) and the voltage converter (0.1% of reading), the overall uncertainty of the steam mass ﬂux is ±3.196 kg/m2 s at a 95% conﬁdence level (k-factor 1.96). 4.2.3. Pressure Uncertainty of the nozzle exit pressure measured by the pressure senor (Rosemount 3051S, 0.15% of span) was estimated to be ±3.127 kPa at a 95% conﬁdence level (k-factor 1.96). 4.2.4. Velocity The bias error of the instantaneous velocity vector measured by the PIV technique is comprised of two major error sources due to the timing interval and the peak displacement detected during the correlation calculation. Typically, a FFT-based correlation algorithm has an accuracy of about 0.25–0.1 pixels, whereas the time interval error can be considered to be negligible. Another source of an uncertainty that can occur in the experiment is one induced by distorted images which result from a local temperature gradient, that is, a non-uniform refractive index. Such an undesirable effect, however, is not so dominant in our experiment. Steam temperature decreases rapidly due to a thermal mixing with a highly subcooled water. Actually, except for the region downstream of the steam discharge nozzle, the maximum temperature difference is only within a few degrees, so that this effect on the uncertainty could be insigniﬁcant. Consequently the uncertainty of the instantaneous velocity measurement is conservatively estimated to be 1% of the absolute value with a consideration of the other uncertainty sources such as the scaling factor between the image and real dimensions, an optical distortion of the observation window, etc. Finally, if an additional random error by averaging the instantaneous velocities (300–800 samples) is considered together with two sigma (2), the total uncertainty of the velocity measurement could be estimated approximately as 1.7–2.5% of an absolute value. 5. Results and discussion The present experimental study is focused on understanding the hydraulic characteristics of a turbulent jet and the pool mixing driven by a steam injection. The results of these two topics will be discussed hereunder. 5.1. Turbulent jet driven by a condensing steam jet Analytical and experimental approaches for the mean quantities of free shear ﬂows have been established comparatively well as far as a single phase jet, i.e., air-to-air and liquid-to-liquid is considered. It is evident that further researches on a steam jet-driven turbulent jet with a condensation process, as in this research unlike a single phase jet, is required. Therefore, it is expected that the results described in this section could be used in many relevant researches, which include the validation of a CFD simulation. 5.1.1. Instantaneous and mean velocity ﬁeld The typical contours of the instantaneous velocity vectors and their magnitude between z/d = 36 and 55, i.e., in region-2 in Fig. 4a are presented in Fig. 6a. The inherent oscillating manner of the jet is clearly shown, reﬂecting the feature of an entrainment of the jet and its interaction with the surrounding water. Evidently as well, the velocity in the central region is high. On the other hand, the mean velocity (Fig. 6b) shows clear proﬁles. In practice, some physical assumptions for a free shear layer (jet, wake and simple shear layer) allow for the turbulent ﬂow to be transformed into a mathematically analyzable form. Also the theoretical description of the mean ﬂow characteristics of the single phase turbulent jet may be applicable to a steam jet-driven turbulent jet. Consequently, understanding of the characteristics of the mean ﬂow in a turbulent jet could be very valuable for describing a turbulent jet. So our experimental results will be analyzed in this manner. Fig. 7 shows the entire vector ﬁeld which was measured and integrated by means of scanning the target region over 6 intervals. This is, in appearance, similar to the case of a single phase turbulent jet. Actual measured region is up to z/d = 100 in all the cases of the turbulent jet experiments. It is clearly observed that the velocities at the center lines are decayed due to a turbulent dissipation and Y.J. Choo, C.-H. Song / Nuclear Engineering and Design 240 (2010) 2215–2224 2221 Fig. 7. Overall velocity pattern: (a) M300T60, (b) M650T60. the velocity proﬁles are spreading to the extent of the rate at which the shear layer grows laterally with the axial distance. 5.1.2. Self-similarity The concept of a self-similarity, or self-preservation, implies that the ﬂow has reached a dynamic equilibrium or asymptotic state in which the mean and higher-order moments evolve together (Townsend, 1976). Typically, self-similar quantities are represented by some scaled dependent variables and show a universal aspect over a fully developed region. Two general characteristic scales are the mean centerline maximum velocity, UC (z) = U(z,0), and a jet’s half width (r1/2 ) in a round shear jet. In addition, since a jet’s half width is dependent on (z − z0 ), a dimensionless scale, r/(z − z0 ), can be an alternate cross-stream scale. Consequently the cross-stream similarity variable can be taken to be either = r r1/2 or = r , z − z0 along the dimensionless scale, . Generally, a Gaussian proﬁle can be ﬁtted accurately with experimental data: U = exp(−K2 ) UC where K is a constant to represent the shape of a mean velocity proﬁle and it is determined from experimental data. The proﬁle of U/UC in the case of G = 450 kg/m2 s and Tp = 60 ◦ C is typically shown in Fig. 9. The coincidence of all the measurements onto a single ﬁtting curve reﬂects that the jet has a good self-similarity feature. (1) where z0 is a jet’s virtual origin. Measurements of single-phase jets indicate that in the far-ﬁeld the centerline velocity UC is inversely proportional to the axial distance: UC = C z − z0 (2) with a coefﬁcient C determined experimentally. The development of the mean center-line velocity as a function of the distance from a nozzle is shown in Fig. 8. From these results, a coefﬁcient C and virtual origin z0 can be determined by ﬁtting the measured data to Eq. (2). Other self-similar feature of a turbulent jet is the mean axial velocity proﬁle normalized by the center-line velocity, U/UC , (3) Fig. 8. Centerline velocity as a function of the distance to the steam nozzle. 2222 Y.J. Choo, C.-H. Song / Nuclear Engineering and Design 240 (2010) 2215–2224 Table 2 Fitted coefﬁcients of the self-similar turbulent ﬂow for all the test matrices (95% conﬁdence interval within parentheses). Test I.D. Decay coefﬁcient (C) Virtual pole (z0 ) Velocity proﬁle constant (K) Spreading rate (S) G300T30 G300T60 G450T30 G450T40 G450T50 G450T60 G650T30 G650T60 Other literature 457.1 (446.3–467.8) 460.2 (454.9–465.5) 586.7 (578.2–595.3) 580.8 (573.9–587.7) 587.2 (583.1–591.4) 596.5 (587.0–606.0) 716.1 (706.6–725.6) 720.1 (711.0–729.2) N/A −2.6D (−3.7 to −1.6) −3.1D (−3.6 to −2.5) −1.7D (−2.4 to −1.0) −0.5D (−1.0 to 0.0) −0.8D (−1.1 to −0.4) −2.5D (−3.2 to −1.7) −1.0D (−1.6 to −0.4) −0.6D (−1.1 to −0.0) 0–5D Present Dependency (G) Dependency (Tp ) 457–720 Strong Increase with Tp −0.5D to −3D Decrease with increasing G Weak 86.0 84.4 79.3 82.9 81.9 72.4 78.8 75.0 76.1 and 75.2 Boersma et al. (1998) and Panchapakesan and Lumley (1993) 72.4–86.0 Not clear Not clear 0.0898 0.0906 0.0935 0.0914 0.0920 0.0979 0.0938 0.0961 0.094 Van Wissen et al. (2005) and Hussein et al. (1994) 0.0898–0.979 Not clear Not clear The spreading rate S, which is another coefﬁcient to describe the shape of a jet, is deﬁned as follows: S= r1/2 (z) z − z0 , (4) where r1/2 (z) is the width at which a jet’s axial velocity is half of the maximum axial velocity UC (z) in the corresponding cross section, z. This quantity reﬂects the rate at which the shear layer grows laterally with the axial distance. Furthermore a straightforward transformation using the relation between K and S gives the following explanation: ln2 1/2 C =S (5) All the ﬁtted coefﬁcients mentioned above together with those of a single phase jet and their dependency on G and Tp are summarized in Table 2. The center-line velocity decay rate C is a key feature of the steam jet-induced turbulent jet since a jet’s momentum induced by a steam injection can affect the integrity of the submerged structures in a pool. The center-line decay coefﬁcient C is strongly dependant on G; it increases with G. The center-line decay rate shows the tendency of an increase with Tp even though it is relatively not clear when compared to G. In contrast to most of the previous results found in open literature on single phase non-condensing jets, the virtual origin z0 for this condensing jet is always negative. There is no doubt that the virtual origin is mostly decided by the initial condition of the jet. In the present case of a condensing jet, a sudden phase change from steam to water occurs in the initial region of the jet and the Fig. 9. Self-similar proﬁle of the mean axial velocity along the radial direction. steam jet near the exit of the discharge nozzle has a peculiar shape depending on the mass ﬂux and the pool temperature, which is quite different from the case of a non-condensing jet. Quite naturally, the strong driving force and phase change could inﬂuence the near-ﬁeld condition of the jet and the difference in the virtual origin of a condensing jet from a single phase jet results from the inherent nature of a steam jet-driven turbulent jet. The dependency of z0 on G shows the tendency of a decrease with an increasing G due to the increase of the height of the steam jet, whereas it shows no clear evidence for a dependency on Tp . Both quantities of the velocity proﬁle constant K and the spreading rate S are correlated with each other by Eq. (5). These quantities were estimated with experimental data at a height of 200 mm or above where a jet is fully developed and they show a universal feature. The value of the K and S constants were found to be between 72.4–86.0 and 0.090–0.098, respectively, and they are almost similar to those of a single phase non-condensing jet, which is about 76.1 and 0.097, respectively. These results are consistent with the previous observations not only for a condensing jet by Van Wissen et al. (2005) but also for a noncondensing jet by other researchers. The dependency of K and S on G and Tp , however, did not show a clear tendency in the present work. 5.2. Internal circulation driven by a steam injection The turbulent jet, which is strongly induced by a steam injection, entrains the surrounding water and creates an internal circulation pattern within a pool; it governs the content of a pool mixing. Fig. 10 demonstrates that a coherent circulating ﬂow pattern is created by the steam injection. As expected, a stronger internal driving ﬂow can be observed with an increasing mass ﬂux. Key features of the internal ﬂow pattern in the pool mixing are the location of the center of the recirculation and the existence of a secondary ﬂow. For all the tests, the eye of a strong recirculation was placed at the bottom right-hand corner. For illustrating the typical features of the experimental observation, three local regions were selected and the apparent differences between G = 300 kg/m2 s and 650 kg/m2 s are shown in Fig. 11. The region-A is a central part of the pool’s bottom where a jet bounces to form a weak impinging jet. Due to a stronger re-circulating current (the region-B), the main current of the jet in the case of G = 300 kg/m2 s is narrower than that in the case of G = 650 kg/m2 s (region-A). With an increasing mass ﬂux, the eye of the recirculation was moved upward by the relatively strong entrainment and a bouncing ﬂow (region-B). Moreover, an apparent secondary ﬂow (region-C of G = 650 kg/m2 s) appears for the case of a mass ﬂux at 650 kg/m2 s. It is caused by the stronger bouncing ﬂow along the right wall which tows the comparatively still water at the upper right region along with it. Y.J. Choo, C.-H. Song / Nuclear Engineering and Design 240 (2010) 2215–2224 2223 Fig. 10. Internal circulation pattern and velocity ﬁeld for the mass ﬂuxes of 300, 450 and 650 kg/m2 s with a pool water temperature of 45 ◦ C. Fig. 11. Local ﬂow patterns and their comparison between G = 300 kg/m2 s and 650 kg/m2 s. 6. Conclusions Experimental study on the turbulent jet and mixing pattern produced by a steam injection in a pool was conducted separately using the PIV measurement technique. Self-similar features of the turbulent jet in an axi-symmetric test domain were measured in detail and the constants to describe the shape of the jet were presented for all the test matrices. The pool mixing pattern for an injected steam mass ﬂux was measured over the whole test domain. The experiment results for both viewpoints reveal the detailed velocity structures quantitatively and could be used as the benchmarking data for the validation of a CFD simulation of 2224 Y.J. Choo, C.-H. 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