Karen Vierow

Reflux Condensation Heat Transfer of Steam-Air Mixture under Turbulent Flow Conditions in a Vertical Tube

Under certain hypothetical accident circumstances in a pressurized water reactor, reflux condensation in the steam generator U-tubes may be an effective heat removal mechanism. Non-condensable gas (air) may be present in the reactor coolant system and is well known to inhibit steam from condensing. In a previous study, local condensation heat transfer coefficients for reflux condensation with air were measured, and an empirical correlation intended for a laminar flow of steam-air mixtures was developed, which was a function of the partial pressure ratio, (P steam=P air). In this study, heat transfer coefficients measured under turbulent flows were used to modify the empirical correlation for improved prediction accuracy. The modified empirical correlation considers convection and is proportional to (P steam/P air)0.75 Re g 0.8 where Re g is the steam-air mixture Reynolds number. The correlation was verified against the data of Moon et al. and then incorporated into the transient analysis code RELAP5/SCDAPSIM/MOD3.2. The temperature distributions of the steam-air mixture calculated by the code for six reflux condensation tests are shown to agree well with the measured results.

Evaluation of Reflux Condensation Heat Transfer of Steam-Air Mixtures under Gas-Liquid Countercurrent Flow in a Vertical Tube

Reflux condensation in steam generator (SG) is one of the major heat removal mechanisms in a loss of residual heat removal (RHR) system event in mid-loop operation during a pressurized water reactor (PWR) plant outage. In order to evaluate the effectiveness of reflux condensation in SG U-tubes, the condensation heat transfer characteristics in the presence of a non-condensable gas must be clarified. Local temperature data were previously measured for steam-air mixtures under gas-liquid countercurrent flow, in a vertical tube of inner diameter 19.3 mm. In this study, local reflux heat transfer coefficients were calculated by evaluating steam flow rate profile along the tube at low heat fluxes assuming saturated steam conditions and empirical correlations were derived. The correlations are valid over a range 2–9,000W/m2-K for 0.1–0.4MPa, 0.014–0.2 air mass fraction. The axial distributions of the steam—air mixture temperatures calculated using the correlation agreed well with the measured results and validity of evaluation methods and the correlation were verified.

Development of design and simulation model and safety study of large-scale hydrogen production using nuclear power.

Before this LDRD research, no single tool could simulate a very high temperature reactor (VHTR) that is coupled to a secondary system and the sulfur iodine (SI) thermochemistry. Furthermore, the SI chemistry could only be modeled in steady state, typically via flow sheets. Additionally, the MELCOR nuclear reactor analysis code was suitable only for the modeling of light water reactors, not gas-cooled reactors. We extended MELCOR in order to address the above deficiencies. In particular, we developed three VHTR input models, added generalized, modular secondary system components, developed reactor point kinetics, included transient thermochemistry for the most important cycles [SI and the Westinghouse hybrid sulfur], and developed an interactive graphical user interface for full plant visualization. The new tool is called MELCOR-H2, and it allows users to maximize hydrogen and electrical production, as well as enhance overall plant safety. We conducted validation and verification studies on the key models, and showed that the MELCOR-H2 results typically compared to within less than 5% from experimental data, code-to-code comparisons, and/or analytical solutions.

Temperature Boundary Analysis of Condensation Jets Using Discrete Wavelets Multiresolution and 2 Dimensional Image

This paper describes the application of discrete wavelet transform to the analysis of condensation jets in order to clarify the fluid and heat transfer phenomenon. The condensation jets in nozzle vicinity are experimentally visualized with laser light sheet method to obtain the condensation particle density images of the jets. The image of the condensation particle density in the jet is decomposed to the mean value and the fluctuation value images by means of wavelet multiresolution. The dominant temperature boundary and the mean component outside boundary were provided from wavelet separation images. These boundaries were compared with the temperature distributions provided from experimental results.Copyright

Relationship Between Temperature Distribution and 2D Image of Condensation Jets Using Discrete Wavelets Multiresolution

This paper describes the application of discrete wavelet transforms to the analysis of condensation jets in order to clarify the associated fluid and heat transfer phenomena. An experimentally obtained, two-dimensional image of the condensation particle density around the jet was decomposed into 7 levels of resolution with their respective wavelengths. Based on the known physical characteristics of turbulent flow around the jet, levels 0 and 1 were shown to represent the steady components of the condensation particle density and the higher levels represent the fluctuating components. From the analysis images, the width of the condensation zone was obtained and this compared well with the width inferred from temperature measurements. Thus, the method was verified and also provided data not available experimentally.Copyright