An integrated approach to steam condensation studies inside reactor containments: A review

Dimensionless Profiles of Temperature and Steam Mass Fraction in Flows of Steam-Air Mixtures on a Flat Plate

Wall functions are generally used in a turbulent analysis with a computational fluid dynamics (CFD) code and large computation cells. The logarithmic law based on the analogy between momentum, energy, and mass transfer is widely used in wall functions for turbulent flows, but its validity in the turbulent boundary layer has not been confirmed for dimensionless profiles of temperature and steam mass fraction in flows of steam and noncondensable gases. In this article, therefore, we evaluated dimensionless profiles of temperature and steam mass fraction in flows of steam and air on a flat plate by using existing data. From the heat and mass transfer equations at the condensation surface based on the gradient of temperature or steam mass fraction, we showed that the convection heat flux qconv (which is used for the definition of the dimensionless temperature T+) should include the term of condensate mass flux ms and that the dimensionless steam mass fraction Ys+ should be a function of the dimensionless distance y+ (= uτ y/ν where uτ is the friction velocity), the Schmidt number Sc and the air mass fraction (1−Xs). Values obtained from the newly defined T+ and Ys+ and the existing data agreed relatively well with the linear function near the viscous sublayer (a few data points were there) but were much smaller than the existing logarithmic law due to condensation in the turbulent boundary layer (i.e., mist generation). On the other hand, the T+ and Ys+ values obtained by using the local Nusselt number Nuy and the local Sherwood number Shy (which were proposed in our previous study), respectively, agreed well with the logarithmic law.

Design of Condensation Heat Transfer Experiment to Evaluate Scaling Distortion in Small Modular Reactor Safety Analysis

Designing a novel scaled modular test facility as a part of an experiment for condensation heat transfer (CHT) in small modular reactors (SMRs) is the main focus of this study. This facility will provide data to evaluate models' scalability for predicting heat transfer in the passive containment cooling system (PCCS) of SMR. The nuclear industry recognizes SMRs as future candidates for clean, economic, and safe energy generation. However, licensing requires proper evaluation of the safety systems such as PCCS. The knowledge gap from the literature review showed a lack of high-resolution experimental data for scaling of PCCS and validation of computational fluid dynamics tools. In addition, the presently available test data are inconsistent due to unscaled geometric and varying physics conditions. These inconsistencies lead to inadequate test data benchmarking. To fill this research gap, this study developed three scaled (different diameters) condensing test sections with annular cooling for scale testing and analysis. This facility considered saturated steam as the working fluid with noncondensable gases like nitrogen and helium in different mass fractions. This facility also used a precooler unit for inlet steam conditioning and a postcooler unit for condensate cooling. The high fidelity sensors, instruments, and data acquisition systems are installed and calibrated. Finally, facility safety analysis and shakedown tests are performed.

Steam Condensation Heat Transfer During Initial Blow-Down Period of a Severe Nuclear Accident

Heat transfer coefficient (HTC) relations developed using steady-state experimental data are used for capturing the complete heat transport characteristic in a severe nuclear accident. It is important to verify the applicability of these correlation(s) at an early stage of the accident where heat transfer is transient in nature. In this paper, an experimental study is executed for this purpose. High-pressure steam (at 0.26 MPa (2.6 bar) and 0.41 MPa (4.1 bar) absolute pressure) is leaked into the closed containment initially filled with atmospheric air, and filmwise condensation is studied on an isothermally maintained vertical stainless steel test plate. During the experiment, temperature variation across the test plate at specified locations and inside the containment are recorded using the microthermocouples. The steam–air mixture composition is also examined using an online mass-spectrometry system. An inverse heat conduction (IHC) technique, validated using air-jet impingement heat transfer data, is used to estimate the time-varying condensation heat flux. It is found that the existing correlations based on the steady-state experimental data predict the transient condensation flux quite well, except in very early transient situation with a time scale of ∼20 s.

Heterogeneous nucleation of argon vapor on the nanostructure surface with molecular dynamics simulation

The study of vapor condensation on surface has important engineering significance. The condensation nucleation process of vapor on substrates with different pillar structures is studied through molecular dynamic simulation. The condensation droplets on the pillar with various heights and solid fractions exhibit Wenzel state, Cassie state and the transformation from Wenzel state to Cassie state. The results show that the condensation efficiencies are correlated with the state of droplet and it is explained from the perspective of heat transfer. For the Wenzel state, the droplet fills the gap of pillar and the form of the heat conduction change with the growth of cluster. In the initial of condensation droplets, the heat conduction is similar with various heights of pillar. As the condensation droplets grow, the efficiency of heat conduction enhances with the increasing of height of pillar. For the Cassie state, the form of heat conduction is perpetual during the condensation process with the thermal resistance of the droplet dominated due to the droplets suspended on the pillar. The efficiency of heat transfer is insensitive to the height of pillar. The form of heat conduction for the transformation state transforms from Wenzel state to Cassie state leading to the reduction of condensation rate. The droplet formed in the Wenzel state has the higher transfer efficiency than the Cassie one.