Dounan Jia

Theoretical Study on Density Wave Oscillation of Two-Phase Natural Circulation under Low Quality Conditions

A theoretical study of the Density Wave Oscillation (DWO) of a natural circulation loop is presented in this paper. The nonlinear analysis based on the drift flux model is performed. The momentum equation is integrated around a closed loop, and the energy equation is integrated separately for every component. The equations are solved numerically using the Gear method, suitable for solving nonlinear stiff equations, with a newly developed Nonlinear Time Domain Computer Code (NTDCC). The Marginal Stability Boundary (MSB) of DWO of the low Temperature Heating Reactor (THR) designed in China was obtained by NTDCC. The results obtained by NTDCC are in good agreement with the experimental results.

Application of an Artificial Neural Network in Reactor Thermohydraulic Problem: Prediction of Critical Heat Flux

A new method for predicting Critical Heat Flux (CHF) with the Artificial Neural Network (ANN) method is presented in this paper. The ANNs were trained based on three conditions: type I (inlet or upstream conditions), II (local or CHF point conditions) and III (outlet or downstream conditions). The best condition for predicting CHF is type II, providing an accuracy of ±10%. The effects of main parameters such as pressure, mass flow rate, equilibrium quality and inlet subcooling on CHF were analyzed using the ANN. Critical heat flux under oscillation flow conditions was also predicted.

Applications of Artificial Neural Network for the Prediction of Flow Boiling Curves

An artificial neural network (ANN) was applied successfully to predict flow boiling curves. The databases used in the analysis are from the 1960s, including 1,305 data points which cover these parameter ranges: pressure P=100–1,000 kPa, mass flow rate G=40–500 kg/m2-s, inlet subcooling ΔTsub =0–35°C, wall superheat ΔTw = 10–300°C and heat flux Q=20–8,000kW/m2. The proposed methodology allows us to achieve accurate results, thus it is suitable for the processing of the boiling curve data. The effects of the main parameters on flow boiling curves were analyzed using the ANN. The heat flux increases with increasing inlet subcooling for all heat transfer modes. Mass flow rate has no significant effects on nucleate boiling curves. The transition boiling and film boiling heat fluxes will increase with an increase in the mass flow rate. Pressure plays a predominant role and improves heat transfer in all boiling regions except the film boiling region. There are slight differences between the steady and the transient boiling curves in all boiling regions except the nucleate region. The transient boiling curve lies below the corresponding steady boiling curve.

Experimental research on heat transfer to liquid sodium and its incipient boiling wall superheat in an annulus

Abstract Liquid sodium is mainly used as a cooling fluid in the liquid metal fast breeder reactor (LMFBR), whose heat transfer, whether convective heat transfer or boiling heat transfer, is different from that of water. So it is important for both normal and accidental operations of LMFBR to perform experimental research on heat transfer to liquid sodium and its boiling heat transfer. This study deals with heat transfer with high temperature (300–700°C) and low Pe number (20∼70) and heat transfer with low temperature (250∼270°C) and high Pe number (125∼860), and its incipient boiling wall superheat in an annulus. Research on heat transfer involves theoretical research and experiments on heat transfer to liquid sodium. It also focuses on the theoretical analysis and experimental research on its incipient boiling wall superheat at positive pressure in an annulus. Semiempirical correlations were obtained and they were well coincident with the experimental data.

Theoretical calculation of annular upward flow in a narrow annuli with bilateral heating

Based on separated flow, a theoretical three-fluids model predicting for annular upward flow in a vertical narrow annuli with bilateral heating has been developed in present paper. The theoretical model is based on fundamental conservation principles: the mass, momentum, and energy conservation equations of liquid films and the momentum conservation equation of vapor core. Through numerically solving the equations, liquid film thickness, radial velocity, and temperature distribution in liquid films, heat transfer coefficient of inner and outer tubes and axial pressure gradient are obtained. The predicted results are compared with the experimental data and good agreements between them are found. With same mass flow rate and heat flux, the thickness of liquid film in the annular narrow channel will decrease with decreasing the annular gap. The two-phase heat transfer coefficient will increase with the increase of heat flux and the decrease of the annular gap. That is, the heat transfer will be enhanced with small annular gap. The effects of outer wall heat flux on velocity and temperature in the outer liquid layer, thickness of outer liquid film and outer wall heat transfer coefficient are clear and obvious. The effects of outer wall heat flux on velocity and temperature in the inner liquid layer, thickness of inner liquid film and the inner wall heat transfer coefficient are very small; the similar effects of the inner wall heat flux are found. As the applications of the present model, the critical heat flux and critical quality are calculated.

A Theoretical Model of Annular Upward Flow in a Vertical Annulus Gap

This paper presents a separated flow model of annular upward flow in a vertical narrow annular channel with bilateral heating. The theoretical model is based on fundamental conservation principles: the mass, momentum and energy conservation equations of liquid films and the momentum conservation equation of vapor core. Through numerically solving the equations, liquid film thickness, radial velocity and temperature distribution in liquid films, heat transfer coefficient of inner and outer tubes and axial pressure gradient are obtained. The predicted results of heat transfer coefficients and axial pressure gradient are compared with the experimental data and good agreements between them are found.

Experimental research on flow instability in vertical narrow annuli

Abstract A narrow annular test section of 1.5mm gap and 1800mm length was designed and manufactured, with good tightness and insulation. Experiments were carried out to investigate characteristics of flow instability of forced-convection in vertical narrow annuli. Using distilled water as work fluid, the experiments were conducted at pressures of 1.0 ∼ 3.0MPa, mass flow rates of 3.0 ∼ 25kg/h, heating power of 3.0 ∼ 6.5kW and inlet fluid temperature of 20°C, 40°C or 60°C. It was found that flow instability occured with fixed inlet condition and heating power when mass flow rate was below a special value. Effects of inlet subcooling, system pressure and mass flow rate on the system behavior were studied and the instability region was given.

Experimental Study on Heat Transfer of Single-Phase Flow and Boiling Two-Phase Flow in Vertical Narrow Annuli

Water single-phase and nucleate boiling heat transfer were experimentally investigated in vertical annuli with narrow gaps. The experimental data about water single-phase flow and boiling two-phase flow heat transfer in narrow annular channel were accumulated by two test sections with the narrow gaps of 1.0mm and 1.5mm. Empirical correlations to predict the heat transfer of the single-phase flow and boiling two-phase flow in the narrow annular channel were obtained, which were arranged in the forms of the Dittus-Boelter for heat transfer coefficients in a single-phase flow and the Jens-Lottes formula for a boiling two-phase flow in normal tubes, respectively. The mechanism of the difference between the normal channel and narrow annular channel were also explored. From experimental results, it was found that the turbulent heat transfer coefficients in narrow gaps are nearly the same to the normal channel in the experimental range, and the transition Reynolds number from a laminar flow to a turbulent flow in narrow annuli was much lower than that in normal channel, whereas the boiling heat transfer in narrow annular gap was greatly enhanced compared with the normal channel.Copyright

Theoretical investigation on the steady-state natural circulation characteristics of a new type of pressurized water reactor

Abstract This article presents a theoretical investigation on the steady-state natural circulation characteristics of a new type of pressurized water reactor. Through numerically solving the one-dimensional steady-state single-phase conservative equations for the primary circuit and the steady-state two-phase drift-flux conservative equations for the secondary side of the steam generator, the natural circulation characteristics were studied. On the basis of the preliminary calculation analysis, it was found that natural circulation mass flow rate was proportional to the exponential function of the power and that the value of the exponent is related to the operating conditions of the secondary side of the steam generator. The higher the outlet pressure of the secondary side of the steam generator, the higher the primary natural circulation mass flow rate. The larger height difference between the core center and the steam generator center is favorable for the heat removal capacity of the natural circulation.

A Thermohydraulic Code for Low Temperature Nuclear Heating Reactor and Its Passive Residual Heat Removal Systems

A code, THSAC-LHRARRS, which is the thermohydraulic safety analysis code for the 200 MW Low Temperature Nuclear Heating Reactor (LTNHR) designed by China and its Passive natural circulation Residual Heat Removal System (PRHRS) is successfully developed in the present paper. The code is based on the mathematical and physical models of the LTNHR and its PRHRS, and it adopts numerical methods to correctly simulate real physical process of the systems. The heat-removal capacity in the steady state of the LTNHR-PRHRS is examined by THSAC-LHRARRS. The transition behaviors of the systems from start-up to stable operation are simulated. THSAC-LHRARRS can be used to evaluate inherent safety of the reactors that depend on natural circulation heat-removal capacity of the PRHRS. The good agreements between the results of the main models in THSAC-LHRARRS and those of the experiments show that the models are reliable and accurate.