Hanliang Bo

Effect of Feeder Inner Structure on Feeding Performance for Absorber Sphere Pneumatic Conveying

The sphere feeder is an important component of the absorber sphere shutdown system for absorber sphere conveying. Absorber sphere is entrained and fluidized in the feeder by conveying gas to form gas-solid flow. The effect of feeder inner structure, i.e. the draft tube height, on the feeding performance was investigated. Experiments were conducted in the positive pressure conveying system with ambient air as the source gas. The glass sphere was used to replace the absorber sphere. Three types of feeder inner draft tube relative position were considered. Five combinations of the draft tube height were tested with feeder inlet air velocity in the range of 15∼30 m/s. Experimental results showed that feeder inner draft tube height played an important role on the feeding performance. Different characteristics for the starting process of the sphere conveying were observed. The difference of sphere blown away pressure and steady conveying pressure could be reduced to about 5 kPa, which was negligible from the view point of conveying blower selection in engineering application. Sphere stagnation region was observed near the bottom of the feeder. The obvious boundary of stagnated sphere and fluidized sphere was formed for the steady conveying. Two types of control model were observed for sphere steady feeding rate. One was that the sphere steady feeding rate was determined by sphere flow through the orifice. The other was that the sphere steady feeding rate was determined by gas-sphere fluidization and entrainment. These results were important for optimization sphere feeder design.Copyright

Experimental Study on Restart Performance of Absorber Sphere Pneumatic Conveying

In the high-temperature gas-cooled reactor pebble-bed module (HTR-PM), absorber sphere shutdown system is the second shutdown system. Absorber spheres are transported back to storage vessel by pneumatic conveying when reactor needs to be started. The restart reliability of absorber sphere pneumatic conveying is quite important. Experimental system for absorber sphere pneumatic conveying has been built to investigate the gas-solid flow characteristics of pneumatic conveying. Restart experiments were conducted to study the restart performance of pneumatic conveying. Ambient air was used as source gas and absorber sphere was replaced by glass sphere. The inlet steady gas velocity of the sphere feeder was in the range of 17∼27 m/s. Pneumatic conveying could be restarted in all the experiments, which showed the good reliability of the pneumatic conveying process. The maximum relative deviation of the spheres pile heights in the riser was 4.1%, which showed a good repeatability. Pressure drop of feeder during steady stage was in the range of 4∼8 kPa. Furthermore, the restart experiments were also conducted in the full scale experimental system with helium as the source gas and the pressure of 2 MPa, the results also showed the good reliability of pneumatic conveying process.Copyright

Study of the Numerical Solving Methods of the Motion Model of Polydispersed Droplets

Moisture separation is one of crucial devices in PWR power plant for it plays an irreplaceable role in eliminating droplets from steam and supplying dry-saturated for turbines. It would be helpful to design and optimize the structure of moisture separator through analyzing the behaviors of droplets. This paper studies the numerical solving methods of the motion model of polydispersed droplets. The equations of model belong to the field of nonlinear stiff ordinary differential equations, thus backward differentiation formula, a kind of multi-steps methods are used which advance in solving stiff different equations. The coefficients of equations involve the velocity and rotation of flow field in separator, and these parameters are given by the output of Fluent. After solving the differential equations we can get the velocity and angle velocity of droplets in different locations and the movement track of droplets in separator, as well as the separation efficiency of moisture separator for polydispeased droplets with special distribution. Finally through the numerical solving of the motion model of polydispersed droplets in chevron-type separator, we find that multi-steps method improves the numerical stability and reduces the steps of iteration under the same calculation precision compared with classical methods such as fourth-order Runge-Kutta method. So it lays the foundation for development of moisture separator program suit for engineering computing.Copyright

Predictions of Heat Transfer Coefficients and Pressure Drops to Supercritical Pressure HCFC22 Flowing in a Small Tube

In this paper, experimental flow and heat transfer data of supercritical pressure HCFC22 flowing in a uniformly heated smooth tube with inner diameter of 1.004 mm at p/pc=1.1 obtained by the authors are analyzed accounting for the influence of the thermophysical properties variation, the buoyancy effect, as well as the flow acceleration effect due to thermal expansion. These analyses indicate that both of the sharp thermophysical properties variation in the fluid adjacent to the wall with low density, low specific heat and low thermal conductivity and the flow acceleration effect due to thermal expansion have significant negative effects on the heat transfer under the present study conditions for HCFC22, while for the friction factor, the thermophysical properties variation is the predominant factor. The buoyancy effect on the flow and heat transfer is negligible.A new semi-empirical local heat transfer correlation accounting for the thermophysical properties variation and the flow acceleration effect due to thermal expansion for supercritical pressure fluids flowing through a vertical small tube during heating is proposed. The predicted values agree with 95% of the measured data within ±25%. In addition, a flow correlation with thermophysical properties variation correction terms to predict the friction factors for supercritical pressure fluids is proposed which predicts the measured friction factors within ±25%.© 2014 ASME

Falling Characteristic Analysis of Passive Drive Mechanism of Absorber Ball Shutdown System for HTR-PM

The absorber ball shutdown system is a key system and related to reactivity control in HTR-PM, which has once achieved power regulation and cold shutdown of the nuclear reactor. Passive drive mechanism of absorber ball shutdown system has been designed for HTR-PM reactor safety before. Ball dropping valve can be automatically opened by gravity when loss of offsite power happens, then a mass of balls with BC4 fall into reactor core for function implementation. Therefore drive mechanism reliability is fairly important for absorber ball shutdown system in HTR-PM. Experiments on passive drive mechanism have been carried out in this study. Falling distance and falling time of drive mechanism have been recorded and analyzed with and without absorber ball, as well as at ambient temperature and in the heating conditions. Experimental results demonstrate that designed passive drive mechanism can shift reliably. Ball dropping valve can freely open each time without absorber balls in the storage vessel. Basically present design of passive drive mechanism for absorber ball shutdown system can meet the requirement of actual reactor application.Copyright

Theoretical Analysis of the Working Performance of the Hydraulic Control Rod Driving System in Perturbation or Inclination

A new type of control rod driving system, the hydraulic control rod driving system (HCRDS) with a hole-hole step cylinder, has been applied in the 5-MW nuclear heating reactor of Tsinghua University for several years and has performed well all along. A second-generation HCRDS has been developed based on operational experience, and further improvements are being carried out. This paper focuses on the first-generation HCRDS, analyzing in detail its working performance in an unstable state. The control rod stability after minute perturbation and the operation of the control rod in an incline state have been theoretically calculated. The study proves the self-lock design characteristic of the system. The calculated results also indicate that the control rod step-up, step-down, and scram operations function properly. The theoretical analysis proves the HCRDS reliable and safe, establishing a baseline for further research and development for wide use in portable seawater distillation systems.

The temperature feature on the step-up process of the hydraulic control rod driving system

Abstract As a new type of control rod driving system, the hydraulic control rod driving system (HCRDS) has long been applied in a 5-MW nuclear heating reactor, and the safety and the reliability of the system have been proven. The principle of the work and the step-up operation of the HCRDS have been introduced in this paper. Based on the theoretical model, the temperature influence on the static holding-flow rate, the dynamic holding-flow rate, and the working holding-flow rate has been studied. It indicates that with the increase of the temperature, the static and dynamic holding-flow rates will increase while the working holding-flow rate will decrease. A detailed analysis of the step-up process on various temperature conditions has been carried out. Considering the great temperature influence on the step-up operation of the system, the method of temperature compensation to select suitable delay time and working holding-flow rate in a certain temperature province is put forward to offset the influence. The analysis can be conducive to widespread availability of the HCRDS and establish a basis for further research and improvement.