Chen Ting-kuan

Pressure drop, heat transfer and performance of single-phase turbulent flow in spirally corrugated tubes

Abstract The paper presents the results of an experimental study that was carried out to determine turbulent friction and heat transfer characteristics of four spirally corrugated tubes, which have various geometrical parameters, with water and oil as the working fluids. Experiments were performed under conditions of Reynolds number varying from 6000 to 93,000 for water, and from 3200 to 19,000 for oil, respectively. The results show that the thermal performance of these tubes was superior compared to a smooth tube, but the heat transfer enhancements were not as large as the friction factor increases. Friction factors and heat transfer coefficient in these rough tubes were analyzed on the basis of momentum and heat transfer analogy, and the correlations obtained were compared with the present data and also the results of previous investigators. A mathematical model to evaluate the performance of spirally corrugated tube, which takes account of the large variation of fluid Prandtl number with temperature, was developed by the extension of previous work of Bergles and Webb. The results reported enable practical designs with standard products and optimization of tube geometry for specific conditions.

Two-Phase Critical Discharge of Initially Saturated or Subcooled Water Flowing in Sharp-Edged Tubes at High Pressure

The transient critical flow experiment with sharp-edged tubes as the break geometries is conducted in high pressure convective circulation test loop of Xi’an Jiaotong University. The initial steady operation pressure is up to 22.0MPa. An empirical correlation was made to obtain the critical mass flow rates, the critical pressure ratio and the thermal nonequilibrium number were correlated as the functions of the tube length to tube diameter ratioL/D. The predicted critical mass flow rate gets a higher accuracy for short tubes withL/D 12.The transient critical flow experiment with sharp-edged tubes as the break geometries is conducted in high pressure convective circulation test loop of Xi’an Jiaotong University. The initial steady operation pressure is up to 22.0MPa. An empirical correlation was made to obtain the critical mass flow rates, the critical pressure ratio and the thermal nonequilibrium number were correlated as the functions of the tube length to tube diameter ratioL/D. The predicted critical mass flow rate gets a higher accuracy for short tubes withL/D<12, the prediction accuracy is higher than that of Henry model prediction for long tubes withL/D>12.

An investigation into the heat transfer characteristics of spiral wall with internal rib in a supercritical sliding-pressure operation once-through boiler

Within the pressure range of 9–28 MPa, mass velocity range of 600–1 200 kg/(m2·s), and heat flux range of 200–500 kW/m2, experiments were performed to investigate the heat transfer to water in the inclned upward internally ribbed tube with an inclined angle of 19.5 degrees, a maximum outer diameter of 38.1 mm, and a thickness of 7.5 mm. Based on the experiments, it was found that heat transfer enhancement of the internally ribbed tube could postpone departure from nucleate boiling at the sub-critical pressure. However, the heat transfer enhancement decreased near the critical pressure. At supercritical pressure, the temperature difference between the wall and the fluid increased near the pseudo-critical temperature, but the increase of wall temperature was less than that of departure from nucleate boiling at sub-critical pressure. When pressure is closer to the critical pressure, the temperature difference between the wall and the fluid increased greatly near the pseudo-critical temperature. Heat transfer to supercritical water in the inclined upward internally ribbed tube was enhanced or deteriorated near the pseudo-critical temperature with the variety of ratio between the mass velocity and the heat flux. Because the rotational flow of the internal groove reduced the effect of natural convection, the internal wall temperature of internally ribbed tube uniformly distributed along the circumference. The maximum internal wall temperature difference of the tube along the circumference was only 10 degrees when the fluid enthalpy exceeded 2 000 J/g. Considering the effect of acute variety of the fluid property on heat transfer, the coreelation of heat transfer coefficient on the top of the internally ribbed tube was provided.

Simulation studies of runback based on power plant simulator

This paper describes the simulation studies of runback condition of power plant based on power plant simulator. Four items of runback, which are designed for a power plant are simulated and studied in detail. The results of the simulation studies will provide a useful operation guide to the plant operator and helpful improvement ideas to the designer of the control system.

Experimental Investigation of Transient Heat Transfer in the Once-Through Boiler Water Separator

The transient heat transfer between working fluid and inner wall of 600 MW supercritical pressure boiler’s water separator model during start-up was experimentally explored. The test conditions for water steam two-phase were as follows: pressure P=3–11 MPa, mass flow M=0.2–0.35 kg/s, and mass quality x=0.2–0.8; for subcooled water P=3–11 MPa, M=0.2–0.35 kg/s, and subcooled degree Δθ=10°C. By using an accurate and tractable inverse heat conduction solution, the correlations of single-phase and two-phase transient heat transfer coefficients were obtained. The experimental results demonstrated the heat transfer enhanced for subcooled water and water steam mixture compared with fully developed turbulent flow in tube. The increasing heat transfer effect may be attributed to the deformation or destruction of the boundary layer.

A Numerical Model Prediction for Boiling Multi Channel Flow Rate Distribution and Application in 600MW Supercritical Variable-Pressure Once-Through Boiler with Vertical Tube Coils

Flow rate distribution is important in a multi channel system when the flow is heated non-uniformly. This paper describes a steady state approach for obtaining the flow distribution among various tubes of complex multi channel system. Based on the present approach, a program has been developed, which is directly applied in thermal hydraulic design and investigation of 600MW supercritical variable-pressure once through boiler.