Tingkuan Chen

An investigation on heat transfer to supercritical water in inclined upward smooth tubes

Within the range of pressures from 23 to 30 MPa, mass velocities from 600 to 1200 kg/(m2s), and heat fluxes from 200 to 600 kW/m2, experiments have been performed for an investigation on heat transfer to supercritical water in inclined upward smooth tubes with an inner diameter of 26 mm and an inclined angle of 20° from the horizon. The results indicated that heat transfer characteristics of supercritical water are not uniform along the circumference of the inclined tube. An increase in the mass velocity of the working fluid can decrease and even eliminate the non-uniformity. Properties of supercritical fluid acutely vary with the temperature near the pseudocritical point. While the ratio of the mass velocity to the heat flux exceeded 2.16 kg/(kWs), heat transfer enhancement occurred near the pseudocritical point; conversely, heat transfer deterioration occurred while the ratio of the mass velocity to the heat flux was lower than 2.16 kg/(kWs). As the pressure increased far from the critical pressure, the amount of deterioration decreased. Correlations of heat transfer coefficients of the forced-convection heat transfer on the top and bottom of the tube have been provided, and can be used to predict heat transfer coefficient of spirally water wall in supercritical boilers.

Acoustic wave prediction in flowing steam-water two-phase mixture

The transient two-fluid model has been used to develop a general relation for acoustic waves. The analysis is valid in principle over the whole void fraction region. Flow pattern transitions from one flow regime to the other are assumed to occur at certain void fractions. Different correlations are used to calculate the interfacial area and interfacial drag force per unit mixture volume for bubbly flow, slug flow and annular flow respectively. The vapour-liquid interphase heat flux is derived from the one dimensional Fourier heat conduction equation to evaluate the interphase evaporation or condensation rate.

Influence of sleeve tube on the flow and heat transfer behavior at a T-junction

Abstract The flow structure of a sleeved jet into a main crossflow was experimentally investigated employing particle imaging velocimetry technology and numerically simulated using a CFD code. The jet-to-crossflow velocity ratio, VR, was ranged from 0.5 to 8. Three basic flow patterns were marked, namely attaching jet, lift-off jet and impinging jet as VR gradually increased. The flow in the main duct was characterized by a stream of discharge from the annular space at the rear part of the sleeve near the jet exit, which primarily came from the upstream crossflow. This annulus discharge isolated the leeward wall from the jet fluid and also caused weak local heat transfer in the large momentum deficiency region, and hence could supply an effective protection of the leeward wall from the thermal shock caused by a very cold jet injection.

A Nonlinear Solution of Inverse Heat Conduction Problem for Obtaining the Inner Heat Transfer Coefficient

When steam-water two-phase mixtures flow in inclined or horizontal tubes that are heated by alternating current, the circular angle-dependent temperatures on the outer radius imply that the inner heat transfer coefficients also vary with circular angle. The inner heat transfer coefficients are difficult to measure directly, but may be determined with the aid of inverse heat conduction theory. The direct model calculates the temperature field inside a half-pipe. This is subjected to a given heat transfer coefficient angular profile on its inner radius. The inverse heat conduction model calculates the temperature field under the conditions of the measured discrete temperatures and the heat-insulated boundary on the outer radius. Variation of the cylinder heat conductivity and specific resistance versus temperatures are considered in both models. The prediction accuracy is analyzed with a numerical test. The inverse heat conduction problem solution is verified as a useful tool for obtaining the inner heat tr...

Experimental Investigation of Two-Phase Flow Instabilities in Low-Mass-Flux Water Wall Tubes of Supercritical Circular Fluidized Bed Boilers

For the purpose of disclosing the hydrodynamic flow characteristics, under the low mass velocity conditions of the 600-MW supercritical circular fluidized beds boilers, experimental studies on instability of two-phase flow in parallel vertical internally ribbed tubes were conducted. Two kinds of oscillations, pressure-drop oscillation and density-wave oscillation, have been observed. In the range of test parameters the effects of pressure, mass flux, inlet subcooling, compressible volume, exit throttle, and asymmetric heat flux to the two-phase instability were explored and analyzed. Indications from experiment data are: To increase system pressure, mass flux and inlet subcooling will intensify the stability of water wall tubes. To increase exit throttle will intensify the instability of water wall tubes. The bounding pressure and bounding mass flux of density-wave oscillations and the bounding pressure of pressure-drop oscillation have been obtained. Based on the results of testing and using a homogeneous model, the threshold relational expressions of instability were obtained. The results may be used for the design and safe operation of parallel vertical rifled water wall tubes of supercritical circular fluidized beds boilers.

Investigation on the mechanism of abnormal heat transfer of supercritical pressure water in vertically‐upward tubes in the large specific heat region

The heat transfer characteristics of water at supercritical pressures in a vertically‐upward internally‐ribbed tube are investigated experimentally to investigate the mechanism of abnormal heat transfer of supercritical pressure water in the so‐called large specific heat region. One kind optimized internally‐ribbed tube is used in this study. The tube is made of SA‐213T12 steel with an outer diameter of 31.8 mm and a wall thickness of 6 mm and the mean inside diameter of the tube is measured to be 17.63 mm. According to experimental data, the characteristics and mechanisms of the heat transfer enhancement and also the heat transfer deterioration of supercritical pressure water in the large specific heat region are discussed respectively. The heat transfer enhancement of the supercritical pressure water in the large specific heat region is believed to be a result of combined effect caused by the rapid variations of thermophysical properties of the supercritical pressure water in the large specific heat reg...

Experimental studies on the enhanced flow boiling heat transfer and pressure drop of organic fluid with high saturation temperature in vertical porous coated tube

The characteristics of flow boiling heat transfer and pressure drop of organic fluid with high saturation temperature in a vertical porous coated tube are experimentally studied in this paper. The experiments are performed at evaporation pressure of 0.16-0.31MPa, mass flux of 390-790kg/m2s, and vapor quality of 0.06-0.58. The variations of heat transfer coefficient and pressure drop with vapor quality are measured and compared to the results of smooth tube. Boiling curves are generated at mass flux of 482 and 675kg/m2s. The experimental results indicate that the heat transfer coefficients of the porous tube are 1.8-3.5 times those of smooth tube, and that the frictional pressure drops of the porous tube are 1.1-2.9 times those of smooth tube. The correlations for heat transfer coefficient and frictional pressure drop are derived, in which the effect of fluid molecular weight is included. The experiments show that significant heat transfer enhancement is accompanied by a little pressure drop penalty, the a...

Study on the Minimum Drag Coefficient Phenomenon of Supercritical Pressure Water in the Pseudocritical Region

With the development of supercritical (and even ultra-supercritical) pressure boilers (SCBs) with high capacities, and at the same time, with the consideration of supercritical pressure water-cooled reactors (SCWRs) as one of the six most promising reactor concepts accepted in the Generation IV International Forum (GIF), flow and heat transfer of supercritical water becomes more and more important for both the design and operation safety of the related facilities. Thermo-hydraulic characteristics are among the issues, which are of special significance for the SCBs and SCWRs. It has been found that at supercritical pressures, the hydraulic resistance of water exhibits special characteristics in regions near its pseudo-critical point, which is hereafter called the minimum drag coefficient phenomenon. Experimental investigation was carried out in the present study to investigate further the characteristics of drag coefficient of supercritical pressure water under different conditions. The total pressure drop characteristic of water flowing in smooth tube and internally ribbed tube under the supercritical pressures was measured in experiments with a wide range of operational parameters, such as the system pressures ranging from 23 to 28 MPa, the average heat fluxes varied from 100 kW/m2 to 500kW/m2, and the mass fluxes of water in a range of 600 ∼ 1050 kg/m2s. The experimental data were compared with prediction results calculated by existing common correlations for single phase pressure drops, and large discrepancies were observed between the experimental data and the prediction results. Furthermore, the pressure drops characteristics of supercritical pressure water in cases with different tube arrangement and test conditions were compared with each other, such as that in horizontal tubes and vertical tubes, and that in isothermal flows and in non-isothermal flows. Additionally, this phenomenon observed in the present studies was also analyzed by using computational fluid dynamics technology, and the mechanism of pressure drop variation was reasonably explained. It was found that the deviation appeared between the previously proposed drag coefficient correlations and the present experimental data was mainly owning to ignoring the variation of an existence of the minimum drag coefficient in the pseudo critical region in previous studies, and based on the data obtained in this study, a new correlation for drag coefficient for supercritical pressure water was presented.Copyright

Study of the Effect of Buoyancy on Flow and Heat Transfer of Supercritical Pressure Water in Horizontal Pipes

The present paper is devoted to clarify the effect of buoyancy on the flow and heat transfer of supercritical pressure water flowing in horizontal pipes at supercritical pressures. A series of experiments have been designed and carried out in Xi’an Jiaotong University, Xi’an, China to obtain data in relation to flow and heat transfer of supercritical pressure water in pipes with different arrangements. The experimental parameters are as follows: pressures ranging from 23 to 28MPa, heat flux being up to 600 kW/m2 , and the fluid mass fluxes being in the range from 100 to 1000kg/(m2 s). In this study, distributions of the local wall temperatures and the local heat transfer coefficients around the circumference of the tube are measured at different cross-sections along the flowing direction. On the basis of the experimental data obtained in the study, some criteria available in open literatures, including Gr/Re2.7 , Gr/Re2 , and Grq/Grth, are employed to estimate the magnitude of buoyancy and the effect of buoyancy on the flow and heat transfer behavior of the supercritical fluid. It is showed that buoyancy is of particular importance for horizontal flows, but play significantly different role in different regions having different characteristics of the specific heat capacity. Strong buoyancy effect exists in the large specific heat region, but in the enthalpy region which is far away from the LSHR, the discrepancy between the temperature of the top wall and that of the bottom wall is small, indicating that the buoyancy effect can be negligible. Based on the present study, it was found that the criteria Grq/Grth is better than others in terms of the capability of evaluating the effect of the buoyancy on the flow and heat transfer of supercritical water.Copyright

Experimental investigation on the dynamic characteristics of molten droplets and high‐temperature particles falling in coolant

This paper presents the dynamic characteristics of molten droplets and hot particles at the very beginning of their falling into coolant pools, which are of importance to the subsequent interactions such as fragmentation of the droplets in coolants. The falling course of a single droplet or a single hot particle was recorded by a high‐speed camera and a curve of velocity vs. time was obtained. Emphasis was placed on the effects of the droplet’s size and temperature, the coolant’s temperature and properties, and the droplet’s physical properties on the moving behavior. Tests with hot particles were also performed for a comparison with the droplets. The results for the all cases showed that the velocity of a falling droplet/particle decreased rapidly but rebounded shortly, at the beginning of droplet/particle falling in the coolant. Following such a V‐shaped evolution in velocity, the droplet/particle slows down gradually till a comparatively steady velocity. An increase in either coolant temperature or dro...