Hydraulic Resistance of Subcritical and Supercritical Water Flowing in a Rifled Tube

Large capacity supercritical boiler is at the leading edge of efficiency boost for thermal power plant. Water wall design is a key issue for a supercritical boiler. To ensure successful design and safe operation of water wall, studying hydraulic resistance of water is significant. Considerable work on frictional pressure drop of gas-liquid two-phase flow in tubes has been done and various correlations have been proposed to predict it. However, these correlations are restricted to particular rib geometries and flow conditions. Because of significant variations in thermo physical properties near the critical and pseudo-critical points, pressure drop at supercritical pressures is different from that at subcritical pressures. However, limited studies have been devoted to estimate hydraulic resistance of supercritical water. More work need be conducted to develop prediction method for pressure drop at supercritical pressures. Therefore, to accumulate fundamental experimental data for the design of a supercritical boiler, an experiment on hydraulic resistance of water was performed in a vertical upward rifled tube. The experiment was carried out in the high-temperature and high-pressure steam-water test loop at Xi’an Jiaotong University. Based on the experimental data, the two-phase frictional multiplier was calculated to analyze the two-phase frictional pressure drop. At low to moderate vapor quality, the two-phase frictional multiplier increases rapidly and reaches a peak. When the vapor quality exceeds a certain value, the two-phase frictional multiplier starts to decrease with increasing vapor quality. It is because the tube wall is covered by liquid film at low to moderate vapor quality. Within the high vapor quality region, the high-speed vapor tears the liquid film and the flow pattern turns to mist flow with lower frictional pressure drop. Increasing pressure decreases the two-phase frictional multiplier and when the pressure approaches the critical pressure, the multiplier is close to 1. The effect of mass flux on the multiplier is so weak that it can be neglected. At supercritical pressures, the pressure drops due to frictional resistance and flow acceleration both increase with bulk fluid enthalpy. Increasing pressure decreases the frictional pressure drop. This result is mainly attributed to pressure approaching the critical point. Frictional pressure drop is significantly affected by fluid property variations; in particular, severe density decreases with increasing bulk fluid enthalpy. Acceleration pressure drop increases with decreasing pressure and increasing heat flux. When heat flux increases, the density difference between the inlet and the outlet increases with the same mass flux, which results in a considerable acceleration pressure drop. Decreasing pressure results in a similar acceleration pressure drop variation because of the same reason. The frictional resistance coefficient was calculated to analyze the supercritical frictional pressure drop. In the large specific heat region, the frictional resistance coefficient peaks at a certain enthalpy in the vicinity of the pseudo-critical point, and increasing mass flux reduces the magnitude of the peak value.

Numerical Investigation on Resistance Reducing Effect by Mass Injection through Porous Wall

A numerical study of flow in two-dimensional turbulent boundary layer flow with mass injection through a porous wall is conducted by Reynolds averaged numerical simulation (RANS) in this paper. Numerical results with available experimental data show that Wilcox (2006) k-w turbulence model can give good prediction in this complex flow. The comparison between mass injection and no mass injection for the local frictional resistance coefficient are performed. Numerical investigation indicates that mass injection may reduce the resistance significantly, which is confirmed by comparison of velocity profiles qualitatively.

Experimental Study on Frictional Resistance Characteristics of CO2-Emulsified Viscoelastic Surfactant Fracturing Fluid

Rheological properties and friction resistance properties of CO2-emulsified viscoelastic surfactant fracturing fluid were investigated on the large-scale test loop of foam fracturing fluid. When the velocity is below 2.8 m·s-1, the friction pressure drop gradient gradually decreases with the increase of foam quality, however, when the velocity is above 2.8 m·s-1, the friction pressure drop gradient of VES-CO2with higher foam quality is higher than lower foam quality. In addition, frictional pressure drop gradient of the pure CO2is higher than the VES-CO2fracturing fluid system when the velocity is more than 1.6 m·s-1. And frictional resistance coefficient decreases with the increase of foam quality and increases slightly with the increase of temperature. Experimental correlation between frictional resistance coefficient and Reynolds number is obtained and has high precision.

Statistical Analysis for Ventilation Resistance Characteristics of Bolting and Shotcrete Roadway in Nanyangpo Coal Mine

The statistical analysis for frictional resistance of bolting and shotcrete roadway is carried out by using the software of SPSS and statistical principle and combining the coal mine ventilation theory with the actual situation in Nanyangpo coal mine. The results show that the frictional resistance coefficient does not follow normal distribution and the 95% confidence interval is 0.0063~0.0087 N.s2/m4 for frictional resistance coefficient of bolting and shotcrete roadway. The comparison analysis of hectometer friction ventilation resistence is carried out between the statistical results with the actual measurement data in Nanyangpo Coal Mine, and its correlation is highly significant. It verifies that the statistical results is right. It has important application value for increasing the ventilation management level and ensuring the safety production of coal mining enterprises.

DETERMINATION OF HEAD LOSSES IN PIPE-LINES LOSSES DURING HYDRAULIC CALCULATIONS FOR RINGED WATER NET

This paper provides the results of theoretical and experimental researches of head losses in industrial pipelines, which have technical coarseness. In the Nikuradzes researches values for frictional resistance coefficient were determined for artificial even-grained sandy roughness. The pipe-lines, which are used for water-supply in practice, have natural technical coarseness. The coarseness has different structure: it can have corrugated or saw-tooth surfaces and there can be also protective coat.The comparative analysis is provided for different methods of hydraulic losses calculations for head losses in pipe-lines for ringed water net. Recommendations for usage are also presented.

CFD Analysis of Turbulent Flow in Typical Rod Bundles in Rolling Motion

The influence mechanism of rolling motion on the flowing and heat transfer characteristics of turbulent flow in typical four rod bundles is investigated with FLUENT code. The flowing and heat transfer characteristics of turbulent flow in rod bundles can be affected by rolling motion. But the flowing similarity of turbulent flow in adiabatic and non-adiabatic can not be affected. If the rolling amplitude is big or if the rolling period is small, the radial additional force can make the parameter profiles and the turbulent flowing and heat transfer change greatly. And the frictional resistance coefficient and heat transfer coefficient can not be solved by the correlations in steady state. In rolling motion, as the pitch to diameter ratio decrease, especially if it is less than 1.1, the flowing and heat transfer of turbulent flow in rolling motion change significantly.

The Flowing and Heat Transfer Models of Turbulent Flow in Rolling Motion

The flowing and heat transfer characteristics of turbulent flow in tubes in rolling motion are investigated theoretically. The flowing and heat transfer models of turbulent flow in rolling motion are established. The correlations of frictional resistance coefficient and Nusselt number are derived. The results are also validated with experiments. The effects of several parameters on Nusselt number are investigated. The oscillating amplitude of Nusselt number is in direct ratio with Prandtl number and rolling frequency approximately. The more the flowing velocity is, the less the effect of rolling motion on the flow is. The variation of initial phase difference between Nusselt number and rolling motion with rolling frequency is very limited.

Frictional Resistance of Antifouling Coating Systems

An experimental study has been made to compare the frictional resistance of several ship hull coatings in the unfouled, fouled, and cleaned conditions. Hydrodynamic tests were completed in a towing tank using a flat plate test fixture towed at a Reynolds number ReL range of 2.8×106-5.5×106 based on the plate length and towing velocity. The results indicate little difference in frictional resistance coefficient CF among the coatings in the unfouled condition. Significant differences were observed after 287 days of marine exposure, with the silicone antifouling coatings showing the largest increases in CF. While several of the surfaces returned to near their unfouled resistance after cleaning, coating damage led to significant increases in CF for other coatings. The roughness function ΔU+ for the unfouled coatings showed reasonable collapse to a Colebrook-type roughness function when the centerline average height k=0.17Ra was used as the roughness length scale. Excellent collapse of the roughness function for the barnacle fouled surfaces was obtained using a new roughness length scale based on the barnacle height and percent coverage.