Ling Zhou

Investigation of Hydraulic Transients of Two Entrapped Air Pockets in a Water Pipeline

AbstractTransient pressure associated with a rapidly filling pipeline containing two entrapped air pockets is investigated experimentally and numerically. A multiple-air-pocket elastic-water model considering multiple moving boundaries of water columns is developed by neglecting inertia and head loss of a short water column near air–water interfaces. The proposed model is validated by experimental data. Results show that when two air pockets in length are much different, the maximum pressure always arises in the smaller air pocket regardless of the blocking column’s length. The case of the upstream air pocket with a similar length to the downstream is the most complicated and dangerous because (1)xa0the maximum pressure may alternately arise in two air pockets as the blocking column increases, and (2)xa0interaction of two air pockets could cause a huge pressure surge, which is likely much higher than with only one air pocket. The existing single-air-pocket model cannot effectively simulate pressure surge of t...

Phenomenon of White Mist in Pipelines Rapidly Filling with Water with Entrapped Air Pockets

The phenomenon of white mist in a rapidly filling pipeline containing an entrapped air pocket is numerically and experimentally investigated. The air-water flow patterns, pressure, and temperature histories are synchronously recorded to illustrate their interrelations. The white mist phenomenon is particularly observed during fast transients, especially during the first compression of the air pocket. Comparisons between calculations and experiments indicate that the white mist primarily reflects a condensation process. More specifically, the air temperature increases because of rapid compression of an entrapped air pocket, and the high temperature could cause water to adhere to vapor at the pipe surface. For fast transients, the first compression causes a near-adiabatic air compression, but heat exchange effects become more significant in the subsequent compression and expansion cycles. As the initial air length decreases, the maximum pressure first increases and then declines, with the most dangerous air length occurring when about 3.4% is initially occupied by air. The ratio of the maximum pressure to the driving pressure increases approximately linearly with respect to the upstream pressure. A local-interpolation elastic-water model is developed by considering air-temperature change and its validity is confirmed by comparing the model and experimental results.

CFD Approach for Column Separation in Water Pipelines

AbstractLiquid column separation (LCS) in pressurized pipelines may occur if a water hammer event drops the local pressure to the liquid’s vapor point. Numerical simulations of LCS have traditionally been based on one-dimensional (1D) transient flow theory; here, a two-dimensional (2D) computational fluid dynamics (CFD) model is used to investigate the complicated nature of LCS and to help characterize the limitations of the traditional 1D models. To this end, the Schnerr–Sauer cavitation model with a shear-stress transport (SST) k−ω turbulence model is employed, whereas the Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations are solved for the mixture of liquid and vapor. 2D model results are compared to both experimental data and to those of the 1D discrete vapor-cavity model (DVCM), thus demonstrating that the 2D method effectively simulates the pressure variations while helping to visualize the associated physical processes. More specifically, the 2D simulations vividly reveal the growth and th...

Temporal-Spatial Distribution and Risk Assessment of Estrogenic Compounds in the Rivers around the Northern Taihu Lake

Investigate Five Estrogenic compounds (E1, E2, E3, EE2, and BPA) in the rivers around the northern Taihu Lake to realize their distributions in different regions. The results show the median concentrations of four estrogenic compounds range from 1.96 to 143.29ng/L, with the detection proportions ranging from 12.5% to 100%, respectively. The concentrations of estrogenic compounds in waters reveal regular changes with seasons, higher contents in winter. Besides, considerable variations spatially are observed in the different rivers. Levels of estrogenic compounds in rivers of Yixing City are higher than those of Suzhou City and Wuxi City. Using the calculation of risk quotient (RQ) assessed the risk. The RQ values of E1, E2, E3 and BPA are 0.02~1.87, 1.28~23.22, 0.01~0.80 and 0.03~0.44 respectively, which indicate that harmful ecological effects might happen in some rivers.

THE DYNAMIC BEHAVIOR OF ONCE-THROUGH DSG SOLAR TROUGH COLLECTOR ROW UNDER MOVING SHADOW CONDITIONS

Compared with recirculation and injection modes, once-through direct steam generation (DSG) parabolic troughs are simpler to construct and require the lowest investment. However, the heat transfer fluid (HTF) in once-through DSG parabolic trough systems has the most complicated dynamic behavior, particularly during periods of moving shadows caused by small clouds and jet contrails. In this paper, a nonlinear distributed parameter dynamic model (NDPDM) is proposed to model the dynamic behavior of once-through DSG parabolic trough solar collector row under moving shadow conditions. Compared with state-of-the-art models, the proposed NDPDM possesses three characteristics: (a) adopting real-time local values of the heat transfer and friction resistance coefficients, (b) simulating the whole collector row, including the boiler and the superheated sections, and (c) modeling the disturbance of direct normal irradiance (DNI) level on DSG parabolic trough solar collector row under moving shadow conditions. Validated using experimental data, the NDPDM accurately predicts the dynamic characteristics of HTF during periods of partial and moving DNI disturbance. The fundamental and specific dynamic process of fluid parameters for a DSG parabolic trough solar collector row is provided in this paper. The results show the following: (a) Moving shadows have a significant impact on the outlet temperature and mass flow rate, and the impact lasts up to 1000 s even after the shadows completely leave the collector row. (b) The time for outlet steam temperature to reach a steady-state value for the first time is independent of the shadow width, speed, and moving direction. (c) High-frequency chattering of the outlet mass flow rate can be observed under moving DNI disturbance and will have a longer duration if the shadow width is larger or the shadow speed is slower. Compared with cases in which the whole system is shaded, partially shading cases have shown a longer duration of high-frequency chattering. (d) Both wider widths and slower speeds of shadow will cause a larger amplitude of responses in the outlet temperature and mass flow rate. When the shadow speed is low, there is a longer delay time of response in the mass flow rate of the outlet fluid. (e) The amplitude of response in the outlet temperature does not depend on the direction of clouds movement. However, if the DNI disturbance starts at the inlet of the collector row, there will be significant delay times in both outlet temperature and mass flow rate, and a larger amplitude of response in outlet mass flow rate. [DOI: 10.1115/1.4036331]

Conceptual analogy for modelling entrapped air action in hydraulic systems By Sandra C. Martins, Helena M. Ramos, and António B. Almeida

The presence of entrapped air pockets in water pipelines during rapid filling frequently causes abnormal transient pressures which are capable of inducing accidents and causing serious damage (Wylie, Streeter, & Suo, 1993; Zhou, 2000). The combination of fast transients in systems with entrapped air is of practical importance but also of great theoretical complexity for those undertaking pipeline design and operation. This topic has recently captured the attention of various researchers (e.g. Lee, 2005; Zhou & Liu, 2013; Zhou, Liu, & Karney, 2013; Zhou, Liu, Karney, & Zhang, 2011). In this context, the Authors’ contribution is welcome. The paper under discussion presents an interesting numerical model for simulating the dynamic behaviour of an isolated entrapped air pocket in a confined pipe system, and specifically uses the conceptual analogy of a “spring-damper” mechanical system. Key system parameters, including the polytropic exponent and the model’s damping coefficient, are extracted from an analysis of experimental data. The Discussers wish to elaborate on some of the details of the presented approach.

Rapid air expulsion through an orifice in a vertical water pipe

ABSTRACT Transient flow caused by air expulsion is investigated. Earlier experimental studies involved the horizontal or horizontal–vertical pipe cases, or the vertical pipe case with relatively less test range. This paper focuses on the vertical pipe case with much broader ranges of orifice size and air length to more completely characterize the transient response. Observations show air release undergoes two distinct stages: stage 1 with pressurization, expansion and release of air pocket; stage 2 with an impacting water hammer pressure when water reaches the pipe end. Two types of pressure oscillation patterns are found, depending on orifice size. When orifice sizes are small, air cushioning effect prevents high water hammer pressures from being generated. As orifice size increases, the water hammer pressure is dominant. As initial air length increases, the maximum pressure firstly increases and then decreases. An elastic-water model could well reproduce the measured air pressure oscillations and impact pressure.

Investigation on the Mode of Investment Management and Value Compensation in Pumped Storage Power Plant

This paper briefly introduces the development of constructing Pumped Storage Power Plant(‘PSP’ for short) and discusses the income form of PSP’s gained subject as well as the existing problems. Meanwhile, the modes of investment management and value compensation and the corresponding differences are also analysed. According to the principle of ‘responsibility for individuals and revenue sharing’, the related mathematical model is developed in this paper, and the ‘quota system’ mode of investment management and value compensation in China is also proposed. The mode is beneficial to the reform of investment and construction system, and can provide fresh energy to the development of construction of PSP in China.

Study on the wind speed frequency distribution with AR-GARCH model

The main existing mathematical models that describe wind speed frequency distribution were introduced in this paper, and the characteristics and limitations of each model were analyzed. Then, based on the considerations of the actual wind speed frequency distribution features, AR-GARCH model was adopted here in order to fully reflect the randomicity and wave character of the wind speed varied with time, which can effectively avoid large fitting errors in low-speed and zero-speed zone existing in current-used models, especially for those distribution curves with multiple peaks, and has the most strong universal applicability. Finally, the validity and correctness of the simulation method using AR-GARCH model were verified by the calculation and analysis of three typical engineering projects.