Deyou Liu

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...

Development of knowledge base of fault diagnosis system in solar power tower plants

Solar Power Tower (SPT) plant is a hugeous and complicated system, thus there have not been relative research productions on the record in the aspect of developing the knowledge base of its Fault Diagnosis System (FDS) in the whole world yet. In this paper, a modular and hierarchical knowledge base of FDS is designed and developed to use in SPT plants according to the characteristics of structure and operation of SPT plants. This knowledge base consists of Main Control Module, Concentrator Subsystem, Receiver Subsystem, Heat Storage Subsystem, Generating Subsystem and Assistant Subsystem. Each subsystem module contains a sub-control module and some secondary subsystem modules. In the knowledge base, knowledge is divided into metaknowledge, facts and rules. Moreover, rules are separated into meta rules, goal rules and diagnosis rules. Production rule representation is adopted to express the knowledge. Uncertainty of knowledge is described in this paper additionally. According to the application of the knowledge base in SPT plant, it is validated that the knowledge base developed in this paper has the characteristics of simple structure and high inference efficiency, which are favorable to simplify the design and development of inference engine.

Investigation and analysis on the combined operation of solar thermal power and conventional thermal power

The main constitution and the performance characteristic of Solar Thermal Power System (STPS) were introduced, and the thermal losses law of the recycled working substance of the conventional thermal power generation unit was analyzed in this paper. The key technical choke points currently existing in high-temperature solar thermal power system were demonstrated in the aspect of technical feasibility and economical efficiency. And then, the combined operation scheme of solar thermal power and conventional thermal power was introduced in this paper. In this hybrid system, the normal and low temperature water vapor can be obtained by solar power and utilized efficiently, in additional, those technical choke points existing in high-temperature solar thermal power can be avoided. With higher comprehensive efficiency and obvious technical and economic performance, the combined operation of solar thermal power and conventional thermal power can be the most important alternative scheme in the reformation progress of the energy conservation and environment protection in conventional thermal power plants, and the most significant way to utilize solar power efficiently.

The energy-saving benefit and economic evaluation analysis of cooling tower with flue gas injection

The cooling tower is a significant device of the circular cooling water system in thermal power plants, whose cooling performance will directly affect the operation stability of steam-turbine unit and the efficiency of cold-end system. As the construction and development of thermal power plants, especially nuclear power plants and solar power plants, the requirement for the construction cost of cooling tower and its performance is increasing. In recent years, the cooling tower with flue gas injection has attracted wide concerns for its advantage of low costs. However, the study on the energy-saving benefit and economic evaluation analysis of large cooling tower lags behind the demand of actual engineering design and construction. Based on the analysis of the energy-saving benefit and economic evaluation models of the conventional cooling tower and the discussion of their defects, a multi-objective optimization mathematical model for energy-saving benefit and economic evaluation analysis suitable for natural draft cooling tower with flue gas injection was built, and is proved to be practical by means of calculation and analysis of engineering project as the example. The results indicate that cooling tower with flue gas injection is not only economic but also has the distinct energy-saving benefit, and is worthy of promoting.

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]

Analysis of the volumetric phenomenon in porous beds subject to irradiation

ABSTRACT This work examines the volumetric effect of convection within a packed bed in the presence of collimated irradiation. Using a modified P-1 approximation incorporating a local thermal nonequilibrium (LTNE) model, the energy transportation through convection and thermal conduction, and collimated and diffuse radiative transfer are investigated. The impact of pertinent parameters such as porosity φ, pore diameter dp, and optical thickness τ on the volumetric effect are analyzed. In addition, the mechanisms of how the volumetric effect impacts LTNE and radiative heat loss are revealed. The effect of the volumetric heat transfer coefficient hv, the fluid flow velocity u, and the ratio of solid to fluid thermal conductivities ζ versus the volumetric effect are systematically analyzed and displayed through a number of contour maps to assess the efficiency η. Our analysis shows that enhancing the volumetric effect and extending the thickness of the porous medium improves the efficiency η.

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.

Development and research on fault diagnosis system of solar power tower plants

According to the system configuration and operating characteristic of a constructing Solar Power Tower (SPT) plant in China in this paper, the Fault Diagnosis System (FDS) was researched and developed. Furthermore, evaluation system of fault grade was established by the method of fuzzy comprehensive evaluation. In this FDS, the fault diagnosis structure was designed to adopt the expert system for priority and the Radial Basis Function (RBF) neural network for assistant. The monitoring index of diagnosis object was built in expert system to set the fault symptom threshold and represent the fault symptom in quantification with the comprehensive methods of expert knowledge, fuzzy mathematics, and low probability identification and so on. The model of neural networks is established based on the structure of RBF multi-neural subnets. According to the analysis and verification results of a fault case, the structure design is reasonable and diagnosis methods are feasible in this FDS. Moreover, the fault could be accurately diagnosed and the evaluation of the fault grade could be made reliably with the great practical value.