Non-critical Flow Research Articles

An Efficient Pro-Active Fault-Tolerance Scheduling of IEEE 802.1Qbv Time-Sensitive Network

Time-sensitive network (TSN) has emerged as one of the enhancement Ethernet technologies of real-time applications for future industrial networks. However, the data of TSN messages may be unexpectedly changed within the transmission duration due to electromagnetic interference. A cyclic redundancy check (CRC) can detect such errors and notify the sender node to retransmit the erroneous message through automatic repeat request (ARQ). The time when the error occurs is uncertain. Consequently, the time when performing the retransmission requests is also random, which results in different transmission sequences and violates the deterministic transmission of TSN. In addition, the returned CRC detection messages also might be at fault during transmission. In order to provide the fault tolerance capability of critical flows in TSN without violating the nature of deterministic transmission, this article proposes a pro-active fault-tolerant TSN scheduling algorithm (PFT-TSN), which not only transmits a certain number of instance copies for critical flows but provides network transmission services for noncritical flows. The challenge is that schedulability and safety of critical flows are tradeoffs in terms of the number of transmissions per instance of critical flows and the schedulability. Moreover, the transmission service of noncritical flows can also affect the schedulability of critical flows. We conduct comprehensive experiments with synthetic networks to show that the proposed method can meet both safety and schedulability requirements for critical flows, and noncritical flows are also allowed to be transmitted by the service degradation.

ADS-IRWST transient evaluation model for AP1000 SBLOCA analysis

The AP1000 nuclear power plant safety system is characterized by its unique passive Emergency Core Cooling System (ECCS), including Core Makeup Tanks (CMTs), Automatic Depressurization System (ADS), and In-containment Refueling Water Tank (IRWST), to mitigate SBLOCA accident. The most challenging period of AP1000 SBLOCA transient is the transition from CMT injection to IRWST injection after the actuation of the fourth stage ADS (ADS4). This paper is to report a transient evaluation model for AP1000 SBLOCA analysis during CMT to IRWST transition. The model simulates ADS4, CMT injection, IRWST injection, reactor core mixture level and upper plenum entrainment to hotlegs. Both critical and non-critical flow models are used to calculate mass flow loss through ADS1-4 vents. The most important feature of this model is that it constantly traces core/upper plenum two-phase mixture level, which demonstrates cooling capability of ECCS during the transient. A baseline case is analyzed to study the ADS-IRWST transient using AP1000 prototypic information. In addition, a sensitivity analysis is performed to further study the robustness of AP1000 ECCS during SBLOCA transient.

Performance Enhancement of High-Availability Seamless Redundancy (HSR) Networks Using OpenFlow

The High-availability Seamless Redundancy (HSR) protocol guarantees zero recovery time in case of failure in ethernet networks. However, the management of HSR networks is static and inflexible. This, added to the bandwidth reduction due to data duplication, makes it difficult to efficiently control the network resources. An integration of HSR and OpenFlow technologies is proposed to provide redundancy control and traffic prioritization. As a result, a node can distinguish between critical and noncritical flows, protecting them according to their needs. The effectiveness of the priority-aware network is assessed in terms of throughput efficiency.

Numerical simulation and validation of HFC-134a fluid flow through short-tube orifices considering metastable conditions

One-dimensional numerical modelling of the fluid-flow behaviour inside short-tube orifices (expansion devices) has been carried out. Governing equations (continuity, momentum, energy, and entropy) for describing the fluid flow have been solved by using a fully implicit step-by-step method. A numerical treatment has been codified for considering thermodynamic and flow transitions (subcooled liquid region, metastable liquid region, metastable two-phase region and equilibrium two-phase region). Sudden contraction and enlargement at inlet and outlet sections were also considered. Fluid-flow variables (e.g., enthalpies, temperatures, pressures, mass fractions, and heat fluxes) and thermophysical and transport properties of fluid were numerically evaluated at each grid point in a discretized domain. The physical model used for solving the fluid-flow problem enabled an analysis of geometry, fluid type, critical and non-critical flow conditions, metastable regions, and transient effects to be performed. A comparison and validation analyses of the simulation results were carried out by using a wide range of mass flow rate experimental data (No = 634), which have been reported in the literature for the refrigerant 134a. Using a comprehensive statistical analysis, based on weighted linear regressions with an outlier detection/rejection algorithm at 95% of confidence level, the prediction performance of the numerical model was evaluated. Linear relationships between mass flow rate (predicted) and experimental mass flow rate data were statistically demonstrated. A global statistical evaluation of deviation errors between mass flow rate experimental data and predicted simulation results was also calculated. Average deviation error of ±8.9% was consistently computed between numerical model and experimental data, which demonstrates the good capability of the model developed for predicting the fluid-flow processes.

NUMERICAL AND EXPERIMENTAL INVESTIGATION OF THE FLOW CHARACTERISTICS OF R134a FLOWING THROUGH ADIABATIC HELICAL CAPILLARY TUBES

This paper presents numerical and experimental results of the flow characteristics of R134a flowing through adiabatic helical capillary tubes. The local pressure distribution along the length of the capillary tubes is measured at inlet pressures ranging from 10 to 14 bar, mass flow rates from 8 to 20 kg h-1, and degrees of subcooling from 0.5°C to 15°C. The theoretical model is based on conservation of mass, energy and the momentum of the fluids in the capillary tube. The model is divided into three regions: subcooled liquid region, metastable liquid region and equilibrium two-phase region and can be applied for various tube geometries, new alternative refrigerants and critical or noncritical flow conditions. The model is validated by comparing results from the present experimental data with that of the available literature. Based on the comparison results, the model used in the present study provides reasonable agreement with the experimental data.

Seamless internet 3G and opportunistic WLAN vehicular connectivity

Most of the cellular network operators are nowadays striving to solve the problem caused by the increasing demand of mobile data users. In the near future, vehicles will be equipped not only with cellular connectivity, but also with dedicated short-range wireless devices, used to connect via single or multiple hops to fixed road side units attached to the infrastructure network to gain Internet access. Taking this hybrid-connectivity scenario, we propose S eamless I nternet 3G and Opportunistic WL AN V ehicular I nternet Co nnectivity (SILVIO), a solution for providing Internet connectivity in multi-hop vehicular ad hoc networks. Vehicles use the cellular network to assure always-on connectivity, while they opportunistically select to offload some non-critical flows to the multi-hop wireless local area network (WLAN). The advantages of this approach are twofold: the users can benefit from a higher bandwidth, while the operators can alleviate their overloaded cellular networks. SILVIO makes use of existing standard mobility mechanisms integrated, enhanced and extended to provide a seamless connectivity experience without introducing much complexity nor signalling overhead. One of the main contributions of this article is the proposal and analysis of different handover strategies between 3G and multi-hop WLAN networks for the vehicular scenario. A trace-driven simulator was developed to evaluate the performance improvements provided by SILVIO. Real traffic traces from the city of Madrid were used to feed the simulator which considers large vehicles as obstacles, as well. The obtained results show that using SILVIO the cellular network can be offloaded by a factor up to 80%.

Numerical simulation of non-adiabatic capillary tubes considering metastable region. Part II: Experimental validation

A detailed one-dimensional steady and transient numerical simulation of the thermal and fluid-dynamic behavior of capillary tube–suction line heat exchangers considering metastable region and separated flow has been developed in Part I of this paper. The developed numerical model allows analysis of aspects such as geometry, type of fluid, critical or non-critical flow conditions and metastable region. The accuracy of the detailed simulation model is demonstrated in this part (Part II) of the paper by comparing simulation results with a wide range of steady state experimental data from the technical literature, which include the refrigerant mass flow rate, outlet suction line temperature, and temperature profile along concentric and lateral capillary tube–suction line heat exchangers. Of the 196 data points evaluated for mass flow rate 96.4% are within an error of ±15%, 81.1% are within ±10% with a mean deviation of ±6.3%. Of the 143 data points evaluated for outlet suction line temperature 89.5% are within an error of ±2 °C, with a mean deviation of ±0.98 °C. The numerical results obtained are used to understand the refrigerant flow behavior inside non-adiabatic capillary tubes. Some divergence problems in the numerical solution process is found to be the discontinuity in non-adiabatic capillary tube flow characteristics caused by re-condensation of the refrigerant within the heat exchanger zone; this aspect needs special attention while modeling the non-adiabatic capillary tube flow. Other important parameter to be evaluated experimentally with special care is the capillary tube internal diameter due to its strong influence on the refrigerant flow results (results of any study based on the nominal diameter are to be used with caution).

Numerical simulation of non-adiabatic capillary tubes considering metastable region. Part I: Mathematical formulation and numerical model

A detailed one-dimensional steady and transient numerical simulation of the thermal and fluid-dynamic behavior of capillary tube–suction line heat exchangers has been carried out. The governing equations (continuity, momentum, energy and entropy) for fluid flows, together with the energy equation in solids, are solved iteratively in a segregated manner. The discretized governing equations in the zones with fluid flow are coupled using a fully implicit step-by-step method. An implicit central difference numerical scheme and a line-by-line solver were used in solids. A special treatment has been implemented in order to consider transitions (subcooled liquid region, metastable liquid region, metastable two-phase region and equilibrium two-phase region). All the flow variables (enthalpies, temperatures, pressures, mass fractions, heat fluxes, etc.) together with the thermophysical and transport properties are evaluated at each point of the grid in which the domain is discretized. The numerical model allows analysis of aspects such as geometry, type of fluid, critical or non-critical flow conditions, metastable regions and transient cases. Comparison of the numerical simulation with experimental data presented in the technical literature will be shown in Part II of the present paper.

Numerical simulation and experimental validation of coiled adiabatic capillary tubes

The objective of this study is to extend and validate the model developed and presented in previous works [O. García-Valladares, C.D. Pérez-Segarra, A. Oliva, Numerical simulation of capillary tube expansion devices behaviour with pure and mixed refrigerants considering metastable region. Part I: mathematical formulation and numerical model, Applied Thermal Engineering 22 (2) (2002) 173–182; O. García-Valladares, C.D. Pérez-Segarra, A. Oliva, Numerical simulation of capillary tube expansion devices behaviour with pure and mixed refrigerants considering metastable region. Part II: experimental validation and parametric studies, Applied Thermal Engineering 22 (4) (2002) 379–391] to coiled adiabatic capillary tube expansion devices working with pure and mixed refrigerants. The discretized governing equations are coupled using an implicit step by step method. A special treatment has been implemented in order to consider transitions (subcooled liquid region, metastable liquid region, metastable two-phase region and equilibrium two-phase region). All the flow variables (enthalpies, temperatures, pressures, vapor qualities, velocities, heat fluxes, etc.) together with the thermophysical properties are evaluated at each point of the grid in which the domain is discretized. The numerical model allows analysis of aspects such as geometry, type of fluid (pure substances and mixtures), critical or non-critical flow conditions, metastable regions, and transient aspects. Comparison of the numerical simulation with a wide range of experimental data presented in the technical literature will be shown in the present article in order to validate the model developed.

Numerical simulation of trans-critical carbon dioxide (R744) flow through short tube orifices

A detailed one-dimensional numerical simulation of the fluid-dynamic behaviour of short tube orifices expansion devices working with trans-critical carbon dioxide (CO 2 or R744) has been developed. The discretized governing equations are coupled using an implicit step by step method. A special treatment has been implemented in order to consider transitions (subcooled liquid region and equilibrium two-phase region). The numerical model allows analysis of aspects such as geometry, different working conditions, critical or non-critical flow conditions, etc. Comparison of the numerical simulation with experimental data presented in the technical literature will be shown in the present article.

The Effect of the Angular and Radial Distributions of Trajectories on the Structure of Axisymmetric Electron and Ion Beams with Compensated Charge in a Longitudinal Magnetic Field

The structure of beams with compensated charge is described using a multiflow collisionless model in which the current is split into N interacting tubes of current. The effect of the boundary angular distribution of the tubes of current, as well as of the boundary radial distribution of current, on the configuration of electron and ion beams is studied. It is demonstrated that a crisis of flow arises in the absence of an external magnetic field at a certain value of current. An external longitudinal magnetic field expands the region of noncritical flow and promotes the laminarity of flow. The boundaries of the critical mode are determined for different angular and radial distributions, and the trajectories of the tubes of current in the subcritical and supercritical regions are calculated.

Numerical simulation of capillary tube expansion devices behaviour with pure and mixed refrigerants considering metastable region. Part I: mathematical formulation and numerical model

A detailed one-dimensional steady and transient numerical simulation of the thermal and fluid-dynamic behaviour of capillary tube expansion devices working with pure and mixed refrigerants has been developed. The discretised governing equations are coupled using an implicit step by step method. A special treatment has been implemented in order to consider transitions (subcooled liquid region, metastable liquid region, metastable two-phase region and equilibrium two-phase region). All the flow variables (enthalpy, temperatures, pressures, vapour quality, velocities, heat fluxes, etc.) together with the thermophysical properties are evaluated at each point of the grid in which the domain is discretised. The numerical model allows analysis of aspects such as geometry, type of fluid (pure substances and mixtures), critical or non-critical flow conditions, metastable regions, adiabatic or non-adiabatic capillary tubes and transient aspects. Comparison of the numerical simulation with experimental data presented in the technical literature will be shown in part II of the present article.

Numerical simulation of capillary-tube expansion devices

A numerical method has been developed to simulate the thermal and fluid-dynamic behaviour of capillary-tube expansion devices. The governing equations of the flow (continuity, momentum and energy), written in one-dimensional and transient form over finite control volumes, have been solved using an implicit step-by-step numerical technique. This formulation requires the use of additional equations for the evaluation of convective heat transfer, shear stress and void fraction. A special treatment of the point of transition between single-phase and two-phase fluid flow has been implemented together with a Newton-Raphson algorithm for the evaluation of the inlet mass flow rate corresponding to the given boundary conditions. The numerical model allows analysis of aspects such as geometry, type of fluid, critical and non-critical flow conditions, boundary conditions (heat transfer, inlet and discharge pressures etc.) and transient aspects. Good agreement between numerical and experimental data from three different authors (Bolstand and Jordan, Whitesel, Mikol) has been obtained. Some illustrative results are presented to indicate the main characteristics of the numerical model.

Compressibility Effect in Two-Phase Flow and Its Application to Flow Metering With Orifice Plate and Convergent-Divergent Nozzle

The effect of solution gas on the two-phase flow behavior through an orifice plate and a convergent-divergent nozzle has been investigated with regard to the flow metering of compressible two-phase mixtures. A proper thermodynamics approach to consider more accurately the compressibility effect in an accelerated two-phase flow, in particular that through an orifice and Laval’s nozzle in the presence of the solution gas, has been developed. From this approach an equation of state of mixture was derived and used in determining the orifice equation. An analysis of flow behavior has been performed and several illustrative plots were presented in order to evaluate the gas solubility effect in the flow metering with an orifice plate or a convergent-divergent nozzle. A delimitation between critical and noncritical flow has been established in terms of measured parameters and a relationship between the critical pressure and gas-liquid mass ratio was also shown.

Determining Multiphase Pressure Drops and Flow Capacities in Down-Hole Safety Valves

A new relationship describing dynamic multiphase orifice pressure drops and fluid flow capacities has been derived and tested with field data. The mathematical model relates dynamic orifice behavior in both critical and noncritical flow regions. Correlations are presented for predicting the ultimate (critical) capacity of an presented for predicting the ultimate (critical) capacity of an orifice for any given set of dynamic conditions. Introduction A new relationship describing dynamic, multiphase orifice pressure drops and fluid flow capacities has been derived and tested with actual field data. The mathematical model relates dynamic orifice behavior in both critical and noncritical flow regimes. Orifice pressure drops and capacities are related to pertinent fluid properties and choke dimensions. Graphical pertinent fluid properties and choke dimensions. Graphical correlations are also presented to predict the ultimate (critical) capacity of an orifice for any given set of dynamic conditions. To verify the model, a field test was designed and carried out in a flowing oil well. Both orifice pressure drops and fluid flow rates were measured in the well and the information was compared with analogous data predicted by the model. Comparable information was then predicted by the model. Comparable information was then used to compute an "orifice discharge coefficient" that enables calculation of actual orifice capacities from theoretical ones. The discharge coefficients are presented for 14/64-, 16/64- and 20/64-in. orifice diameters. The collected data reflect the behavior of an Otis Engineering Corp. J-type 22J037 safety valve. However, the model may be used to estimate multiphase pressure drops through restrictive beans in safety valves of other internal geometrical configurations. Discussion The increased need for more accurate settings on downhole, self-contained, flowing safety devices (storm chokes) has prompted efforts by many oil-producing companies to develop new multiphase orifice flow relationships. Interest in antipollution devices, especially in offshore oil-producing areas, has also encouraged the major oil companies to re-evaluate old, established procedures for the design of oil- and gas-well safety procedures for the design of oil- and gas-well safety valves. A review of the existing orifice flow literature and analysis of standard safety-valve design procedures yielded the following facts concerning noncritical multiphase orifice flow.Most orifice flow models do not adequately reflect the compressible nature of actual oilwell multiphase orifice flow. Consequently, models now in use do not adequately describe the dynamic behavior of orifice flow.The existing orifice flow relationships become less exact as the dynamic conditions approach the critical value; that is, at a given upstream pressure, no further flow-rate increase occurs through the orifice, regardless of the pressure drop across the orifice. Those who are involved in manufacturing down-hole, pressure-drop-operated safety valves are aware of the pressure-drop-operated safety valves are aware of the problems associated with accurate prediction of orifice problems associated with accurate prediction of orifice flow behavior. Most agree that a more rigorous mathematical model is needed to describe the mechanics of orifice flow under all oilfield conditions. The orifice relationships used by design engineers, though acceptable under certain flow conditions, are questionable for applications falling outside these specifications. A more rigorous procedure applicable to oilfield JPT P. 1145

The interaction of large amplitude shallow-water waves with an ambient shear flow: non-critical flows

This paper describes the behaviour of large amplitude, long gravity waves as they move over a horizontal bed into a region where the flow is steady but sheared in a vertical direction. A new class of exact solutions to the nonlinear hydraulic flow equations is derived. These solutions describe progressing waves and are sufficiently general to allow both the shape of the free surface at any instant and the shear profile of the undisturbed flow to be specified. The waves are examples of neutrally stable disturbances in the sense that they neither grow nor decay in amplitude, although, like simple waves on an unsheared flow, they can break.