Archive for October, 2011

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Velocity field measurements in critical nozzles using recovery temperature anemometry (RTA)

Monday, October 31st, 2011

Publication year: 2011
Source: Flow Measurement and Instrumentation, Available online 28 October 2011

Masahiro Ishibashi, Toshihiro Morioka

Recovery temperature anemometry (RTA) was used to investigate flow fields in critical flow nozzles without perturbing the flows. In RTA, the recovery temperature in the flow field is measured by using a very thin thermocouple wire, and the measured temperature is then converted into a flow velocity on the basis of the recovery factor. Because the sensitivity of the thermocouple wire is concentrated precisely at its contact point, the spatial resolution of RTA is extremely high, for example, 10–50 μm in the present measurements. Results measured by RTA using the square root of the Prandtl number as the recovery factor agreed well with one- and two-dimensional theoretical predictions. RTA was also shown to be capable of detecting the boundary layer generated on the throat wall of the nozzle. The results also revealed the presence of an interaction between a moving shock wave, the location of which depended on the pressure ratio, and an oblique shock system, the position of which was fixed by the geometry of the nozzle; this interaction is considered to be related to the premature unchoking phenomenon in which a critical nozzle fails to choke at high pressure ratios.

Highlights

► RTA (Recovery Temperature Anemometry) measures transonic flow velocity fields. ► RTA measures at resolution of 10–50 μm without disturbing the flow field. ► Measurements are verified quantitatively by 1D, 2D and boundary layer theories. ► Interactions of strong shock and oblique shock system are investigated in detail. ► Boundary layer generated on the throat wall of critical nozzle is detected.

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A mini fluidic oscillating flowmeter

Monday, October 31st, 2011

Publication year: 2011
Source: Flow Measurement and Instrumentation, Available online 20 October 2011

Matteo Martinelli, Vladimir Viktorov

This paper presents a mini fluidic oscillating flowmeter. This device is composed by three microfluidic laminar bistable amplifiers. The microfluidic amplifiers are connected in a way that, the measured flow through the mini fluidic oscillating flowmeter, generates a periodical pressure signal, with high value of SNR (signal to noise ratio). The frequency of the pressure signal is proportional to the measured flow. The mini fluidic oscillating flowmeter works with gas or liquid. To calibrate the mini fluidic oscillating flowmeter, for gas flows, a volumetric flowmeter was used. To calibrate it for liquid flows, an experimental test bench was realized. The gas operating range of the mini fluidic oscillating flowmeter is up to Re=1500 starting from Re=200; the liquid operating range is up to Re=5700 starting from Re=170. The maximum error of the measurement is <2% of the full scale value, the reading error is < 3% for gas flows and <3.8% for liquid flows.

Highlights

► This paper presents a mini fluidic oscillating flowmeter. ► the device is composed by 3 microfluidic amplifiers. ► The mini fluidic oscillating flowmeter works with gas or liquid. ► The frequency of the pressure signal is proportional to the measured flow ► To calibrate the device an experimental test bench was realized.

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Laboratory validation of ADCP techniques for suspended sediments investigation

Monday, October 31st, 2011

Publication year: 2011
Source: Flow Measurement and Instrumentation, Available online 19 October 2011

M. Guerrero, N. Rüther, R.N. Szupiany

The aim of this paper is to validate a method of investigating the grain size distribution of suspended sediments using acoustic Doppler current profilers (ADCP) and to compare different calibration strategies of ADCP backscattering power, which can be correlated with the concentration of corresponding sediments. Over the last two decades, the methods for suspended sediment investigation using backscattering power of ADCP have been gaining increasing acceptance within the river engineering community. This acceptance is due to acoustic backscattering providing the opportunity to indirectly quantify suspended sediment by non-intrusive measurements with high temporal and spatial resolution. We have already presented the method using 2 ADCPs working at different frequencies (600 and 1200 kHz) on the same water column to profile concentration and grain size in the Paranà River (Argentina). The present work, as a complement to the Paranà application, demonstrates the reliability of the method by a lab validation of monitored concentrations and known grain size distributions. The context of our research is introduced in a discussion of the topic of river sediment transport measurement using ADCP. Then, the underwater acoustic physics is briefly presented with a focus on acoustic backscattering (ABS) methods for the estimation of suspended sediment grain size. The laboratory tests, which were conducted at the sediment tower-mixing facility using four different known distributions of sand in a range of 50-700 μm, are described in detail to demonstrate the reliability of the ABS methods and to justify the adopted experimental strategies to overcome undesired air bubble interference with the ABS due to injected sand.

Highlights

► Multi-frequency Acoustical Backscattering (ABS) investigation. ► Laboratory validation of grain size distribution estimation by means of two ADCP. ► Validation of ABS-sediment concentration calibration using average values. ► Experimentation of grain size importance affecting ABS methods.

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Analytical solution for water surface profile along a side weir in a triangular channel

Monday, October 31st, 2011

Publication year: 2011
Source: Flow Measurement and Instrumentation, Available online 19 October 2011

Ali R. Vatankhah

Side weirs are widely used for water level control in irrigation and drainage systems. These structures are also used to divert excess water from a main channel into a side channel. Computation of water surface profile along the side weir is essential to determine the discharge over the side weir. Estimation of discharge over the side weirs is still an important issue. Most previous research works for the side weir were carried out in channels with rectangular, trapezoidal and circular cross sections. An analytical solution for water surface profile along a side weir is available in the technical literature only for the special case of rectangular channel on the basis of a constant specific energy assumption (De Marchi’s water surface profile). No analytical solution is available for the case of triangular channel. This research presents an elegant analytical solution for establishing the water surface profile along a side weir in a triangular channel. The solution, which yields a direct computation of the flow profile, should be a useful tool for evaluation and design of the side weirs in the triangular channels.

Highlights

► Analytical solution for water depth along a side weir in a triangular channel. ► Simple estimation of discharge over the side weir. ► Simple equation to design and evaluating of the side weir.

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Calibration of laminar flow meters for process gases

Monday, October 31st, 2011

Publication year: 2011
Source: Flow Measurement and Instrumentation, Available online 19 October 2011

John D. Wright, Thiago Cobu, Robert F. Berg, Michael R. Moldover

We calibrated three models of commercially-manufactured, laminar flow meters (LFMs) at four pressures (100 kPa, 200 kPa, 300 kPa, and 400 kPa) with five gases (N2, Ar, He, CO2, and SF6) over a 10:1 flow range using NIST’s primary flow standards as references. We combined three items: (1) the calibration data acquired with N2, (2) gas-property data from NIST’s database REFPROP 9.0, and (3) a physical model for each LFM that accounts for the effects of viscosity, entrance and exit effects, gas expansion, gas non-ideality, and slip. This combination predicted the calibrations for the flow of Ar, He, CO2, and SF6with a maximum error of 0.8 % for Reynolds numbers500. Under these conditions, the present LFM model allows prediction of calibration results for other gases with approximately 3 times more accuracy than conventional approaches that plot the flow coefficient as a function of the viscosity coefficient orRe. We represented the calibration data for SF6 in the range 5002000 by adding an empirical quadratic function to the model for one of the LFMs.

Highlights

► Calibrated 3 laminar flow meters designs at 4 pressures with 5 gases over a 10:1 flow range. ► Combined (1) N2calibration data, (2) REFPROP gas-property data, and (3) a physical model for each LFM. ► The LFM model accounts for viscosity, entrance and exit effects, gas expansion, gas non- ideality, and slip. ► The calibrated model predicted the flow of Ar, He, CO2and SF6with a maximum error of 0.8 % for Reynolds numbers. ► Flows for SF6in the rangefitted by adding a quadratic function to the model for one of the LFMs.

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Novel viscosity determination method: validation and application on fuel flow

Monday, October 31st, 2011

Publication year: 2011
Source: Flow Measurement and Instrumentation, Available online 19 October 2011

N. Gascoin, G. Fau, P. Gillard

The kinematic viscosity is a major physical property to be used in numerical, experimental and analytical work in all the related fields of fluid flow research. Its determination can be based on experiments with viscometer and on calculations for single or multi-species components, possibly through the use of mixture law and other intermediate parameters. Its experimental estimation for multi-species and/or supercritical hydrocarbon mixtures under high temperature and pressure remains quite absent. The novel approach proposed in this paper is based on fluid permeation through characterized porous media. The Darcian law or the Darcy-Forchheimer equation are used depending on the flow regime. First tests have been realized with pure gaseous nitrogen at ambient then hot temperature (1200 K) for several varying pressures (up to 60 bar). The accuracy of the methods can be as low as 5 % by comparison to National Institute of Standards and Technology data. The main source of uncertainty is found to be linked to the characteristics of sensors. The method has been applied to liquid dodecane (from 300 K to 700 K and up to 60 bar) with the same order of accuracy before testing it on supercritical n-dodecane (658 K to 700 K up to 60 bar) for which no validation data have been found. By comparisons with computations for multi-species mixture, even multi-phase, a reasonable agreement is found. The novel viscosity determination technique opens a new field of fluid characterization in extreme operating conditions.

Highlights

► An innovative technique is proposed to determine fluid kinematic viscosity. ► The kinematic viscosity is determined up to 1200 K and 60 bar on reactive process. ► Comparison between numerical simulation and experimental data is of good agreement. ► Validation of the novel method is achieved with inert flow (accuracy around 5%). ► Multiphase flow can be handled to determine average viscosity.

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An EM algorithm for dynamic estimation of interfacial boundary in stratified flow of immiscible liquids using EIT

Monday, October 31st, 2011

Publication year: 2011
Source: Flow Measurement and Instrumentation, Available online 13 October 2011

Anil Kumar Khambampati, Sin Kim, Kyung Youn Kim

Estimation of interfacial boundary between two immiscible liquids in two-phase flows through pipe line provides information about the flow characteristics and thus can aid in design and monitoring of the flow process. The interfacial boundary can be represented in several ways, one such method is the front point approach. Front points describe the location and the shape of the interfacial boundary separating the immiscible liquids. During the flow process, due to fluctuations the interfacial boundary and so the front points which describe the boundary changes with time. The time-varying interfacial boundary can be estimated using dynamic inverse algorithms based on Kalman filter. However, algorithms based on Kalman filter require complete knowledge of model parameters (initial states, state transition matrix, and noise covariance matrices) for implementation. In processes involving complex flow pattern such as two-phase flows, it is difficult to represent the model parameters in a prior form. This uncertainty in model parameters causes suboptimal performance of the Kalman type filters. In this paper, we employ expectation maximization algorithm (EM) to estimate model parameters along with the interfacial boundary using electrical impedance tomography (EIT). The estimation of model parameters reduces the modeling uncertainty and thus results in improving the tracking of interfacial boundary. Numerical and experimental studies are performed to validate the performance of the proposed method.

Highlights

► EM based estimation to track boundary of immiscible liquids is presented. ► Interfacial boundary is represented using front points. ► EM algorithm is used to estimate the front point’s location and model parameters. ► EM reduces the modeling uncertainty and thus improves estimation performance. ► Numerical and experimental studies are done to validate the proposed method.

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Egg-shaped cross section: Uniform flow direct solution and stability identification

Monday, October 31st, 2011

Publication year: 2011
Source: Flow Measurement and Instrumentation, Available online 2 October 2011

M. Bijankhan, S. Kouchakzadeh

The complexity of egg-shaped cross section makes developing a straightforward formula to calculate the normal depth a challenging task. In this paper, the inadequacy of the power regression based model employed so far for estimating the normal depth in these conduits was presented based on the relative hydraulic sensitivity of structures. A set of precise iterative formulas for normal depth solution were developed which facilitate the calculation of the normal depth especially using spreadsheets. Also, Accurate and direct equations to determine the uniform flow depth in an egg-shaped cross section were obtained by using an alternative regression based model developed according to the concept of the relative hydraulic sensitivity. The maximum relative error associated with the proposed equations compared to the precise iterative formulas results is less than 1%. In addition, to design a sewer system especially in relatively steep urban areas direct formulas were developed to distinguish between sub- and supercritical flow regimes and to categorize the uniform flow stability condition in such channels.

Highlights

► Sensitivity analysis is used to show the drawback of current direct solutions. ► An exponential regression model is developed to estimate the normal depth directly. ► Direct formulas were presented to classify the uniform flow regime and stability.

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Discharge characteristics of small sonic nozzles in the shape of pyramidal convergent and conical divergent

Monday, October 31st, 2011

Publication year: 2011
Source: Flow Measurement and Instrumentation, Available online 29 September 2011

Chih-Chung Hu, Win-Ti Lin, Chun-Min Su, Wen-Jay Liu

This study combined KOH anisotropic etching with laser machining to fabricate small sonic nozzles in the shape of a pyramidal convergent inlet followed by a conical diffuser with a divergent angle of 5°. The diffuser was made into three different lengths. The throat diameters were around. Experiments were performed to obtain discharge coefficients and critical back pressure ratios in Reynolds numbers ranging fromto. The critical back pressure ratio for one of the nozzle types examined reached 0.486 at. Numerical simulations were also performed to obtain the flow fields at an upstream pressure of 203 kPa. The simulation results revealed that besides flow separation, the first set of oblique shocks appeared in the nozzle jet could also lead to tremendous pressure loss. The weaker the oblique shocks, the higher the critical back pressure ratio would be obtained.

Highlights

► Small sonic nozzles with pyramidal convergent and conical diffuser were studied. ► For small sonic nozzles, a proper diffuser can improve theCBPR. ► The simulation results showed that the longer the diffuser length, the smaller theCdvalue was. ► The first set of oblique shocks in the nozzle jet could lead to tremendous pressure loss.

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Experimental and theoretical investigation of thermoacoustic oscillations in natural gas metering stations

Monday, October 31st, 2011

Publication year: 2011
Source: Flow Measurement and Instrumentation, Available online 29 September 2011

A. Brümmer, R. Edlerherr, J. Lenz

In natural gas flow metering and pressure regulation stations flowmeters, heat exchangers and control valves are usually connected in series. Especially in case of two and more measuring bars sometimes at minor flow rates untypical pipe vibration together with flow metering faults are observed. Based on field investigations the dependencies between the pipe vibration level, the gas pulsation inside the pipe and the operating conditions of the heat exchanger are analysed. It turns out that with increasing heat flow rates into the natural gas the pulsation and hence the metering faults as well as the pipe vibrations are amplified.In order to understand the physical dependencies of this phenomenon besides experiment a theoretical study is performed. The origin of the vibration turns out to be a thermoacoustic instability. According to the Rayleigh–Criterion gas pulsations are amplified, if heat will be given to the gas in the moment of greatest condensation. Based on detailed theoretical investigations by means of the method of characteristics using a Rijke tube model the physical dependencies are analysed. Finally potential solutions to avoid this vibration problem at natural gas metering stations are introduced.

Highlights

► Thermoacoustic instability leads to pipe vibrations and metering faults. ► The Rijke tube is simulated using the 1D-Method of characteristics. ► Physical dependencies of thermoacoustic instabilities are analysed. ► Remedial actions to avoid thermoacoustic instabilities are outlined.

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