Constant Temperature Anemometer Research Articles

Influence of Inner Secondary Air Vane Angle on Combustion Characteristics and NOx Emissions of a Down-Fired Pulverized-Coal 300 MWe Utility Boiler

Using an IFA300 constant temperature anemometer system, cold air experiments on a quarter-scaled burner model sited in a 300 MWe down-fired boiler were conducted to investigate the influence of various inner secondary air vane angles on the flow characteristics in the burner nozzle region. By increasing vane angles, no central recirculation zone appeared, the axial velocity decay rate increased, radial velocities increased at the jet boundary, and tangential velocities clearly increased in the inner secondary air zone. Industrial experiments were also performed on a down-fired pulverized-coal 300 MWe utility boiler with swirl burners. Gas temperature, concentrations of gas components (O2, CO, and NOx) in the burning region, and carbon content in the fly ash were measured with inner secondary air vane angles of 42°, 47°, 53°, and 60°. By increasing vane angles up to 53°, NOx emission and boiler efficiency increased; when vane angles were increased to 60°, NOx emission increased, but boiler efficiency decreased.

Wave Packet Excitation and its Development in Supersonic Boundary Layer

A method of exciting of artificial disturbances localized in space and time (wave packets) in a supersonic boundary layer is developed. Experimental investigations are carried out in the low noise supersonic wind tunnel T-325 at Mach M = 2. A model of a flat steel plate with a sharp leading edge is used. Measurements of mean flow and fluctuations are performed by using a constant temperature anemometer. To generate controlled fluctuations the short time surface glow discharge is used. Measurements of controlled disturbances are synchronized in time with glow discharge ignition. To increase the signal-to-noise ratio the time trace averaging technique is applied. Electrical power and polarity of the glow discharge initiation are changed to see their influence on the initial wave packet amplitude. Optimal glow discharge parameters for generation of artificial disturbances are found. The experimental data on the localized disturbances evolution in boundary layer are received. It is obtained that the velocity of the wave packet propagation has speed close to the free stream for the leading wave edge. The trailing edge of the wave packet spreads with subsonic speed relatively the supersonic flow. The wave packet propagates in both the streamwise and spanwise directions. Half-angle of this spreading is approximately equal to 10 degrees relative to the free stream direction. It has been found, that the wave packet is developed inside the boundary layer near of the artificial pulsations source. However the evolution of controlled disturbances leads to their radiation into free flow

Influence of turbulence kinetic energy on bubble size in different scale flotation cells

Although the impact of hydrodynamic conditions in a flotation cell is often evaluated by correlating impeller tip speed with bubble size, the literature reports inconsistent results, some showing a reduction in bubble Sauter mean diameter (d32) with increasing impeller speed, others showing little to no effect. A review of these results indicate that cell size may be a factor where small laboratory-scale cells, smaller than 50L, tend to support the correlation while larger machines do not. This paper demonstrates an alternative approach using the average turbulent kinetic energy (TKE) in place of the impeller speed. Results were obtained using two cells with the same geometry but different size, 5L and 60L. Bubble size (d32) was measured using the Anglo Platinum Bubble Sizer. Local velocity and velocity fluctuation were measured using a constant temperature anemometer to estimate the average turbulent kinetic energy (TKE). The effect of impeller tip speed on d32 and TKE as a function of air rate was determined. Combining the results for the two cells showed that d32 initially decreased with increasing TKE to become constant above a critical TKE. The TKE region below critical was associated largely with the 5L cell and the region above critical more associated with the 60L cell. The inconsistent data in the literature has been explained by introducing the concept of the critical TKE and it has been confirmed that the reported effect of increasing impeller speed may have its origin in the size of the cells tested: laboratory scale cells showing an effect on reducing bubble size as TKE is below critical while large and industrial scale cells may not as TKE is above critical.

Effect of Declination Angle of Vent Air on Flow Characteristics of a Scale Model of a Down-Fired Utility Boiler with Swirl Burners

AbstractW-shaped furnaces equipped with swirl burners suffered from high carbon content in fly ash and high NOx emission. Using an IFA 300 constant-temperature anemometer system, cold air experiments on a scale model of a 300-MW of electrical output down-fired pulverized-coal utility boiler with swirl burners were performed to investigate the effect of the declination angle of vent air on flow characteristics of the furnace. When the angle of vent air was 28°, 35°, and 40°, the flow field in the furnace has good symmetry, which was beneficial to the stable combustion of the flame. As the angle of vent air increased, the mixing of downward airflow and vent air was delayed. At a vent-air angle of 45°, the flow field in the furnace was deflected. The deflected flow field would result in a flame short circuit, the local high temperature, an increase in the carbon content in fly ash, and a reduction of boiler efficiency. The angle of vent air had little effect on the mixing of downward airflow and staged air. ...

Rotary slanted single wire CTA – a useful tool for 3D flows investigations

The procedure is described of experimental investigation of a statistically stationary generally nonisothermal 3D flow by means of a constant temperature anemometer (CTA) using single slanted heated wire, rotary round the fixed axis. The principle of this procedure is quite clear. The change of the heated wire temperature modifies ratio of CTA sensitivities to temperature and velocity fluctuations. Turning the heated wire through a proper angle changes the sensitivity to components of the instantaneous velocity vector. Some recommendations are presented based on long time experiences, e.g. on the choice of probe, on the probe calibration, to the measurement organization and to the evaluation of results.

S054024 5角形ダクトから流出する噴流([S054-02]噴流、後流およびはく離流れ現象の探求と技術革新(2))

The purpose of this work is to control the diffusion and the direction of the jet flow issuing from the pentagonal duct. In this study, the velocity measurements of the jet flow issuing from the pentagonal duct with and without the synthetic jet were carried out using hot wire sensors and the constant temperature anemometer. In order to grasp the flow feature the flow visualization was also performed by the LIF method. And decays of the maximum velocity and the jet half value widths were investigated by analyzing the velocity distributions. As a result, it has been found that the jet width with synthetic jet becomes large, comparing with that of the jet without one. Moreover it has been also clarified that the jet is induced by the synthetic jet.

S054013 コアンダ効果を利用した非接触吸着デバイスの流れの可視化([S054-01]噴流、後流およびはく離流れ現象の探求と技術革新(1))

This paper describes the experimental study of the characteristics of a non-contact type suction device using Coanda effect. The present study has been carried out for flow analysis around a non-contact suction device. The main aim was to obtain the useful data for CFD analysis by suitable visualization. TiO_2 particle shows the difference of the flow pattern around the non-contact suction device with work and without work well. It is found that the range of the flow velocity is too wide to fix the suitable photography condition. Constant Temperature Anemometer (CTA) is also applied to measure the flow velocity. The strong turbulence of air flow is observed around the non-contact suction device.

Measuring Aerodynamic Characteristics Using High Performance Low Speed Wind Tunnel at Universiti Teknologi Malaysia

This paper describes the capability and activities on utilizing a low speed wind tunnel facility at Universiti Teknologi Malaysia (UTM -LST) since its first operation in year 2001 till 2012. The laboratory is setup to meet the educational, research and industrial needs of Malaysia’s developing aero industry. The wind tunnel has high flow quality and can deliver speed up to 288 km/hr. UTM-LST has experiences on a wide range of testing such as aircraft, automotive, civil structure and building, ship and offshore structure. The wind tunnel is primarily equipped with flow visualization facility including Particle Image Velocimetry (PIV), pressure measurement, force measurements and Constant Temperature Anemometer (CTA). Most of the primary aerodynamic parameters can be measured in this facility such as measurement of aerodynamic lift and drag, static stability and control derivatives of aircraft. Measurement of automotive drag, down force and crosswind stability, and measurement of wind loads on civil structures. Correlation between wind tunnel measurements and numerical simulation using Computational Fluid Dynamics (CFD) are becoming more demanding especially related to unsteady aerodynamics. Currently, research related to unsteady aerodynamics such as helicopter rotor wakes, automotive wake turbulence and oscillating aerofoil are more demanding and requires upgrading to the current facility.

Active control of flow around a square prism by slot jet injection

The main aim of the experimental study is to determine both the most effective injection surface and rate in order to ensure minimum drag and fluctuating forces on a square prism subjected to crossflow. All predetermined jet injection surfaces i.e. front, side, and rear, tested separately for injection ratios of IR = 0, 1, 1.5, 2 at Reynolds number of Re = 16,000. Surface pressures were measured by differential pressure transducer whereas instantaneous velocity measurements were performed by using multichannel Constant Temperature Anemometer (CTA). It was concluded that jet injection, especially from the rear surface, brought noticeable improvements to the flow characteristics of a square prism. For rear jet configuration with IR = 1.5, the mean drag coefficient () was reduced to 79.4% and CP RMS level on side surfaces was reduced to 20% of that of the single square prism. In addition, instantaneous flow visualization photographs and Strouhal number (St ) distribution across the injection ratio were also presented to identify the flow patterns and underlying mechanism of drag and fluctuating force reduction of square prism with rear jet configuration.

An Adaptive Response Compensation Technique for the Constant-Current Hot-Wire Anemometer

An adaptive response compensation technique has been proposed to compensate for the response lag of the constant-current hot-wire anemometer (CCA) by taking advantage of digital signal processing technology. First, we have developed a simple response compensation scheme based on a precise theoretical expression for the frequency response of the CCA (Kaifuku et al. 2010, 2011), and verified its effectiveness experimentally for hot-wires of 5 μm, 10 μm and 20 μm in diameter. Then, another novel technique based on a two-sensor probe technique—originally developed for the response compensation of fine-wire thermocouples (Tagawa and Ohta 1997; Tagawa et al. 1998)—has been proposed for estimating thermal time-constants of hot-wires to realize the in-situ response compensation of the CCA. To demonstrate the usefulness of the CCA, we have applied the response compensation schemes to multipoint velocity measure- ment of a turbulent wake flow formed behind a circular cylinder by using a CCA probe consisting of 16 hot-wires, which were driven simultaneously by a very simple constant-current circuit. As a result, the proposed response compensation techniques for the CCA work quite successfully and are capable of improving the response speed of the CCA to obtain reliable measurements comparable to those by the commercially-available constant-temperature hot-wire anemometer (CTA).

Preliminary experimental investigation of boundary layer in decelerating flow

Investigations of characteristics of turbulence inside boundary layer under decelerating flow were studied by means of constant temperature anemometer. The decelerating flow was simulated in the closed circuit wind tunnel 0.9 m × 0.5 m at IT AS CR. The free stream turbulence was either natural or risen up by square mesh plane grid. The details of experimental settings and measurement procedures of the instantaneous longitudinal velocity component are described and the distributions of intensity, skewness and kurtosis of turbulent fluctuations are discussed in the contribution.

A New Approach about Heat Transfer of Hot-Wire Anemometer

The hot-wire anemometer is a famous thermal transducer for turbulence measurements. The fundamental principle of hot-wire anemometer is based on the convective heat transfer, since the heat transfer is directly proportional to the temperature difference between the sensor and the fluid, hence ambient temperature variations are one of the most important error sources in the measurements with the hot-wire anemometers. Many methods have been proposed to compensate for the ambient temperature variations. In such methods the effect of temperature drift is only considered and the effect of Nusselt number is ignored. In the present research the effect of air flow temperature variations on the response of constant temperature anemometer has been studied experimentally. Furthermore, with the basis of air flow velocity and ambient temperature variations, the percentage errors in velocity measurements have been estimated. Finally, based on achieved results, an accurate method has been proposed to compensate the air flow temperature variations.

An analysis of flow and heat transfer in separated flows over blocked surface

The flow and heat transfer characteristics of flat and blocked surfaces were experimentally examined under the influence of the free stream velocity of 3, 5, 10 and 15 m/s encompassing laminar, transitional and turbulent flows. A constant-temperature hot wire anemometer was used for the velocity and turbulent intensity measurements, and copper-constant thermocouples and a micro-manometer for temperature and static pressures measurements, respectively. The flow over blocked surface separated in front of the first block and attached on it, then circulated between blocks, and then reattached behind the last block. The results showed that the flow separation before the first block occurred earlier in laminar–laminar separated–reattached flow than the transitional and turbulent flows and turbulent–turbulent separated–reattached flow leading to a shorter reattachment region with high free-stream turbulence. The presence of the separation and reattachment caused the heat transfer enhancement, which was more pronounced in the laminar flow and new empirical equations were developed for the local Stanton numbers.

Research on the elliptic aerodynamic field in a 1000 MW dual circle tangential firing single furnace ultra supercritical boiler

An IFA300 constant temperature anemometer system is adopted to perform cold air experiments on a scale model of a dual circle tangential firing single furnace ultra supercritical boiler to investigate the causes and influencing factors of jet deviation in the furnace, which is the main cause of the elliptical aerodynamic field. The elliptic aerodynamic field could cause heat imbalance in the burner zone, in which case high temperature corrosion and slagging might happen on the high-temperature furnace wall. Theoretical derivations and analysis have been carried out before any experimental studies, and an equation determining the influencing factors of the jet deviation has been established. The experimental results agree well with the equation. The jet deviation becomes more problematic when the velocity ratio of the impacting jet and the impacted jet increases from 0.85 to 1.30. A reduction in the distance from the impacting position to the root of the impacted jet also increases the jet deviation as well as the angle between the impacting jet and impacted jet. The results of the theoretical analysis and experiments provide some transformations within the boiler that could be adopted to avoid the formation of the oblique ellipse flow field.

Streambank shear stress estimates using turbulent kinetic energy

In tidal environments, the boundary shear stress (BSS) is directly proportional to the turbulent kinetic energy, with a reported proportionality coefficient of 0.19. This coefficient was calculated using velocity time series to determine Reynolds stresses and, ultimately, to estimate the BSS. The coefficient has not been evaluated using direct measurements of BSS or for environments other than tidal systems. This laboratory flume study examines the validity of this relationship for a sloping streambank with and without vegetation. BSSs and near-bank Reynolds stresses were calculated using a constant temperature anemometer and velocity measurements, respectively. The coefficient ranged from 0.11 to 0.53 when calculated with the measured values of BSS, and 0.09 to 0.37 when calculated with Reynolds stresses. The variation was attributed to differences in turbulence generation, coefficient development, and instrumentation.

Effects of Nonuniform Reactant Stoichiometry on Thermoacoustic Instability in a Lean-Premixed Gas Turbine Combustor

Detailed experimental investigations of the amplitude dependence of flame describing functions (FDF) were performed using a stratified swirl-stabilized combustor, in order to understand the combustion–acoustic interactions of CH4/air flames propagating into nonhomogeneous reactant stoichiometry. Phase-synchronized OH planar laser induced fluorescence (OH PLIF) measurements were used to investigate local reaction zone structures of forced flames. To determine the amplitude- and frequency-dependent forced flame response, simultaneous measurements of inlet velocity and heat release rate oscillations were made using a constant temperature anemometer and photomultiplier tubes with narrow-band OH*/CH* interference filters. The measurements were made over a wide range of stratification ratios, including inner stream enrichment (ϕ i > ϕ o ) and outer stream enrichment (ϕ o > ϕ i ) conditions, and compared to the baseline condition of spatially and temporally homogeneous cases (ϕ i = ϕ o ). Results show that for the inlet conditions investigated, fuel stratification has a significant influence on local and global flame structures of unforced and forced flames. Under stratified conditions, length scales of local contours were found to be much larger than the homogeneous case due to high kinematic viscosities associated with high temperature. Stratification has a remarkable effect on flame–vortex interactions when the flame is subjected to high-amplitude acoustic forcing, leading to different evolution patterns of FDF (amplitude and disturbance convective time) in response to the amplitude of the imposed inlet velocity oscillation. The present experimental investigation reveals that intentional stratification has the potential to eliminate or suppress the occurrence of detrimental combustion instability problems in lean-premixed gas turbine combustion systems.

An experimental investigation of flow and heat transfer characteristics over blocked surfaces in laminar and turbulent flows

Flow and heat transfer measurements were obtained over a blocked surface mounted on a low speed wind tunnel in order to investigate the combined the effects of free stream velocities and the different size of rectangular blocks on the flow and heat transfer characteristics. Mean velocity and turbulence intensities were measured by a constant temperature anemometer and wall temperatures by copper-constant thermocouple and static pressures by a micro-manometer, respectively. It was found that the flow separations and reattachments were occurred before the first blocks, on the first blocks, between blocks and after the last blocks. The blocked surface area and flow separation caused not only heat transfer enhancement but higher turbulence levels as well. The average Stanton numbers, for block heights of 10, 15 and 20mm, were higher than those of flat surface by 82%, 95%, 113% in laminar and 27%, 38%, 50% in turbulent, respectively. These results showed that heat transfer enhancement on the blocked surface increased with block heights and become more pronounced in laminar than that of turbulent flows.

Development of the Wave Packets-Forerunners at the Straight Wing Boundary Layer

This work is devoted to the study of wave packets (forerunners) formed in straight wing boundary layers in the regions preceding a drastic change in the flow velocity inside the boundary layer, near the fronts of streaks. The investigations were carried out in the subsonic low turbulence wind tunnel. Measurements of the flow fields were carried out using a single-wire probe of a constant-temperature hot-wire anemometer. It was shown that the localized structures, which modeled artificially from incoming flow, generate streaks in a boundary layer. The wave packets (forerunners) are appears in the regions preceding a drastic change of flow velocity inside the boundary layer at the streaks fronts. The characteristics of the forerunners, affected by the external-flow pressure gradient, intensity of streak, and local velocity gradients near the front of the streak were investigated

Extrapolation of calibration curve of hot-wire spirometer using a novel neural network based approach

Hot-wire spirometer is a kind of constant temperature anemometer (CTA). The working principle of CTA, used for the measurement of fluid velocity and flow turbulence, is based on convective heat transfer from a hot-wire sensor to a fluid being measured. The calibration curve of a CTA is nonlinear and cannot be easily extrapolated beyond its calibration range. Therefore, a method for extrapolation of CTA calibration curve will be of great practical application. In this paper, a novel approach based on the conventional neural network and self-organizing map (SOM) method has been proposed to extrapolate CTA calibration curve for measurement of velocity in the range 0.7-30 m/seconds. Results show that, using this approach for the extrapolation of the CTA calibration curve beyond its upper limit, the standard deviation is about -0.5%, which is acceptable in most cases. Moreover, this approach for the extrapolation of the CTA calibration curve below its lower limit produces standard deviation of about 4.5%, which is acceptable in spirometry applications. Finally, the standard deviation on the whole measurement range (0.7-30 m/s) is about 1.5%.

Response Compensation of Constant-Current Hot-Wire Anemometry Based on a Theoretical Solution of Response Characteristics

Hot-wire anemometry (HWA) is used for measuring velocity fluctuations such as turbulent flows. It is generally operated in the following three modes; constant-temperature (CT), constant-current (CC) and constant-voltage (CV) ones. The constant-temperature anemometer (CTA) has long been the mainstream of normal turbulent flow measurement, while the others are rarely used in the measurement because of their insufficient response speed. However, since the constantcurrent anemometer (CCA) can be composed of simple circuits, the HWA will be realized at quite a low cost. In this study, the response characteristics of the CCA were theoretically analyzed, and a sophisticated compensation scheme based on the analysis has been proposed. The scheme is experimentally tested in a turbulent wake flow formed behind a cylinder. As a result, it has been confirmed that the root-mean-square (rms) velocities and the power-spectrum distributions compensated by the present scheme agree well with those measured with the CTA. Hence, the CCA provides reliable measurement of turbulent velocity fluctuations.