Exhaust Duct Research Articles

Experimental Study on Air Leakage between Smoke Exhaust Opening and Duct

Experimental Study on Air Leakage between Smoke Exhaust Opening and Duct

Experimental Research on the Smoke Control System in a Complex Road Tunnel Fire

Abstract Twelve full scale experiments are carried out to research the effectiveness of smoke control system designs in a complex road tunnel in the event of a fire. The segment of the tunnel used for the experimental program is equipped with mechanical exhaust ducts and mechanical air supply ducts along the tunnel. In the experiment program, two sizes of fires are included, having heat release rates of 1.5 and 3.8 MW. A variety of smoke control strategies are included in the program in order to compare smoke movement behavior and the relative effectiveness of the smoke control strategies. The experiments demonstrated that the spread of the smoke can be contained effectively within two zones with an adjusted transverse smoke control system.

Similarity criteria of target thermal radiation characteristics and their application to infrared radiation of jet engine exhaust system

In this study, the similarity criteria for thermal radiation characteristics of the target, such as gas flow, heat transfer, mass transfer and thermal radiation coupling effect, were considered. Only in the case where the criteria are based on the similarity of geometry, gas flow, heat transfer and component transportation, can the similarity of thermal radiation be possible. Similarity criteria of different physical mechanisms were obtained by adopting a dimensionless analysis of their governing equations. Every similarity criterion features the impact of each physical mechanism on thermal radiation of target. Thermal radiation similarity theory was applied to a single duct exhaust system and after theoretical analysis, the dominant similarity criteria were selected, while the others were neglected. It was pronounced that there are only three dominant similarity criteria for single duct exhaust system: a) the nozzle pressure ratio, b) the total temperature of the inlet and c) the optical depth. Three cases were simulated numerically using k-ε turbulent viscosity model and backward Monte-Carlo method for the verification of the above conclusion. The boundary conditions and characteristic lengths of the three cases were different but the dominant similarity criteria were respectively the same. Therefore, the results coincided adequately with each other, conclusion that corresponds to the predictions of the theory.

Lean methane flame stability in a premixed generic swirl burner: Isothermal flow and atmospheric combustion characterization

Gas turbine combustors operating in lean premixed mode are known to be susceptible to flame blowoff due to competing influences of increasing chemical timescales and decreasing flow time scales under these conditions. In this study, combustion stability and the onset of flame blowoff in particular, are characterized in a new swirl burner operated with fully premixed methane (CH4) and air at thermal power of 55 kW, atmospheric combustor inlet pressure, and ambient (∼290 K) combustor inlet temperature. The onset of flame blowoff was shown repeatedly to exhibit high amplitude, low frequency combustion instabilities as a result of periodic flame extinction and reignition events. In addition to detailed isothermal characterization of the burner velocity field using particle image velocimetry, a combination of dynamic pressure sensing and optical combustion diagnostics, including OH∗ chemiluminescence and OH planar laser induced fluorescence, give indication of the combustion rig acoustic response and changes in flame acoustic response, heat release, and flame anchoring location related to the onset and occurrence of blowoff. This analysis shows that the onset of this instability was preceded by a marked reduction in dominant frequency and amplitude until frequency collapse and high amplitudes were observed throughout the burner inlet mixing plenum, burner pilot, combustion chamber, and exhaust ducting. Acoustic and optical signal analysis show potential viability for use in practical applications for precursor indications of lean blowoff. The flame anchoring location within the combustion chamber was shown to detach from the burner exit nozzle and stabilize within the outer and central recirculation zones near the lean blowoff limit, providing evidence of changes to both chemical and flow time scales. Chemical kinetic modelling is used in support of the empirical studies, in particular highlighting the relationship between maximum heat release rate and OH∗ chemiluminescence intensity.

Dust dispersion in a coal roadway driven by a hybrid ventilation system: A numerical study

Abstract Dust contamination to ventilation systems is a common issue for mine operators during underground coal mining. In the present study, dust dispersion driven by a hybrid ventilation system in an underground mine has been investigated via a computational fluid dynamics (CFD) model. Specifically, the numerical model was developed based on the Euler–Lagrange method where the trajectory of dispersed dusts was solved individually. Dust dispersion induced by turbulence was considered by a stochastic tracking model. Effects of key parameters (e.g., gas velocity and exhaust duct length) on dust dispersion characteristics throughout the coal roadway have been examined. The results showed that the distribution of dusts exhibited extreme non-uniformity with a significantly higher concentration present near the mining face, particularly on the exhaust side. The cross-sectional average dust concentration substantially decreased along the axial direction in the front part of the coal roadway. Intense circumfluence and secondary sedimentation of dusts were found to be the main mechanisms that drove the non-uniform distribution of dusts. The model is shown to be capable of reproducing the dust dispersion process captured in the experiments and the prediction results agree well with the experimental data.

Developing the Cascade Thermal Circuit for the Turbine Unit Operating on Low-Boiling Working Medium Intended for Agricultural Power Engineering

The modes of operation of the appropriate cogeneration unit of a low power (~80 kW) whose closed cycle uses a low-boiling working medium have been analyzed. The engineering solution on the improvement of power plant has been suggested. Realization of the two-cascade thermal circuit would allow us to operate mini-heat and power plants (HPP) both during the winter period and in summer provided that the electric power is increased by 20 to 25 kW. The available low-boiling working media for the second cascade were analyzed and those were selected that maximally meet the requirements set to the thermodynamic efficiency, operation performances, ecological safety and the operation reliability. Using the program system developed by the IPMash of the National Academy of Ukraine the team carried out computation investigations of thermal circuits for two-cascade power units. Performances for the power unit operating during the summer period on low-boiling working medium with hot water supply and in the condensation mode have been obtained; the electric efficiency for such modes will be equal on average to 22 % and 27 %, respectively. The computation data for the performances of the second cascade of mini-HPP with the working medium of R-600a were given for 100 % modes and partial modes used for the hot water supply (HWS) that showed the efficiency of the unit operation in the entire loading range. For the regular electric power generation by the cogeneration unit the option of thermal circuit with the parallel mounting of the boiler and the air capacitor at the turbine exhaust duct of the second cascade was calculated that would allow for the operation of the power system in any HWS mode.

Air tightness measurements in older Danish single-family houses

This paper reports and discusses the air tightness of the building envelope in existing single-family houses in Denmark. The air tightness of the building envelope depends in particular on the performance of specific construction details. There is a lack of knowledge about the air tightness of the building envelope of older buildings despite the fact that the air tightness has a major influence on the energy use. In connection with renovation of the Danish building stock, the coming years will see increased focus on the air tightness of the building envelope like in other countries.This paper presents the results of measurements in 16 single-family houses built between 1880 and 2007. The air tightness of the building envelope was measured according to EN ISO 9972 using the blower-door technique. The results are compared with measurement results of the average air-change rate in the same houses measured over a period of 1-3 weeks when the houses were in normal use.The measurement results of the air tightness of the building envelope range from 1.1 to 5.8 l/(s·m²) at 50 Pa. The investigated houses are all naturally ventilated. The results of the ventilation measurements showed an outdoor air supply ranging from 0.09 to 0.28 l/(s·m²) per heated floor area, which is below the requirement stipulated in the Danish Building Regulations of 0.3 l/(s·m²).Typically, leaks are observed in connection with penetrations of the envelope, e.g. for electrical installations, exhaust ducts and chimneys. In addition, leaks are observed around older windows and doors and in connection with wooden ceilings and attic hatches. The findings should be taken into account when renovating older single-family houses.

휠로더 흡배기구의 유동손실계수를 적용한 열유동해석

휠로더 흡배기구의 유동손실계수를 적용한 열유동해석

Электромагнитные излучения в выхлопной части паровой турбины

Электромагнитные излучения в выхлопной части паровой турбины

Hybrid System for Electricity Generation using Waste Heat & Wind from Exhaust Duct of Generator

Hybrid System for Electricity Generation using Waste Heat & Wind from Exhaust Duct of Generator

Hybrid approach to noise control of industrial exhaust systems

This study aims to present a procedure for optimal design of hybrid noise control systems for exhaust ducts from large fans and high radiated sound power, in an industrial environment. Reactive, resistive or hybrid silencers are considered as alternatives with the possibility of adding a supplementary active noise control system to mitigate remaining noise of multiple low frequencies, which are difficult to be attenuated by passive means.Algorithms are proposed for the implementation of optimal hybrid passive/active design and the main theoretical and practical fundamentals involved are showed.Two effective solutions for a real industrial exhaust system are presented as examples of applications of hybrid optimal design procedure proposed. The first one uses of Helmholtz resonators (to attenuate lower frequencies) and resistive silencer parallel lamellae (to lower the midrange and high frequencies). The second one adopts resistive silencer of parallel lamellae and a forward active noise control system.This is a hybrid approach that is not treated in this manner in the available literature, especially in the text books of applied acoustics engineering.

Pressure drop measurements for woven metal mesh screens used in electrical safety switchgears

The paper deals with an experimental investigation of the pressure drops and friction factors induced by sets of metal woven screens in the case of an incompressible fluid flow, namely water flow. These woven screens are of metallic type and are used in electrical safety devices, especially at the end of exhaust duct of low voltage circuit breakers. In a first step, the whole of the set-up is used to check some approximations dedicated to pressure drops due to sphere beds around 275µm and 375µm as diameters. Results are discussed in terms of Darcyan and non-Darcyan permeabilities compared with published data and are analyzed in terms of the Blake-type friction factor. In the second step, the pressure drops are measured for stacks composed of eight different woven screens (of plain dutch type) formed with millimetric wires. Various formulations of the pressure drops and friction factors published elsewhere are tested with a special care dedicated to the choice of the geometry for the flow pattern (hydraulic diameter, spherical diameter, cylindrical diameter) and to the consideration of laminar and turbulent contribution. We then give the formulation that characterizes the fluid flowing through stacks of woven screens used in electrical safety applications.

Local linear stability analysis of cyclone separators

Local linear stability analysis is applied to the flow inside a cyclone separator to investigate the unsteady precession of the vortex core. The results of the stability analysis are compared with experimental measurements of the vortex oscillations using high-speed photography with particle seeding and hot-wire anemometry. The experiments reveal distinct spatial variation in the oscillation behaviour within the cyclone. The unsteady motion is focused at each end of the device, at both the narrow cone tip and just below the exhaust duct at the top of the cone, which is known as a vortex finder. The local stability analysis shows that an absolute instability is present throughout the flow for some non-zero azimuthal wavenumbers. The unsteady flow is observed to be driven by coupling between the shear layer and inertial waves confined within the vortex core. Comparison of the stability analysis with experiments shows the same frequency and mode shape behaviour and suggests that the local analysis accurately predicts the unstable modes of the system. The precessing vortex core is responsible for a narrow-band acoustic noise. Comparisons are also drawn with acoustic measurements made on cyclones in which the system is defined by key non-dimensional parameters, such as the swirl number and outlet diameter ratio. The results in this study demonstrate the applicability of local stability analysis to a complex swirling system and yield credible details about the underlying mechanisms of the unstable flow inside the cyclone.

INFLUENCE OF HIGH ALTITUDE ON COMBUSTION EFFICIENCY AND RADIATION FRACTION OF HYDROCARBON FIRES

Fire behaviors of three gaseous hydrocarbon fuels were experimentally measured and compared at two different altitudes (Lhasa city, 64 kPa at an altitude of 3650 m; Hefei city, 100 kPa at an altitude of 50 m). The heat release rates were calculated through a simplified thermochemistry based on the measured concentrations of O-2 and CO2 in the exhaust duct, then the combustion efficiencies and the radiation fractions were compared at the two altitudes. The heat release rates and combustion efficiencies were higher at lower pressure, and the overall temperatures of methane fires rose at a lower pressure. The radiative heat fluxes and radiation fractions at a low pressure were smaller than those at a normal pressure, while the smoke transmittances of acetylene fires at a low pressure were higher.

The stratification study of public buildings microclimate parameters with supply and exhaust ventilation

The paper presents the results of the UFAD system numerical modeling where the air is supplied through diffusers installed in a floor of a room. Warm air is removed from the upper zone of the room through the exhaust duct. The purpose of this study is to determine the magnitude of the temperature stratification in various areas of an office premise in the conditions of the under floor air distribution. Enclosed volume with local heat sources has been chosen as the computational domain: people, computers, and lighting. The problem is solved in a stationary setting using the k-omega SST turbulence model. As a result of the study the temperature distribution throughout the room has been obtained and the influence dependence of wall temperature on an average air temperature in the room has been defined. The numerical data received are in good agreement with the results of the borrowed experimental study that demonstrate the adequacy of the developed numerical model as well as the possibility of its further use for the optimization of the considered ventilation systems.

Particulate Matter and Carbon Monoxide Emission Factors from Incense Burning

Indoor air quality is a growing concern in the world. People spend a considerable amount of time in indoor environments such as homes, workplaces, shopping malls, stores and places of worships such as churches, temples and mosques. Most often incense burning takes place in places of worship which are enclosed spaces full of worshippers. Incense burning releases pollutants such as particulate matter (PM), carbon monoxide (CO) and volatile organic compounds. Exposure to these kinds of pollutants can result in adverse health effects. The purpose of this research is to determine the particulate matter and carbon monoxide emission factors (EFs) from incense stick burning. A test chamber with a rectangular exhaust duct, a fan to exhaust air with pollutants in it and pollutant sensors were used to achieve the project goals. Several experiments were performed with different cases/ scenarios to accurately estimate the EFs and several test runs were conducted for each case to test the repeatability of the results. EFs for CO (mass), PM2.5 (mass), PM2.5 (number), PM10 (mass), PM10 (number) were developed in this research which should help in (a) assessing exposures, (b) designing ventilation systems and (c) assessing potential health risks.

Design and Calibration of Chambers for the Measurement of Housed Dairy Cow Gaseous Emissions

Abstract. The increased global demand for milk and other dairy products over the past decade has heightened concerns about the potential for increased environmental impacts. Accurate measurement of gas emissions from dairy cows is essential to assess the effects of cow diets and other management practices on both the composition and rate of gas emissions. In this article, methodologies are described to instrument, calibrate, and assess the uncertainty of gas emissions by cows housed in chambers that simulate production settings. The supply and exhaust ducts of each chamber were equipped with pitot tubes, temperature and relative humidity probes, and gas samplers to monitor airflow rates, gas composition, and gas emission rates. A Fourier transform infrared spectroscopy (FTIR) instrument was used to quantify gaseous concentrations in the gas samples on a semi-continuous basis. The measurement uncertainty of the rate of gaseous emission from the chambers was quantified, and gas concentration and differential pressure, as measured by the pitot tubes, were identified as the primary parameters contributing to gas emission uncertainties. Mass recovery tests determined that the recovery of methane from each chamber was within 10% of the released mass. Fan operating curves were experimentally determined to identify optimum differential chamber pressures to minimize gas leakage from the chambers. A computational fluid dynamics model was developed to assess air mixing patterns and define steady-state conditions. The model was validated with experimental data of air velocity within each chamber. These procedures will facilitate accurate measurement of gas emissions from housed dairy cows and provide a laboratory to test various gas mitigation treatments. Keywords: Computational fluid dynamics, Dairy, Emission chamber.

Suppression of gas-dynamic self-oscillations in the outflow line of a gas control valve

This article is devoted to the investigation of the causes and peculiarities of high-frequency gas-dynamic self-oscillations arising in the outflow line of gas control valves. We have demonstrated that these self-oscillations result in a substantial increase in the level of dynamic loading of the control valve elements due to the occurrence of intense tonal components in the pressure fluctuation spectra in the pipeline, the vibrations of the output flange of the control valve, as well as the external noise of the whole assembly. We have provided the results of investigating the conditions for high-frequency gas-dynamic self-oscillations arising from the gas flow interaction with the control valve elements, as well as with supporting pylons of the central fairing. It is shown that an increase in the flow above a certain value of output speed (40 m/s) results in tonal components of the spectrum of pressure pulsations. We have described the measures to suppress gas-dynamic self-oscillations by means of a perforated sleeve installed in the outflow line of the control valve. Three modifications of the sleeve design have been modeled, numerical simulation of gas-dynamic processes in the control valve exhaust duct with a perforated sleeve installed has been carried out. It is shown that complete elimination of gas-dynamic self-oscillations can be made possible by installing the sleeve in the control valve exhast duct.

An exhaust heat recovery system utilising thermoelectric generators and heat pipes

Exhaust heat recovery systems are used to make use of otherwise wasted heat from a car engine. The purpose of exhaust heat recovery systems is to potentially reduce the fuel consumption of the car and consequently reduce CO2 emissions and running costs. The system design described herein utilises thermoelectric generators (TEGs) and heat pipes with its key advantage being it is a passive solid state design. The use of heat pipes allows for more flexible designs as the TEG location is not limited to the exhaust pipe surface. Testing was undertaken on a car with a 3.0L V6 engine. In all test conditions the power loss due to pressure drop in the exhaust duct was always lower than the electrical power output. Repeat tests were conducted and the results were found to be consistent. When testing the system at different orientations, the bottom heat mode was found to be the best option. After all testing, the maximum power output of the system was 38W from the eight 62mm×62mm TEGs used. The rate of heat transfer in this case was 1541W with the resultant TEG efficiency being 2.46%. The calculated potential reduction in CO2 emissions, fuel consumption and fuel costs was 1.57%.

Acoustical design of the ELA4 launch pad for the Ariane 6 launcher

A new launch pad, ELA4, is going to be built in Kourou (French Guyana) for the future launcher Ariane 6. As the A64 version of the launcher will be more powerful at lift-off than Ariane 5, the exhaust ducts and the water injection systems have to be carefully designed, in order to be as effective as possible, and to reduce the acoustics on the payloads and the launcher. This has been done using the experience acquired and Ariane 5 and VEGA launch pads, as well as the understanding of the complex phenomena obtained by research activities. The general design have been validated and optimized by subscale test campaigns at the MARTEL test bench. Numerous configurations and parameters have been tested, including the geometry of the ducts and the launch table, the altitude of the launcher, the position and the mass flow rate and the spray type of the water injection systems. [These works have been done in collaboration between ESA, CNES, ASL, ONERA and PPRIME.]