On non-invasive ultrasonic flowmeasurement

This thesis is concerned with non-invasive ultrasonic flow measurement, using the transit time principle. The errors associated with the transit-time flowmeter are investigated and a design of flowmeter is suggested. A theoretical and experimental study of the transmission of sound through pipe walls is carried out where it is shown that advantage can be taken of the excitation of Lamb modes. A design of transducer arrangement is made from the results of the work. A solution to the difficult problem of measuring very small times is provided in the form of a novel vernier timing system. The benefits and disadvantages of this timing system are discussed along with the design aspects of other electronic circuits required in the construction of the flowmeter. The flawmeter has been built and tested in the laboratory and is shown to be highly repeatable and accurate. The results of testing the flowmeter compare favourably with tests conducted on a commercial instrument. Improvements to the design and construction and suggestions for further work are given

Metering of two-phase slug flow

This thesis describes the development of a novel system, for metering of two-phase (gaswater) slug flows. The approach combines a model for stable slug flow, a non-intrusive set of conductance sensors, and appropriate closure relationships. This system allows each of the parameters in the model to be determined. The slug flow model is analysed, to determine the sensitivity of the phase flowrates to each measurement parameter. A metering system is then proposed which combines ring-shaped electrodes, electronic instrumentation, and processing software. The ring electrodes are optimised, for the measurement of the phase fraction and the translation velocity. New instrumentation is developed to activate the electrodes, with high measurement accuracy and a wide bandwidth. Analysis software is developed, to process the sensor data, provide suitable closure relations, and deliver the flowrates. A unique feature of this software is its ability to calculate uncertainty margins in the predicted flowrates. The NEL multiphase facility is used, to obtain data for developed, horizontal, gas-water slug flow in a 4-inch pipe. The data span the range of liquid phase superficial velocities 0.1 m s⁻¹ to 1.0 m s⁻¹ , and gas phase superficial velocities 0.6 m s⁻¹ to 6.0 m s⁻¹. The analysis software is used to obtain the flowrate predictions and estimates for the uncertainty margins. The stable slug flow model does not give good results. The relative error in the gas phase prediction is between 10% and 100%, and for the liquid phase prediction, between 50% and 500%. The uncertainty margins are also of comparable magnitude. Proposals for improving the accuracy of the translation velocity measurement, and for directly measuring the local velocities in the slug body (using a pressure transducer) are presented. These proposals aim to reduce the uncertainty that is caused by the use of the empirical closure relationships in the model.This thesis describes the development of a novel system, for metering of two-phase (gaswater) slug flows. The approach combines a model for stable slug flow, a non-intrusive set of conductance sensors, and appropriate closure relationships. This system allows each of the parameters in the model to be determined. The slug flow model is analysed, to determine the sensitivity of the phase flowrates to each measurement parameter. A metering system is then proposed which combines ring-shaped electrodes, electronic instrumentation, and processing software. The ring electrodes are optimised, for the measurement of the phase fraction and the translation velocity. New instrumentation is developed to activate the electrodes, with high measurement accuracy and a wide bandwidth. Analysis software is developed, to process the sensor data, provide suitable closure relations, and deliver the flowrates. A unique feature of this software is its ability to calculate uncertainty margins in the predicted flowrates. The NEL multiphase facility is used, to obtain data for developed, horizontal, gas-water slug flow in a 4-inch pipe. The data span the range of liquid phase superficial velocities 0.1 m s⁻¹ to 1.0 m s⁻¹ , and gas phase superficial velocities 0.6 m s⁻¹ to 6.0 m s⁻¹. The analysis software is used to obtain the flowrate predictions and estimates for the uncertainty margins. The stable slug flow model does not give good results. The relative error in the gas phase prediction is between 10% and 100%, and for the liquid phase prediction, between 50% and 500%. The uncertainty margins are also of comparable magnitude. Proposals for improving the accuracy of the translation velocity measurement, and for directly measuring the local velocities in the slug body (using a pressure transducer) are presented. These proposals aim to reduce the uncertainty that is caused by the use of the empirical closure relationships in the model

Use of catalytic membrane reactors for in situ reaction and separation

SIGLEAvailable from British Library Document Supply Centre-DSC:DXN029705 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Effect of water injection on boiler performance

A 20kW commercial boiler has been modified to enable the injection of water into its combustion air, with the aim of reducing the emissions of carbon monoxide (CO) and oxides of nitrogen (NOx) and increasing heat transfer efficiency.It was identified that water injection had been used for efficiency and emissions control in both gas turbine and internal combustion engines. NOx reductions were consistently achieved however CO reductions were application dependant. The lack of literature relating to water injection in boilers provided an opportunity for novel research.An experimental setup was designed to investigate the effect of water injected into the combustion air on the heat-transfer efficiency of the boiler system, as well as its emissions of CO and NOx. The differences between liquid water and steam, injecting at points internal and external to the burner, and with or without the use of nozzles was also explored.NOx and CO reductions of up to 40% and 93% were achieved with water injected inside the burner through a nozzle with no significant change in heat-transfer efficiency. The CO reduction effectiveness was found to be dependent on several factors. These included: the method and location of the injection, whether the fluid was vaporised, and the air-to-fuel equivalence ratio. The majority of experimental cases resulted in NOx reductions.</div

Experimental investigations of two-phase flow measurement using ultrasonic sensors

This thesis presents the investigations conducted in the use of ultrasonic technology to measure two-phase flow in both horizontal and vertical pipe flows which is important for the petroleum industry. However, there are still key challenges to measure parameters of the multiphase flow accurately. Four methods of ultrasonic technologies were explored. The Hilbert-Huang transform (HHT) was first applied to the ultrasound signals of air-water flow on horizontal flow for measurement of the parameters of the two- phase slug flow. The use of the HHT technique is sensitive enough to detect the hydrodynamics of the slug flow. The results of the experiments are compared with correlations in the literature and are in good agreement. Next, experimental data of air-water two-phase flow under slug, elongated bubble, stratified-wavy and stratified flow regimes were used to develop an objective flow regime classification of two-phase flow using the ultrasonic Doppler sensor and artificial neural network (ANN). The classifications using the power spectral density (PSD) and discrete wavelet transform (DWT) features have accuracies of 87% and 95.6% respectively. This is considerably more promising as it uses non-invasive and non-radioactive sensors. Moreover, ultrasonic pulse wave transducers with centre frequencies of 1MHz and 7.5MHz were used to measure two-phase flow both in horizontal and vertical flow pipes. The liquid level measurement was compared with the conductivity probes technique and agreed qualitatively. However, in the vertical with a gas volume fraction (GVF) higher than 20%, the ultrasound signals were attenuated. Furthermore, gas-liquid and oil-water two-phase flow rates in a vertical upward flow were measured using a combination of an ultrasound Doppler sensor and gamma densitometer. The results showed that the flow gas and liquid flow rates measured are within ±10% for low void fraction tests, water-cut measurements are within ±10%, densities within ±5%, and void fractions within ±10%. These findings are good results for a relatively fast flowing multiphase flow

A scale model study of displacement ventilation with chilled ceilings

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Architecture, 1995.Includes bibliographical references (p. 81-84).Displacement ventilation is a form of air-conditioning which provides good air quality and some energy savings. The air quality is better than for a conventional mixed ventilation system. The maximum amount of cooling that displacement ventilation can provide whilst maintaining a comfortable space is between 25 and 40 W/m2. Chilled ceilings can be added to increase the cooling capacity of the system. A scale model study was carried out to determine comfort levels at different conditions, to establish maximum cooling loads and to observe flow patterns in a typical office room with displacement ventilation and a chilled ceiling. Refrigerant R114 was used as the scaling fluid and an existing test box was used as the model room. Heat sources were simulated using electric resistances in aluminum enclosures. A gas and a water circuit were built to supply ventilation and cooling to the room. Flow visualization was carried out by injecting refrigerant laden with ammonium chloride smoke into the supply point. The smoke was lit by a spotlight shone between two pieces of cardboard and images were taken using a video camera. The results showed that for displacement ventilation alone, the temperature distribution was within stringent comfort levels for heat loads up to 25 W/m2 with an air change rate of 7.5. When a chilled ceiling was added, up to 40 W/m2 could be cooled within comfort levels. The refrigerant was radiatively absorbing, so the radiation cooling from the ceiling was reduced. Therefore, this maximum cooling load is probably an underestimate. Some displacement occurred at low levels for this cooling load, which indicated good air quality, but it was below the breathing zone. At higher loads, the flow appeared to be mixed. Therefore, the benefit of enhanced air quality with displacement ventilation was lost when a chilled ceiling was added. The use of a scale model allowed the study of ventilation systems without building a full scale room. It was of limited use for this study because the heat transfer by radiation could not be modelled correctly with this refrigerant. Further experiments could be carried out with lower supply air rates. The experiments could be improved by ensuring more accurate measurement of the water and gas flow rates and temperatures, reducing heat losses. Flow visualization could be improved by injecting smoke at different points within the room and by using a stronger, more focused plane of light. The apparatus could be used for future work on heat transfer that does not involve a significant amount of radiation. It is recommended that a more leak-tight box with a greater height is built and a more environmentally friendly refrigerant is used.by Katherine J.A. Holden.M.S

Some aspects of the use of water-filled heat stores in gas-fired central-heating systems

Water-filled heat stores present a convenient, relatively inexpensive means of optimising the use of diminishing gas stocks for the central-heating of buildings. The British Gas Corporation recently launched a series of central-heating units with storage, for use in the domestic sector, whose benefits include: - reduced boiler size, more efficient boiler operation, load-levelling at the hours of peak gas demand. This thesis is divided into three parts. Part I examines the inherent advantage of a with-storage, domestic, central-heating system over a conventional system, by means of two simple computer-simulation programs. A minimum efficiency advantage of about 5% is anticipated; the variation of this advantage with the values of certain key parameters has been assessed. Part II is an interim report of a full-scale field trial in the commercial sector; a large (3.3m3) store was fitted in the heating system of a London school, and its performance during the first weeks of its operation is presented here. Returning to the domestic sector, Part III presents a study of the use of two integral heat exchangers in the storage vessels of the above domestic units, whereby hot water can be drawn instantaneously. An attempt to optimise this domestic hot-water facility has been made