Xiaoan Mao
University of Leeds
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Featured researches published by Xiaoan Mao.
Measurement Science and Technology | 2010
Xiaoan Mao; Artur J. Jaworski
This paper describes the development of the experimental setup and measurement methodologies to study the physics of oscillatory flows in the vicinity of parallel-plate stacks by using the particle image velocimetry (PIV) techniques. Parallel-plate configurations often appear as internal structures in thermoacoustic devices and are responsible for the hydrodynamic energy transfer processes. The flow around selected stack configurations is induced by a standing acoustic wave, whose amplitude can be varied. Depending on the direction of the flow within the acoustic cycle, relative to the stack, it can be treated as an entrance flow or a wake flow. The insight into the flow behaviour, its kinematics, dynamics and scales of turbulence, is obtained using the classical Reynolds decomposition to separate the instantaneous velocity fields into ensemble-averaged mean velocity fields and fluctuations in a set of predetermined phases within an oscillation cycle. The mean velocity field and the fluctuation intensity distributions are investigated over the acoustic oscillation cycle. The velocity fluctuation is further divided into large- and small-scale fluctuations by using fast Fourier transform (FFT) spatial filtering techniques.
Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy | 2013
Artur J. Jaworski; Xiaoan Mao
This paper is intended as a technical overview of the research and development work initially undertaken at the University of Manchester and subsequently transferred to the University of Leicester as part of the EPSRC-funded SCORE project (Stove for Cooking, Refrigeration and Electricity supply). The objectives of the work were twofold: Firstly, to develop an early demonstrator of a low-power electricity generator (to deliver approximately 10–20 W of electricity). This was to be based on the concept of using low-cost materials, working fluids and linear alternators suitable for deployment in rural areas of developing countries. The issues of concern here were the development of a suitable thermoacoustic engine topology and control measures; design of suitable heat exchanger configurations from initial use of electrical heaters to heat input through propane combustion; and characterisation of commercial loudspeakers to work as linear alternators and subsequent incorporation of selected models for engine prototyping purposes. These matters will be illustrated by a number of demonstrators and their testing in the laboratory environment. Secondly, to develop a demonstrator of a combustion driven thermoacoustic cooler for storage of vital medical supplies in remote and rural areas where there is no access to electricity grid. To this end, the paper will describe the design, construction and test results of an electrically driven demonstrator of a standing wave thermoacoustic engine coupled to a travelling wave thermoacoustic cooler. The final part of the paper will summarise the achievements to date and outline future work that has spun out from the original SCORE project. This will in particular include the current work on a scaled up version of electricity generator designed to deliver 100 W of electricity by using a two-stage engine configuration and the issues of integration of the thermoacoustic electricity generator and thermoacoustic cooler into one system.
Archive | 2007
Xiaoan Mao; David Marx; Artur J. Jaworski
In thermoacoustic devices, an acoustic wave interacts with a stack of tightly spaced plates either to produce acoustic power, induced by a temperature gradient, or to obtain a refrigeration effect, induced by an acoustic wave. This is based on the thermoacoustic effect whereby appropriately phased pressure and velocity oscillations enable the compressible fluid to undergo a thermodynamic cycle in the vicinity of a solid body. The interaction of the acoustic field with the solid boundary is governed by complex thermo-fluid processes, which are not fully understood, especially for large acoustic excitations (drive ratios Dr>1%, where Dr is defined as the max acoustic pressure divided by the mean pressure) with large fluid displacements [1]. This work is driven by research into the fluid-mechanical aspects of thermoacoustic systems, in particular the identification of the flow morphology and turbulence characteristics in the vicinity of the parallel-plate thermoacoustic stack.
web science | 2010
Xiaoan Mao; Artur J. Jaworski
This paper addresses the physics of the oscillatory flow in the vicinity of a series of parallel plates forming geometrically identical channels. This type of flow is particularly relevant to thermoacoustic engines and refrigerators, where a reciprocating flow is responsible for the desirable energy transfer, but it is also of interest to general fluid mechanics of oscillatory flows past bluff bodies. In this paper, the physics of an acoustically induced flow past a series of plates in an isothermal condition is studied in detail using the data provided by PIV imaging. Particular attention is given to the analysis of the wake flow during the ejection part of the flow cycle, where either closed recirculating vortices or alternating vortex shedding can be observed. This is followed by a similarity analysis of the governing Navier-Stokes equations in order to derive the similarity criteria governing the wake flow behaviour. To this end, similarity numbers including two types of Reynolds number, the Keulegan-Carpenter number and a non-dimensional stack configuration parameter, d/h, are considered and their influence on the phenomena are discussed.
ASME 2014 International Mechanical Engineering Congress and Exposition | 2014
Olusegun M. Ilori; Xiaoan Mao; Artur J. Jaworski
Thermoacoustic systems rely on conversion between thermal and acoustic (i.e. mechanical) forms of energy. The technology lends itself to various applications such as waste heat recovery to produce useful electricity or cooling power or gas liquefaction and regasification in oil and gas industry. Detailed understanding of the fluid flow processes within the internal structures of thermoacoustic systems, especially the heat exchangers, is seen as one of the ways by which the performance of next generation of thermoacoustic systems can be improved. The current study uses 2-D computational fluid dynamics (CFD) model to perform numerical investigations of thermoacoustic heat exchangers placed in an oscillatory flow induced by a standing wave. The computational domain is chosen from a thermoacoustic rig that is built for characterisation of heat exchangers for thermoacoustic applications. Validation of the present numerical approach is first established. Then the numerical analysis is extended by modifying the geometrical and operating parameters. The geometrical parameter considered is the curvature radius of the aerodynamic shapes attached to the entrance and exit of gas channels of the heat exchangers, mainly to modify the flow characteristics. Cases are run for the drive ratios (i.e. the ratio of maximum pressure amplitude to the mean pressure) ranging from 0.3–3.0%. Turbulent model as suitable for thermoacoustic analysis is selected from the literature. Results are discussed based on velocity profiles and the pressure difference obtained as functions of phase angles in the acoustic flow cycle.Copyright
ASME 2010 10th Biennial Conference on Engineering Systems Design and Analysis, Volume 1 | 2010
Xiaoan Mao; Patcharin Saechan; Artur J. Jaworski
In a thermoacoustic refrigerator, energy conversion between thermal and acoustic power is achieved by means of an oscillatory motion of a compressible fluid along a solid body referred to as “stack”. Traditionally, stacks have been most often made by arranging large number of thin plates at equal spacing to fill out the cross section of a thermoacoustic resonator. Other geometries such as circular pores, square or hexagonal pores (honeycombs) or pin-arrays can also be considered. Most common irregular geometry includes layers of woven wire mesh stacked along the resonator length. The advantages of thermoacoustic engines over other conventional energy conversion devices lie in their relatively simple hardware assembly, without the need for any dynamic sealing and lubrication. However, the fabrication of stacks, for example made out of very thin parallel plates, is usually costly and impractical, while using pre-fabricated stacks (e.g. ceramic catalytic converter substrates or honeycomb used in aerospace industry) has high materials costs, which limits the cost advantages of thermoacoustic engines. However, many of these problems could be avoided if irregular stack geometries made out of random (very often waste) materials could be used. There is a wide range of such candidate materials, including glass or steel wool, ceramic chippings, waste material from metal machining (swarf, Scourers), beds of glass or metal balls etc. However the main difficulty is the lack of experimental data characterising the performance of such stacks at the design stage. In this paper, the performance of a standing wave thermoacoustic refrigerator with a stack made of a few chosen random materials, is measured and compared to the one with a parallel plate stack. It is hoped that this work will be beneficial for developing low-cost thermoacoustic prime movers and heat pumps.Copyright
ASME 2010 10th Biennial Conference on Engineering Systems Design and Analysis, Volume 2 | 2010
Xiaoan Mao; Lei Shi; Artur J. Jaworski; Wasan Kamsanam
In thermoacoustic devices, an acoustic wave interacts with internal solid structures such as thermoacoustic stacks (regenerators), to either produce acoustic power due to an imposed temperature gradient, or to produce a heat pumping effect by an acoustic excitation. A cold and hot heat exchangers are usually placed on either side of these internal solid structures to enable heat communication between the thermoacoustic devices and their surroundings. Heat exchangers of various geometries have been extensively studied in steady flows and results are available from a collection of published articles and handbooks. However, there is still a lack of data for heat exchangers in an oscillatory flow, because the interaction of oscillatory flow with the solid boundary is governed by complicated fluid flow and heat transfer processes that are not fully understood. This work is a step towards a better understanding of the heat transfer mechanisms in the acoustically induced oscillatory flow within thermoacoustic systems, in particular obtaining the quantitative description of the heat transfer between heat exchangers and the stack. The assembly of a stack and heat exchangers is replaced by a simplified “stack-less” pair of heat exchangers, in order to focus on the generic heat transfer processes rather than the intricacies of practical thermoacoustic systems. The fins of the hot and cold heat exchangers are kept at constant temperatures by virtue of resistive heating and water cooling, respectively. Planar Laser Induced Fluorescence (PLIF) and Particle Image Velocimetry (PIV) are used to obtain the temperature and velocity fields around the fins. The heat flux between the heat exchanger fins and the fluid is analyzed phase-by-phase. The time dependent local heat transfer coefficient is obtained from the temperature gradient in the thermal boundary layer. The measurements are conducted at various levels of acoustic excitation in order to study the correlation between the non-dimensional heat transfer coefficient Nu and the Reynolds number. The effect of the flow behaviour at the end of the plates on the temperature field in the region is also studied. It is hoped that this work could lead to a better understanding of heat transfer on short plates in the acoustically induced oscillatory flows.Copyright
Applied Acoustics | 2006
David Marx; Xiaoan Mao; Artur J. Jaworski
Experiments in Fluids | 2008
Xiaoan Mao; Zhibin Yu; Artur J. Jaworski; David Marx
International Journal of Heat and Mass Transfer | 2014
Zhibin Yu; Xiaoan Mao; Artur J. Jaworski