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  • 1
    Online Resource
    Online Resource
    Investigation of Working Fluid Performance through a Centrifugal Compression System
    MDPI AG ; 2022
    In:  Applied Mechanics Vol. 3, No. 3 ( 2022-07-02), p. 815-829
    Details
    In: Applied Mechanics, MDPI AG, Vol. 3, No. 3 ( 2022-07-02), p. 815-829
    Abstract: Commonly, researchers have investigated many factors that impact the performance of air conditioning and refrigeration systems, such as varied cooling configurations, operating conditions and optimization of specific system components. Although there is an abundance of research detailing the importance of working fluid selection, very few studies focus on how the working fluid selection influences the performance of the individual components of the system, such as the compressor. In this paper, the performances of a selection of working fluids are compared through a centrifugal compressor using CFD. The working fluids considered are R1234ze, R1234yf, R152a, R444a, R445a, R290 and R600a and were selected due to suitability as replacements to R134a. Each fluid, including R134a, was compared based on the performance of a centrifugal compressor with fixed inlet conditions across two operational speeds. The results indicate that R1234ze and R1234yf demonstrated the best performance as replacements to R134a, achieving the highest overall pressure ratios. Additionally, R1234ze also displayed similar power required through the compressor to R134a indicating greater suitability as a drop-in replacement. The working fluids R444a and R445a both displayed performance similar to that of R134a across both operational speeds, indicating reasonable suitability as a replacement to R134a. Alternatively, R152a, R290 and R600a displayed reduced performance compared to R134a and subsequently, are not suitable replacements based on the compression system considered in this study. As well as considering the observed differences in the performance from the selected working fluids, the implications of the results for industrial applications are also considered, along with avenues for further work.
    Type of Medium: Online Resource
    ISSN: 2673-3161
    URL: Article
    DOI: 10.3390/applmech3030048
    Language: English
    Publisher: MDPI AG
    Publication Date: 2022
    detail.hit.zdb_id: 3001011-1
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  • 2
    Online Resource
    Online Resource
    Heat Exchanger Sizing for Organic Rankine Cycle
    MDPI AG ; 2020
    In:  Energies Vol. 13, No. 14 ( 2020-07-14), p. 3615-
    Details
    In: Energies, MDPI AG, Vol. 13, No. 14 ( 2020-07-14), p. 3615-
    Abstract: Approximately 45% of power generated by conventional power systems is wasted due to power conversion process limitations. Waste heat recovery can be achieved in an Organic Rankine Cycle (ORC) by converting low temperature waste heat into useful energy, at relatively low-pressure operating conditions. The ORC system considered in this study utilises R-1234yf as the working fluid; the work output and thermal efficiency were evaluated for several operational pressures. Plate and shell and tube heat exchangers were analysed for the three sections: preheater, evaporator and superheater for the hot side; and precooler and condenser for the cold side. Each heat exchanger section was sized using the appropriate correlation equations for single-phase and two-phase fluid models. The overall heat exchanger size was evaluated for optimal operational conditions. It was found that the plate heat exchanger out-performed the shell and tube in regard to the overall heat transfer coefficient and area.
    Type of Medium: Online Resource
    ISSN: 1996-1073
    URL: Article
    DOI: 10.3390/en13143615
    Language: English
    Publisher: MDPI AG
    Publication Date: 2020
    detail.hit.zdb_id: 2437446-5
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  • 3
    Online Resource
    Online Resource
    Investigation of non-linear acoustic losses at the open end of a tube
    Acoustical Society of America (ASA) ; 2011
    In:  The Journal of the Acoustical Society of America Vol. 129, No. 3 ( 2011-03-01), p. 1261-1272
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 129, No. 3 ( 2011-03-01), p. 1261-1272
    Abstract: At high acoustic level, non-linear losses at the end of a tube are usually interpreted as the consequence of a jet formation at the tube end resulting in annular vortices dissipating part of the acoustic energy. Previous work has shown that two different regimes may occur. The present work, using particle image velocimetry visualization, lattice Boltzmann method simulation in 2D, and an analytical model, shows that the two different regimes correspond to situations for which the annular vortices remain attached to the tube (low acoustic particle velocity) or detached (high acoustic particle velocity).
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.3543987
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 2011
    detail.hit.zdb_id: 1461063-2
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  • 4
    Online Resource
    Online Resource
    Numerical Study of Flow around Two Circular Cylinders in Tandem, Side-By-Side and Staggered Arrangements
    MDPI AG ; 2023
    In:  Fluids Vol. 8, No. 5 ( 2023-05-07), p. 148-
    Details
    In: Fluids, MDPI AG, Vol. 8, No. 5 ( 2023-05-07), p. 148-
    Abstract: Simulations are presented for flow around pairs of circular cylinders at a Reynolds number of 3900. The flow is assumed to be two-dimensional and incompressible in nature and the simulations are performed using a RANS (Reynolds Averaged Navier Stokes) approach with a k-ε model. Simulations are performed for three different configurations of the cylinders: A tandem configuration where the line joining the centre of the cylinders is parallel to the mean flow direction; side-by-side, where the centre line is perpendicular to the mean flow direction; and staggered where the centre line is an angle α to the flow direction. Simulation results are presented for cylinder separations ranging from 1.125 to 4 diameters and for values of α between 10° and 60°. The results are presented and discussed in terms of the lift and drag coefficients, the Strouhal number, the vorticity field and the flow regimes observed. The results and flow regimes are also compared to previous observations at lower Reynolds numbers to investigate the Reynolds number dependence of the phenomena.
    Type of Medium: Online Resource
    ISSN: 2311-5521
    URL: Article
    DOI: 10.3390/fluids8050148
    Language: English
    Publisher: MDPI AG
    Publication Date: 2023
    detail.hit.zdb_id: 2882362-X
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  • 5
    Online Resource
    Online Resource
    An Improved Design for Flow Conditioning in Waste Water Pipes
    MDPI AG ; 2023
    In:  Waste Vol. 1, No. 2 ( 2023-04-18), p. 414-425
    Details
    In: Waste, MDPI AG, Vol. 1, No. 2 ( 2023-04-18), p. 414-425
    Abstract: In practical applications, waste water piping includes elbows and bends which give unrepeatable, asymmetric and swirling flow profiles, which result in flow meter inaccuracy. Flow conditioners can be inserted into the pipe network to remove these flow patterns prior to a flow meter, to improve the accuracy of the measurement and to reduce the length of straight-run which would otherwise be required. In this investigation, a new design of flow conditioner is considered in two configurations, with and without vanes. The performance of the conditioner is considered by exposing it to a swirling flow that was disturbed by two 90° bends. The flow downstream of the conditioner was simulated using CFD software STAR-CCM+ 12 to find the downstream axial velocity profile, swirl angle and pressure drop. The vane-less conditioner provided a suitable axial profile for flow measurement 2D downstream, at which point the swirl was removed. This illustrated the improved performance compared to other conditioners in the literature, but came at the price of a somewhat higher pressure drop. The addition of vanes improved the performance slightly in terms of regulating the flow and removing swirl, while at the same time increasing the pressure drop further.
    Type of Medium: Online Resource
    ISSN: 2813-0391
    URL: Article
    DOI: 10.3390/waste1020025
    Language: English
    Publisher: MDPI AG
    Publication Date: 2023
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  • 6
    Online Resource
    Online Resource
    Comprehensive Review of Liquid Air Energy Storage (LAES) Technologies
    MDPI AG ; 2023
    In:  Energies Vol. 16, No. 17 ( 2023-08-27), p. 6216-
    Details
    In: Energies, MDPI AG, Vol. 16, No. 17 ( 2023-08-27), p. 6216-
    Abstract: In recent years, liquid air energy storage (LAES) has gained prominence as an alternative to existing large-scale electrical energy storage solutions such as compressed air (CAES) and pumped hydro energy storage (PHES), especially in the context of medium-to-long-term storage. LAES offers a high volumetric energy density, surpassing the geographical constraints that hinder current mature energy storage technologies. The basic principle of LAES involves liquefying and storing air to be utilized later for electricity generation. Although the liquefaction of air has been studied for many years, the concept of using LAES “cryogenics” as an energy storage method was initially proposed in 1977 and has recently gained renewed attention. With the growing need for alternative energy storage methods, researchers have increasingly explored the potential of cryogenic media, leading to the development of the first LAES pilot plant and a growing body of research on LAES systems. However, one notable drawback of LAES is its relatively low round-trip efficiency, estimated to be around 50–60% for large-scale systems. However, due to its thermo-mechanical nature, LAES offers versatility and can be easily integrated with other thermal energy systems or energy sources across a wide range of applications. Most of the existing literature on LAES focuses on thermodynamic and economic analyses, examining various LAES configurations, and there is a clear lack of experimental studies in this field. This paper aims to conduct a comprehensive review of LAES technology, with a focus on the performance enhancement of these systems. Future perspectives indicate that hybrid LAES solutions, incorporating efficient waste energy recovery sections, hold the most promise for enhancing the tech-no-economic performance of standalone LAES systems.
    Type of Medium: Online Resource
    ISSN: 1996-1073
    URL: Article
    DOI: 10.3390/en16176216
    Language: English
    Publisher: MDPI AG
    Publication Date: 2023
    detail.hit.zdb_id: 2437446-5
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  • 7
    Online Resource
    Online Resource
    CFD Modelling of a Centrifugal Compressor with Experimental Validation through Radial Diffuser Static Pressure Measurement
    Hindawi Limited ; 2019
    In:  International Journal of Rotating Machinery Vol. 2019 ( 2019-05-19), p. 1-12
    Details
    In: International Journal of Rotating Machinery, Hindawi Limited, Vol. 2019 ( 2019-05-19), p. 1-12
    Abstract: This paper compares experimental static pressure measurement with CFD simulation in a centrifugal compressor at 12 points through the diffuser. Three mass flow rates are selected, each for three operating speeds giving nine total operating conditions. The results show that the CFD model generally slightly underpredicts the static pressure value as compared to the experimental results. The discrepancy between experimental and numerical results ranges between -8% and +6% and is fairly consistent for a given operating condition, except for close to the blade trailing edge where the pressure variation is less regular and where the pressure is increasing most rapidly with radial position. In the consistent region, where the pressure gradient is low, the discrepancy is around two percent or less for simulations close to the design operating point. Away from the design operating point the errors increase up to approximately 5%. The simulation results were also used to investigate the effect of the position (from the blade trailing edge) of the impeller-diffuser interface (a characteristic of the frozen rotor simulation approach). Here an optimal position for the interface was found to be 2% of the blade radius. This value gave improved agreement with the experimental result in the initial region of the diffuser up to a distance of approximately 10% of the radius. At greater distances the position of the interface became less important. The results also highlighted a change in the pressure along the spanwise direction close to the tips. A dip in the pressure, which was observed in the experimental results, was only observed in the simulations close to the shroud. Close to the hub the simulation results recorded a small local peak. The simulation approach was then applied to further study the flow characteristics by examining the full-field velocity and pressure contours in the impeller and diffuser regions to identify changes due to the different operating conditions.
    Type of Medium: Online Resource
    ISSN: 1023-621X , 1542-3034
    URL: Article
    DOI: 10.1155/2019/7415263
    Language: English
    Publisher: Hindawi Limited
    Publication Date: 2019
    detail.hit.zdb_id: 2032559-9
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  • 8
    Online Resource
    Online Resource
    Lattice Boltzmann methods in acoustics
    Acoustical Society of America (ASA) ; 1998
    In:  The Journal of the Acoustical Society of America Vol. 103, No. 5_Supplement ( 1998-05-01), p. 2975-2975
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 103, No. 5_Supplement ( 1998-05-01), p. 2975-2975
    Abstract: The lattice Boltzmann model is a recently developed technique for the numerical simulation of fluid motion. It has been successfully applied to a variety of incompressible fluid phenomena and has been shown to be an efficient simulation tool which is ideally suited for implementation on massively parallel computers. Here the application of the lattice Boltzmann model is considered to simulate acoustical processes in which the fluid can, to a first approximation, be considered to be incompressible. The validity and limitations of this approach are considered and the results of simulations performed on the Cray T3D at Edinburgh University are presented. These include sound propagation in tubes, modeling of air flow in the mouthpiece of brass instruments, and the simulation of acoustic streaming in tubes and around cylinders. In each case the fluid velocity, density, and pressure are found at each grid point and each time-step of the simulation, allowing flow patterns and density changes to be observed. The results of the simulations are compared to the predictions of theory and/or experimental observations and suggest that the lattice Boltzmann method can be used as a numerical tool to give insight into complex acoustical situations.    
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.422412
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 1998
    detail.hit.zdb_id: 1461063-2
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  • 9
    Online Resource
    Online Resource
    Acoustic reflectometry in the manufacture of reproductions of historical wind instruments
    Acoustical Society of America (ASA) ; 2001
    In:  The Journal of the Acoustical Society of America Vol. 110, No. 5_Supplement ( 2001-11-01), p. 2649-2649
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 110, No. 5_Supplement ( 2001-11-01), p. 2649-2649
    Abstract: Acoustic reflectometry has become a well-established technique for investigating the internal bore profile of cylindrically symmetrical ducts. Although the method has previously been applied with some success to the study of musical wind instrument bores, there are practical problems which limit the accuracy of bore reconstruction of instruments which are long or widely flaring, or which have side finger holes. This paper reports on a collaboration with Christopher Monk Instruments Ltd., a London-based firm specializing in the reproduction of cornetts and serpents. These are lip-reed instruments with side finger holes, and a curved bore center line which inhibits the use of conventional bore measuring techniques. It is demonstrated that acoustic reflectometry can provide bore profiles of these instruments with sufficient precision to be a valuable guide in their construction or repair. The precautions necessary to achieve this level of accuracy are described, and prospects for further refinements are discussed. [The collaboration of Keith Rogers and Jeremy West of CMI Ltd. is gratefully acknowledged. Work supported by the Engineering and Physical Sciences Research Council, U.K.]
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.4776996
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 2001
    detail.hit.zdb_id: 1461063-2
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  • 10
    Online Resource
    Online Resource
    Investigation of hemodynamic markers for stenosis development
    Wiley ; 2021
    In:  Engineering Reports Vol. 3, No. 10 ( 2021-10)
    Details
    In: Engineering Reports, Wiley, Vol. 3, No. 10 ( 2021-10)
    Abstract: Different hemodynamic markers for stenosis development are considered, assessed and compared. A recently proposed numerical approach is employed, where stenosis development is modeled based on the local hemodynamic conditions at the artery wall, determined using the lattice Boltzmann method. A range of hemodynamic markers, commonly associated in the literature with the progression of atherosclerosis, were considered. It was observed that using the oscillatory shear index, which is related to the wall shear stress oscillating from its mean direction, did not produce a realistic stenosis development. The other markers produced stenosis growth comparable with observations from the literature.
    Type of Medium: Online Resource
    ISSN: 2577-8196 , 2577-8196
    URL: Issue
    URL: Article
    DOI: 10.1002/eng2.v3.10
    DOI: 10.1002/eng2.12389
    Language: English
    Publisher: Wiley
    Publication Date: 2021
    detail.hit.zdb_id: 2947569-7
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