- Tadcaster, United Kingdom
Quasi one-dimensional chamber models and experimental methods are commonly adopted by researchers to predict and validate the performance of the oil free screw compressors. However, to understand the scope for improvement in performance... more
Quasi one-dimensional chamber models and experimental methods are commonly adopted by researchers to predict and validate the performance of the oil free screw compressors. However, to understand the scope for improvement in performance as impacted by compressor ports, one needs to know the details of physical processes happening in compression chamber. This can be done by understanding flow field such as internal temperature and pressure with the help of CFD model. With this CFD setup, comparison of specific power consumption of oil free screw compressor between the axial and radial suction flange is presented in this paper. A hexahedral numerical mesh is used to represent flow field which is generated by SCORGTM. Flow solver ANSYS CFX has been used for study with these single domain deforming rotor grids. This paper presents the methods used for setting up the CFD model and analysis of specific power consumption for two different suction port geometries, an axial and the radial suction flange. At the design operating condition, although axial suction flange seems to be more favourable in terms of lower suction pressure drops at high operating speed, the radial suction flange when simulated using CFD model predicts almost the similar performance. However, radial suction flange gives an added advantage for ready adaptability with the suction elements like the suction filter. The results of the simulation show that the radial suction flange can be adopted for better compatibility with the oil free package and the CFD model used for the analysis can be used for optimization of the air-end at various operating conditions.
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Performance and reliability of screw compressors is highly dependent on their operational clearances. Compressor structural parts including rotors and the casing are affected both by pressure and temperature of the working fluid to which... more
Performance and reliability of screw compressors is highly dependent on their operational clearances. Compressor structural parts including rotors and the casing are affected both by pressure and temperature of the working fluid to which they are exposed. The standard approach when simulating performance is to neglect these deformations and assume rigid compressor elements. In this paper a numerical solution which combines the solution of fluid field from Computational Fluid Dynamics (CFD) and Finite Element Analysis (FEA) of solid elements is used to calculate deformations of the compressor elements. The temperature field obtained from CFD is extracted and applied to the surface of the solid parts where it was averaged in time and served as boundary conditions for solid body calculations. The FEM analysis performed in ANSYS showed encouraging results which can be used for analysis of changes in compressor clearances.
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Injecting oil inside the compressor chambers of the oil-flooded, twin-screw compressors has several advantages. Oil cools the compressing fluid upon mixing with it and hence the compression process is brought nearer to the ideal... more
Injecting oil inside the compressor chambers of the oil-flooded, twin-screw compressors has several advantages. Oil cools the compressing fluid upon mixing with it and hence the compression process is brought nearer to the ideal isothermal compression process. The oil also serves as a lubricant between the meshing rotors and other clearance gaps in the compressor. The thin film of oil formed in the clearance gaps prevents internal leakages too; enhancing the volumetric efficiency of the compressor. Among these desirable effects of injecting oil in screw compressors, there is an undesirable effect too. The interaction (friction) of oil films formed in various clearance gaps with the rotors leads to a drag power loss. Recent studies such as Abdan et al. have proposed more detailed and accurate methods to estimate the oil drag losses in screw compressors. These methods enable the modelling of the effect of even minor changes in rotor profile on the drag loss power. Predictions of this ...
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Screw rotors are the heart of screw compressors. And the energy efficiency of industrial machines is a matter of tremendous significance now more than ever. Historically, rotor profile developments have played a key role in making screw... more
Screw rotors are the heart of screw compressors. And the energy efficiency of industrial machines is a matter of tremendous significance now more than ever. Historically, rotor profile developments have played a key role in making screw compressors energy efficient and commercially viable. Further attention to manufacturing aspects of rotor profiles and the invention of the rack generated rotor profiles led to rotor profiles having good manufacturability. The principles of rotor profile generation and manufacturing are available in open literature since 1960’s. But more and more literature on rotor profiling has been published since then. Modern screw rotor profiles (patented close to and in the 21st century) have all the principles of a good profile incorporated in their design. Hence the industry and profile designers at large are aware of the increasing difficulty to further make the twin screw compressor rotor profiles more energy efficient. This paper tries to quantify the cont...
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Close control of the clearances between the rotors and the casing is essential for efficient and quiet oil free compression or expansion in twin screw machines. Differential thermal expansion between these components can therefore have... more
Close control of the clearances between the rotors and the casing is essential for efficient and quiet oil free compression or expansion in twin screw machines. Differential thermal expansion between these components can therefore have adverse effects, especially when both functions are performed by the use of only one pair of rotors in a single casing. A plain compressor and a combined compressor-expander are analysed and it is shown how good results can be obtained by the use of different materials for each component. The analytical results show good agreement with experimentally derived data.
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Screw compressors have been widely investigated for many applications including air and process gas compression, and refrigeration systems. There is however a surprising lack of literature for low pressure ratio application of these... more
Screw compressors have been widely investigated for many applications including air and process gas compression, and refrigeration systems. There is however a surprising lack of literature for low pressure ratio application of these machines, defined here as application requiring volume ratios in the range of 1-1.5. The aim of this paper is to characterise the loss mechanisms for oil injected screw compressors with low volume index (defined as the ratio of maximum to minimum volumes during the internal compression process), V i. This knowledge will be applied in the future to identify appropriate optimisation of rotor profiles and porting geometry for a range of low-pressure ratio applications. The current study involves the use of chamber models to investigate the influence of wrap angles and porting. This initial analysis will be developed in future work to allow a detailed parametric study of the factors that limit the performance of low V i oil-injected screw compressors.
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Designing twin-screw compressors to safely operate at higher than normal temperatures poses a challenge as the compressor must accommodate larger peak thermal distortions while maintaining efficiency at nominal operating conditions. This... more
Designing twin-screw compressors to safely operate at higher than normal temperatures poses a challenge as the compressor must accommodate larger peak thermal distortions while maintaining efficiency at nominal operating conditions. This paper will present a case study of an oil-injected compressor tested at elevated discharge temperatures with original and revised clearances. A procedure is presented to use boundary conditions derived from a chamber model to approximate component temperature distributions that are then used to predict possible thermal distortions and the resulting effect on clearance gaps. The original and revised clearance designs are evaluated and performance penalties incurred due to the modifications are discussed.
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Research Interests: Engineering and Ta
Twin screw compressors are positive displacement machines commonly used in industrial applications. Due to constraints of conventional manufacturing techniques these are usually produced with helical rotors of uniform pitch. However,... more
Twin screw compressors are positive displacement machines commonly used in industrial applications. Due to constraints of conventional manufacturing techniques these are usually produced with helical rotors of uniform pitch. However, other twin screw machines, such as vacuum pumps more often use variable pitch rotor for improved efficiency. Single screw machines are of nonparallel axes and cross sectional profile which changes along the rotor axis. Their manufacturing is more challenging compared to twin screw compressors. With advancements in manufacturing technologies, the new generation of screw machines may see rotors with variable pitch and variable profile which could lead to improved efficiency and extension of operating range of such machines. The performance analysis of such machines by use of chamber models is difficult and in some cases impossible. The alternative is Computational Fluid Dynamics (CFD).
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A detailed study of the fluid flow and thermodynamic processes in positive displacement machines requires 3D CFD modeling in order to capture their real geometry, including leakage gaps. However, limitations in the conventional... more
A detailed study of the fluid flow and thermodynamic processes in positive displacement machines requires 3D CFD modeling in order to capture their real geometry, including leakage gaps. However, limitations in the conventional computational grids, used in commercial software packages, exclude their use for classical twin screw machines. The screw compressor rotor grid generator (SCORG) is a customized grid generation tool developed to overcome these limitations. This paper shows how it can be further extended to include non-conventional rotor designs, such as those with variable lead or profile variation and even internally geared machines with conical rotors. Other arrangements possible with this improvement include multiple gate rotors to increase volumetric displacement or dual lead, high wrap angle rotors for very high-pressure differences and vacuum applications. A case study of a water-injected twin screw compressor is included to demonstrate its use for both detailed flow an...
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The 18th International Conference on Engineering and Product Design Education (EP alternately taking place in the UK and abroad. Its objective is to facilitate the bringing together of people from within education and industry who are... more
The 18th International Conference on Engineering and Product Design Education (EP alternately taking place in the UK and abroad. Its objective is to facilitate the bringing together of people from within education and industry who are interested in sharing expertise on the implementation and analysis of contemporary and developing methodologies in engineering and design education. It provides educators and researchers from product development, engineering and industrial design, together with industry and government representatives, with a platform for discussion on topical educational issues in design education and its future direction.
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Modelling of screw compressors using Computational Fluid Dynamics (CFD) offers better insight into the working chamber of twin screw machines when compared with chamber models. As shown by authors in earlier publications, CFD models... more
Modelling of screw compressors using Computational Fluid Dynamics (CFD) offers better insight into the working chamber of twin screw machines when compared with chamber models. As shown by authors in earlier publications, CFD models predict performance of dry gas and refrigeration compressors fairly accurately. However numerical flow models used for modelling of oil flooded twin screw compressors are still at the development stage. This is mainly due to the lack of understanding of the flow complexity and the techniques used for solving coupled equations that represent interactions between the gas and the oil in such machines. This paper presents the modelling approach used for calculation of the performance of an oil flooded screw compressor. It requires a structured numerical mesh which can represent all moving parts of the compressor in a single numerical domain. Such mesh is generated by SCORGTM using novel boundary distribution technique called casing-to-rotor conformal boundar...
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EGPR (European Global Product Realisation) is an undergraduate project, which involves collaboration between 5 European universities and an industrial partner. The aim of the course is to develop students’ engineering design skills and to... more
EGPR (European Global Product Realisation) is an undergraduate project, which involves collaboration between 5 European universities and an industrial partner. The aim of the course is to develop students’ engineering design skills and to build confidence in being part of a team in different locations. Usually, engineering students are placed in international teams, which use videoconferencing tools to hold regular meetings and online storage facilities to share documents. Videoconferencing tools are also used to enable all students to attend lectures given by staff from the participating universities. At the end of each design phase reviews are held where each team presents and produces a report showing their main findings or deliverables. The design process and deliverables from the EGPR project held from February to June 2013 are explained in this report. Lectures delivered by staff through two EGPR projects have been evaluated. The first project involved only engineering student...
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Studies on the effectiveness of New Product Development (NPD) in countries of partner organizations of EGPR (European Global Product Realisation) course discovered that the end phases of the process are most challenging. These are... more
Studies on the effectiveness of New Product Development (NPD) in countries of partner organizations of EGPR (European Global Product Realisation) course discovered that the end phases of the process are most challenging. These are identification of market needs on one end and commercialization on the other. CODEVE (COllaborative DEsign in Virtual Environment) teaching methodology is developed within EGPR course. EGPR is joint educational project of four European universities running since 2004. CODEVE is tested through the Erasmus+ funded project called NARIP (Networked Activities for Realization of Innovative Products). The goal of developing this teaching methodology was to establish suitable means by which students can learn NPD process and how to implement it in their professional career. NARIP project is funded by EU over three years to develop, test and implement this methodology within partner academic institutions from the UK, Croatia, Slovenia and Hungary. It is expected th...
Research Interests: Engineering, Engineering Management, Erasmus, New Product Development, Qa, and 4 moreCommercialization, Ta, Lb, and TJ
In order to reduce internal leakage in screw compressors, efforts are continually being made to produce them with smaller clearances. However, since their rotors deform due to the high pressure loads under which they operate, a reliable... more
In order to reduce internal leakage in screw compressors, efforts are continually being made to produce them with smaller clearances. However, since their rotors deform due to the high pressure loads under which they operate, a reliable estimate of the interaction between rotor deflection and fluid flow is needed to maximise the compressor performance while avoiding contact with the casing. A 3-D numerical grid comprising both solid and fluid domains, applied to a commercial computer code for simultaneous calculation of the fluid flow and compressor structure, is presented here. This demonstrates the effects on compressor torque, volume flow, efficiency and specific power due to the change in working clearances caused by rotor deformation.
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Paper describes the CODEVE (COllaborative DEsign in Virtual Environment) methodology, developed in the first year of the educational project NARIP (Networked Activities for Realization of Innovative Products), funded by ERASMUS+ . Four... more
Paper describes the CODEVE (COllaborative DEsign in Virtual Environment) methodology, developed in the first year of the educational project NARIP (Networked Activities for Realization of Innovative Products), funded by ERASMUS+ . Four European universities launched this project with goal to develop a concept and to produce a physical product prototype within one academic semester in dislocated, virtual environment. In order to expose students to real life situations, the educational process is being conducted in tight collaboration with development focused industrial partner company.
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European Global Product Realisation (EGPR) is an undergraduate group design project for the final year engineering students at City University, London. It involves collaborating with students from five different European universities on a... more
European Global Product Realisation (EGPR) is an undergraduate group design project for the final year engineering students at City University, London. It involves collaborating with students from five different European universities on a commercial design project for an industrial partner. The aim of the project is to equip students with the necessary skills to solve real multidisciplinary design problems, using a systematic and structured engineering design process. In order to acquaint the students with the engineering design process, a preparatory project was set up between a UK-based manufacturer of screw compressors and the students at City University, London, prior to the main EGPR project. The task was to develop a concept for a remote monitoring system to be integrated into a screw compressor produced by Howden Compressors Ltd, with the aim of gathering operational parameters including power and mass flow rate. During the project, the students were required to use their exi...
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Based on the dynamic mesh technology, the moving grids of the double-suction screw multiphase pump were generated by the software SCORG. Then the three-dimensional transient simulation model was established to investigate the two-phase... more
Based on the dynamic mesh technology, the moving grids of the double-suction screw multiphase pump were generated by the software SCORG. Then the three-dimensional transient simulation model was established to investigate the two-phase flow mechanism inside the screw pump under different inlet gas volume fraction (IGVF). The results show that the pressure inside the working chamber increases step by step from inlet to outlet and is symmetrical. The pressure drops sharply at the inlet of circumferential clearance and then decrease linearly in the clearance. The curved flow in suction and discharge flow passage causes the gas separation and high gas volume fraction (GVF) area in suction and discharge chamber. Four vortices in cross section of discharge pipe cause four high GVF areas due to the centrifugal force produced by the vortices. The high GVF areas scatter in working chambers and change slightly with the rotation angle except the last chamber under the IGVF 10%. The two-phase l...
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Improving the efficiency of the screw machine is highly significant for industry. Numerical simulation is an important tool in developing these machines. The 3D computational fluid dynamic simulation can give a valuable insight into the... more
Improving the efficiency of the screw machine is highly significant for industry. Numerical simulation is an important tool in developing these machines. The 3D computational fluid dynamic simulation can give a valuable insight into the flow parameters of screw machines. However, it is currently difficult to generate high quality computational grids required for screw rotors with large helix angle. This is mainly due to the excessively high cell skewness of the rotors with large helix angel, which would introduce errors in numerical simulation. This paper presents a novel grid generation algorithm used for the screw rotors with large helix angel. This method is based on the principles developed for the grid generation in transverse cross-section. Such mesh is generated by SCORGTM using normal rack grid generation method which means numerical meshes are generated in a plane normal to the pitch helix line. The mesh lines are then parallel to the helix line and thus an orthogonal mesh ...
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The 18th academic conference hosted by the Design Management Institute (DMI) of Boston, Mass., attracted a greater number of papers than any previous conference. The event was intended to highlight the importance of the contribution of... more
The 18th academic conference hosted by the Design Management Institute (DMI) of Boston, Mass., attracted a greater number of papers than any previous conference. The event was intended to highlight the importance of the contribution of design to organisational effectiveness and success, particularly in the ways that it can improve the new product development process,contribute to better strategic thinking and decision-making, and be an important element in the leader’s toolkit. The conference was a means for researchers and thinkers to celebrate the importance of design and to work towards becoming a credible and full participant in the work of organisations.We were proud and deeply honoured to have Professor Roger Martin, Dean of the Rotman School of Business at the University of Toronto, as our keynote speaker. He has been an inspirational thinker and one of the foremost and most passionate advocates of the methodologies and thinking of design as important and under-utilised organ...
Research Interests: Business, Marketing, Business Administration, Engineering, Design, and 15 moreBrand Management, Strategic Brand Management, International Business, Innovation statistics, Industrial Design, Business Process Management, Strategic Management, Graphic Design, Product Design, Design Innovation, International Marketing, New Product Development, Branding, Business Management, and Innovation
The market for twin screw compressors is highly competitive, especially in compressed air and refrigeration systems, and new designs are continually being introduced which are more efficient and cost effective than their predecessors.... more
The market for twin screw compressors is highly competitive, especially in compressed air and refrigeration systems, and new designs are continually being introduced which are more efficient and cost effective than their predecessors. However, because of the high cost of development of new machines, manufacturers seek to maintain their existing designs for as long as possible. Closer study of many
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It is estimated that about 17% of the world’s generated power is used for compression. Thus all, even minor improvement of the efficiency of compressors will substantially reduce CO2 emission. This paper presents development of family of... more
It is estimated that about 17% of the world’s generated power is used for compression. Thus all, even minor improvement of the efficiency of compressors will substantially reduce CO2 emission. This paper presents development of family of energy efficient oil-flooded screw compressors for Kirloskar Pneumatic Company Ltd. The developmental techniques adopted to improve efficiency such as introduction of superior ‘N’ rotor profile, rotor clearance management, performance calculation using 3D CCM (Computational Continuum Mechanics), direct parametric interface to CAD (Computer Aided Design), which contains bearing selection for complete 3D solid modelling. Also, contemporary prototyping and experimental investigation is supported by the fully computerised data acquisition and processing. The cumulative improvement of all these elements of the design process resulted in a very efficient machine which guarantees the competitive position of Kirloskar Pneumatic Company Limited in the screw ...
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Abstract Twin-screw compressors used in refrigeration, gas and air compression represent approximately 80% of the millions of industrial positive displacement compressors produced globally each year. More than 95% of these are oil... more
Abstract Twin-screw compressors used in refrigeration, gas and air compression represent approximately 80% of the millions of industrial positive displacement compressors produced globally each year. More than 95% of these are oil injected. Oil injected twin-screw compressor is just one type of multiphase screw machines. Other include twin-screw expanders, multiphase pumps and motors. Multiphase twin-screw machines are traditionally analysed and designed by use of chamber thermodynamic models. However, for further improvement of efficiency and reliability, it is necessary to use more advanced modelling techniques such as 3D Computational Fluid Dynamics (CFD). In order to obtain a fast and accurate solution of multiphase screw machines using CFD, it is important that a numerical grid of the highest quality is generated quickly and reliably. For that purpose, a deforming grid of a twin-screw machine is generated using algebraic transfinite interpolation upon which elliptic partial differential equations (PDE) of the Poisson's form are solved numerically to produce smooth final computational mesh. This chapter gives a review of the current state of the art in the application of CFD in modelling of multiphase twin-screw machines including compressors, expanders and pumps. Future challenges and development trends in the application of CFD for multiphase twin-screw machines are also shown in the chapter.
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The use of Computational Fluid Dynamics (CFD) and Computational Continuum Mechanics (CCM) for analysis of rotary positive displacement machines is exponentially increasing which was mostly allowed by the development of methods for... more
The use of Computational Fluid Dynamics (CFD) and Computational Continuum Mechanics (CCM) for analysis of rotary positive displacement machines is exponentially increasing which was mostly allowed by the development of methods for generating numerical grids of complex domains within the machines. However there are several challenges with the commercial CFD/CCM codes which are preventing generic use of CFD. These are conservativeness of spatial discretisation caused by the inappropriate grid generation, numerical instabilities and dissipations caused by misalignments and application of inappropriate discretisation of equations and the speed and accuracy of multiphase models used in CFD of positive displacement machines. In this paper the authors will review methods used for modelling of rotary positive displacement machines and challenges which developers and users of these methods face. The paper will also offer some solutions and directions for resolving these issues.
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Collaborative design practice in distributed student teams is becoming more popular as technology makes it easier to communicate ideas with others that are geographically distant. However, a challenge for students is to use design tools... more
Collaborative design practice in distributed student teams is becoming more popular as technology makes it easier to communicate ideas with others that are geographically distant. However, a challenge for students is to use design tools which they are not familiar with. These design tools usually differ from each other and engineers may find it much more difficult to share their ideas. This could make the whole design process longer and less successful. Each year the University of Malta, City University London and University of Strathclyde organise a joint collaborative design project, involving engineering students with different disciplines and cultural backgrounds. In this paper, the patterns of use of design tools by students to collaborate with each other are investigated. Based on survey results of students, this paper proposes an approach which can be utilised by engineering students to enhance collaboration in multidisciplinary distributed design teams.
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This paper presents results of an experiment set up to exploit the impact of using Augmented Reality (AR) whilst groups of engineering design students from Malta, Scotland, London and Hungary were collaborating on designing different... more
This paper presents results of an experiment set up to exploit the impact of using Augmented Reality (AR) whilst groups of engineering design students from Malta, Scotland, London and Hungary were collaborating on designing different parts making up a car seat belt mechanism. In particular, the experiment focuses on the distributed, real-time evaluation of the emerging design solution. The results achieved are encouraging and the paper contributes insights of the suitability of using AR in distributed and collaborative design evaluation scenarios.
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In view of the fact that traditional liquid propellants cannot meet the design requirements of large-thrust flight vehicle, it has become a new trend to add nano-metal powder to liquid propellants to greatly increase density and specific... more
In view of the fact that traditional liquid propellants cannot meet the design requirements of large-thrust flight vehicle, it has become a new trend to add nano-metal powder to liquid propellants to greatly increase density and specific impulse. In order to achieve the variable flow-rate and variable-proportion transportation of aviation fuel with nano-aluminum, a new type of solid-liquid mixing pumping system is designed, including powder conveying device, stirring device, pump and corresponding drive and transmission system. For the purpose of avoiding the frictional contact between the rotors, which will bring potential hazard to nano-aluminum powder, a non-contact twin-screw pump with synchronous gears is designed. Among them, based on the considerations of flow pulsation, volumetric efficiency and manufacturing difficulty, cycloid profile is adopted for screw rotors. After completing the functional design, geometric parameter design, structural design, 3D modeling, prototype m...
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In order to investigate the flow characteristics and the formation process of cavitation in twin-screw pumps, three-dimensional computational fluid dynamics numerical analysis has been carried out. A conformal structured moving mesh... more
In order to investigate the flow characteristics and the formation process of cavitation in twin-screw pumps, three-dimensional computational fluid dynamics numerical analysis has been carried out. A conformal structured moving mesh generated by an in-house code SCORG was applied for the rotor domain. The volume of fluid method has been adopted for dealing with the liquid-gas two-phase flow, while the bubble dynamics was handled by a homogenous cavitation model. By changing the rotation speed and discharge pressure, the intensity, distribution area and variation of cavitation at different rotor angle were obtained. The effects of rotation speed and discharge pressure on cavitation characteristics have been analysed. Calculation results with cavitation model are compared with the results without cavitation and the experimentally obtained values. The influence of cavitation on the performance of a screw pump in terms of the mass flow rate, pressure distribution, rotor torque and the s...
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The paper presents an extensive investigation of a small-scale sliding vane rotary expander operating with R245fa. The key novelty is in an innovative operating layout, which considers a secondary inlet downstream of the conventional... more
The paper presents an extensive investigation of a small-scale sliding vane rotary expander operating with R245fa. The key novelty is in an innovative operating layout, which considers a secondary inlet downstream of the conventional inlet port. The additional intake supercharges the expander by increasing the mass of the working fluid in the working chamber during the expansion process; this makes it possible to harvest a greater power output within the same machine. The concept of supercharging is assessed in this paper through numerical computational fluid dynamics (CFD) simulations which are validated against experimental data, including the mass flow rate and indicated pressure measurements. When operating at 1516 rpm and between pressures of 5.4 bar at the inlet and 3.2 bar at the outlet, the supercharged expander provided a power output of 325 W. The specific power output was equal to 3.25 kW/(kg/s) with a mechanical efficiency of 63.1%. The comparison between internal pressu...