Twin Screw compressors are widely used in the refrigeration sector, chillers, and applications like heat pumps due to their high durability and reliability. In this study, the use of an ultra-low GWP refrigerant R1234ze(E) and oil injected operation of a test compressor is evaluated using thermodynamic chamber model. A 4/5 lobe combination with an N type rotor profile is used. Design exploration is set up to analyse parameters of wrap angle, rotor length and built-in volume index to improve the rotor geometry at a rated pressure ratio of 8 and speed of 10,000 rpm. A full operating condition performance map is then obtained on the improved geometry. A 12

The performance and reliability of screw compressors depend significantly on the precise geometry and placement of the contact belt, the region where the male and female rotors engage along their helical profiles. This is significant for screw compressors, in which the male rotor drives the female rotor through the contact belt. This study investigates the effects of clearance variation on the force and sliding velocity in the contact of screw compressor rotors. By examining the sealing line between the rotors and adjusting the contact placement, this research aims to optimise the sealing efficiency, minimise leakage, and ensure effective torque transmission between rotors whilst maintaining reasonably low pressure and load on rotor bodies. The analysis considers the influence of different clearance variations and profiles, focusing on how these parameters affect force distribution, contact pressure, and sliding velocity. The key aspect of this investigation was achieved by using SCORG (an in-house computational tool) to place the contact belt to involute the pitch circle, which directly impacts the load and friction between the rotors. Preliminary findings demonstrate that optimising the contact belt placement can balance contact forces, reduce Hertzian stresses, and maintain acceptable sliding velocities, contributing to enhanced efficiency and longevity. This study highlights the trade-offs between stress reduction, leakage minimisation, and manufacturing tolerances, offering guidelines for the design and operation of high-performance screw compressors.

Water-injected and lubricated compressors face specific complications due to water low viscosity, poor film formation, causing high corrosivity, leading to potential wear and abrasion damage. Therefore, certain coatings are required to address the wear and corrosion challenges on the rotor helical surfaces to maintain their safe operating characteristics, especially in their direct drive configuration. A coating provides homogeneous surface qualities with low material utilisation, making it an efficient and economical solution to the high cost of advanced bulk materials. This study reviewed various coating methods and materials for water-lubricated rotors. The coating processes can be utilised by electrodeposition, physical vapour deposition (PVD) techniques, chemical vapour deposition (CVD) techniques, and thermal spray. Several additional methods are also explored, such as the wet paint spray coatings, and dip coatings. A wide range of coating materials are reviewed in this study, such as alloys, tungsten carbide-cobalt (WC–Co), tungsten carbide-cobalt-chromium (WC–CoCr), graphite composites, molybdenum disulphide, diamond-like carbon (DLC), carbides and flash carbide (WC–10Co–4Cr). Wear resistance and hydrophilicity are assessed for carbon fibre composites and polymers such as hydrophilic polyether ketone (PEEK) and polytetrafluoroethylene (PTFE). By concentrating on “as-coated” solutions, the study presented in this paper seeks to find materials and procedures that maintain rotor clearances while satisfying functionality and cost-efficiency of water injected screw compressors. The results shed light on the advanced solutions, process optimisation, and material selection for the water-lubricated compressors.

The Internally Geared Screw Machine (IGSM) is a novel type of compressor inspired by the gerotor pump, which is widely used in fuel and oil distribution systems. By adding a twist to the straight rotors used by the gerotor pump to create separate working chambers, the internal mechanism can be envisaged to function as a compressor instead. To achieve compression, ported end plates are used so that the fluid can enter and exit at the desired volume ratio. While previous studies have focused on aspects such as rotor profiling, chamber modeling, optimization, and the characterization of discharge pressure pulsations, limited research has addressed the complete acoustic profile of the IGSM. This paper aims to fill this gap by providing a comprehensive analysis of the vibrations and acoustic characteristics of the IGSM, exploring the vibrational modes of the compressor as well as the acoustic radiation generated by these vibrations.

The internally geared screw machine is a rotary positive displacement machine with two helical rotors rotating in the same direction on offset parallel axes. Working chambers are formed by continuous contact points, with their volume varying cyclically. By controlling the timing of fluid entry and exit, the machine achieves compression. Rotor profile design is a critical phase in compressor development, as it influences working chamber volumes, contact forces, and overall performance. Various established methods, such as the rack and pin-generation methods, use precise mathematical formulations to define rotor profiles. A more advanced approach involves deep learning. Artificial intelligence (AI) is transforming many fields, including compressor design. Recent research has demonstrated its potential in generating rack profiles for conventional screw machine rotors. However, internally geared screw machines impose additional design constraints. This paper presents a preliminary study on training a Wasserstein Generative Adversarial Network (WGAN) to generate rotor profiles that ensure continuous contact. The feasibility of this approach is demonstrated through generated profiles, and future research will explore integrating efficiency-related constraints to enhance rotor design.

Internally geared screw machines (IGSMs) are a class of positive displacement compressors introduced in recent years. Their design involves two intermeshing rotors, denoted as the main (inner) and gate (outer), which rotate in the same direction on parallel but offset axes. Unlike conventional twin screw machines, which implement two externally geared rotors positioned side by side, IGSMs feature internal gearing, with one rotor enclosed within the other. While conventional twin screw compressors are widely used and extensively studied, IGSMs remain relatively novel. Previous research has primarily focused on their geometric feasibility and potential advantages using simplified performance models. This paper contributes by presenting a detailed geometrical model of an internally geared screw machine, enabling the calculation of geometry relevant parameters and integration with a well-established one-dimensional chamber model for performance prediction. The chamber model is compared to Computational Fluid Dynamics (CFD) for a single IGSM design operating under both oil-free and oil-injected conditions. Furthermore, the IGSM design is compared with a conventional twin screw configuration to provide a preliminary assessment of relative performance for a small-scale air compression application. The results are analysed, and directions for future work are outlined to support continued development and validation of this novel machine concept.

This research examines the transformative impact of synthetic lubricants, particularly polyglycol-based oils, on the operational efficiency of screw compressors, emphasising the advancement of sustainable industrial practices. The synthetic oil, noted for its superior oxidation stability, prolongs oil change intervals and enhances the longevity of filters and separators. The integration of specialised inhibitors guarantees the preservation of internal compressor cleanliness, resulting in continued high efficiency. Experimental investigations comparing synthetic polyglycol oil to conventional mineral oil in screw compressors indicate substantial enhancements in overall efficiency. The synthetic oil offers extended maintenance intervals, achieving up to 8,000 operating hours in oil-injected screw-type compressors and 40,000 operating hours in turbocompressors, alongside prolonged filter and separator lifespans and diminished cleaning expenses due to its exceptional dirt-dissolving properties. Additionally, the synthetic oil aids in sustaining low oil vapour levels in compressed air, minimising oil use, and averting the gumming of pneumatic valves. The synthetic oil adheres to industrial requirements (DIN 51506-VDL and ISO 6743-3 L-DAJ) and demonstrates outstanding wear prevention for steel friction components. Possessing a kinematic viscosity of 55 mm ^2 /sec at 40 ^∘ C, it exceeds bearing life specifications, hence forming an efficient lubricating coating for anti-friction bearings. The study highlights the considerable potential of sustainable lubricants, especially polyglycol-based oils, in improving efficiency and reinforcing the environmental sustainability of screw compressors. This study offers significant insights into the practical applications of synthetic lubricants in industrial settings, highlighting polyglycol-based oils as a viable solution for enhancing screw compressor technology. The study elucidates a vital element of sustainable materials within the industrial sector, providing an in-depth comprehension of their influence on machinery efficacy.

High-pressure sectors like mining and construction require multi-stage screw compressors that can operate reliably at pressures over 16 bar. Single-stage compressors frequently encounter constraints such as elevated temperatures, rotor bending deformation, imperfect cooling effect of the injected oil, condensate, and diminished bearing longevity, rendering them inadequate for these specifications. This paper introduces a comprehensive modelling and optimisation approach for multi-stage screw compressors, integrating a physics-based chamber model with machine learning via Gaussian process regression. The framework employs Bayesian optimisation to methodically refine stage-specific parameters, enhancing performance and dependability while ensuring computing economy. The innovation is in its capacity to precisely forecast the performance of both individual and final stages, experimentally validated with a two-stage air screw compressor for water-well applications, attaining an error margin below 5%. A case study illustrated the framework's efficacy by decreasing specific power usage by 2% via the optimisation of fluid injection parameters. This approach represents a significant advancement in compressor technology, providing a scalable and efficient solution for designing and optimising multi-stage screw compressors in high-pressure applications.

This study explores the application of the rack method, traditionally used for generating rotor profiles in spur gears and twin screw compressors, to rotor profile generation of internally geared positive displacement machines. The necessary conditions for ensuring continuous contact in these profiles are examined. An analytical approach is proposed, where a rack profile based on trochoidal curves generates the inner rotor profile, from which the outer rotor profile is derived. Additionally, a numerical approach is introduced, demonstrating feasibility using a sine wave rack profile to generate the outer rotor, from which the inner rotor profile is derived. The methodology could be applied to rotor profiles with a non-zero minimum working chamber area, as found in gerotor pumps, and modified profiles with a zero minimum area, as required for internally geared screw machines. This work provides the first demonstration of general rack-generated rotor profiles for internally geared positive displacement machines. It establishes a foundation for refining the rack method and developing advanced numerical techniques for machine design and optimisation.

Oil-free positive displacement machines are used in various industries where presence of oil in the process is prohibited. Due to the lack of cooling, they experience high temperatures and thermal growth of rotors and casing. Therefore, clearances between rotors and casing are increased to avoid contact. It is important to minimise operational clearances but retain reliable operation. This requires numerical methods able to calculate leakage flows accurately. A recent PIV measurement revealed that leakage flows in radial gap of roots blower are sensitive to rotor speed. This research is aimed to perform a numerical study to evaluate various grid generation and modelling techniques for estimation of leakage flows and comparing results with data obtained by Particle Imaging Velocimetry measurements. This study considered 2D static mesh with moving wall boundary condition, 2D unsteady dynamic layering mesh and full 3D deforming rotor grid model. Additionally, to accurately replicate the shape of the rotor tip and gap size, a deforming 3D grid with filleted tip and hybrid gap model was developed. CFD model also included change in air density due to the seeding required for PIV.Velocity magnitude and profiles in clearances, discharge flow and gas temperature predictions were validated against experimental data. Full 3D grid with hybrid gap, 5 % smoke seeding and axial gap size of 80 µm agree more with experimental data than simplified models. Discharge flow and temperature deviations from experiment were within 7 %. The validated model captured leakage flows accurately and can be applied to various rotor profile shapes.

Screw compressors are essential elements in various industrial sectors, such as manufacturing, energy, and construction, representing roughly 10%–20% of industrial electricity usage. Notwithstanding their prevalent application, the energy requirements of multi-stage screw compressors substantially contribute to carbon emissions. The global market for screw compressors is anticipated to expand at a compound yearly growth rate (CAGR) of 6.5%, achieving a market value of $19.37 billion by 2030. This highlights the increasing demand for more energy-efficient compressor systems. The utilisation of multi-stage screw compressors for applications surpassing 30 bar is constrained by issues including rotor bending deformation, diminished bearing longevity, inadequate oil cooling, and condensate separation in oil separators. Moreover, screw compressors encounter operational constraints in multi-staging, even at reduced pressure ranges, when compared to reciprocating compressors. This study seeks to examine the existing constraints of multi-stage screw compressors and investigates potential solutions for power levels of 22–315 kW and delivery pressures of 6–12 bar. A cost-effective compressor design was designed by utilising modern rotor profiles and optimising sealing and cooling systems. A prototype two-stage oil-flooded air screw compressor, intended for water-well applications, was fabricated and evaluated for performance and dependability. The efficacy of the two-stage compressor was evaluated against that of a single-stage air screw compressor of comparable capacity. An extensive economic evaluation, grounded in lifecycle costs, was performed over a decade. The results indicate that the two-stage compressor reduces operational expenses by roughly 20%–75%, leading to markedly lower lifecycle costs. These insights underscore the capability of multi-stage screw compressors to provide improved performance and economic advantages, promoting broader implementation in applications necessitating mid-range pressures.

The increasing demand for enhanced performance and reliability in twin-screw compressors necessitates the application of advanced optimisation tools to improve performance. This study employs response surface methodology (RSM) to optimise the profile parameters of a standard 5/6 compressor, specifically targeting reduction in specific power. Key factors such as axis distance between rotors and female rotor outer diameter, which define the rotor depth, were included in the present optimisation process. Following the optimisation of the rotor profile, port optimisation was also conducted using the same methodology. A multi-chamber thermodynamic analysis was performed with SCORGTM software, which allowed for the calculation of geometric values and thermodynamic quantities. The results of the rotor optimisation revealed notable improvements: a 4.30 % reduction in specific power, a 2.73 % increase in volumetric efficiency, a 3.93 % enhancement in adiabatic efficiency, and a 2.88 % rise in volumetric flow rate compared to the reference design. After port optimisation, both volumetric and adiabatic efficiencies of the optimised rotor profile remained comparable, while specific power was further reduced by 1.37 %. To validate the performance of the optimised compressor, computational fluid dynamics (CFD) analysis was conducted using a conformal mesh generated by SCORGTM and ANSYS CFX multiphase solver. The maximum deviation between the optimal results from SCORGTM and CFD was only 0.19 %, indicating strong agreement between the two methodologies. This study highlights the significant impact of optimisation techniques on the performance of twin-screw compressors.

Optimizing the performance of screw compressors is critical for achieving high efficiency and reducing costs in various industrial and engineering applications. Often, the design and optimization processes are time-consuming owing to the underlying iterative complex analyses. In this context, the present research investigates the potential of Gaussian Process Regression (GPR) and Bayesian optimization for the prediction and optimization of the performance of an oil-flooded screw compressor. Specifically, the GPR-based surrogate model is developed to predict the compressor performance characteristics based on its four main geometrical design parameters such as wrap angle, relative length, tip speed of the male rotor and built-in volume ratio. The model is trained using a dataset comprising 19,200 data points relating the input design parameters with the compressor performance, obtained using physics-based multi-chamber thermodynamic models. While four different learning algorithms such as Support Vector Machine (SVM), Artificial Neural Network (ANN), Polynomial regression and GPR are explored, the GPR performed the best resulting in an R2 value of 0.99 for the test dataset after hyperparameter tuning. Further, the model is also experimentally validated on a completely unseen dataset, showing very good predictions with a maximum error of 5%. The resulting surrogate model is then used to optimize the compressor design parameters using Bayesian optimization. The results are compared with optimization using Genetic Algorithm (GA) and physics-based multi-chamber thermodynamic model. It was shown the proposed approach results in similar optimal design parameters but with a significantly less optimization time by a factor of 7. The study highlight the potential of machine learning-based prediction and optimization of screw compressors in engineering applications.

A novel prototype design of an internally geared twin screw compressor for air, with oil injection has been analysed using a custom developed numerical grid. A two-fluid Eulerian-Eulerian CFD model has been applied for the calculations. Compressor performance at various operating conditions has been evaluated together with an analysis of the flow at the suction, discharge, and injection ports. Over the calculated range of speed and pressure, a specific power of 2–4 kW/m3/min was estimated with a maximum volumetric efficiency of 95

A Roots Blower is rotary positive displacement machine, commonly used for low pressure applications [3]. However, the gaps between the rotors and the housing are the main source of volumetric inefficiency and are required to be minimised. This has limits due to thermal expansion of compressor elements. Improvements can also be done by minimising leakage flows using different configurations of rotor tip profiles for which careful analysis is required. An optical Roots Blower from Howden is being investigated using experimental and numerical tools for the effects of heat transfer and tip geometry on leakage of gas. To closely study the leakage through the clearance gaps, a 2D simplification (Fig. 1b) of this 3D model is proposed in this paper. A local flow is evaluated in steady and transient state conditions using only through the tip leakage gap between the rotor and the housing on one rotor lobe. Using data from PIV measurements, the base tip design on the rotor profile is analysed and used for validation of the 2D model. Following this, variants of the tip-shape, namely equal-cavity and unequal-cavity tip profiles with alterations, have been numerically evaluated. These results will help in implementation of such a tip profile design in conventional oil free twin screw compressors to meet demands of efficiency improvements.

Gerotor machines are commonly used as oil and fuel pumps, and as hydraulic pumps and motors. They also have the potential to be used as positive displacement compressors, which is the focus of current research. The mechanism consists of an inner and outer rotor which rotate in the same direction but are each centred on offset parallel axes. The rotor profiles are specified such that multiple continuous contact points occur between them forming several separate working chambers, whose volume varies from minimum to maximum and back to minimum during rotation of the rotors. For a gas or two-phase working fluid, varying the discharge port geometry allows internal compression to occur prior to discharge. Furthermore, adding helical twist to the rotors allows the forces and torques acting on the rotors to be modified in order to minimize contact forces and power transfer between the driven and idler rotors. Previous research has investigated the operation of these internally geared screw machines via characterization of key geometrical properties and simplified analysis of the compression process. The current paper describes progress made on incorporating the geometrical analysis of these machines with the existing quasi one-dimensional chamber model within the in-house performance prediction software. This has allowed the compression process to be analysed in detail, including consideration of leakage flows and port flow losses. The influence of a range of factors including rotor profile, dimensions, built-in volume index and wrap angle have been considered via a parametric study over a range of inlet and discharge conditions.

Rotary twin screw compressors are widely used because of their high efficiency and reliability. Their most common mode of operation is as oil-flooded machines when delivering air and gases at moderate pressures and flow rates. In order to achieve the best performance, it is essential to be able to predict the optimum amount of oil, required for the oil injection process, accurately. Analytical procedures for the design and performance estimation of twin screw compressors are well developed and widely available, but the determination of oil drag losses, in oil-flooded machines is only guesstimated. This paper describes a more detailed and accurate procedure for estimating oil drag loss, using a combined Couette-Poiseuille flow model and gives the results of studies on three sizes of machines operating over a range of pressure ratios and speeds. To this end, a parametric analysis has been developed based on a combined Couette-Poiseuille flow model and has been used to estimate the individual effects of pressure ratio, the various clearances and the oil viscosity on the total drag loss, for different sizes of the compressor. It can be seen from the results that at pressure ratios of up to 8.5, the drag loss due to the discharge axial clearance gap is nearly 2/3rd of the total, while nearly 1/3rd is due to the radial clearance. At normal operating speeds, the loss due to the interlobe clearance is insignificant, but as the pressure ratio increases, this rises more rapidly than that due to the axial and radial losses. The gain in the drag loss due to greater oil viscosity becomes more significant as the compressor size is increased. In larger machines, when clearance values are increased, the radial and axial elements of the drag loss are reduced more rapidly than that due to the interlobe loss.