Built-in Volume Research Articles

Modeling and analysis of a novel CPSC/CI combined profile for scroll compressors

The scroll profile design has become a research hotspot and plays a decisive role in scroll machines. However, the modeling process is complicated due to different expressions of peripheral and central profiles in most full meshing profile (FMPs). Moreover, systematic modeling and in-depth property investigation of scroll profile are still insufficient. Herein, this study simplifies scroll profile modeling by constructing a novel FMP that combines a cubic power series curve (CPSC) with a circular involute (CI) to improve the properties of scroll compressors. An analytical model of CPSC/CI scroll wraps is proposed using the orthogonal components approach and validated by numerical examples. Geometric models to calculate chamber volume and gas load action length, and gas load models, are established. The effects of the CPSC/CI on the scroll wrap tip, built-in volume ratio and gas load are investigated. The proposed CPSC/CI enhances scroll compressor's properties by providing favorable properties not only with wider range of variation in scroll wrap tip and built-in volume ratio but also smaller gas load vibrations due to its superior flexibility, compared to circular arc/CI. This study provides new possibilities for enhancing scroll compressor performance through the design of scroll wrap profile.

Fast and accurate modelling of twin-screw compressors: A generalised low-order approach

Twin-screw compressors (TSC) are commonly used in heat pump processes due to their robustness and flexibility. They exhibit two core properties, i.e. the swept volume and the built-in volume ratio (BVR), which heavily influence their capacity limits and off-design efficiency. This work presents a new low-order model (i.e. a polynomial model), which can accurately predict a TSC’s behaviour. The model uses the external pressure ratio and volumetric compressor inlet flow rate to calculate isentropic efficiency and compressor speed. The input parameters are normalised with a reference flow rate (calculated from the swept volume) and the BVR, respectively. This results in a generalised model of low numerical cost, which can be used for explorative studies independent of the specific machine size and BVR. A gain in computational speed by a factor of 375 is achieved compared to a semi-empiric reference model. The model displays very good predictive accuracy when used to predict the performance of machines with similar BVRs, but different sizes. A mean deviation from the manufacturer data of 4.29%, 0.88°C and 1.38% for the shaft power, the outlet temperature and the compressor speed can be observed, respectively. When there is a difference in size and BVR, the prediction accuracy is still reasonable but significantly declines for small and very large pressure ratios. Nevertheless, the proposed new approach extends the state-of-the-art by introducing a low-order model, which combines the advantages of low computational cost, high accuracy, physically correct predictions over a wide operational range and scalability to different machine capacities and BVRs. The validation for different fluids indicates a good general prediction accuracy relatively independent of the used fluid.

Nearly isothermal compression characteristics of the helium oil-flooded scroll compressor

The helium compressor is a crucial component in cryocooler refrigeration systems. Oil-flooding is a promising technique to solve the cooling and leakage challenges in helium scroll compressors, facilitating nearly isothermal compression. In this paper, the validated numerical model is employed to investigate the nearly isothermal compression characteristics of the two-phase mixture of helium and oil in a scroll compressor. Results indicate that the discharge temperature can be remarkably lowered from 455 °C to approximately 64 °C with the injection of an appropriate amount of oil into the working chamber. Moreover, the sealing effect of oil enhances the volumetric efficiency from approximately 66 % to 93.6 %. These advantages of oil flooding ensure an internal indicated efficiency that exceeds 100 % and results in superior isothermal efficiency. However, the polytropic exponent during the nearly isothermal compression process is smaller than the theoretical value, which imposes higher requirements on the built-in volume ratio for the helium oil-flooded scroll compressor.

Numerical investigation of bubble dynamics and flow boiling heat transfer in cylindrical micro-pin-fin heat exchangers

Micro-pin-fin evaporators are a promising alternative to multi-microchannel heat sinks for two-phase cooling of high power-density devices. Within pin-fin evaporators, the refrigerant flows through arrays of obstacles in cross-flow and is not restricted by the walls of a channel. The dynamics of bubbles generated upon flow boiling and the associated heat transfer mechanisms are expected to be substantially different from those pertinent to microchannels; however, the fundamental aspects of two-phase flows evolving through micro-pin-fin arrays are still little understood. This article presents a systematic analysis of flow boiling within a micro-pin-fin evaporator, encompassing bubble, thin-film dynamics and heat transfer. The flow is studied by means of numerical simulations, performed using a customised boiling solver in OpenFOAM v2106, which adopts the built-in geometric Volume of Fluid method to capture the liquid–vapour interface dynamics. The numerical model of the evaporator includes in-line arrays of pin-fins of diameter of 50μm and height of 100μm, streamwise pitch of 91.7μm and cross-stream pitch of 150μm. The fluid utilised is refrigerant R236fa at a saturation temperature of 30 °C. The range of operating conditions simulated includes values of mass flux G=500–2000kg/(m2s), heat flux q=200kW/m2, and inlet subcooling ΔTsub=0–5K. This study shows that bubbles nucleated in a pin-fin evaporator tend to travel along the channels formed in between the pin-fin lines. Bubbles grow due to liquid evaporation and elongate in the direction of the flow, leaving thin liquid films that partially cover the pin-fins surface. The main contributions to heat transfer arise from the evaporation of this thin liquid film and from a cross-stream convective motion induced by the bubbles in the gap between the cylinders, which displace the hot fluid otherwise stagnant in the cylinders wakes. When the mass flow rate is increased, bubbles depart earlier from the nucleation sites and grow more slowly, which results in a reduction of the two-phase heat transfer. Higher inlet subcooling yields lower two-phase heat transfer coefficients because condensation becomes important when bubbles depart from the hot pin-fin surfaces and reach highly subcooled regions, thus reducing the two-phase heat transfer.

Geometric and thermodynamic analysis of a fully meshed double-scroll compressor

The double-scroll wrap can effectively increase the volume flow rate compared with the commonly used single-scroll structure, but its built-in volume ratio is extensively reduced. With the aim of improving its built-in volume ratio, this study presented a fully meshed double-scroll profile, or called modified double-scroll, and proposed a generation method for it; its profile equations as well as relationships between its geometric parameters were obtained, and effects of the geometric parameters on the compressor performance were analyzed. Moreover, thermodynamic characteristic and working process of the double-scroll compressor were numerically simulated and verified with its performance experiment. It is found that the proposed fully meshed double-scroll significantly increases the built-in volume ratio by 33.8 %; meanwhile, it increases the volume flow rate, reduces the friction velocity between the orbiting and fixed scrolls, and decreases scroll dimensions. The proposed fully meshed double-scroll can be applied to the design and manufacture of scroll compressors.

Performance prediction and Bayesian optimization of screw compressors using Gaussian Process Regression

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.

Development of Dual Intake Port Technology in ORC-Based Power Unit Driven by Solar-Assisted Reservoir

The ORC-based micro-cogeneration systems exploiting a solar source to generate electricity and domestic hot water (DHW) simultaneously are a promising solution to reduce CO2 emissions in the residential sector. In recent years, a huge amount of attention was focused on the development of a technological solution allowing improved performance of solar ORC-based systems frequently working under off-design conditions due to the intermittence of the solar source availability and to the variability in domestic hot water demand. The optimization efforts are focused on the improvement of component technology and plant architecture. The expander is retained as the key component of such micro-cogeneration units. Generally, volumetric machines are adopted thanks to their better capability to deal with severe off-design conditions. Among the volumetric expanders, scroll machines are one of the best candidates thanks to their reliability and to their flexibility in managing two-phase working fluid. Their good efficiency adds further interest to place them among the best candidate machines to be considered. Nevertheless, similarly to other volumetric expanders, an additional research effort is needed toward efficiency improvement. The fixed built-in volume ratio, in fact, could produce an unsteady under- or over-expansion during vane filling and emptying, mainly when the operating conditions depart from the designed ones. To overcome this phenomenon, a dual intake port (DIP) technology was also introduced for the scroll expander. Such technology allows widening the angular extension of the intake phase, thus adapting the ratio between the intake and exhaust volume (so called built-in volume ratio) to the operating condition. Moreover, DIP technology allows increasing the permeability of the machine, ensuring a resulting higher mass flow rate for a given pressure difference at the expander side. On the other hand, for a given mass flow rate, the expander intake pressure diminishes with a positive benefit on scroll efficiency. DIP benefits were already proven experimentally and theoretically in previous works by the authors for Sliding Rotary Vane Expanders (SVRE). In the present paper, the impact of the DIP technology was assessed in a solar-assisted ORC-based micro-cogeneration system operating with scroll expanders and being characterized by reduced power (hundreds of W). It was found that the DIP Scroll allows elaboration of a 32% higher mass flow rate for a given pressure difference between intake and expander sides for the application at hand. This leads to an average power increase of 10% and to an improvement of up to 5% of the expander mechanical efficiency. Such results are particularly interesting for micro-cogeneration ORC-based units that are solar-assisted. Indeed, the high variability of hot source and DHW demand makes the operation of the DIP expander at a wide range of operating conditions. The experimental activity conducted confirms the suitability of the DIP expander to exploit as much as possible the thermal power available from a hot source even when at variable temperatures during operation.

Numerical modeling of flashing in TFC expanders for the efficient exploitation of low-grade heat

This paper presents a novel semi-empirical thermodynamic model for the simulation of two-phase expansion in twin-screw expanders. The model utilizes a limited number of unknown parameters, the values of which are calculated through a calibration-optimization process that exploits numerical experiments available in the literature. Two-phase expansion simulations are performed for a wide variety of operating conditions, revealing that the vapor quality at the suction port of the expander is the main factor affecting its efficiency. Increased vapor qualities at the onset of expansion lead to an increase in the expander’s efficiency because a better matching between the WF’s volume ratio and the expander’s built-in volume ratio can be achieved. The thermodynamic model is applied to assess the performance of a TFC engine operating under varying heat duties and temperatures of the heat source, indicating that a detailed analysis is necessary to conclude whether the TFC or the ORC is the optimal solution for a given application.

Experimental and numerical investigation of a micro-ORC system for heat recovery from data centers

In the effort to enhance the recovery of waste energy, data centers are drawing attention because of the huge amount of heat discharged from the computer racks. Organic Rankine cycle (ORC) power systems are a viable solution to exploit servers’ waste heat, as it is available at very low temperatures. The purpose of this study is to assess the feasibility of integrating a micro-ORC system into data centers cooling systems and its potential energy saving. An experimental analysis is carried out on a kW-scale ORC test bench, with R134a as working fluid. Heat is supplied at temperatures and flow rates in the range respectively 40-55 °C and 1.8-5 m3/h, consistently with typical values observed in data centers application, showing the second law efficiency varying between 5% and 13%. Furthermore, a steady-state model of the micro-ORC has been recalibrated and validated against experimental data; the built-in volume ratio of the reciprocating piston expander has been optimized to improve the filling performance of the machine. A parametric analysis, varying the boundary conditions within their range of interest for this application, and the working fluid (R1234yf and R1234ze(E)), shows that a maximum second law efficiency of 30% is achievable with R1234ze(E).

Design and analysis of conical rotary compressor

Conical Rotary Compressor (CRC) is a screw type Positive Displacement Machine (PDM) consisting of one inner rotor rotating inside an outer rotor. The conical internal meshing rotors with the feature of variable pitch and rotor profile have an inherent capability to operation at high pressure ratio due to high built-in volume ratio and low leakage. CRC has potential to run in various applications such as Heating, Ventilation, and Air Conditioning (HVAC) system, vacuum pumps, and air compressors. The performance of the machine is heavily affected by rotor profile and rotor geometry. In this paper, non-parallel axis conical rotor is firstly introduced according to current successful design and manufacture practice, then parallel axis conical rotors are design based on meshing theory. Then, geometrical parameters such as meshing line length, cross section area, chamber volume and relative velocity are analysed. Finally, the experiments were conducted under different pressure ratio up to 26 and the volume flow rate, specific power, volumetric efficiency, and isentropic efficiency are compared. As a result of this study, CRC could maintain high level of volumetric and isentropic efficiency under wide range of pressure ratio. Improvement of the compressor design can be made to limit increases in temperature, reduce relative velocity and increase the overall efficiency of the machine.

Design parameter study to extend the capacity range of dry twin screw compressors

The possibility for extending the capacity range for oil-free dry twin screw compressors has been studied. Basic geometry parameters influence on compressor performance has been derived. The two parameters shaft speed and rotor diameter are critical. The lower capacity limit for dry screw compressors depends on maximum acceptable shaft speed, considering bearings, gearbox or power electronics. The higher capacity limit depends on rotor size, considering machining costs and tolerances for large rotor diameters. Thermodynamic efficiency and optimal rotor tip speed are dependent on internal throttling and leakage losses. Simplified analytical modelling has been applied, neglecting detailed geometry with minor influence on compressor performance. Basic kinematic relations give shaft speed as dependent on screw geometry non-dimensional specific displacement, on rotor tip speed (moderately dependent of machine size), and on capacity. Basic kinematic relations also define the rotor diameter dependence on these three parameters, specific displacement; tip speed, and capacity. The rotor profile geometry, i.e. number of lobes, rotor lobe depth/diameter, male tip width/diameter; as well as rotor length/diameter ratio and wrap angle determine the specific displacement. The specific displacement is non-dimensional and hence independent of the machine size or capacity. Also the specific internal leakage path lengths in the rotor mesh and between rotors and casing, as well as the specific outlet port size will be determined by the rotor profile major geometry parameters. Here specific means in relation to the male rotor diameter. A fixed internal pressure ratio (volume ratio) has been assumed.A simplified computerized model was developed to calculate the necessary geometry data and in particular the specific displacement and the optimal tip speed, from basic geometry parameters. For the case of constant specific clearances (non-dimensional), the optimal tip speed is constant, independent of compressor size and capacity. For the case of constant absolute clearances, the optimal tip speed is slightly dependent on the compressor size and capacity. A simplified, non-female addendum, point generated, asymmetric profile was assumed. Rotor profile details with minor influence on performance have then been omitted. A cylindrical part of the male tip would allow a bigger outlet port while maintaining the built-in volume ratio.The theoretical results from this study indicate that optimal compressor data should primarily be dependent on the number of male lobes and the lobe depth, i.e. the specific displacement. A screw profile with a lower number of lobes will result in a lower optimal shaft speed and should hence enable the design of dry screw compressors for lower capacity than the commonly used 4:6 lobe configuration, without exceeding the drive train high speed constraint. A screw profile with a higher number of lobes would result in a higher optimal shaft speed and in particular reduced rotor size (rotor diameter). It should hence enable the design of dry screw compressors for higher capacity than for the commonly used 4:6 lobe configuration, without having the machining problems of too large a rotor diameter.Considering both the potential capacity range extension and the efficiency, low capacity dry screw compressors with fewer rotor lobes, e.g. 2:4, might be the most promising option.

Conjugate heat transfer effects on flow boiling in microchannels

• Heat distributes nonuniformly around the perimeter of microchannels in evaporators. • In single-phase flow, low aspect-ratio channels yield best heat transfer. • In two-phase flow, the Nusselt number trends vs. aspect-ratio are mixed. • High aspect-ratio channels exhibit larger thermal resistance and higher evaporator temperatures. • Conjugate heat transfer should be included in design models for evaporators. This article presents a computational study of saturated flow boiling in non-circular microchannels. The unit channel of a multi-microchannel evaporator, consisting of the fluidic channel and surrounding evaporator walls, is simulated and the conjugate heat transfer problem is solved. Simulations are performed using OpenFOAM v2106 and the built-in geometric Volume Of Fluid method, augmented with self-developed libraries to include liquid-vapour phase-change and improve the surface tension force calculation. A systematic study is conducted by employing water at atmospheric pressure, a channel hydraulic diameter of D h = 229 µm, a uniform base heat flux of q b = 100 kW / m 2 , and by varying the channel width-to-height aspect-ratio and channel fin thickness in the range ϵ = 0.25 –4 and W f = D h / 8 − D h , respectively. The effects of conjugate heat transfer and channel aspect-ratio on the bubble and evaporative film dynamics, heat transfer, and evaporator temperature are investigated in detail. This study reveals that, when the flow is single-phase, higher Nusselt numbers and lower evaporator base temperatures are achieved for smaller channel aspect-ratios, from Nu ≃ 4 and T b − T s a t ≃ 9 K when ϵ = 4 , to Nu ≃ 6 and T b − T s a t ≃ 2 K when ϵ = 0.25 , for same fin thickness W f = D h / 8 . In the two-phase flow regime, Nusselt numbers in the range Nu = 12 − 36 are achieved. The trends of the Nusselt number versus the aspect-ratio are non-monotonic and exhibit a marked dependence on the channel fin thickness. For small fin thicknesses, W f = D h / 8 and W f = D h / 4 , an overall ascending trend of Nu for increasing aspect-ratios is apparent, although in the narrower range ϵ = 0.5 –2 the Nusselt number appears weakly dependent on ϵ . For thicker fins, W f = D h / 2 and W f = D h , the Nusselt number decreases slightly when increasing the aspect-ratio in the range ϵ = 0.5 –2, although this trend is not monotonic when considering the entire range of aspect-ratios investigated. Nonetheless, due to conjugate heat transfer, Nusselt numbers and evaporator base temperatures follow different trends when varying the aspect-ratio, and channels with ϵ < 1 seem to promote lower evaporator temperatures than higher aspect-ratio conduits.

Design and development of an oil-free double-scroll air compressor used in a PEM fuel cell system

The purpose of this study is to arrive at an optimum design of a scroll compressor with requirements of a relative high volume flow rate and a compact structure, which is suitable for the use of hydrogen proton exchange membrane fuel cell (PEMFC) in the automotive application. An analytical model of multi-scroll compressors with arbitrary number of involute scrolls was established, and their working characteristics including the volume flow rate, built-in volume ratio, relative friction speed between the orbiting and fixed scrolls, and dimensions of scrolls were analyzed. An optimized double-scroll compressor, which can simultaneously meet the design requirements of the volume flow rate, structure size and oil-free lubrication, was designed, and a compressor prototype was developed and tested. Furthermore, numerical simulations of the working process of the double-scroll compressor were carried out and verified, and then p-V indicated diagram and the compressor performance were studied. Results show that the developed double-scroll compressor remarkably increases the volume flow rate, and reduces the relative friction speed between two scrolls simultaneously, compared with the conventional single-scroll structure; and therefore it shows very superior performance as an oil-free scroll air compressor used in the PEMFC of the automotive application.

Two-phase expansion processes in heat pump – ORC systems (Carnot batteries) with volumetric machines for enhanced off-design efficiency

Carnot batteries enable novel perspectives for decarbonizing the energy sector as an emerging technology for electrical energy storage. A power-to-heat process stores excess electrical energy as thermal energy which is transferred back to electrical energy on demand by a power cycle. This paper focuses on Carnot batteries by means of heat pumps and organic Rankine cycles (HP-ORC systems) as these systems combine the advantages of technically mature components, effective integration of heat sources and low-cost scalable storage. In combination with low-enthalpy geothermal heat, Carnot batteries offer an efficient synthesis of electrical energy storage and upgrading of low-enthalpy geothermal energy. Previous works highlighted that two-phase expansion can enhance the efficiency of heat recovery cycles. The present paper discusses partial evaporation and flash evaporation in Carnot batteries based on organic Rankine cycles and organic flash cycles (OFC) with volumetric machines as they enable two-phase expansion processes. The three investigated cycles ORC, OFC and OFC with two-phase expander are systematically analyzed in three steps. First, the potential cycle performances are identified without restrictions of volumetric machines. Afterwards, the effects of under- and over-expansion due to fixed built-in volume ratios are taken into account. Finally, a validated screw expander model is utilized to determine the performance of the three cycles in off-design conditions. The results show that the vapor quality of the partially evaporated ORC as well as the flash pressure ratio of the OFC both indicate a specific optimum depending on the storage temperature. The fixed built-in volume ratio of volumetric machines limits the efficiency of partial evaporation in the ORC due to strong under-expansion. Notably, the built-in volume ratio does not affect the optimal flash pressure ratio in the OFC. Partial evaporation increases the power output at the cost of efficiency which can be utilized during temporary peak loads. The ORC yields higher efficiencies than the basic OFC in all operating conditions due to the throttling losses of the OFC. Contrarily, the OFC with two-phase expander increasingly outperforms the ORC with rising storage temperature spread. This advantage increases in part load conditions as the OFC becomes less sensitive to the flash pressure ratio. Hence, this facilitates the control of flash pressure ratio and enables advantageous efficiencies. Thus, partial evaporation and flash evaporation can enhance the performance of Carnot batteries throughout a wide operational range.

Optimal design and development of two-segment variable-pitch screw rotors for twin-screw vacuum pumps

The built-in volume ratio of the twin-screw vacuum pump plays a crucial role in determining its applications. The screw rotor with larger built-in volume ratio has lower power consumption and lower discharge temperature, which is beneficial to obtain a higher ultimate vacuum. In order to improve the built-in volume ratio of screw rotors, and then develop a twin-screw vacuum pump with high ultimate vacuum, this paper presented a two-segment variable-pitch screw rotor generated by sweeping a constant cross-sectional profile along helixes. Effects of geometric parameters including the radius ratio and central angle on the rotor structure, area utilization and pumping speed of the proposed variable-pitch screw rotor were analyzed. Consequently, a pair of intermeshing two-segment variable-pitch screw rotors were optimized and manufactured, and a prototype of a twin-screw vacuum pump was developed. The performance of the proposed variable-pitch screw rotor was verified by the performance experiment of the developed prototype. Results show that the proposed two-segment variable-pitch screw rotors exhibits many distinct advantages of high ultimate vacuum, easy to process, and low noise and vibration; and its ultimate vacuum can quickly reach 0.1Pa. The developed screw rotors are of great significance for improving the performance and application of the twin-screw vacuum pump.

Experimental investigation of a revolving vane expander in a micro-scale organic Rankine cycle system for low-grade waste heat recovery

Organic Rankine cycles (ORCs) are a reliable solution for power generation from low-temperature waste heat. While the ORC is a mature technology in medium to large scale applications, several challenges remain to be solved for its widespread adoption in micro-scale, including the development of a low-cost, reliable, and efficient expander. In this study, a modified revolving vane expander (M-RVE) prototype is experimentally tested in a micro-scale ORC system for the first time. The M-RVE is tested in the range of suction pressures of up to 13.0 bar(a), suction temperatures of up to 63 °C, and shaft speeds of up to 1850 rpm. The M-RVE demonstrated filling factors of 1.2–2.7, an isentropic efficiency of up to 42.5%, and shaft power of up to 134 W. The significant impacts of lubrication on the performance of the M-RVE are discussed. A comparable performance with existing expanders in the literature is achieved, especially at pressure ratios close to the expander built-in volume ratio. The results of this study provide better guidance for further use of the M-RVE in micro-scale ORC systems and provide a benchmark for future improvements of the M-RVE prototype.

Study on novel cross-axis conical screw rotors with large built-in volume ratio for twin-screw expanders used in energy recovery systems

The twin-screw expander is widely used in many low-grade energy recovery systems. Its built-in volume ratio has a crucial impact on the system performance. Large built-in volume ratio can expand both the application and scope of the twin-screw expander, and can improve the efficiency of the power generation cycle as well. In this study, a novel pair of intermeshing cross-axis conical twin-screw rotors (CCSRs) with large built-in volume ratio and large expansion ratio for the twin-screw expander was proposed. The conjugate meshing of CCSRs can be achieved by using spherical-sectional profiles. Geometric performance of the proposed CCSRs was studied. Moreover, a thermodynamic model and numerical simulations of the working process of the proposed cross-axis conical twin-screw expander (CCSE) were established, and the working performance and thermodynamic characteristics during the expansion process were analyzed. Study results indicate that the proposed CCSRs exhibit a larger built-in volume ratio, and the corresponding twin-screw expander has a larger expansion ratio than that of the traditional one. The contents will be beneficial to the improvement and development of the twin-screw expander and energy recovery systems.

A Review of Recent Research and Application Progress in Screw Machines

Screw machines, mainly including single-screw type and twin-screw type, have gone through significant development and improvement during the past decade. This paper reviews the relevant studies available in the open literature for acquiring insight into and to establish the state of the art of the research and application status of screw machines. The related research on different aspects, which would affect the performance and reliability of screw machines includes rotor profile and geometric characteristics, thermodynamic modelling, vibration and noise, lubrication and wear, control of capacity and built-in volume ratio, and liquid injection technology. In the aspect of thermodynamic modelling, the available methods, i.e., empirical or semi-empirical model, lump model, and 3D CFD model, adopted for the performance prediction and optimal design of screw machines are summarized. Then, the review covers the application status of screw machines in the fields of air compression and expansion, refrigeration and heat pump, organic Rankine cycle (ORC), and other popular applications, with an emphasis on the reported performance and progress in technologies of screw machines. Finally, conclusions and perspectives for future research in the area of screw machines are presented. The review provides readers with a good understanding of the research focus and progress in the field of screw machines.

Задача об оптимальном расположении включений для композитных тел с отдельными и соединенными жесткими включениями

Nonlinear mathematical models describing an equilibrium state of composite bodies which may come into contact with a fixed non-deformable obstacle are investigated. We suppose that the composite bodies consist of an elastic matrix and one or two built-in volume (bulk) rigid inclusions. These inclusions have a rectangular shape and one of them can vary its location along a straight line. Considering a location parameter as a control parameter, we formulate an optimal control problem with a cost functional specified by an arbitrary continuous functional on the solution space. Assuming that the location parameter varies in a given closed interval, the solvability of the optimal control problem is established. Furthermore, it is shown that the equilibrium problem for the composite body with joined two inclusions can be considered as a limiting problem for the family of equilibrium problems for bodies with two separate inclusions.

Geometric model and pressurization analysis on a novel sliding vane compressor with an asymmetrical cylinder profile

The cylinder profile primarily determines the working performance of the sliding vane compressor. In order to increase the built-in volume ratio and compression ratio of the compressor, in this study, a novel asymmetrical cylinder profile composed of an exponential spiral was proposed, and then a novel asymmetrical sliding vane compressor was obtained. A geometric model of the proposed asymmetrical cylinder profile was established, and effects of power exponent n on the built-in volume ratio, area utilization ratio and acceleration of the cylinder profile were discussed. Furthermore, the working process of the proposed sliding vane compressor were simulated using structured dynamic grids, distributions of flow fields in the working chambers were obtained, and the gas pressure varying with the rotational angle was also analyzed. The study results show that the proposed sliding vane compressor has many remarkable advantages, small discharge volume, large built-in volume ratio and large compression ratio, compared with the traditional sliding vane compressor with the symmetrical cylinder of a circle profile under the same geometric size. The contents of this study are of great significance for promoting the development and application of sliding vane compressors.