Twin-screw Expander Research Articles

Potential Evaluation of Twin-Screw Air Expanders with Dual-Lead Rotors Used in PEMFC Systems

The reduction in the power cost of air supply systems has emerged as a critical challenge in the development of polymer electrolyte membrane fuel cells. This study proposes the use of dual-lead rotors to improve the performance of twin-screw expanders for the purpose of boosting expanders’ recovery power and consequently lowering the power cost of the air supply subsystem, which is hardly investigated in previous publications. For this purpose, a mathematical model is built to assess the potential of improving the expander performance by means of the dual-lead rotors. And the influence of lead and length of the high-pressure rotor segment and overall rotor length are analyzed. The results demonstrate that the smaller lead and larger length of the high-pressure rotor segment result in better geometric characteristics and thus thermodynamic performance. For example, case #4 with dual-lead rotors exhibits a larger rotating angle at the suction end and a larger suction area than those of constant-lead rotors by 43° and 100%, respectively, which further lower the suction pressure loss. Compared with constant-lead rotors, the maximum increments in the mass flowrate and indicated power are observed as 45% and 25.4%, respectively. However, the dual-lead rotors could not effectively contribute to an increase in the isentropic indicated efficiency of twin-screw expanders due to the severe leakage, and hence, it becomes crucial to address the leakage issues in twin-screw expanders.

Research and clearance analysis on of steam twin-screw expander employed in indutrial waste heat recovery

In actual factories, screw expanders frequently operate under partial loads.To address the lack of theoretical research and the risks of errors in engineering design associated with steam pressure differential power generation under these conditions,a simulation of the twin-screw expander's working process was developed. The rotor profile was designed, geometric variables such as rotor mesh clearance were calculated, and models for leakage and heat transfer were established. A suction pressure correction model was proposed for the suction process under partial loads, along with correction parameters to simplify simulations.Experimental results demonstrate that the twin-screw expander operates stably under highly fluctuating conditions, demonstrating excellent variable load performance.As the load decreases, the loss of suction pressure reduces the expander's pressure differential, leading to lower leakage and improved efficiency. When the load is reduced from 100 % to 65 %, the volumetric efficiency increases from 78.87 % to 84.76 %, and the isentropic efficiency rises from 66.81 % to 74.25 %.Compared to experimental data, the flow calculation error of the suction pressure correction model presented in this study is controlled within 3 %.This model addresses performance calculations under partial loads, ensuring that theoretical models better align with real-world applications and supporting accurate selection of twin-screw expanders.This model enables appropriate selection of expanders to reduce pressure losses and enhance economic efficiency.

Experimental analysis of a pilot plant in Organic Rankine Cycle configuration with regenerator and thermal energy storage (TES-RORC)

Applying thermal energy storage in a Regenerative Organic Rankine Cycle system is a possible combination of energy storage for renewable and waste energy sources. This research presents an experimental analysis of a regenerative organic Rankine cycle pilot plant, incorporating a thermal energy storage chamber based on a phase change materials to obtain thermal inertia in the system. The primary heat source is the residual heat of combustion gases at a temperature of approximately 320 °C coming from a generating set that operates within a thermal power generation plant. The prototype uses a twin-screw expander modified to work as a turbine. Novec 649 was used as the working fluid which is an organic compound. The experimental evaluation of the regenerative organic Rankine cycle with thermal energy storage has been carried out through energy and exergetic efficiency analysis to verify the operation of the pilot plant. Values of 13.2 % were obtained for the exergetic efficiency and 2.67 % for the global efficiency of the cycle, with a maximum expander work of 11.8 kW. It was demonstrated that the thermal energy storage system provides energy in response to the plant's operating inertia for 17.5 min, sufficient time for the gradual shutdown of the plant equipment, maintaining the working power of the regenerative organic Rankine cycle.

Implementation of a waste heat recovery prototype facility based on the Rankine cycle with a twin-screw expander

Considering the energy needs of developing countries, thermal power plant facilities are necessary for power generation. However, usable thermal energy is lost because the necessary technologies to exploit the waste heat from industrial processes have not yet been implemented. In this sense, the present analysis shows the experimental study of a prototype Steam Rankine Cycle energy system. The prototype uses the residual heat of the combustion gases from one of the generators installed in a thermal power plant as a heat source, the maximum temperature of these gases is 320 °C. This prototype is considered the first in the region to perform heat recovery with a power cycle with water as the working fluid. Considering the country’s economic constraints, the prototype was built using a 20 kW twin-screw compressor modified to function as a turbine. This prototype aims to increase the overall performance of the generating unit. For the characterization of this prototype plant, energy and exergetic efficiency analysis was carried out using the experimental data. The application showed that the measured efficiency of the twin-screw expander was low at 18.44 %. In contrast, the maximum expander work was 15.81 kW, the overall cycle efficiency was 3.52 %, and the exergetic efficiency was 5.45 %.

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.

The Investigation of Two-Phase Expansion Performance with Indicator Diagram in a Twin-Screw Expander

Volumetric expanders are proven to be more suitable for small-scale waste heat recovery applications because of their simplicity, reliability, lower rotational speed and lower cost. Unlike turbines, volumetric expanders can work in the two-phase fluid state, which broadens their application fields. To investigate the two-phase performance of volumetric expanders, a specific twin-screw expander was chosen and modeled. The leakage loss and the suction pressure loss were primary concerns in this research. The two-phase expansion process in the expander is presented in detail using the developed mathematical model with an indicator diagram. The influence of several factors, including inlet vapor quality, rotational speed and intake pressure, are investigated. The influence mechanism of the vapor phase and the liquid phase on expander performance is clarified. In brief, this paper presents an illustrative understanding of the two-phase expansion process in twin-screw expanders.

Performance improvement of twin-screw air expander used in PEMFC systems by two-phase expansion

Performance improvement of twin-screw air expander used in PEMFC systems by two-phase expansion

A CFD-based study of twin-screw expander performance and inlet structure optimization

Twin-screw expanders are widely used for small to medium-sized organic Rankine cycle (ORC) power generation. In order to improve the performance of twin-screw expanders in ORC, this study aims to improve the inlet efficiency and reduce the inlet pressure loss by changing the geometry of the inlet and shell. The CFD transient simulation is used to study the pressure, gas flow conditions and other parameters in the working chamber that are not easily obtained through experiments. The effects of improved size, speed, pressure ratio and internal volume ratio on the performance of the expander are analyzed based on the results. The results show that for the three expanders with different internal volume ratios, the optimized expander power and filling factor increases by 2%-14%. Isentropic efficiency of the expander reaches a maximum value of 0.73 when the pressure ratio is slightly greater than the internal volume ratio.

Two-phase mass flow rate through restrictions in liquid-flooded twin-screw compressors or expanders

Liquid flooded twin-screw machines are commonly used as compressors for different applications and offer excellent prospects for energy conversion in lower and medium power ranges as expansion engines in Rankine cycles for example with regard to either waste heat recovery or electrical power generation from regenerative heat sources. With the aim of minimising internal leakages, lubricating moving machine parts, or reducing thermal stress and providing the benefits of wet expansion, a twin-screw machine can be operated with an auxiliary liquid or a two-phase working fluid. In this context, the present work provides a basic approach addressing the two-phase mass flow rate calculation in water-flooded twin-screw machines. Based on a generic inlet-geometry model, two-phase mass flow rates are recorded for different operating conditions and mass dryness fractions in particular. Appropriate approaches for the theoretical two-phase mass flow rate and discharge coefficient calculation considering restrictions in the flow section—such as orifices and nozzles—are applied. Finally, the two-phase discharge coefficients are compared with flow coefficients determined by means of experimental and theoretical two-phase mass flow rates revealing the limits and uncertainties of the models applied in this study.

A two-phase approach for simulation of water-flooded twin-screw machines validated for expander applications

In the lower and medium power range, twin-screw machines offer a high potential for energy conversion in various compressor applications with liquid injection or as expanders with respect to electrical power generation from regenerative and exhaust heat sources in trilateral or wet Rankine cycle systems, for instance. Aiming high efficiencies and reliability, the design of liquid-flooded twin-screw machines as a critical system component presents particular challenges for the engineers. Hence, reliably representative simulations to guide design are mandatory. In this context, this study presents a two-phase approach for simulation of the operational behaviour of water-flooded twin-screw machines. The thermodynamic fluid state is calculated using the humid air model that considers the two-phase mixture in thermal equilibrium. Additionally, dissipative two-phase mass flow rates are predicted regarding a slip-flow model and two-phase discharge coefficients. The proposed two-phase approach including liquid distribution in the working chamber is validated for expander applications considering available experimental data of the test twin-screw expander SE 51.2 in terms of indicator diagrams, indicated power, mass flow rate, and outlet temperature.

Thermodynamic simulation and experimental validation of an oil-free twin-screw expander

The chamber model method is still a powerful tool for the thermodynamic simulation of screw machines and is widely used in the industry and in science. When choosing adequate submodels for the compressible flows through machine clearances and the machine ports high simulation accuracy can be reached with minimal computation resources. However, detailed modelling is required when the complex geometry of twin-screw machines is abstracted to a time-dependent zero-dimensional chamber model. In this paper a two-chamber model simulation tool is used for the thermodynamic simulation of an oil-free twin-screw expander operating with dry air as working fluid. Insights into the modelling process are presented and the importance of precise modelling of gap flows between adjacent capacities is discussed. The simulation results are finally validated against experimental data. Integral values obtained from the experiments, such as expander mass flow rate, indicated power, and effective power, are in good agreement with the numerical calculations. To gain a deeper understanding of the thermodynamics of the expander working cycle, additional investigations are carried out at zero speed. The mass flow rates measured for a variation of stationary rotor positions are compared to values calculated with the two-chamber model method.

Experimental Research on the Effects of Suction Ports on Twin Screw Expander Performance

An organic Rankine cycle (ORC) system is an efficient technology for generating power from low-grade thermal sources. Twin screw expanders are widely used in ORC systems. Pressure loss caused by a suction port influences the suction process and the system performance. In this paper, the effects of suction ports on twin screw expander performance are experimentally investigated. The pressure loss value of R245fa is measured under different working conditions, and its effects on the suction coefficient are discussed. Results show that a lower rotation speed results in a lower pressure loss value and a higher suction coefficient under certain working conditions. Increasing the suction pressure leads to a higher pressure loss value but a lower pressure loss ratio. Discharge pressure has little effect on the suction process.

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 novel method for rotor profile optimization of high temperature screw expanders employed in waste heat recovery systems

High temperature expanders have always been employed in industrial waste heat recovery systems, where twin-screw expanders were frequently adopted. However, the significant thermal deformation of rotors contributes to much technical difficulty on the designation and manufacturing of high temperature twin-screw expanders. The profile should be optimized with consideration of its thermal deformation in high temperature working conditions. In this article, a novel method for twin-screw expander profile optimization is developed. The thermal deformation of rotors is considered with meshing pair rules and interlobe clearance presetting. Theoretical analysis on interlobe clearance is made any steam inlet temperature from 20°C to 400°C, while experimental facility was built to figure out its reliability at high temperature. The optimized profile proved the effectiveness of this method. The clearance decreases significantly, decreasing from 1.28 mm at the working temperature of 20°C to 0.16 mm at 400°C. The testing results illustrated that the significant thermal deformation of rotors causes much interlobe abrasion once the operating temperature reached 400°C. With clearance of 0.1 mm and the radius correction angle of 0.0758°, the screw expander was proved to be reliably working at 400°C.

Гриб М., Брюммер А. Исследование эффектов поверхностной конденсации в паровых двухвинтовых детандерах = Grieb M., Brümmer A. Investigation into the effects of surface condensation in steam-driven twin screw expanders / пер. с англ. М. А. Федоровой

During the operation of twin screw expanders with slightly superheated vapours or even two-phase fluids, surface condensation on machine parts occurs during the filling period and the expansion phase when the working fluid is in contact with cooler inner surfaces. This heat exchange from the working fluid to adjacent machine parts effects the working cycle and the efficiency of these machines. Short time scales and the periodicity of the process indicate the condensation process is best described by models for dropwise condensation. In this paper the effects of surface condensation on the operation of twin screw expanders are initially discussed in a simulation-based investigation. Chamber model simulation coupled with a thermal analysis is used for the thermodynamic simulation, whereby heat transfer coefficients are systematically varied. It is found that during the inlet phase condensate emerges on the inner surfaces of the machine being substantially cooler than the working fluid. This results in a higher mass being trapped within the working chamber and, thus, an increasing mass flow rate of the machine. An increase in power output is, however, not observed. The results obtained from chamber model simulations are finally compared against experimental data of a screw expander prototype

Overview of the Development and Application of the Twin Screw Expander

With the development of society, the energy crisis has become increasingly prominent, which greatly affects the sustainable development of the economy of various countries. Industrial energy consumption accounts for more than 70% of China’s total energy consumption, of which more than 50% is converted to industrial waste heat, and recyclable waste heat resources account for about 60% of the total waste heat resources, while China’s current utilization rate of industrial waste heat only reaches about 30%. The development of renewable energy and recovery of low-grade waste heat in industry is the key to solve the problem. As a type of volumetric expander with full flow expansion, the screw expander is extensively applied in the industrial waste heat recovery and geothermal energy generation industry because of its effective utilization of low enthalpy energy. Improving the performance of the screw expander as the core, the paper concludes and summarizes the research status of the leakage, rotor geometry, sealing and lubrication, processing and manufacturing, which can affect the performance of the screw expander. In addition, it also introduces the application status and potential utilization of screw expander.

Experimental investigation, model validation and application of twin-screw expanders with different built-in volume ratios

Organic Rankine Cycles (ORC) are a promising technology to generate power from low temperature heat sources and can therefore help transform current energy systems into renewable ones. However, ORCs are often affected by a wide range of operating conditions with a high share of part load operation. Therefore, detailed component models are necessary for the design of these ORC modules. In this study, systematical experimental investigations were conducted on two identical twin-screw expanders with different built-in volume ratios. The expander measurements covered the entire operational range of the ORC test rig and the expander by methodically varying rotational speed, mass flow, inlet pressure and superheating at constant expander outlet pressure. The experimental data is then utilized to validate a semi-empirical model of the twin-screw expander. Subsequently, the validated expander model is used to determine the optimum built-in volume ratio of an expander supplied by a wide range of heat source temperatures and mass flows and fluctuating heat source mass flows.The experimental results show increasing filling factors with decreasing rotational speeds and maximum isentropic efficiencies at intermediate pressure ratios. The maximum isentropic efficiency achieved is 64%. The model validation shows a satisfactory accuracy of the model within a 10% deviation for data with the same built-in volume ratio. Changing the built-in volume ratio requires the adjustment of the model parameters, because the amount of internal leakage changes. The simulations used to determine the optimum built-in volume ratio show the importance of the selection of the optimum built-in volume ratio in dependency of the heat source. Furthermore, particular attention has to be paid to the operational range of the expander (mainly the rotational speed), since it can significantly limit the power output.

Analysis of real gas equation of state for CFD modelling of twin screw expanders with R245fa, R290, R1336mzz(Z) and R1233zd(E)

Abstract Positive displacement expanders are widely investigated and theirs models commonly use the REFPROP database to evaluate fluid properties. However, estimating procedures in CFD models using REFPROP result in heavy use of CPU time. Therefore, a study has been carried out to determine if simpler methods for fluid property estimation are suitable. The ANSYS CFX solver used includes a number of cubic equations of state, namely, the Redlich Kwong, Soave Redlich Kwong, Aungier Redlich Kwong and Peng Robinson. To determine their suitability, performance simulations were carried out with each of them, on a twin screw expander with a 4/5 rotor configuration and an “N” rotor profile, operating with R245fa, R290, R1336mzz(Z) and R1233zd(E). For each considered equation, the expander's performance results deviation from those obtained using REFPROP is evaluated. These results show that the ideal gas equation of state gives predictions of flow and power that deviate significantly from those determined with REFPROP. The alternatively available cubic equations give far better agreement. Of these, the RK equation has the highest deviation, although it differs by only 2.2% maximum from the REFPROP values. The PR equation yields the closest agreement with a deviation of the order of only 0.8%, while the deviation with both SRK and ARK equations is less than 1.1% maximum, practically negligible. Apart from the good agreement obtained, the use of the real gas equations, in place of REFPROP, resulted in a saving of approximately 43% in CPU operating time to obtain same level of convergence of the solver.

Development of a non-linear state estimator for advanced control of an ORC test rig for geothermal application

Abstract Organic Rankine Cycle systems are increasingly installed in low-enthalpy geothermal plants to supply efficiently heat and power. The variation in heat demand and the possible contribution to grid ancillary services result in part-load operation and flexibility challenges for the ORC. A suitable control system, able to maximize the power output and guarantee high profits, can be achieved by state-based multivariable advanced controllers. These are based not only on the error on the controlled variables, but also on the information of the system state, which is often non-fully measurable. Therefore, this work focuses on the development of a non-linear discrete state estimator to estimate the state of the compound evaporator/expander of the ORC. First, a dynamic model of the full ORC test rig in Dymola is developed and validated against experimental data, with relative root mean squared error for the major variables below 3.5%. A non-linear state estimator (Unscented Kalman Filter) using a finite volume discretized evaporator coupled with a twin-screw expander is designed and tested on a benchmark case in Simulink. Both the dynamic and the observer model are in good agreement with the experimental data. The observer converges to the evaporator wall temperature with sufficient speed and high accuracy.

Twin Screw Expanders Profile Optimization Using Surrogate-Based Modelling

Abstract. Twin screw machines can be used as an expander to recover the lost power in various processes that cause pressure exergy loss. Twin screw expanders (TSEs) have caught the attention of many researchers due to low capital, maintenance, and operation costs, longer lifespan, and usage in two-phase fluids. However, many efforts need to be made to enhance their performance. This research described the optimization of the profile of a TSE with 4-6 lobe configuration - using surrogate-based modeling (SBM). For this purpose, based on the in-house code developed within FORTRAN, a TSE profile was designed and validated against available data. Then, a mathematical model was developed by the design of experiments (DOE), and the effects of four main profile parameters were investigated on the expander performance in the entire design space. Finally, an optimized combination of parameters was derived using a multi-objective genetic algorithm. 3D computational fluid dynamics (CFD) results showed that the optimized profile had more than 7% exergy efficiency compared to the base profile.