Variable Compressor Research Articles

Experiment investigation on secondary flow loss and flow control mechanisms in a variable compressor cascade with penny cavities

Variable Stator Vanes (VSVs) with penny cavities are an important method to improve the efficiency of compressors. However, the annular and radial gaps in VSVs introduce complex flow structures, posing challenges in enhancing compressor efficiency. This article employs low-speed wind tunnel experiments to study the impact mechanisms of VSVs' adjustment angle and radial gap size on secondary flow losses and implements single-hole suction as a means of flow control to reduce total pressure loss. The results indicate that radial gap leakage has a certain inhibitory effect on annular gap leakage at general adjustment angles. Total pressure loss decreases initially as the radial gap increases but once the radial gap further enlarges and dominates the loss components, the total pressure loss increases proportionally with the radial gap. At extreme adjustment angles, where the lateral pressure gradient is significant, radial gap leakage intensity is high and comprises the major part of the loss, leading to an increase in total pressure loss in proportion to radial gap enlargement. Additionally, single-hole suction is effective under various conditions, with the potential to reduce total pressure loss by up to 19.4 %. These findings provide guidance for the application of VSVs in further improving compressor efficiency.

Experimental study on pulsed suction under different momentum coefficients in variable compressor cascade with annular gaps

Variable Stator Vanes (VSVs) with penny cavities are crucial in the compressors of variable cycle engines, where complex interactions between annular and radial gaps can adversely affect aerodynamic performance. Unsteady active flow control techniques have significant potential for reducing secondary flow losses in compressors. This research investigates the internal flow characteristics of a variable compressor cascade with penny cavities using low-speed wind tunnel experiments and flow visualization techniques. This study is the first to experimentally explore the relationship between loss reduction and momentum coefficient using pulsed suction (PS) compared to steady continuous suction (SCS), evaluating the effects of various excitation frequencies. The findings show that at a momentum coefficient of 0.11 and an excitation frequency of 100 Hz, PS achieves optimal aerodynamic performance, reducing total pressure losses by 11.59 %, marking a 92.59 % improvement over SCS. As the momentum coefficient increases, the effectiveness of PS control significantly improves, whereas the changes in SCS effectiveness are less pronounced. The control effects of PS under varying excitation frequencies are complex and influenced by multiple factors. At higher momentum coefficients, the loss reduction effectiveness of PS is strongly correlated with excitation frequency, while at lower coefficients, performance changes due to frequency variations are minimal. This study provides valuable guidance for the design of modern multistage variable compressors.

Integrated Design of a Variable Cycle Engine and Aircraft Thermal Management System

Abstract The integrated design of a variable cycle engine (VCE) and an aircraft thermal management system (TMS) is investigated. The integrated system is designed using the multiple design point approach in order to achieve required performance metrics at points other than the cycle design condition. The VCE architecture is a three stream design where the third stream is split off after the fan, exhausting through a separate third-stream nozzle. The primary air stream passes through a low-pressure compressor before splitting into an inner bypass stream and a core stream. The inner streams mix aft of the low-pressure turbine and exhaust through a core nozzle. The variable cycle engine utilizes variable compressor inlet guide vanes, a variable area bypass injector at the core stream mixing plane, and variable throats in the two exhaust nozzles. The TMS architecture is an air cycle system using air bled from the high-pressure compressor. The effect of integrating the TMS into the engine design loop is investigated. A comparison is made to prior studies where the same TMS architecture was connected to a low bypass ratio turbofan engine. The comparison shows that the variable cycle engine is able to improve heat dissipation capability versus a ram air cooled system, while eliminating the airframe integration impact that comes with a separate ram-air stream. Lastly, the impact of modulating the variable geometry features on overall cooling capability is investigated. Results are presented for individual operating points as well as at the aircraft mission level.

Modeling and Experimental Verification of the Electrical Efficiency for Variable-Frequency Rolling Piston Compressor under Variable Suction Conditions

The frequency and the suction refrigerant state are complex in the actual operation of variable compressors, which leads to the variability of compressor performance under different operating conditions. The characterization and the modeling of the compressor have become hot research topics. For modeling, the electrical efficiency model of the compressor, which could be applied to the suction refrigerant state at both the superheated and the two-phase stages, the compressor frequency, the pressure ratio, and the evaporation temperature, is analyzed through experiments in this paper. The results show that the linear electrical efficiency decreases with the declining superheated temperature and the increasing suction vapor quality when the system is at the fixed and evaporating temperature. Moreover, the slope of the two-phase suction is above that of the superheated suction. In addition, the system’s electrical efficiency at the fixed pressure ratio is inversely proportional to the evaporation temperature, and the electrical efficiency of the system at the fixed evaporating temperature is also inversely proportional to the pressure ratio. The higher the variation of the pressure ratio, the smaller the evaporation temperature influences. To demonstrate the precision of the model, the theoretical value is compared with a confirmatory experiment in this paper. The maximum relative error is 1.81%, and the minimum is 0.035%.

Maximising the benefit of variable speed heat-pump water heater with rooftop PV and intelligent battery charging

Domestic applications of thermal energy storage, interacting with rooftop PV and batteries can substantially reduce consumer electricity costs, whilst assisting grid stability. Air source heat pump water heaters (HPs) with inherent thermal storage offer significant purchased energy savings, however, their typical control only considers stored water temperature. We demonstrate that further energy and cost reductions are possible using variable compressor speed controls that optimise thermal performance in real-time, whilst coordinating energy consumption to match available PV or shifting consumption to off-peak hours. The incremental complexity of variable-speed HP water heaters can reduce HP electricity consumption from the grid by up to 28% without PV or battery, 88% with PV, and 99% using PV and battery storage. By integrating the HP and all other domestic electrical loads, we exploit the combination of thermal and battery energy storage using rules-based and machine-learnt hierarchical controls to reduce the net household energy cost. Machine-learnt grid battery charging is shown to reduce annual grid energy consumption by 84%, delivering 99% of the potential energy cost savings. We conclude that a HP with inherent thermal storage, interacting with rooftop PV offers the most cost-effective home energy storage solution, lowering net lifetime costs by up to 27%.

Full-envelope acceleration control method of turbofan engine based on variable geometry compound adjustment

In order to reduce the influence of compressor stability margin constraint and enhance the full envelope acceleration performance of turbofan engine, a full envelope acceleration control method of turbofan engine based on variable compressor intermediate stage bleed and adjustable low-pressure (LP) turbine guide vane is proposed. Firstly, a high confidence turbofan engine component level model is established, which is capable of modifying the compressor adiabatic efficiency caused by variable intermediate stage bleed and adjusting the LP turbine guide vane adaptively. Then, the main combustion chamber fuel flow, compressor intermediate stage bleed flow and LP turbine guide vane angle are selected as the optimization variables. Meanwhile, the PSO-SQP (Particle Swarm Optimization-Sequential Quadratic Programming) method is adopted to obtain the acceleration compound control schedule. Finally, the full envelope compound adjustment acceleration control plan is available based on the similarity conversion theory of consistent engine inlet total temperature. The simulation results demonstrate that the acceleration control method based on variable geometry compound adjustment can significantly promote engine acceleration performance in the left flight envelope, shorten the maximum acceleration time by more than 50%, and dramatically improve the stability margin of the compressor during acceleration phase. In the right flight envelope, the variation law of the minimum surge margin during acceleration procedure almost coincides with the engine inlet isotherm. It proves that the method proposed possesses good applicability and feasibility in the full envelope.

Comprehensive vibro-acoustic characteristics and mathematical modeling of electric high-speed centrifugal compressor surge for fuel cell vehicles at various compressor speeds

The electric high-speed centrifugal compressor is the mainstream air compressor in present fuel cell vehicles. Surge strongly limits the stable operating range of centrifugal compressors. Therefore, it is of tremendous significance to study transient vibro-acoustic characteristics of the compressor surge evolution and early warnings of compressor surge. In this paper, comprehensive vibro-acoustic experiments of the compressor surge evolution are first conducted, and time-varying frequency characteristics are visualized through the short-time Fourier transform. The results show that the increase and fluctuation of the total sound pressure level at deep surge are mainly caused by the pressure pulsation at the centrifugal compressor outlet. Moreover, a rotating stall onset criterion based on acoustic signals is proposed, and the occurrence of severe rotating stall can be predicted by the precursor about 1.5–3 s in advance. Then, a mathematical model of the centrifugal compressor surge is established considering the variation of sound speed and introducing an additional volume, which unifies centrifugal compressor surge models at different compressor speeds. The maximum prediction error of the surge frequency is 1.95%. The model eliminates the pain point of the traditional Moore-Greitzer model which fails to predict the compressor surge characteristics at variable compressor speeds accurately. Finally, the impact of compression system dimensions on centrifugal compressor surge characteristics is quantitatively analyzed, and corresponding verification experiments are conducted. The proposed surge model can be used not only for quantifying the dynamic characteristics of compressor surge at transient speeds but also for designing active surge control strategies for variable vehicle operating conditions.

Aerodynamic investigation on compact variable compressor for vehicular turbochargers

Abstract In order to install a turbocharger which has wider operating range and higher boost pressure than a current supercharging system to an internal combustion engine (ICE) and a hybrid vehicle (HV), one development focus lies on a variable trim compressor (VTC) which can change passage area upstream a compressor wheel. In this paper, a new variable geometry device which was developed from the VTC mechanism proposed by Fujiwara et al. in 2018 is studied. The experimental result confirmed the performance enhancement associated with the design concept change and the improvement of trim actuation. In addition, the effect of the throat area ratio as design parameter in the new device on performance was numerically analysed. As a result, the optimal design value of passage area size in the VTC was around 60% and the passage area change position should be placed as close as possible to the compressor wheel.

Investigation of Aerodynamic Performance of a Compact Variable Compressor for Vehicular Turbochargers

Investigation of Aerodynamic Performance of a Compact Variable Compressor for Vehicular Turbochargers

Design optimization of external variable displacement compressor with R1234yf for vehicle air conditioning system

Due to the high global warming potential of the HFC-based R134a, it should be replaced by the HFO-based R1234yf as a working fluid for automotive air conditioning systems. In this study, for the external variable compressor whose stroke volume is controlled by the external signal used in the R134a air conditioning system, the optimization design of the compressor as the operating refrigerant changes from R134a to R1234yf is proposed. In order to analyze the working performance of the compressor a compressor simulation program was developed, and the drop-in test with R1234yf has been evaluated to replace R134a in the air conditioner system. From the drop-in test, both the cooling capacity and the coefficient of performance for the R1234yf decrease about 4 ~ 5% under the maximum stroke volume condition depending on the compressor operating speeds. And in the TEO5 control mode, where the lowest air temperature behind the evaporator is controlled at 5°C, it was found that there is only less than 4% reduction of the cooling capacity, while the coefficient of performance drops by up to 17% due to the increased compressor power. From the simulation result, we found that the reduced coefficient of performance of R1234yf might stem mainly from the increased losses by the suction and the discharge valves. By redesigning the suction and discharge valves within the designable range, as the results, the coefficient of performance is improved 1% at the MSV condition and 8% under the TEO5 control mode, respectively.

Experimental study and operation optimization of a parallel-loop heat pump for exhaust air recovery in residential buildings

The indoor space of residential building is limited, especially in building retrofit, to improve the indoor space utilization and the performance of exhaust air heat recovery system, a novel dual-cylinder rotary compressor with independent suction and discharge ports was designed to drive an inverter parallel-loop exhaust air heat pump. Through the experiments and analyzing the parallel-loop exhaust air heat pump system working characteristics under variable compressor frequency and different fresh air volume flow rate, the optimized method is proposed and verified experimentally. Finally, the annual energy efficient operation plan was proposed, and the seasonal performance factor and seasonal average input power under this operation plan in three typical countries/organization were calculated. Results show that the system COP can be greatly improved by applying a mixed air supply method during winter. When the fresh-air-to-return-air ratio is 1:1 and the outdoor temperature is −5 °C, the system COP reached 10.18, which is the highest comparing with the related studies. In summer, the system COP is increased by increasing the ventilation volume flow rate. When the operation of the parallel-loop exhaust air heat pump system follows the energy efficient operation plan to ensure the temperature effectiveness over 100% and the outdoor working condition complies with GB 21455–2013, the heating season performance factor, heating season average input power, cooling season performance factor, and cooling season average input power are 7.22, 0.6909 kW, 2.83, and 0.8167 kW, respectively. The work would provide guidance for the development of exhaust air heat recovery system in residential building.

Accelerating self-optimization control of refrigerant cycles with Bayesian optimization and adaptive moment estimation

This paper presents a model-free self-optimization control algorithm for modulating multiple inputs simultaneously to minimize the power consumption of a vapor compression system (VCS). We propose the use of Bayesian Optimization (BO) to warm-start a state-of-the-art extremum seeking control (ESC) algorithm and then accelerate the ESC on-line with Adam, a well-studied adaptive moment-based optimization method used to solve high-dimensional non-convex optimization problems such as training deep neural networks. BO initializes the ESC at conditions favorable for rapid convergence while concurrently learning a surrogate map of VCS power consumption as a function of the inputs. In addition, the warm-start increases the likelihood of attaining a global optimum for locally convex, but globally non-convex, objective functions by identifying regions where the global optimum most likely resides. The proposed algorithm is evaluated using a Modelica model of an air conditioning system with variable compressor speed, an electronic expansion valve and two variable speed fans. We demonstrate the acceleration of this algorithm in simulations of an occupied space with a realistic heat pump model with realistic ambient temperature profiles, variation in heat-load, and different actuation rates. We also show that, in spite of the presence of unknown exogenous disturbances, the proposed algorithm computes better set-points, faster than the ESC. We also observe that the proposed method improves transient performance compared to the state-of-the-art. • Learn calibration cost functions instead of dynamical models for setpoint optimization. • Energy model learned analytic model of underlying system dynamics. • Accelerate convergence of extremum-seeking algorithms via Bayesian optimization. • Optimize many setpoints at various operating modes without re-estimating gradient. • Case study with high-fidelity Modelica heat pump model in realistic environment.

Adiabatic compressed air energy storage technology

Adiabatic compressed air energy storage technology

Effectiveness of Variable Rotor Blades Technique&Variable Stator Vanes Technique in AdjustingAxial-flow Compressor

Multi-stage Axial-flow compressor is the main driver of continuous transonic wind tunnel and it usually has ultra-wide operating range. High performance wind tunnel generally requires its multi-stage axial-flow compressor has high economic performance and stability in its ultra-wide operating range. The combination of variable compressor rotational speed and variable geometry technique, variable rotor blades technique (VRBT) and variable stator vanes technique (VSVT), has been widely adopted in extending the stable working range with high efficiency of multi-stage axial-flow wind tunnel compressor. Adjusting Effectiveness was defined in this paper to quantify the effectiveness of VRBT and VSVT in extending stable and high aerodynamic efficiency operating range of wind tunnel axial-flow compressor under various operating conditions. The results show that the adjusting effectiveness of VRBT and VSVTis a function of reaction degree, flow coefficient, loading coefficient and the amount of loading coefficient change.

Advanced part-load control strategies for the Allam cycle

The Allam Cycle is a highly regenerative oxy-combustion cycle with very promising net electrical efficiency, low expected cost and near-zero emissions (being directly suitable for carbon capture and storage). In this cycle, the CO2 produced from the oxy-combustion is recycled as temperature moderator and the excess CO2 produced can be captured and stored. In this work, a detailed part-load model of the Allam Cycle is developed considering the off-design performance maps for the compressors, pumps and the turbine. To adjust the cycle load, different part-load control strategies are devised by combining turbine partial-admission, compressor variable guide vanes (at compressor inlet and diffuser) and minimum cycle pressure variation. These control strategies are compared at various part-load conditions ranging from 90% down to 20%. The study shows that the optimal control strategy varies depending on the cycle load. Furthermore, the increase of part-load cycle efficiency using advanced control strategies can reach up to 4.71 percentage points compared to a conventional strategy employing only variable compressor guide vanes. The research shows that close-to-maximum part-load efficiency can be achieved only with the optimized adjustment of compressors guide vanes and the minimum cycle pressure, while partial admission turbine turns out to be essential at very low loads (15–30% load).

Experimental short-term investigation of model predictive heat pump control in residential buildings

This study investigates the potential of model predictive heat pump control in detached houses in terms of electric energy consumption, thermal comfort and photovoltaic energy self-consumption. Two comparable test rigs with identical devices are set up. The test rigs include electrical air source heat pumps with variable compressor speed, thermal energy storages and heat dissipation by heat exchangers. The heat demand is controlled by valves, which are coupled to real-time simulation of building models in compliance with the principle of energy conservation. Measurements confirm test rig comparability. After introducing the model predictive control (MPC) concept, a successive series of six measurements of 120 h each within the heating season is presented. The model predictive heat pump controller is evaluated by comparison to a standard heat pump controller implemented into the reference test rig. Results show an average increase of the heat pump coefficient of performance of 22.2%, an average increase of 234.8% in terms of photovoltaic energy self-consumption as well as a resulting average heat pump operational cost reduction of 34.0% by application of MPC.

가변속 압축기 기구부의 회전운동 추정

가변속 압축기 기구부의 회전운동 추정

MEJORAMIENTO DE LA RESPUESTA TRANSITORIA Y LA EFICIENCIA ENERGÉTICA DE UN SISTEMA DE REFRIGERACIÓN CON COMPRESOR DE VELOCIDAD VARIABLE USANDO METODOLOGÍA ANTI-WINDUP

Este artículo presenta una metodología de control para mejorar el comportamiento transitorio y la eficiencia energética de un sistema de refrigeración que utiliza un compresor de velocidad variable. El objetivo de control es mantener la temperatura del compartimento en el punto de ajuste deseado, a pesar de las condiciones variables de carga térmica o las perturbaciones. Se obtuvo un modelo del sistema de refrigeración. Las variables de interés fueron la temperaturadel compartimento, la temperatura del sobrecalentamiento del evaporador y la velocidad del compresor de velocidad variable. Mediante el uso de simulaciones y pruebas reales del sistema de refrigeración, se encontró que una implementación convencional de un controlador de lazo cerrado causa un fenómeno conocido como “windup”, que conduce a la saturación del compresor de velocidad variable y disminuye el rendimiento transitorio del sistema de refrigeracióny aumenta el consumo de energía. Además, la temperatura del sobrecalentamiento del evaporador no se vio significativamente afectada por la velocidad del compresor variable, por lo que la única opción para mejorar el coeficiente de rendimiento del sistema de refrigeración fue la reducción del consumo de energía del compresor de velocidad variable.Se propuso una topología “anti-windup” para el controlador de lazo cerrado para evitar la saturación del compresor de velocidad variable. Las simulaciones y pruebas del sistema de refrigeración mostraron una mejora importante del comportamiento transitorio y un ahorro del 10,52% en el consumo de energía.

Variable refrigerant flow cooling assessment in humid environment using different refrigerants

Variable Refrigerant Flow (VRF) is a cooling system developed to anticipate and minimize operating and maintenance costs. VRF allows personalized control and maximizes flexibility to accommodate changing tenants in high rise and compound buildings in hot and humid environments. Although many studies have previously modeled VRF systems from an energy perspective, minor attempts have been made to analyze the exergy performance of this technology. The aim of this paper is to present an exergy/energy analysis of VRF technology to address the effect of refrigerant flow as well as the cooling-air flow rates on the electric energy saving in the hot and humid zones. This analysis will be then used to investigate its performance in humid areas, particularly the Gulf region. VRF is an advanced air conditioning system that is developed to manage load variability by controlling the compressor speed and the expansion valve opening. It is proposed that the system be implemented at Masdar City buildings, located in Abu Dhabi.In this study, VRF units from different manufacturers were modeled and compared using engineering equation solver (EES) and IPSEpro software. The models, which were mainly developed on EES were repeated for validation on similar models that have been developed using the IPSEpro software, and the results were in agreement within 6% uncertainty. Parametric studies were done after modeling the system on EES, where both the high and low pressures in the cycle were varied to obtain the corresponding COP and second law efficiency operating range. It was noticeable that COP and second law efficiency are significantly affected by the evaporator and condenser temperatures and pressures. In addition, as significant concern has been raised due to the impact of refrigerants on global warming, different refrigerants were considered and the results showed that refrigerant R-410a would be the second most efficient refrigerant, after ammonia, for such systems. Finally, an effectiveness NTU evaporator model was implemented to minimize the overall power consumption of the VRF system under various zone loads. It was found that, under a typical set of zone loads, the optimal refrigerant evaporating temperature is 11 °C, when the sum of indoor fan power and outdoor unit power is minimized using the exergy balance. These results helped decision makers to install the VRF system for the first time in that hot and humid area. The preliminary results for May and June sowed an average energy saving of 32% with variable evaporators and condenser speed and variable compressor frequency.

МОДЕРНИЗАЦИЯ МОДЕЛИ СУДОВЫХ ХОЛОДИЛЬНЫХ УСТАНОВОК ПРИМЕНЕНИЕМ НЕЧЕТКОЙ ЛОГИКИ ДЛЯ РЕГУЛИРОВАНИЯ ТЕМПЕРАТУРЫ

The paper considers modernization of digital temperature regulators of ship refrigerating units. The comparative analysis of the existing temperature regulators has been carried out, their advantages and disadvantages being determined. The author proposed to use fuzzy logic principles to determine the temperature mode of the refrigeration system and to control the operation of variable-output compressors. There has been developed a temperature control unit based on fuzzy logic in MATLAB/Simulink environment. The control unit processes input signals that are the temperature mismatch value and the temperature mismatch differential. Using a set of logic rules, the control unit generates a control signal and sends it to a variable performance compressor. By means of the model of the refrigeration unit presented in the Simulink mathematical modeling environment operation of the plant is compared in two modes: using temperature control on fuzzy logic and using the relay temperature control. The fuzzy logic controller has been stated to be more efficient due to its higher sensitivity to temperature changes, a logical forecast of the temperature change, and little difference between the required and real temperature of the unit. In terms of fuzzy logic, regulation process is smooth, with a little delay. The simulation results showed significant differences between the temperature logics used to control temperature of a ship refrigerating unit, advantages of fuzzy logic over relay logic.