Rotational Speed Of Compressor Research Articles

Loudness reduction of household refrigerator by structural modification

In this study, loudness reduction of a household refrigerator was attempted by the structure modification. At first, loudness of the radiated noise was analyzed at various operational condition and the loudness was observed to be increased at a specific compressor rotational speed and the large sound pressure level (SPL) at 100 Hz was the main factor. Through the vibration analysis of the refrigerator body, the SPL was found to be increased largely by the resonance between the compressor rotational order input force and the natural frequency of the refrigerator body. Then, for the reduction of the sound, the rubber bush hardness of the compressor mount was softened and the loudness was decreased. However, the door vibration at low rotational speed was increased. Accordingly, we attempted to modify the body structure for the loudness reduction to compatible with small door vibration. Vibration mode analysis indicated that the high contributing vibration behavior of the body increasing the loudness and a countermeasure was applied to constrain the behavior. Finally, the loudness was decreased about 30% and the vibration was not increased at the low rotational speed by the countermeasure.

Visualization of vane chattering in rotary compressor

In this study, the impacts of various factors on the chattering phenomenon in sliding vane compressors, which is a crucial aspect that influences their performance and efficiency were explored. The analysis focused on the compressor rotational speed, pressure ratio, and operating temperature, considering both ambient and heated conditions. The aim was to provide a comprehensive understanding of the relationship between these factors and the occurrence of chattering at different operational intervals, as well as the vane sealing performance and adherence to the chamber wall.The methodology involved examining vane behavior and the chattering occurrence across three intervals under various conditions, specifically looking at oil films formation and sealing performance degradation. The experimental results provided notable insights into the chattering phenomenon. It was shown that as the pressure ratio increased and the compressor rotational speed decreased, the sealing performance deteriorated. Moreover, when operating under heated conditions, a decrease in oil viscosity leads to reduced friction between the vane and bearing, improving vane adherence compared to ambient conditions.The methodology and findings of this study provide insights into the chattering phenomenon in vane compressors by considering the interplay between various factors. The results emphasize the importance of optimizing the compressor oil refueling flow, rotational speed, pressure ratio, and operating temperature, to ensure proper lubrication and efficient interaction between the vanes and compression chamber walls for improved compressor performance and reduced operational challenges.

Centrifugal compressor design and cycle analysis of large-scale high temperature heat pumps using hydrocarbons

Using natural refrigerants in heat pumps, including hydrocarbons, is becoming attractive because of the tightening regulations concerning synthetic refrigerants. In the literature there is lack of studies investigating detailed component design, including compressor design when using hydrocarbons. This study investigates numerically centrifugal compressor design with hydrocarbons for large-scale high-temperature heat pumps. The compressor analysis was combined with a thermodynamic analysis of a two-stage heat pump. The effect of temperature lift and flash intercooler temperature on compressor sizing, rotational speed, efficiency, axial force, and Mach number were investigated. Generally, the use of hydrocarbons with five carbon atoms resulted in higher coefficient of performance and required lower compressor rotational speeds and larger compressor dimensions when compared to the hydrocarbons with four carbon atoms. The simulated rotational speeds were ranging from 8 krpm to 30 krpm, impeller diameters from 0.15 m to over 0.7 m and compressor efficiencies from 77% to over 85%. The use of cyclic molecules, namely cyclopentane and cyclobutene resulted in the highest heat pump coefficient of performance. Also, the flash intercooler temperature had a notable effect on the compressor design and axial force which has to be taken into account in heat pump cycle design.

Aerothermodynamic and rotordynamic performance evaluation to diagnose deposits accumulation in a gas lift centrifugal compressor

The paper presents a case study focusing on the assessment of the aerothermodynamic and rotordynamic performance to diagnose deposit accumulation on the internals of a centrifugal compressor. The case involves a four-stage gas lift centrifugal compressor powered by a 5.9 MW induction motor and utilizing a fluid coupling to regulate the compressor's rotational speed. The Huntington 4-point method was employed to evaluate the polytropic head and efficiency of the four compressor sections over a 20-month period, with pressure and temperature data sampled every 6 hours. The efficiency model was supported by the GERG-2008 equation of state, used to calculate the necessary thermodynamic properties at intermediate and endpoint states. The aerothermodynamic analysis identified a deterioration in polytropic efficiency in compressor section 3, accompanied by a pressure drop and an increase in discharge temperature. Simultaneously, the rotordynamic response was examined through various vibration plots. Although the increase in the vibration amplitudes was not significant, a notable phase shift was observed. This decline in polytropic efficiency and change in vibration patterns were attributed to severe fouling, which was confirmed during the overhaul of the HP compressor. Root cause investigations revealed the deposit as reactive, leading to the installation of an online washing system. Over a nine-month observation period post-maintenance, the compressor operation was stable with no degradation in its polytropic efficiency.

Thermodynamic process control of compression-assisted absorption refrigeration using ocean thermal energy

An efficient control method is crucial for the safe and reliable operation of compression-assisted absorption refrigeration using ocean thermal energy. In this study, a dynamic model of 10 kW compression-assisted absorption refrigeration system is developed, and four integrated control strategies containing two cooling-capacity control approaches (Single input control and Cooperation control) and two temperature glide control approaches (Valve-based control and Compressor-based control) are proposed to control thermodynamic process. The proposed control strategies are evaluated in terms of both control and refrigeration performances. The results indicate that the refrigeration system can operate with stability at 50 % cooling load under the proposed control strategies. Moreover, the cooperative control of the flow rates for both warm-seawater and concentrated solution can significantly speed up cooling-capacity regulation. The rotational speed of compressor is a more suitable manipulated variable for regulating the evaporator temperature glide. The equivalent COP for the compressor-based control strategies is greater than 0.12 at 50 % cooling load, while the equivalent COP for the valve-based control strategies is only 0.064.

Centrifugal compressor design for high-temperature heat pumps

Heat pumps are identified as crucial technology for decarbonising the heat production. Especially for large-scale, high-temperature heat pumps the use of centrifugal compressors has been seen as an attractive technological option. However, there are very few detailed studies available discussing the compressor designs with different refrigerants for high-temperature heat pumps. This study combines the analyses of a 500 kW two-stage heat pump cycle and centrifugal compressor designs. The study qualitatively assesses the feasibility of compressor designs and provides information on how the dimensions, efficiency, and rotational speed are influenced by cycle conditions and the refrigerant. Temperature lift and evaporation temperature were varied with eight working fluids, including hydrocarbons and hydrofluoro-olefins. The estimated COPs were 2.0–2.55 with the highest values observed with pentane and isopentane. The compressor rotational speeds were between 20 – 50 krpm with hydrocarbons requiring higher values than fluids containing fluorine. The predicted compressor efficiencies were between 77% to 84%, with low pressure compressor reaching higher efficiencies than the high-pressure compressor. However, high compressor Mach numbers were observed, and the Mach number seems to be the main obstacle for the increase of the heat pump temperature lift when centrifugal compressors are used.

An empirical model of a split-type inverter air conditioner for building energy simulation

The increasing adoption of air conditioning prompted by climate change and the fourth Industrial Revolution is poised to greatly influence the demand for energy consumption, especially in rapidly developing economies situated in the planet's hottest regions. The overwhelming majority of air conditioners (ACs) in use today around the globe are split systems, and the inverter technology is taking over the market for this kind of equipment, so it is extremely important for researchers to be able to simulate inverter air conditioners (IACs) behavior properly and demonstrate its energy efficiency benefit to help reduce energy consumption demand in the world. For energy performance assessment of buildings equipped with IACs, building energy simulation (BES) tools usually employ empirical models based on data provided by manufacturers to be able to simulate performance, however, even with the most updated standards in place, the data provided is not enough to provide a robust empirical model. The models available to predict IAC performance today are not well suited to be integrated with BES tools therefore this work aims to fulfill this gap by providing an empirical model built by adapting a methodology suggested by ASHRAE and based on 96 experimental tests variations to be able to simulate IAC performance more accurately, considering a wide range of temperature and humidity conditions and different compressor rotation speed values (30 Hz, 60 Hz and 90 Hz). All tests were carried out in a psychrometric calorimeter working according to an ISO standard and following the Air-Enthalpy Method. The paper provides a comprehensive breakdown of the calculation procedures used to ascertain and forecast total cooling capacity, sensible cooling capacity, and energy efficiency ratio, along with their associated uncertainties. This detailed explanation aims to facilitate the replication of the methodology by fellow researchers. The presented model exhibits a strong predictive capability for the tested IAC, boasting mean absolute errors of less than 5 % within an internal wet-bulb temperature range of 10–24 °C and an external dry-bulb temperature range of 25–40 °C. This level of accuracy makes it a suitable candidate for integration into various BES tools.

Komparasi Kinerja AC Kendaraan dengan Menggunakan Refrigeran R-134a, dan R-290

The development of vapor compression refrigeration systems currently depends on the issue of environmental problems related to ozone layer depletion (ODP) and global warming potential (GWP). In addition to environmental issues, low energy use is also in the spotlight of researchers. To solve the problem of refrigeration development, natural refrigeration, especially hydrocarbons, is the focus of attention. Hydrocarbons are refrigerants that have excellent properties to be natural refrigerants. This study aims to compare the performance of refrigerant R-134a with R-290. The research used a standard vapor compression refrigeration system with a TEV-type expansion valve. The system performance is seen through compression, refrigeration effect, and COP with variations in compressor rotational speed of 1000 rpm, 1500 rpm, and 2000 rpm. The results showed that the compression work, refrigeration effect, and coefficient of performance (COP) of R-290 had a more excellent value. R-290 produces the highest compression work at a 2000 rpm compressor speed of 33.34 kJ/kg for the refrigeration effect at 1000 rpm of 353.33 kJ/kg and COP at 1500 rpm 12.32.

Leakage Flow Impact on Shrouded Stator Cavity Flow Topology and Associated High-Speed Axial Compressor Stage Performance

AbstractThis paper presents the investigation of realistic cavity leakage flow for the von Karman Institute for Fluid Dynamics H25 axial compressor stage, equipped with a shroud cavity of average Reynolds number Rer = 2.2 * 106 and average aspect ratio G = 0.06. On top of overall performance measurements, time averaged data from unprecedented experimental dataset are used to characterize the stator hub shroud cavity flow field and its interaction with the power stream. The sensitivity of the stage performance and stability as well as the cavity flow topology is evaluated against injection conditions, compressor throttling, and compressor speed. Parametric steady RANS simulations of the stage under injection are used to support the findings and state on the relevance of such approach in the preliminary design phase of axial compressor components. As an example, a stage efficiency reduction of 0.97% for a leakage fraction of 0.56% at design point is retrieved. This performance drop is attributed to the effect of cavity flow on: the blockage ratio, the boundary layer skewness, and total temperature increase at stator row inlet. It is also presented that there is a mutual interaction between the cavity geometry and the cavity flow field organization. The injection homogenizes the cavity flow field and the associated pressure gradient. The various operating conditions presented also demonstrate that the cavity flow studied is, on average (i.e., time), sensitive to changes in compressor rotation speed and changes in stage loading.

An experimental modal decomposition method to compute sound power of multi-dimensional acoustic waves from turbocharger compressors

The automotive turbocharger compressor in the present experimental study features a ported shroud casing treatment, which is known to elevate tonal noise at the blade-pass frequency (BPF) while reducing broadband whoosh noise and providing higher boost pressures at low mass flow rates. The high operating rotational speeds of such modern turbocharger compressors push the BPF to ranges where acoustic wave propagation is multi-dimensional within the compressor ducting. Simultaneously propagating acoustic modes at the BPF result in strong circumferential and axial variation of in-duct sound pressure levels. This poses a challenge for acoustic characterization and comparison of different hardware since typical measurement techniques do not consider the sensitivity of acoustic pressure to the measurement location. The current work utilizes a steady-flow turbocharger gas stand with a unique rotating compressor inlet duct fitted with multiple wall-mounted dynamic pressure transducers capable of performing a modal decomposition of the acoustic field. The decomposition is done using time-resolved acoustic pressure measurements from different orientations of the rotating inlet duct during steady compressor operation. The resulting modal amplitudes are then used to determine the sound power level, a quantity that is independent of the acoustic pressure measurement locations. Therefore, in addition to revealing the modal content of noise at the compressor inlet, the rotating inlet duct experimental setup better characterizes the acoustic field with sound power levels across the operating flow range at various compressor rotational speeds.

Co-regulation of integrated thermal management based on refrigerant cooling for electric vehicles

As an essential part of an electric vehicle thermal management system, collaborative regulation of power battery thermal management and AC temperature is imperative to maximize the vehicle's driving range and energy utilization effectiveness. This work proposes a joint control pattern for the compressor (Com) and variable opening valves (VOVs) with a dual-evaporator system. Specifically, the compressor rotation speed is the dominant control variable, and the battery's thermal behavior and system COP are investigated. The analytic results demonstrate that when the system is under moderate and high thermal loads, the Com-VOVB-VOVC strategy can regulate the temperature of both the battery and AC temperature. Meanwhile, the goal of low energy consumption is optimized. Nevertheless, when the thermal load is low, the Com-VOVB strategy can attain steady temperature regulation for the dual-evaporator and decrease the complexity of the system control. In addition, a Map approach to the temperature regulation is presented, enhancing the effectiveness and dynamism of thermal management control. The common control method for an integrated thermal management system can effectively confront system thermal load changes and decrease energy consumption.

Experimental study on the performance and control strategy of a water-cooled subcooler-assisted carbon dioxide heat pump for combined cooling and heating

Carbon dioxide heat pump is considered a potential low-carbon combined cooling and heating solution. However, there is a strong need for simple methods to improve the energy efficiency of the carbon dioxide heat pump due to the larger throttling losses that result in poor performance. Given this, a compact water-cooled subcooler-assisted carbon dioxide heat pump for combined cooling and heating is designed in this paper. An experimental test platform is built, where experimental investigations are performed to reveal the working performance. Furthermore, a matching control strategy is developed and verified as well. The experiments demonstrated that the adoption of the water-cooled subcooler has significantly improved the cooling performance. The cooling capacity (Q̇c) and cooling coefficient of performance (COPc) are increased by up to 20.2% and 31.5%, respectively. Moreover, the optimal discharge pressure is lowered by 0.5 MPa. However, the heating performance is somewhat degraded, for which the control strategy with the synergistic variation of subcooling degree and compressor rotation speed is developed. The deteriorated heating performance is thus mitigated. The developed control strategy has been verified in practice, and the carbon dioxide heat pump performance could be maintained at the highest possible level. Q̇c and COPc are further improved by a maximum of 40.7% and 37.7%, respectively. The heating and overall coefficient of performance could reach 2.55 and 5.10 at the return water and outlet water temperatures of 40 °C and 75 °C, respectively.

Simulation of single and two-phase refrigerant compression in rotary compressors

Liquid slugging, which often happens during startup and defrosting processes of the air conditioning, is a great threat to the reliability of rotary compressors, because of its high pressure in the compression chamber. In this paper, a coupled mathematical model that can predict the compression process of refrigerants in three different states in the compressor cylinder is proposed. The refrigerant phase change, heat exchange between refrigerant and wall, leakage through leak passage and refrigerant kinetic energy change rate are considered in the model. The coupled solution method and its Fortran calculation program are carried out. This mathematical model is experimentally verified by using R290 as refrigerant. The results show that the simulation results of pressure variation in the compressor cylinder during the refrigerant two-phase compression and discharge processes are consistent with the experimental values. The liquid slugging happens with the maximum pressure of 2400 kPa in the cylinder under low suction gas mass fraction. The R290 is more prone to condense during in-cylinder compression than that of R22 and R410A under low wall temperature condition. The larger the volume change rate of the compression chamber, the higher compressor rotation speed, and the smaller the flow area at the end of discharge process will exacerbate the liquid compression phenomenon.

Performance Evaluation of Centrifugal Refrigeration Compressor Using R1234yf and R1234ze(E) as Drop-In Replacements for R134a Refrigerant

With the increasing global requirements for environmental protection, refrigerants with ODP of 0 and low GWP are widely concerned and applied. In this paper, the CFD numerical method simulates the R134a centrifugal compressor directly replaced by R1234yf and R1234ze(E). The results show that at the same compressor rotational speed, using R1234yf to replace R134a directly can obtain a higher cooling capacity, but it reduces COP by about 12.5%; using R1234ze(E) to replace R134a directly reduces the cooling capacity under partial working conditions, the COP is reduced by about 7.0%. When the evaporation temperature, condensation temperature, and cooling capacity are the same, compared with the R134a unit, the COP of the R1234ze(E) unit is reduced by about 5.14%, and it is reduced by about 8.93% for the R1234yf unit. For the R134a centrifugal chiller, the drop-in replacement of R134a with R1234ze(E) can obtain better system performance compared with R1234yf.

Turbocharger surge behavior for sudden valve closing downstream the compressor and effect of actuating variable nozzle turbine

Surge is an unstable phenomenon appearing when a valve closing reduces the compressor flow rate. This phenomenon is avoided for automotive turbochargers by defining a surge margin during powertrain system design. This surge margin established with measurements in steady state testing regime limits the maximal engine torque at low levels of output. An active control of the compressor could reduce the surge margin and facilitate a transient compressor operation for a short time in surge zone. In this paper, an experimental study of the transient operation of a turbocharger compressor entering the surge zone is performed. Control of the turbocharger speed is sought to avoid unsteady operation using the variable geometry turbine (VGT) nozzle actuator. From a given stable operating point, surge is induced by reducing the opening of a valve located downstream of the compressor air circuit. The effect of reducing the speed of rotation by controlling the VGT valve is investigated, as this should lead to more stable compressor operation. The rotation speed of the turbocharger is controlled to avoid an unstable operating point using servo-actuator of variable geometry turbine. From a stable operating point, the surge appearance is caused by closing a butterfly valve downstream the air circuit of the compressor. The effect on the compressor rotation speed when the opening of variable geometry turbocharger valve is modified is studied. Measurements have been conducted for different control profiles of the VGT valve placed downstream the compressor. This article presents the means used to carry out these tests as well as the results of the measurements of the instantaneous signals of pressure, temperature, flow rate and rotation speed, allowing the analysis of the surge phenomenon.

A Comparative Performance Study of an Ejector-Expansion Refrigeration Cycle Using R134a and its Alternatives: Application of Automobile Air Conditioning

In this study, the performance of ejector-expansion refrigeration cycle (EERC) with R134a alternative refrigerants (R152a, R1234yf, R404A, R407C, R507A and R600a) for automobile air-conditioning application is investigated numerically. The ejector is modeled with a constant mixing-pressure assumption taking into consideration the friction effect in the ejector mixing section. The studied refrigerants are compared based on the optimum area ratio, discharge temperature, compressor input power, volumetric cooling capacity, exergy destruction, COP, exergy efficiency and COP improvement. The results show that R152a and R1234yf have the closest performance to R134a and can be considered the most suitable alternative refrigerants for R134a. The COP and exergy efficiency are improved by 2.26% and 2.27%, respectively, using R152a compared to the use of R134a, whereas they are reduced by 2.89% and 2.88% using R1234yf. The volumetric cooling capacity is reduced for both R152a and R1234yf by 6.14% and 6.8%, respectively. In addition, the effect of compressor rotational speed on the performances is reported.

Analytical Study on the Performance Characteristics of Automobile Air-Conditioning System Using the Mixed Refrigerant R134a/R1234yf for Varying Compressor Rotation Speeds

This study presents the performance analysis for an automobile air-conditioning system using the mixed refrigerant R134a/R1234yf with varying compressor rotation speeds. Accordingly, the compressor, condenser, expansion device, and evaporator of the automobile air-conditioning system were designed using the EES program, and the cooling capacity and COP of the automobile air-conditioning system using the mixed refrigerant were comparatively analyzed for simulated data. The cooling capacity using the mixed R134a/R1234yf(30%) system at a compressor rotation speed of 2500 rpm was about 6.13% lower than that using the R134a system alone. Moreover, the COP using the mixed R134a/R1234yf(30%) system at a compressor rotation speed of 2500 rpm was about 7.45% lower than that using the R134a system alone. The use of the R134a /R1234yf mixed refrigerant can thus reduce global warming potential; further, as there is no significant difference in performance compared with the system using only R134a, the applicability of the mixed R134a/R1234yf refrigerant is confirmed.

Deep Reinforcement Learning Guided Cascade Control for Air Supply of Polymer Exchange Membrane Fuel Cell

The power consumption of an electric air compressor becomes the major parasitic energy waste leading to the deterioration of net efficiency of the fuel cell system (FCS). Optimal control of the oxygen excess ratio (OER) is recognized as a feasible way to resolve the paradox of stack health and system efficiency. Herein, a novel cascade control scheme that leverages model predictive control (MPC), fuzzy Proportion Integral control (FPI), and deep reinforcement learning technique is proposed to regulate the OER for a 75 kW FCS. The master‐slave control structure is adopted, and a reference air mass flow rate and the motor voltage of the air compressor are taken as control targets, respectively. A deep deterministic policy gradient (DDPG) algorithm is used as a parameter tuner for MPCProportion Integral (PI) controller. The results indicate that both MPCFPI and DDPGMPCPI can achieve better control performance indices in comparison to classic controller under step response and a typical driving cycle. The DDPG‐guided cascade controller is also capable of regulating the OER tracking error and the derivative of rotation speed of the air compressor, which reveals the potential for extending the longevity of the FCS.

Experimental performance analysis of a novel ultra-low charge ammonia air condensed chiller

• A novel design of an Ultra-Low-Charge ammonia chiller is proposed and experimentally tested. • The chiller includes semi-hermetic compressor, micro-channel condenser and dry-expansion plates heat exchanger. • The miscible lubricant allows the use of a single-stage oil-separator while ensuring a proper oil return. • The optimized system achieved a charge 40% lower than the current systems in the market with up to 20% extra COP. • The package technology assessed simplifies the installations thanks to the use of secondary fluids. Environmental restrictions on the use of fluorinated refrigerants are turning the attention to natural solutions. Ammonia is historically proven as a refrigerant that requires low purchasing costs, has superior thermodynamic properties, and exhibits great values of coefficient of performance. Therefore, considering ammonia safety issues, solutions able to prevent leakages and minimize the charge of refrigerant are kind of welcomed. This paper conducts an investigation focused on the experimental analysis of the refrigerant charge and performance of a novel ultra-low charge air-cooled packaged chiller for medium temperature industrial applications. The unit is developed using emerging technology to reduce the amount of ammonia charge, such as the microchannel condenser, semi-hermetic screw compressor, miscible lubricant, single-stage oil separator, and dry-expansion plates heat exchanger. In doing so, the empirical adjustment of the ammonia charge revealed that there is an optimum that maximizes the coefficient of performance and the cooling capacity of the system. A charge capacity ratio of 75 g/kW was achieved for a unit with a rated cooling capacity of 230 kW and a gross coefficient of performance of 2.3, i.e, a reduction of 50% in the specific charge and an improvement of 20% in the performance, with regard to the systems in the market. Moreover, the system performance, such as operating temperatures, evaporator effectiveness, and oil return, are assessed for a wide range of conditions and compressor rotational speeds.

Effect of Pulsating Flow on Surge Frequency of a Turbocharger Compressor

Turbocharger compressors operate under pulsating flow due to continuous opening and closing of engine valves placed downstream of the compressor but exhibit a hysteresis loop deviating from steady characteristics. As the flow in a compressor is throttled, both pressure and flow discharge unstably oscillate. The instability is known as surge and it affects not only the compressor itself but also its whole engine-turbocharger system. For estimating the stable operation range, partial flow tests of a turbocharger compressor under pulsating flow were conducted. Using a compressor test apparatus with a pulsating flow generator and a tank whose capacity can be changed, the flow rate was controlled by a valve. Under steady flow, surge hysteresis loops caused by oscillating pressure and flow rate were obtained in each rotational speed. By Fast Fourier Transform (FFT) of pressure signals, the occurrence of surge with different frequencies was confirmed depending on the tank capacity. Next in pulsating flow tests, a compressor rotational speed is fixed, and pulsating frequencies given by the pulsating flow generator are changed. The obtained surge frequencies were different from those in steady flow tests. Especially, it is likely to be drawn to the frequency that is equal, two times and a half rate of the pulsating frequency. Numerical computation with one-dimensional calculation is conducted to investigate such a phenomenon.