Compressor Operating Conditions Research Articles

Evaporating temperature estimation of refrigeration systems based on vibration data-driven soft sensors

The evaluation of the operating conditions of refrigeration compressors once installed in household appliances is challenging due to the need to install pressure transducers, a process which requires system evacuation and refrigerant reintroduction. In addition, changes in the piping modify the characteristics of the original product. This paper proposes a soft-sensing technique based on vibration measurements of the compressor surface to predict the evaporating temperature. Different machine learning (ML) techniques are evaluated as data-driven prediction models, namely multilayer perceptron (MLP) neural networks, least squares boosting, generalized additive model, random forest, extreme learning machine, and random vector functional link neural networks. These techniques were applied to data obtained from a test rig designed to emulate compressor operation in a refrigeration system, with an operating envelope from -30°C to -10°C for the evaporating temperature and from 34°C to 54°C for the condensing temperature. The results showed that, with a single vibration measurement point, it was possible to use an MLP technique to estimate the evaporating temperature with a root mean squared error of 1.74°C in a non-intrusive way. For the other prediction techniques, the errors were a bit higher than for the MLP, but the maximum error value was about 2.5°C in all cases.

RESEARCH ON THE APPLICATION OF ROTARY COMPRESSORS IN GAS TRANSMISSION SYSTEMS

The article provides an analysis of the operating conditions of compressors used for gas transportation in the Azerbaijani gas industry and explores ways to effectively utilize them. It discusses primarily the types, technical specifications, constructions, and application areas of rotary compressors employed in the gas industry. Additionally, information is provided about various types of rotary compressors, including rotary-vane, screw, twin-screw, and scroll compressors. Keywords: gas, vane, screw, rotor, scroll, compressor, cylinder, pressure, piston.

RESEARCH ON THE APPLICATION OF ROTARY COMPRESSORS IN GAS TRANSMISSION SYSTEMS

The article provides an analysis of the operating conditions of compressors used for gas transportation in the Azerbaijani gas industry and explores ways to effectively utilize them. It discusses primarily the types, technical specifications, constructions, and application areas of rotary compressors employed in the gas industry. Additionally, information is provided about various types of rotary compressors, including rotary-vane, screw, twin-screw, and scroll compressors. Keywords: gas, vane, screw, rotor, scroll, compressor, cylinder, pressure, piston.

Stability analysis of axial compressors with wire mesh casing treatment

Experimental results indicate that wire mesh casing treatment (WMCT) enhances the stability of low-speed compressors with little reduction in efficiency. The flow resistance on the surface of the grooves, which are formed by the wire mesh, provides a new variable for the design of WMCT. This paper investigates the stability improvement induced by three different meshes through experiments and steady numerical simulations. A stability prediction model incorporating the effect of WMCT is developed to assess the stability of the steady flow field, and the results show that the predicted stall points of the compressor are close to those of the experimental data. The stability analysis model has a well-defined theoretical foundation in which the meridional flow field of the compressor is considered as the basic flow and the blade is replaced with a body force. This formulation enables fast and accurate stability assessments of compressors incorporating WMCT during the design process. Finally, based on the influence of the different meshes on the steady flow field, the stability-enhancing mechanism of WMCT is analyzed in terms of flow field details and macroscopic physical quantities. WMCT improves the flow around the tip region, shifting the tip blade loading in the aft direction and reducing the tip leakage flow. Macroscopically, the installation of WMCT makes the flow structure in the tip region less sensitive to changes in the compressor operating conditions.

A prototype recuperated supercritical co2 cycle: Part-load and dynamic assessment

High efficiency, flexibility and competitive capital costs make supercritical CO2 (sCO2) systems a promising technology for renewable power generation in a low carbon energy scenario. Recently, innovative supercritical systems have been studied in the literature and proposed by DOE-NETL (STEP project) and by a few projects in the EU Horizon 2020 (H2020) program aiming to demonstrate supercritical CO2 Brayton power plants, promising superior techno-economic features than steam cycles particularly at high temperatures.The H2020 SOLARSCO2OL project, which started in 2020, is building the first European MW-scale sCO2 demonstration plant and has been specifically tailored for Concentrating Solar Power (CSP) applications. After a detailed explanation of the modelling approach for steady and unsteady cycle simulations, this paper presents the off-design and dynamic analysis of such plant layout, which is based on a simply recuperated sCO2 cycle. The entire system model has been developed in TRANSEO environment. The part-load analysis ranged from 50% of nominal up to a 105% peak load, discussing the impact on compressor and turbine operating conditions. Full operational envelop has been determined considering cycle main constraints, such as maximum turbine inlet temperature and minimum pressure at compressor inlet.The off-design performance analysis highlights the most relevant relationships among the main part-load regulating parameters, namely molten salt mass flow rate, CO2 mass flow rate, total CO2 mass in the loop, and shaft line speed. The results show specific features of different control approaches, discussing the pros and cons of each solution, considering also its upscale towards commercial applications. In particular, the analysis shows that at 51% of load an efficiency decrease of 20% is expected. Finally, the dynamic characterization of the closed loop shows the relatively fast responsiveness of the plant to compressor speed variations, causing quick changes in CO2 mass flow rate, together with longer time scale phenomena related to the plant heat exchangers. In this respect, sCO2 plants demonstrate to have the potential to provide primary reserve for the electrical grid, as far as thermal stresses on main plant components are kept under acceptable limits.

Parametric Analysis of Gas Leakage in the Piston–Cylinder Clearance of Reciprocating Compressors

Gas leakage is one of the main sources of inefficiencies in low-capacity reciprocating compressors, undermining the compressor performance by reducing the mass flow rate and increasing the energy consumption. In reciprocating compressors, leakage in the piston–cylinder clearance is driven by the piston motion and pressure difference between the compression chamber and the internal environment of the shell. This paper reports a parametric numerical analysis of leakage in the piston–cylinder clearance of a low-capacity reciprocating compressor. A simulation model based on the Reynolds equation is applied throughout the compression cycle to assess the effect of the compressor operating conditions, clearance geometry, piston velocity and piston secondary motion on the leakage and compressor performance. A 3D CFD model is also developed to validate the Reynolds leakage model and to evaluate the effect of the piston secondary motion on leakage, assuming the piston is fixed with predetermined eccentricities. The results show that the compressibility effects are very relevant to estimate the gas leakage. The simulations also revealed that leakage is more detrimental to the compressor performance when it is operating in low back-pressure conditions. Additionally, the piston secondary motion can intensify the gas leakage in the piston–cylinder clearance by up to 90%. On the other hand, the piston velocity only plays a minor role in assessing the leakage.

Prediction Method of Unsteady Flow Load of Compressor Stator under Working Condition Disturbance

Due to the complexity of the compressor operating conditions and the existence of various disturbances and unsteady effects in the flow field, the analysis of compressor stator vibration characteristics becomes particularly critical. The convolutional neural network model combined with a transient CFD method was introduced to solve the difficulty of analyzing the flow load of the compressor stator blade. This paper mainly focuses on two key points: the complex change of the aerodynamic load and the accurate prediction of the blade excitation. Considering the stator–rotor interference, the unsteady effects, and the variable working condition characteristics, the random disturbance analysis model of the flow field boundary was generated to simulate the unsteady flow excitation of the stator under complex working conditions. By establishing the neural network of boundary disturbance and flow excitation characteristics, the prediction model was trained and generated under the support of large-scale data. The most important role of the model was to establish the end-to-end data mapping between the disturbance condition and the aerodynamic load of the stator blade. The conclusions demonstrate that the introduction of an airflow disturbance is helpful to obtain the excitation characteristics of the stator under complex working conditions. The model established in this paper based on 1000 groups of disturbed working condition data can effectively predict the aerodynamic load of the blades under complex working conditions. In addition, the construction of the model is beneficial for saving a lot of computing resources, and the prediction accuracy also reaches a good level. The method presented in this paper provides a reference for the vibration analysis of the compressor stator.

Experimental performance of a vapor-injection CO2 heat pump system for electric vehicles in −30 °C to 50 °C range

Efficient and wide-range heat pump system is essential to improve the driving range and comfort of electric vehicles. In this paper, a vapor-injection transcritical CO2 heat pump system with a flash tank for electric vehicles was built up, and the heating and cooling performance in a wide range from −30 °C to 50 °C were experimentally studied. The maximum coefficient of performance (COP) at −30 °C/ 20 °C was 1.45, and the maximum COP at 50 °C/ 27 °C was 1.08. By comparing with the basic system without injection, it was found that the heating performance of the vapor-injection system was significantly improved, and the lower the outdoor temperature, the greater the improvement. The COP and heating capacity of the vapor-injection system were increased by 45.5 % and 75.7 % respectively at −30 °C/ 20 °C. Under the cooling conditions, only when the outdoor temperature was lower than 40 °C, the vapor-injection system had an advantage, and the maximum increments of COP and cooling capacity at 35 °C/ 27 °C were 9.5 % and 16.8 %, respectively. Further, a relationship model between vapor injection and compressor structure and operating conditions was established according to the working principle of the twin rotary compressor. The experimental verification showed that the deviation was within 8 %, which could provide a basis for the construction of the CO2 vapor injection heat pump system model.

Thermodynamic analysis of a metal hydride hydrogen compressor with aluminium substituted LaNi5 hydrides

The operating conditions of a Metal Hydride Hydrogen Compressor (MHHC) is often dictated by the hydride used to build it. This research focuses on finding the appropriate operating conditions for MHHC to get the ideal throughput and efficiency using aluminium based hydrides. For this, hydrogen absorption and desorption characteristics of LaNi5-xAlx (where x is 0, 0.2 and 0.4) hydrides were studied for estimating the suitability of these materials for developing hydrogen compressor. From the Pressure Concentration Isotherms (PCIs) and van't Hoff plot, an estimate of the reversible hydrogen weight percent attainable, equilibrium pressure and absorption and desorption temperature range were collected and the effect of aluminium concentration on these properties was studied. Further thermodynamic analysis was made by calculating the performance parameters like thermal efficiency, isentropic work required, theoretical heat supplied and pressure ratio by varying the operating conditions like supply pressure (3–5 bar), absorption temperatures (20–40 °C), and desorption temperature (80–140 °C). It is observed that the higher aluminium content in the hydride allows the hydrogen compressor to be operated at a lower supply pressure. Whereas lower aluminium content in hydrides give higher thermal efficiency and discharge pressure for a particular desorption temperature, while requiring a higher supply pressure to perform efficiently. The maximum thermal efficiency within the studied operating conditions was found to be 0.24 for LaNi5 at 3 bar supply pressure, 30 °C absorption and 140 °C desorption temperature with a pressure ratio of 8.97.

Estimations of Compressor Stall and Surge Using Passage Stall Behaviors

The predictions of the onset of rotating stall and surge are very important in the preliminary design stage of a compressor. Rotating stall and surge are complex instabilities that cause efficiency loss and reduced pressure rise, and, therefore, compressor designers attempt to avoid them in the design stage. There are many criteria for predicting stability limits, including empirical, theoretical, and numerical investigations in the literature. However, these investigations have important limitations. The present study establishes a new method in which the stall and post-stall behavior of a compressor is estimated by an equivalent reconstructed compressor using special combinations of single-passage flow behavior in different mass flow rates. The combinations are generated such that pre-stall, in-stall, and surge flow regimes and between one and eight stall cells are reproduced in the full-annulus compressor. The method requires the least computational requirements and is time efficient. The results indicate that secondary flow total energy and spectral entropy are indeed correlated with compressor operating conditions. The predictions of the onset of stall and surge for the investigated compressor show good agreement with the experimental data.

DESIGN OF SELF-REGULATED FLOW CONTROL MECHANISM FOR A TURBOCHARGER GAS STAND TEST FACILITY

A turbocharger test facility is essential to evaluate the turbocharger’s performance by mapping the turbine and compressor operating conditions. This paper aims to design a self-regulated airflow control mechanism for the turbocharger test facility in UTM LoCARtic. Previously, the gas stand airflow was regulated manually. However, the vast variety of turbocharger design and operating conditions increase the difficulty to continuously and precisely regulate the airflow manually. In this paper, the valve and actuator selection, the mechanical design and the control loop design will be presented. Four valves model have been considered, namely globe type, ball type, butterfly valve and gate valve. The final selection was based on the flow coefficient (Kv), pressure drop, stability and accuracy. The actuation system is also one major consideration to obtain the best accuracy and response time. An electric actuator helps to achieve a self-regulated flow control mechanism. In conclusion, the globe type valve was chosen because of the flow accuracy, flow stability and the Kv value is close to the gas stand’s requirement.

Evaporator Optimization of Refrigerator Systems Using Quality Analysis

In this study, evaporator optimization, via both experimental and simulation methods was conducted. To evaluate the evaporator performance, under the optimal system, the compressor operating time and the effects of oil on the refrigerator system were studied. If the temperature of the refrigerator chamber reaches the setting value, the compressor stops working and it leads to the temperature of the refrigerator chamber slowly increasing, due to the heat transfer to the ambient. When the refrigerator temperature is out of the setting range, the compressor works again, and the refrigerator repeats this process until the end of its life. These on/off period can be controlled through the compressor piston movement. To determine the optimal compressor operating conditions, experiments of monthly power consumption were conducted under various compressor working times and the lowest power consumption conditions was determined when the compressor worked continuously. Lubricating oil, the refrigerator system, using oil, also influenced the system performance. To evaluate the effect of oil, oil eliminated and oil systems were compared based on cooling capacity and power consumption. The cooling capacity of the oil eliminated system was 2.6% higher and the power consumption was 3.6% lower than that of the oil system. After determining the optimal operating conditions of the refrigerator system, visualization experiments and simulations were conducted to decide the optimal evaporator and the conventional evaporator size can be reduced by approximately 2.9%.

РАЗРАБОТКА МАТЕМАТИЧЕСКОЙ МОДЕЛИ ДЛЯ ИССЛЕДОВАНИЯ ДИНАМИЧЕСКИХ ПРОЦЕССОВ В ЛАБИРИНТНОМ УПЛОТНЕНИИ СТУПЕНИ ЦЕНТРОБЕЖНОГО КОМПРЕССОРА

Research of dynamic processes occurring under real operating conditions of centrifugal compressors often require the use of interdisciplinary approaches. This is determined by the character of the processes, which significantly affect each other during the compressor operation. However, when using interdisciplinary approaches, there are difficulties in the numerical implementation. They are associated with the need to take into account all the geometric and physical features of the processes under research, which leads to significant time and computational costs. At this article discusses issues related to the causes of oscillatory processes in the centrifugal compressor stage, in particular, in the labyrinth seal channel. In the article using 2FSI approach allowing to take into account the bilateral interaction of physical process on another. The article discusses issues related to the causes of oscillatory processes in the centrifugal compressor stage, in particular, in the labyrinth seal channel. The computational domain of research is presented, conceptual and mathematical statements are performed, which allow describing, among other things, self-oscillatory processes using the 2FSI approach.

Selection of design parameters of automatic ring valves of reciprocating compressors

One of the main tasks at designing and operation of reciprocating compressors is provision of energy efficient and reliable operation of the automatic valves. Imposed to the automatic valves is a number of requirements (low gas-dynamic impedance to valve flow, timeliness of valve closing, etc.) the fulfillment of which requires multi-variant calculations in order to select efficient valve parameters for the specified operation modes. Given in the study are the results of valve design analysis depending on the compressor operating conditions (at change in the crankshaft speed) and valve parameters (at change in spring tension and maximum valve stroke).

Experimental study on CO2/R32 blends in a water-to-water heat pump system

The purpose of this study is to evaluate the cooling and heating performance as well as the compressor operating conditions of CO2/R32 blends in a water-to-water heat pump system. Experiments were conducted to reveal the effects of the refrigerant compositions, heat source temperatures, and internal heat exchanger (IHX) on the performance of the system. The results show that 23.3% and 65.2% maximum improvement in heating coefficient of performance (COPh) and cooling coefficient of performance (COPc) of the system were obtained when the mass fraction of CO2 was 0.6, respectively. Meanwhile, heating capacity, cooling capacity, and the compressor discharge pressure of CO2/R32 blends were decreased significantly. The thermal matching between the heat source and CO2/R32 blends significantly affected the overall performance of the system. In addition, IHX is recommended in the water-to-water heat pump to improve the system performance.

Analysis of rolling bearing power loss models for twin screw oil injected compressor

The mechanical losses inside a screw compressor limit the performance of the compressor in terms of efficiency. These losses arise due to relative motion between elements inside the screw compressor. The estimation of mechanical losses predicted in the literature is around 10-15% of the total shaft power. One of the elements which contribute significantly to these losses is rolling element bearings. There are numerous mathematical models available which predict power losses in the rolling bearings.The objective of this paper is to study different models to predict power loss for rolling bearings and to predict the power losses for the bearings used for oil injected, twin screw compressor. A comparison between different power loss models for different operating conditions of compressor is also presented in this paper and results of analysis are compared with available experimental observations. The analysis helps to determine suitable power loss model for different operating conditions and more realistic predictions of the power losses. This allows designers for more accurate estimation of the performance of screw compressors.

Numerical calculation and measurement of low temperature thermal conductivity of polyurethane rigid foam

In the structure of cold compressors, polyurethane rigid foams (PURF) are often used as important thermal insulations for large temperature gradient. Heat transfer in PURF occurs by conduction through the solid skeleton and gases trapped in cells as well as radiation. According to the actual structure and operating conditions of helium cold compressors, a heat transfer hierarchical model has been established, which can predict the apparent thermal conductivity of PURF more simply. Meanwhile the thermal conductivity of a sample PURF has been measured in the physical property measurement system from 4.4K to 300K.

Centrifugal Compressor Design for Near-Critical Point Applications

The supercritical CO2 (sCO2) Brayton cycle has been attracting much attention to produce the electricity power, chiefly due to its higher thermal efficiency with the relatively lower temperature at the turbine inlet compared to other common energy conversion cycles. Centrifugal compressor operating conditions in the supercritical Brayton cycle are commonly set in vicinity of the critical point, owing to smaller compressibility factor and eventually lower compressor work. This paper investigates and compares different centrifugal compressor design methodologies in close proximity to the critical point and suggests the most accurate design procedure based on the findings. An in-house mean-line design code, which is based on the individual enthalpy loss models, is compared to stage efficiency correlation design methods. Moreover, modifications are introduced to the skin friction loss calculation to establish an accurate one-dimensional design methodology. Moreover, compressor performance is compared to the experimental measurements.

Experimental study on the tribological characteristic of vane–roller interface of HC290 rotary compressor with mineral oil

As a natural refrigerant, HC290 is considered as an excellent long-term alternative refrigerant applied in room air-conditioners (RAC). In this paper, the experimental study on tribological characteristics of the vane–roller friction pair in HC290 rotary compressors was carried out and friction coefficients and wear depths were measured under the pure HC290 atmosphere, pure mineral oil and HC290/mineral oil mixture environment, respectively. In order to obtain the experimental conditions as close as possible to the actual operating conditions of a HC290 rotary compressor, the mass-produced vanes and rollers were adopted, and all tests were performed with a high-pressure tribometer under various sliding speeds, loads and temperatures which were set to simulate the different actual operating conditions of rotary compressors. Furthermore, the scuffing tests were performed and the Scanning Electron Microscopic has been used to investigate morphological changes occurred after test. The experiment results with the HC290/mineral oil mixture showed that better anti-scuffing ability but a higher friction coefficient of vane–roller interface were acquired compared to HFC410A/polyolester. The results obtained here may provide some guides for further investigations on tribological characteristics of the vane–roller interface of HC290 rotary compressors.

Influence of the piston displacement profile on the performance of a refrigerating cycle equipped with an axial piston compressor

An extended analysis aiming to investigate the influence of the piston displacement in an axial compressor on the thermodynamic cycle of a refrigeration system was carried out. Axial piston compressors are commonly equipped with a rotating disk plate that guides the pistons along a sinusoidal displacement. A proper shape of the rotating disk can lead to a piston displacement that optimizes the power consumption and then the refrigeration cycle efficiency. In this paper, a sensitivity analysis on the compressor cycle characteristics by varying the piston displacement profile and the compressor operating conditions is presented. The mechanical analysis of the forces exerted by the piston on the rotating disk was also carried out to estimate the mechanical stresses acting on the rotating disk.