Indicator Diagram

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Xueyuan Peng - One of the best experts on this subject based on the ideXlab platform.

  • investigation of the thermodynamic process of the refrigerator compressor based on the m θ Diagram
    Energies, 2017
    Co-Authors: Tao Wang, Zhilong He, Xueyuan Peng
    Abstract:

    The variation of refrigerant mass in the cylinder of refrigerator compressor has a great influence on the compressor’s thermodynamic process. In this paper, the m-θ Diagram, which represents the variation of refrigerant mass in compressor cylinder (m) and the crank angle (θ), is proposed to investigate the thermodynamic process of the refrigerator compressor. Comparing with the traditional pressure-Volume (p-V) Indicator Diagram, the refrigerant’s backflow trigged by the delayed closure of valve can be clearly expressed in the m-θ Diagram together with the mass flow rate. A typical m-θ Diagram was obtained by experimental and theoretical investigations. To improve the thermodynamic model of the compressor, a 3D fluid-structure interaction (FSI) FEA model has been introduced to find out the effective flow area of the valves. Based on the m-θ Diagram, the effect of rotating speed on the backflow through the valve, which depends on the movement of the valve, has been investigated. Specific to the compressor used in this study, the maximum backflow through the suction valve and discharge valve occur at 3500 r·min−1 and 5500 r·min−1, respectively.

  • experimental study on p v Indicator Diagrams of twin screw refrigeration compressor with economizer
    Applied Thermal Engineering, 2004
    Co-Authors: Huagen Wu, Xueyuan Peng, Ziwen Xing
    Abstract:

    This paper presents the experimental investigation on the effects of the superfeed pressure together with economizer type on the performance of the twin-screw refrigeration compressor by means of the Indicator Diagram. With a pressure sensor embedded into the groove at the root of the female rotor on the discharge side, the pressure within the working chamber of a semi-hermetic twin-screw compressor with an economizer is recorded and then transformed into the Indicator Diagram. The results thus obtained are utilized to investigate the thermodynamic process of the compressor. It is shown that the compressor with an economizer has higher pressure during almost the whole compression process than without an economizer, resulting in the increase in the indicated power. Under different superfeed pressures, the pressure within the compression experiences different changes. This results in an optimal superfeed pressure for maximized compressor efficiency, which can be identified from the calculated compressor efficiency based on the Indicator Diagrams. It is also found that the pressure has a rapid increase at the beginning of superfeed process, and then a slow rise even a slight drop at the end of superfeed process, which is caused by the dynamic effect during superfeed process. Furthermore, if the superfeed pressure keeps the same, the pressure during compression in the compressor with the heat exchanger economizer is slightly higher than with the flash tank economizer, due to the higher temperature of superfeed refrigerant gas in the former case.

  • analysis of the working process in an oil flooded screw compressor by means of an Indicator Diagram
    Proceedings of the Institution of Mechanical Engineers Part A: Journal of Power and Energy, 2002
    Co-Authors: Xueyuan Peng, Ziwen Xing, Liansheng Li
    Abstract:

    This paper presents the results of an experimental investigation of the thermodynamic processes in an oil-flooded screw compressor. The pressure within the working chamber is measured with a small pressure sensor, embedded in the female rotor on the discharge side. The results so obtained were transformed into an Indicator Diagram. Based on the Indicator Diagrams at various operating conditions, the working process is analysed. Owing to oil restricting back-flow of the gas through the discharge port, constant-volume compression is not evident even at substantial under-compression conditions, thus making the compressor maintain a high efficiency over a wide range of pressure ratios. However, the additional power consumption resulting from over-compression is comparatively large at pressure ratios lower than that for which the compressor was designed. So a compressor with fixed volume ratio should be designed with the built-in volume ratio low enough to avoid this effect. At the end of the discharge process, the pressure rises steeply due to increased resistance to oil flow, and therefore, the design of a flow-guiding slot to assist oil discharge is recommended. Higher rotating speeds increase the pressure slightly, but the losses associated with this are compensated by the increased volumetric efficiency. Thus a screw compressor maintains its isentropic efficiency over a wide range of speeds. Larger oil:gas ratio presents a higher pressure level in the Indicator Diagram, offsetting the improved sealing effect, and test results show that the appropriate oil:gas mass ratio range is between 8:1 and 20:1.

Roberto Cipollone - One of the best experts on this subject based on the ideXlab platform.

  • theoretical modeling and experimental investigations for the improvement of the mechanical efficiency in sliding vane rotary compressors
    Applied Energy, 2015
    Co-Authors: Giuseppe Bianchi, Roberto Cipollone
    Abstract:

    Positive displacement compressors lead the market of compressed air production for industrial applications. Among them, sliding vane rotary compressors represent an energetically virtuous alternative to the current compression technologies. In the present work, the effects of compressor design parameters were investigated through a comprehensive approach that aimed at addressing more efficient machines to promote sliding vane compressors as the key enabling technology in compressed air systems. A comprehensive mathematical model was developed to study the main phenomena occurring in this kind of compressors. The model provides the cell volume evolution over a whole rotation during which filling, compression and discharge processes occur. The first and latter phases are described by the quasi-propagatory approach that represents the inertial, capacitive and resistive features of one-dimensional unsteady flows. The dynamics of the compressor blades led to four different arrangements inside the rotor slots while an analysis of the hydrodynamic lubrication established between blade tip and stator wall focused on the oil film thickness evolution to prevent dry contacts. An extensive experimental campaign on a mid-size industrial compressor allowed the model validation at different outlet pressure levels and revolution speeds using a direct measurement of mechanical power and the reconstruction of the Indicator Diagram from piezoelectric pressure transducers. The friction coefficient at the contact points between blades with stator and rotor was estimated in 0.065 and further improvements of the mechanical efficiency were eventually addressed considering the roles of compressor aspect ratio, revolution speed, and blade tilt. The first two theoretical optimizations might lead to an increase of the compressor efficiency of 2 and 9 percentage points respectively. On the other hand, acting on the blade tilt would not produce relevant improvements.

  • performance enhancement in sliding vane rotary compressors through a sprayed oil injection technology
    2014 Purdue Conferences. 22nd International Compressor Engineering Conference at Purdue., 2014
    Co-Authors: Roberto Cipollone, Stefano Murgia, Giulio Contaldi
    Abstract:

    In Sliding Vane Rotary Compressors, as well as in most of positive displacement machines, the oil is injected to accomplish sealing and lubrication purposes. However, the oil injection could produce an additional outcome during the compression phase with a great saving potential from the energetic point of view. Being the air inside the cell at a higher temperature than the oil injected, a cooling effect could be achieved so decreasing the mechanical power required for the compression. At the moment, the oil is introduced inside the compressor vanes simply through a series of calibrated holes that are only able to produce solid jets. In this way any effective heat transfer is prevented, as demonstrated by p-V measurements inside the cells during the compression phase. In the current study, a theoretical model of a sprayed oil injection technology was developed and further experimentally validated. The oil was injected along the axial length of the compressor through a number of pressure swirl atomizers which produced a very fine spray. The conservation equations, solved with a Lagrangian approach, allowed to track the droplets evolution from the injection until the impingement onto the metallic surfaces of the vanes. The theoretical approach assessed the cooling effect due to the high surface to volume ratio of the droplets and a reduction of the indicated power was predicted. The model validation was carried out through a test campaign on an mid-size sliding vane compressor equipped with a series of pressure swirl injectors. The reconstruction of the Indicator Diagram as well as the direct measurements of torque and revolution speed revealed a reduction of the mechanical power absorbed close to 7% using an injection pressure of 20 bar. The model is in a satisfactory agreement with the tests and it also confirms the experimental trends available in the literature. A parametric analysis on the injection pressure and temperature and on the cone spray angle was eventually carried out in order to identify an optimal set of operating injection parameters.

Shu Pengcheng - One of the best experts on this subject based on the ideXlab platform.

  • theoretical and experimental study on Indicator Diagram of twin screw refrigeration compressor
    International Journal of Refrigeration-revue Internationale Du Froid, 2004
    Co-Authors: Wu Huage, Xing Ziwe, Shu Pengcheng
    Abstract:

    Abstract In this paper a new mathematical model for calculating the Indicator Diagram of twin screw refrigeration compressor is presented firstly. The geometric parameters related to the rotation angle of male rotor are used in the model such as groove volume, suction and discharge port area, slide valve bypass port area, leakage area etc. The effects of internal leakage through five paths, oil injection, gas–oil heat transfer, refrigerant property and partial loading etc. are taken into account simultaneously and separately in the theoretical study. To verify the model and the calculated p–V Indicator Diagram, experimental recording of p–V Indicator Diagram of twin screw refrigeration compressor is carried out. Various Indicator Diagrams are recorded successfully by a small pressure sensor embedded in the bottom of female rotor at the discharge side. The results of theoretical calculation are in good agreement with the measured data, which lead to conclusion that the model can be used as a powerful tool for performance prediction and product development.

Ziwen Xing - One of the best experts on this subject based on the ideXlab platform.

  • experimental study on p v Indicator Diagrams of twin screw refrigeration compressor with economizer
    Applied Thermal Engineering, 2004
    Co-Authors: Huagen Wu, Xueyuan Peng, Ziwen Xing
    Abstract:

    This paper presents the experimental investigation on the effects of the superfeed pressure together with economizer type on the performance of the twin-screw refrigeration compressor by means of the Indicator Diagram. With a pressure sensor embedded into the groove at the root of the female rotor on the discharge side, the pressure within the working chamber of a semi-hermetic twin-screw compressor with an economizer is recorded and then transformed into the Indicator Diagram. The results thus obtained are utilized to investigate the thermodynamic process of the compressor. It is shown that the compressor with an economizer has higher pressure during almost the whole compression process than without an economizer, resulting in the increase in the indicated power. Under different superfeed pressures, the pressure within the compression experiences different changes. This results in an optimal superfeed pressure for maximized compressor efficiency, which can be identified from the calculated compressor efficiency based on the Indicator Diagrams. It is also found that the pressure has a rapid increase at the beginning of superfeed process, and then a slow rise even a slight drop at the end of superfeed process, which is caused by the dynamic effect during superfeed process. Furthermore, if the superfeed pressure keeps the same, the pressure during compression in the compressor with the heat exchanger economizer is slightly higher than with the flash tank economizer, due to the higher temperature of superfeed refrigerant gas in the former case.

  • analysis of the working process in an oil flooded screw compressor by means of an Indicator Diagram
    Proceedings of the Institution of Mechanical Engineers Part A: Journal of Power and Energy, 2002
    Co-Authors: Xueyuan Peng, Ziwen Xing, Liansheng Li
    Abstract:

    This paper presents the results of an experimental investigation of the thermodynamic processes in an oil-flooded screw compressor. The pressure within the working chamber is measured with a small pressure sensor, embedded in the female rotor on the discharge side. The results so obtained were transformed into an Indicator Diagram. Based on the Indicator Diagrams at various operating conditions, the working process is analysed. Owing to oil restricting back-flow of the gas through the discharge port, constant-volume compression is not evident even at substantial under-compression conditions, thus making the compressor maintain a high efficiency over a wide range of pressure ratios. However, the additional power consumption resulting from over-compression is comparatively large at pressure ratios lower than that for which the compressor was designed. So a compressor with fixed volume ratio should be designed with the built-in volume ratio low enough to avoid this effect. At the end of the discharge process, the pressure rises steeply due to increased resistance to oil flow, and therefore, the design of a flow-guiding slot to assist oil discharge is recommended. Higher rotating speeds increase the pressure slightly, but the losses associated with this are compensated by the increased volumetric efficiency. Thus a screw compressor maintains its isentropic efficiency over a wide range of speeds. Larger oil:gas ratio presents a higher pressure level in the Indicator Diagram, offsetting the improved sealing effect, and test results show that the appropriate oil:gas mass ratio range is between 8:1 and 20:1.

Aleksandar Kovacevic - One of the best experts on this subject based on the ideXlab platform.

  • Investigation of the influence of oil injection upon the screw compressor working process
    International Journal of Refrigeration, 1992
    Co-Authors: Nikola Stosic, Lj Milutinović, Kemal Hanjalic, Aleksandar Kovacevic
    Abstract:

    Some results of mathematical modelling and experimental investigation of the influence of oil injection upon the screw compressor working process are presented. Several parameters that characterize oil injection were varied over ranges that were initially determined from a computer model. These include: oil flowrate, inlet temperature, droplet atomization, positions in the casing at which the oil was injected, oil jet speed and angle, and time of oil retention in the working volume. The compressor performances were evaluated from measurements of all important bulk parameters: delivery rate, power consumption, power utilization efficiency, specific power, as well as the instantaneous pressure and temperature at several positions along the working volume, from which the Indicator Diagram was worked out. In addition to the information about the influence of each oil parameter upon the compressor performances, the collected data served to verify and complement the mathematical model of the influence of oil upon the screw compressor working process developed earlier, which has subsequently been employed for computer-aided design of two different screw-compressor oil systems. The experimental results and the application of the computer simulation helped in modifying the oil injection system, which resulted in a saving in compressor energy consumption up to 7%. © 1992.