Showing papers on "Gas compressor published in 2002"

Portable, battery-powered air compressor for a pneumatic tool system

Abstract: A portable pneumatic fastening tool has an onboard compressor assembly to alleviate the need for an external air compressor. The onboard compressor assembly includes a motor and a compressor mounted to the tool body. The motor can be powered by a detachable battery mounted to a cover for covering the onboard compressor assembly. A portable pneumatic fastening tool may also be powered by a portable compressor assembly which can be borne by the user.

Comparitive analysis of an automotive air conditioning systems operating with CO2 and R134a

Abstract: This paper evaluates performance merits of CO2 and R134a automotive air conditioning systems using semi-theoretical cycle models. The R134a system had a current-production configuration,which consisted of a compressor, condenser,expansion device,and evaporator. The CO 2 system was additionally equipped with a liquid-line/suction-line heat exchanger. Using these two systems,an effort was made to derive an equitable comparison of performance; the components in both systems were equivalent and differences in thermodynamic and transport properties were accounted for in the simulations. The analysis showed R134a having a better COP than CO2 with the COP disparity being dependent on compressor speed (system capacity) and ambient temperature. For a compressor speed of 1000 RPM,the COP of CO 2 was lower by 21% at 32.2 � C and by 34% at 48.9 � C. At higher speeds and ambient temperatures,the COP disparity was even greater. The entropy generation calculations indicated that the large entropy generation in the gas cooler was the primary cause for the lower performance of CO2. # 2001 Elsevier Science Ltd and IIR. All rights reserved.

Mathematical modeling of scroll compressors. Part I: compression process modeling

Abstract: This paper presents a detailed model for the compression process of a scroll compressor, which is used for investigating a compressor's performance under different operating conditions and subject to design changes. Upon defining the compressor chambers as suction chambers, compression chambers and discharge chambers, a geometry study was conducted and the governing mass and energy conservation equations were developed for each chamber. Models for the refrigerant flow in the suction and discharge processes, radial and flank leakage, and heat transfer between the gas and scroll wraps were combined with the conservation equations. The state of the refrigerant changes with a period of angle 2π, and thousands of step are used to solve the governing differential equations during each period. It is assumed that in each step the compressor is in steady state. Since the differential equations for the different chambers are coupled, all these equations are solved simultaneously using a nonlinear equation solver. A description of the corresponding computer code and some results are included in this paper. Verification of the compression process model can be referred to that of the overall model, which is described in Chen et al. [Chen Y, Halm N, Braun J, Groll E. Mathematical modeling of scroll compressors—part II: overall scroll compressor modeling. International Journal of Refrigeration 2002;25(6):751–764.].

Passive cooling system for auxiliary power unit installation

Abstract: A passive cooling system for an auxiliary power unit (APU) installation on an aircraft is provided. The system is for an auxiliary power unit having at least a compressor portion of a gas turbine engine and an oil cooler contained separately within a nacelle. The system includes the auxiliary power unit housed within the nacelle of the aircraft, an engine exhaust opening defined in the aft portion of the nacelle and communicating with the gas turbine engine, at least a first air inlet duct communicating with a second opening defined in said nacelle and with said compressor portion and the oil cooler is located within a second duct communicating with an opening other than the engine exhaust opening of said nacelle and with the engine exhaust opening. Exterior cooling air and engine exhaust ejected through said engine exhaust opening entrain cooling air through said second duct to said oil cooler, and thus provide engine oil cooling. An exhaust eductor is also provided.

Ejector cycle system

Abstract: In an ejector cycle system, high-pressure side refrigerant is decompressed by an ejector in cooling operation for cooling a compartment, and is decompressed by a fixed restrictor in heating operation for heating the compartment. Therefore, in the heating operation, the pressure of refrigerant to be sucked into a compressor can be made lower, and the temperature of refrigerant discharged from the compressor is increased. Alternatively, in the cooling operation, a flow direction of refrigerant flowing through at least one of an exterior heat exchanger and an interior heat exchanger is identical to that in the heating operation.

System and methods for controlling rotary screw compressors

Abstract: An electronic control system dynamically varies the output capacity of a compressor by controlling plural valves associated with the compressor to provide pressurized air to a distribution system at an appropriate rate. The control system operates in any of three modes for standalone operation, including continuous run, auto/dual pressure band, and target pressure modes. In the first two modes, pressure bands are dynamically calculated based on load and unload values entered by an operator. These electronic control systems can also be connected in a peer-to-peer network to coordinate control of up to 16 compressors feeding the same distribution system, so as to maintain a desired target pressure in the system. A modem connected to the system supports remote diagnostics, monitoring, and control. Specialized startup, operating, and shutdown diagnostic algorithms prevent damage to the compressor and avert unsafe operating conditions.

Method and apparatus for achieving power augmentation in gas turbines using wet compression

Abstract: A gas turbine unit as well as a method for operating a gas turbine unit is proposed. A very quick and at the same time easily controllable augmentation or reduction of shaft power being produced by the gas turbine can be achieved by providing at least one liquid droplet injection device (32) on the upstream side of compressor (1, 2) for injecting liquid into the stream of intake air (10) in order to increase the shaft power generated by the gas turbine unit. The amount of water mass flow corresponding to the desired increase or decrease of shaft power output of the gas turbine unit is added or reduced in the form of liquid droplets in a substantially stepless manner and immediately within a time interval that is determined by the design characteristics of the liquid droplet injection device (32).

Modeling and experimental evaluation of an automotive air conditioning system with a variable capacity compressor

Abstract: A steady state computer simulation model has been developed for refrigeration circuits of automobile air conditioning systems. The simulation model includes a variable capacity compressor and a thermostatic expansion valve in addition to the evaporator and micro channel parallel flow condenser. An experimental bench made up of original components from the air conditioning system of a compact passenger vehicle has been developed in order to check results from the model. The refrigeration circuit was equipped with a variable capacity compressor run by an electric motor controlled by a frequency converter. Effects on system performance of such operational parameters as compressor speed, return air in the evaporator and condensing air temperatures have been experimentally evaluated and simulated by means of developed model. Model results deviate from the experimentally obtained within a 20% range though most of them are within a 10% range. Effects of the refrigerant inventory have also been experimentally evaluated with results showing no effects on system performance over a wide range of refrigerant charges.

Apparatus for the liquefaction of natural gas and methods relating to same

Abstract: Apparatuses and methods are provided for producing liquefied gas, such as liquefied natural gas. In one embodiment, a liquefaction plant may be coupled to a source of unpurified natural gas, such as a natural gas pipeline at a pressure letdown station. A portion of the gas is drawn off and split into a process stream and a cooling stream. The cooling stream may sequentially pass through a compressor and an expander. The process stream may also pass through a compressor. The compressed process stream is cooled, such as by the expanded cooling stream. The cooled, compressed process stream is expanded to liquefy the natural gas. A gas-liquid separator separates the vapor from the liquid natural gas. A portion of the liquid gas may be used for additional cooling. Gas produced within the system may be recompressed for reintroduction into a receiving line.

Exergy analysis of multistage cascade refrigeration cycle used for natural gas liquefaction

Abstract: This paper provides an exergy analysis of the multistage cascade refrigeration cycle used for natural gas liquefaction. The equations of exergy destruction and exergetic efficiency for the main cycle components such as evaporators, condensers, compressors, and expansion valves are developed. The relations for the total exergy destruction in the cycle and the cycle exergetic efficiency are obtained. Also, an expression for the minimum work requirement for the liquefaction of natural gas is developed. It is shown that the minimum work depends only on the properties of the incoming and outgoing natural gas, and it increases with decreasing liquefaction temperature. The minimum work for a typical natural gas inlet and exit state is determined to be 456.8 kJ kg−1 of liquefied natural gas (LNG), which corresponds to a coefficient of performance (COP) of 1.8. Using a typical actual work input value; the exergetic efficiency of the multistage cascade refrigeration cycle is determined to be 38.5% indicating a great potential for improvements. Copyright © 2002 John Wiley & Sons, Ltd.

The Use of Sweep and Dihedral in Multistage Axial Flow Compressor Blading—Part I: University Research and Methods Development

Abstract: This paper describes the introduction of 3D blade designs into the core compressors for the Rolls-Royce Trent engine with particular emphasis on the use of sweep and dihedral in the rotor designs. It follows the development of the basic ideas in a university research project, through multistage low-speed model testing, to the application to high pressure engine compressors. An essential element of the project was the use of multistage CFD and some of the development of the method to allow the designs to take place is also discussed. The first part of the paper concentrates on the university-based research and the methods development. The second part describes additional low-speed multistage design and testing and the high-speed engine compressor design and test.Copyright © 2002 by ASME

Scroll compressors using gas and liquid injection: experimental analysis and modelling

Abstract: The first part of this paper presents an experimental analysis of different hermetic scroll compressors using different methods of injection: the first one is without injection, the second one uses vapor injection and the third one liquid injection. The analysis reveals the influence of these methods on the compressor behavior. A simplified model of the scroll compressor is then proposed that takes into account not only the different internal processes but also the refrigerant injection. It assumes that the refrigerant mass flow rate is affected by a heating-up due to a uniform wall temperature. This fictitious wall is supposed to gain heat from the electromechanical losses and from the discharged gas and to loose heat to the suction and to the ambient. The compression step is considered isentropic up to the adapted pressure and then at constant volume until the discharge pressure. The model is able to compute variables of first importance like the mass flow rate, the electric power and the discharge temperature, as well as secondary variables as suction heating-up, discharge cooling-down, and ambient losses. The validation based on 45 experimental results shows excellent results.

Compressor diagnostic system

Abstract: A compressor includes a motor protector which stops the compressor's motor when it senses an out of specification condition. A diagnostic system monitors the status of the motor protector. The diagnostic system includes logic circuitry that diagnoses the type of problem the compressor is having based upon the running times and status of the motor in conjunction with the times and status of the motor protector.

Proton Exchange Membrane Fuel Cell System Model for Automotive Vehicle Simulation and Control

Abstract: This paper describes a proton exchange membrane (PEM) fuel cell system model for automotive applications that includes an air compressor, cooling system, and other auxiliaries. The fuel cell system model has been integrated into a vehicle performance simulator that determines fuel economy and allows consideration of control strategies. Significant fuel cell system efficiency improvements may be possible through control of the air compressor and other auxiliaries. Fuel cell system efficiency results are presented for two limiting air compressor cases: ideal control and no control. Extension of the present analysis to hybrid configurations consisting of a fuel cell system and battery is currently under study.

Counter rotating aircraft gas turbine engine with high overall pressure ratio compressor

Abstract: An aircraft gas turbine engine includes high and low pressure turbines having respective counter rotatable low pressure inner and outer rotors with low pressure inner and outer shafts in part rotatably disposed co-axially within a high pressure rotor and drivingly connected to first and second fan blade rows and first and second boosters respectively. A bypass duct radially bounded by a fan casing and an annular radially inner bypass duct wall surrounds the boosters axially located between the first and second fan blade rows. The engine has a high pressure compressor operable to produce an overall pressure ratio in a range of about 40-65 and a fan inlet hub to tip radius ratio in a range between 0.20 and 0.35, a bypass ratio in a range of 5-15, an operational fan pressure ratio in a range of 1.4-2.5, and a sum of operational fan tip speeds in a range of 1000 to 2500 feet per second.

Mathematical modeling of scroll compressors — part II: overall scroll compressor modeling

Abstract: This paper presents the development of a comprehensive simulation model of a horizontal scroll compressor, which combines a detailed compression process model (Chen Y., Halm N., Groll E., Braun J. Mathematical modelling of scroll compressors — part I: compression process modeling, International Journal of Refrigeration 2002;25(6):731–750) and an overall compressor model. In the overall model, compressor components are analyzed in terms of nine different elements. Steady state energy balance equations are established applying the lumped capacitance method. In combination with the detailed compression process model, these equations were implemented into computer code and solved recursively. In this way, the temperature and pressure of the refrigerant in different compressor chambers, the temperature distributions in the scroll wraps, and the temperatures of the other compressor elements can be obtained. Thereafter, power consumption and efficiency of the compressor can be calculated. Tests were used to verify the overall model on a macroscopic basis. Using the simulation program based on the overall compressor model, a parametric study of the scroll compressor was performed, and the effects of internal leakage and heat transfer losses were investigated and some preliminary results were obtained. These results indicate that the comprehensive scroll compressor model is capable of predicting real compressor behavior and useful to the design and optimization of scroll compressors.

Uncoupled, thermal-compressor, gas-turbine engine

Abstract: The invention is for a continuous-combustion, closed-cycle, gas turbine engine with a regenerator and a displacer. It has embodiments that remove heater and cooler interior volumes during gas compression, which enable it to scale well to very large sizes. Low combustion temperatures insure very low emissions. The displacer levitated by an integral gas bearing and small clearance seal and given oscillatory translational motion by electromagnetic forces operates without surface wear. The turbine blades, subjected only to warm gases, are durable and inexpensive. Thus, this engine has a very long, continuous, maintenance-free service life. This gas turbine engine also operates without back work allowing high efficiency for both low and rated output. Pressurized encapsulation permits use of low-cost ceramics for high temperature components. The invention includes a unique monolithic ceramic heater, a compact high-capacity regenerator and a constant-power gas turbine.

Air conditioning systems

Abstract: An air conditioning system includes a refrigerant circuit. The refrigerant circuit includes a compressor for receiving a refrigerant gas and for compressing the refrigerant gas, and a condenser for condensing a portion of the compressed refrigerant gas into a liquid refrigerant. The refrigerant circuit also includes an expansion valve for reducing a pressure of the condensed liquid refrigerant, and an evaporator for evaporating the condensed liquid refrigerant. Moreover, the compressor is driven by an electric motor which controls a rotational speed of the compressor via an inverter, and a temperature of the inverter is decreased by the refrigerant circuit. The system also includes an electric circuit for determining whether a temperature of the inverter is greater than a first predetermined temperature, and an electric circuit for controlling a rotational speed of the compressor. Specifically, when the temperature of the inverter is greater than the first predetermined temperature, the electric circuit decreases the rotational speed of the compressor.

Klystron instability of a relativistic electron beam in a bunch compressor

Abstract: In this paper, we consider a klystron-like mechanism of amplification of parasitic density modulations in an electron bunch passing a magnetic bunch compressor. Analytical expressions are derived for the small-signal gain. The effect of wakefields in front of the bunch compressor is analyzed by using a model of linear compression which assumes linear correlated energy chirp and linear dependence of a path length on energy deviation. Analysis of the density modulation growth due to coherent synchrotron radiation inside bends of the magnetic bunch compressor is done for the simplified case of no correlated energy chirp (no compression). Analytical results of this paper can be used for benchmarking numerical simulation codes.

Thermodynamic Analyses of Wet Compression Process in the Compressor of Gas Turbine

Abstract: Thermodynamic model of wet compression process is established in this paper. The topics of ideal wet compression process, actual wet compression process, water droplet evaporative rate, wet compression work, inlet evaporative cooling, concept of wet compression efficiency, aerodynamic breaking of water droplets etc. are investigated and discussed in this paper.Copyright © 2002 by ASME

Thermodynamic analysis on the performance of a variable speed scroll compressor with refrigerant injection

Abstract: A thermodynamic model for a variable speed scroll compressor with refrigerant injection was developed using continuity, energy conservation and real gas equation. The model included energy balance in the low-pressure shell compressor, suction gas heating, motor efficiency, and volumetric efficiency considering gas leakages as a function of compressor frequency. The developed model was verified by comparing the predicted results for the no injection condition with the experimental data. The deviations of the predicted from the measured values were within 10% for approximately 90% of the experimental data. Based on the model, mass flow rate, suction gas heating, cooling capacity and power consumption of the compressor were estimated and analyzed as a function of frequency. The effects of refrigerant injection on the performance of the compressor were also discussed as a function of frequency, injection conditions, and injection geometry.

Re-fired gas turbine engine

Abstract: In a reheat gas turbine engine for power generation, fuel is burnt with compressed air from a compressor in a first or primary combustor, the combustion products are passed through a high pressure turbine, the exhaust of the high pressure turbine is then burnt together with further fuel in a reheat combustor to consume the excess air, and the exhaust of the second combustor is passed through a lower pressure turbine. Excess air is supplied to the first combustor, thereby enabling so-called “lean burn” combustion for production of low levels of pollutants in the exhaust of the engine. Some turbine components of the turbines, e.g., blades or vanes, are cooled by cooling air supplies tapped off from the compressor. The operating cycle of the gas turbine engine is modified by returning at least some of the spent cooling air from the low pressure turbine to the reheat combustor, where it is burnt with additional fuel to produce a greater volume of exhaust gases, thereby increasing the torque on a shaft and boosting the power output of the generator.

Estimating operating parameters of vapor compression cycle equipment

Abstract: A process for estimating the capacity and the coefficient of performance by taking common measurements and using compressor manufacturer's performance data is presented. A process for determining a capacity index and an efficiency index for a vapor compression cycle relative to desired operating conditions.

Transient simulation of vapour-compression packaged liquid chillers

Abstract: This paper presents a transient simulation model that is useful for predicting the dynamic performance of vapour-compression liquid chillers over a wide range of operating conditions. The model employs a thermal capacitance approach for specific state variables to account for the dynamics of the chiller and ancillaries. The model accounts for the change in heat transfer coefficients throughout the heat exchangers thereby improving both physical realism and the accuracy of the simulation model. The model requires only a select few initial conditions (eg. the chilled water and condenser water temperatures). A simple compressor model based on empirical regression has been employed in the simulation. The outputs of the model include system performance variables such as the compressor electrical work input and the coefficient of performance (COP) as well as states of the refrigerant throughout the refrigeration cycle with respect to time. The model is validated with data from two in -situ screw chillers. Predictions are found to be within ±10%, although for one of the chillers a degree of empiricism was employed for the evaporator tube wall mass in order to give satisfactory results for the start-up process.

Digital scroll condensing unit controller

Abstract: A cooling system controller controls the capacity of a variable capacity compressor based upon the temperature of a housing being cooled, the suction pressure of the compressor or both of these criteria. The cooling system controller is capable of controlling either single-evaporator or multiple-evaporator refrigeration systems. The multiple-evaporator systems can have evaporators of similar temperatures or of mixed temperatures. The controller also allows the use of one or more condenser fans that are operated in a lead/lag fashion to control the cooling capability of the system.