Showing papers on "Gas compressor published in 2012"

A review on two-phase ejector as an expansion device in vapor compression refrigeration cycle

Abstract: This paper presents a comprehensive review of two-phase ejector as an expansion device in vapor compression refrigeration cycle over the past two decades. It also covers research opportunities that are still open in the field of two-phase ejectors as an expansion valve. The studies of the application of ejector as an expansion device are relatively scarce compared to the application of ejector as heat-driven refrigeration system. A better understanding of two-phase flow in the ejector is necessary to optimize energy saving of the system. This paper also presents effects of geometric parameters of the ejector as an expansion valve on the performance of vapor compression refrigeration cycle. In addition, the effect of working fluid on the two-phase expansion refrigeration system is covered. The authors predict that the challenge of future research on design of two-phase ejector is how to generate a pressure rise in diffuser for minimum compressor work and optimum COP improvement.

Experimental characterization of a hermetic scroll expander for use in a micro-scale Rankine cycle

Abstract: This paper presents the results of an experimental study carried out on a prototype of a hermetic scroll expander, integrated into a gas cycle test rig, whose working fluid is HFC-245fa. This system is designed to test only the performance of the expander. It is made up mainly of a scroll compressor, a scroll expander, a heat exchanger, and a by-pass valve. The latter is used to adjust the pressure ratio imposed to the expander. The expander was originally a compressor designed for heat pump applications and is characterized by a nominal power input of 2.5kWe. Performance of the expander is evaluated in terms of isentropic effectiveness and filling factor as functions of the main operating conditions. The study also investigates the impact of oil mass fraction on the expander performance. Maximum overall isentropic effectiveness of 71.03 per cent is measured, which is partly explained by the good volumetric performance of the machine. Using the experimental data, parameters of a semi-empirical simulation model of the expander areidentified. This modelisusedtoanalyse themeasured performance oftheexpander. Finally, a polynomial empirical model of the expander is proposed for fast and robust simulations of organic Rankine cycle systems.

Performance Characteristics of an Operating Supercritical CO2 Brayton Cycle

Abstract: Supercritical CO2 (S-CO2) power cycles offer the potential for better overall plant economics due to their high power conversion efficiency over a moderate range of heat source temperatures, compact size, and potential use of standard materials in construction [1,2,3,4]. Sandia National Labs (Albuquerque, NM, US) and the US Department of Energy (DOE-NE) are in the process of constructing and operating a megawatt-scale supercritical CO2 split-flow recompression Brayton cycle with contractor Barber-Nichols Inc. [5] (Arvada, CO, US). This facility can be counted among the first and only S-CO2 power producing Brayton cycles anywhere in the world.The Sandia-DOE test-loop has recently concluded a phase of construction that has substantially upgraded the facility by installing additional heaters, a second recuperating printed circuit heat exchanger (PCHE), more waste heat removal capability, higher capacity load banks, higher temperature piping, and more capable scavenging pumps to reduce windage within the turbomachinery. With these additions, the loop has greatly increased its potential for electrical power generation — according to models, as much as 80 kWe per generator depending on loop configuration — and its ability to reach higher temperatures.To date, the loop has been primarily operated as a simple recuperated Brayton cycle, meaning a single turbine, single compressor, and undivided flow paths. In this configuration, the test facility has begun to realize its upgraded capacity by achieving new records in turbine inlet temperature (650°F/615K), shaft speed (52,000 rpm), pressure ratio (1.65), flow rate (2.7 kg/s), and electrical power generated (20kWe). Operation at higher speeds, flow rates, pressures and temperatures has allowed a more revealing look at the performance of essential power cycle components in a supercritical CO2 working fluid, including recuperation and waste heat rejection heat exchangers (PCHEs), turbines and compressors, bearings and seals, as well as auxiliary equipment. In this report, performance of these components to date will be detailed, including a discussion of expected operational limits as higher speeds and temperatures are approached.Copyright © 2012 by ASME

Digital Dynamic Range Compressor Design—A Tutorial and Analysis

Abstract: Dynamic range compression, despite being one of the most widely used audio effects, is still poorly understood, and there is little formal knowledge and analysis of compressor design techniques. In this tutorial we describe several different approaches to digital dynamic range compressor design. Digital implementations of several classic analog approaches are given, as well as designs from recent literature, and new approaches that address possible issues. Several design techniques are analyzed and compared, including RMS and peak–based approaches, feedforward and feedback designs, and linear and log domain level detection. We explain what makes the designs sound different and provide metrics to analyze their quality. Finally, we provide recommendations for high performance compressor design.

Air conditioning device for vehicle

Abstract: A vehicle air conditioning apparatus is provided that can extend the mileage of a vehicle by reducing the power consumed by the operation of a compressor and a heater When a required quantity of heating Q_req is acquired, the minimum power sharing ratio between quantity of heat release Q_hpof a water-refrigerant heat exchanger 22 and quantity of heat release Q_htrof a water heater 32 is calculated, which allows the power consumption W_total to be minimized, and a compressor 21 and the water heater 32 is operated based on the result of the calculation

Performance enhancement of CO2 air conditioner with a controllable ejector

Abstract: This study presents performance enhancement of a transcritical CO2 air conditioner with a controllable ejector at variable operating conditions and variable compressor frequencies. The effects of ejector geometries, operating conditions and compressor frequency on the performance of an ejector expansion transcritical CO2 air conditioner were investigated. Experimental results show that the COP of a CO2 air conditioning system can be enhanced by using an ejector expansion device to replace a conventional expansion valve. This enhancement became more significant as the outdoor air temperature increased (COP increased by up to 36%), the compressor frequency decreased (COP increased by up to 147% compared to conventional cycle with compressor frequency at 50 Hz), and the motive nozzle throat diameter decreased (COP increased by up to 60%). In addition, the COP reached a maximum when the distance between motive nozzle exit and mixing section entrance was three times the mixing section diameter.

Power Plant and Control Method

Abstract: Ambient air is compressed into a compressed ambient gas flow (26) with a main air compressor (12). The compressed ambient gas flow (26) having a compressed ambient gas flow rate is delivered to a turbine combustor (32) and mixed with a fuel stream (28) having a fuel stream flow rate and a portion of a recirculated gas flow (50) to form a combustible mixture. The combustible mixture is burned and forms the recirculated gas flow (50) that drives a turbine (34). The recirculated gas flow (50) is recirculated from the turbine (34) to the turbine compressor (30) using a recirculation loop (52). At least one emission level is measured by a first emission sensor (53) in the recirculated gas flow (50) and a first control signal is generated. The fuel stream flow rate is adjusted based on the at least a first control signal to achieve substantially stoichiometric combustion.

Gas turbine engine compressor arrangement

Abstract: A gas turbine engine includes a fan section, a gear arrangement configured to drive the fan section, a compressor section and a turbine section. The compressor section includes a low pressure compressor section and a high pressure compressor section. The turbine section is configured to drive compressor section and the gear arrangement. An overall pressure ratio, which is provided by a combination of a pressure ratio across said low pressure compressor section and a pressure ratio across said high pressure compressor section, is greater than about 35. The pressure ratio across the low pressure compressor section is between about 3 and about 8 whereas the pressure ratio across the high pressure compressor section is between about 7 and about 15.

Environmental control system supply precooler bypass

Abstract: A precooler for cooling compressor bleed air for an environmental control system includes a heat exchanger in fluid communication with a source of cooling air and operable for cooling the bleed air. A variable bypass valve between a bleed air source and environmental control system is operable for bypassing at least a portion of the compressor bleed air around the heat exchanger. The cooling air may be a portion of fan air modulated by a variable fan air valve. The bleed air source may be selectable between the low pressure bleed air source and a high pressure bleed air source. One method includes flowing the compressor bleed air from a single low pressure source only and increasing thrust sufficiently to meet a minimum level of pressure of the bleed air during one engine out aircraft operating condition during approach or loitering.

Flash gas bypass in mobile air conditioning system with R134a

Abstract: This paper demonstrates that the performance of a mobile air conditioning system (with a microchannel evaporator modified to be single pass) operating normally with R134a in direct expansion mode can be significantly improved when switched to flash gas bypass (FGB) mode. When operated at the same compressor speed, the system in FGB mode produces about 13%–18% more cooling capacity at 4%–7% higher COP than DX mode. When the compressor speed was adjusted to maintain the same cooling capacity, the COP improved 37%–55%. Two main reasons are identified and discussed: 1) improved refrigerant distribution and 2) reduction of refrigerant pressure drop.

Computational Fluid Dynamics of a Radial Compressor Operating With Supercritical CO2

Abstract: The merit of using supercritical CO2 (scCO2) as the working fluid of a closed Brayton cycle gas turbine is now widely recognized, and the development of this technology is now actively pursued. scCO2 gas turbine power plants are an attractive option for solar, geothermal and nuclear energy conversion. Among the challenges which must be overcome in order to successfully bring the technology to the market, the efficiency of the compressor and turbine operating with the supercritical fluid should be increased as much as possible. High efficiency can be reached by means of sophisticated aerodynamic design, which, compared to other overall efficiency improvements, like cycle maximum pressure and temperature increase, or increase of recuperator effectiveness, does not require an increase in equipment cost, but only an additional effort in research and development.This paper reports a three-dimensional CFD study of a high-speed centrifugal compressor operating with CO2 in the thermodynamic region slightly above the vapor-liquid critical point. The investigated geometry is the compressor impeller tested in the Sandia scCO2 compression loop facility [1]. The fluid dynamic simulations are performed with a fully implicit parallel Reynolds-averaged Navier-Stokes code based on a finite volume formulation on arbitrary polyhedral mesh elements. The CFD code has been validated on test cases which are relevant for this study, see Ref. [2,3]. In order to account for the strongly nonlinear variation of the thermophysical properties of supercritical CO2, the CFD code is coupled with an extensive library for the computation of properties of fluids and mixtures [4]. Among the available models, the one based on reference equations of state for CO2 [5,6] has been selected, as implemented in one of the sub-libraries [7]. A specialized look-up table approach and a meshing technique suited for turbomachinery geometries are also among the novelties introduced in the developed methodology.A detailed evaluation of the CFD results highlights the challenges of numerical studies aimed at the simulation of technically relevant compressible flows occurring close to the liquid-vapor critical point. The data of the obtained flow field are used for a comparison with experiments performed at the Sandia scCO2 compression-loop facility.© 2012 ASME

Multi-objective optimization of a combined heat and power (CHP) system for heating purpose in a paper mill using evolutionary algorithm

Abstract: SUMMARY The present study deals with a comprehensive thermodynamic modeling of a combined heat and power (CHP) system in a paper mill, which provides 50 MW of electric power and 100 ton h−1 saturated steam at 13 bars. This CHP plant is composed of air compressor, combustion chamber (CC), Air Preheater, Gas Turbine (GT) and a Heat Recovery Heat Exchanger. The design parameters of this cycle are compressor pressure ratio (rAC), compressor isentropic efficiency (ηAC), GT isentropic efficiency (ηGT), CC inlet temperature (T3), and turbine inlet temperature (T4). In the multi-objective optimization three objective functions, including CHP exergy efficiency, total cost rate of the system products, and CO2 emission of the whole plant, are considered. The exergoenvironmental objective function is minimized whereas power plant exergy efficiency is maximized using a Genetic algorithm. To have a good insight into this study, a sensitivity analysis of the results to the interest rate as well as fuel cost is performed. The results show that at the lower exergetic efficiency, in which the weight of exergoenvironmental objective is higher, the sensitivity of the optimal solutions to the fuel cost is much higher than the location of the Pareto Frontier with the lower weight of exergoenvironmental objective. In addition, with increasing exergy efficiency, the purchase cost of equipment in the plant is increased as the cost rate of the plant increases. Copyright © 2010 John Wiley & Sons, Ltd.

Demonstration of Supercritical CO2 Closed Regenerative Brayton Cycle in a Bench Scale Experiment

Abstract: Power generation with a supercritical CO2 closed regenerative Brayton cycle has been successfully demonstrated using a bench scale test facility. A set of a centrifugal compressor and a radial inflow turbine of finger top size is driven by a synchronous motor/generator controlled using a high-speed inverter. A 110 W power generating operation is achieved under the operational condition of rotational speed of 1.15kHz, CO2 flow rate of 1.1 kg/s, and respective thermodynamic states (7.5 MPa, 304.6 K) at compressor and (10.6 MPa, 533 K) at turbine inlet. Compressor work reduction owing to real gas effect is experimentally examined. Compressor to turbine work ratio in supercritical liquid like state is measured to be 28% relative to the case of ideal gas. Major loss of power output is identified as rotor windage. It is found the isentropic efficiency depends little on compressibility coefficient. Off design performance of gas turbine working in supercritical state is well predicted by a Meanline program. The CFD analysis on compressor internal flow indicates that the presence of backward flow around the tip region might create a locally depressurized region leading eventually to the onset of flow instability.Copyright © 2012 by ASME

Experimental performance study of a small wall room air conditioner retrofitted with R290 and R1270

Abstract: An original R22 wall room air conditioner with a cooling capacity of 2.4 kW and energy efficiency ratio (EER) of 3.2 is retrofitted with a compressor of a 20% larger displacement to charge R290 and R1270 for performance experiments. The results show that for R1270, only adopting a same kind mineral lubricant of higher viscosity would supply 2.4% higher cooling capacity and 0.8% higher EER than those of the original R22 system under normal condition, and for R290, adopting the larger displacement compressor simultaneously would also obtain better performance. Alternative systems all have higher increase rate and greater increment in both cooling capacity and EER than the original R22 system when outdoor temperature decreases. The R1270 system has great increase in cooling capacity and negligible decrease in EER. Refrigerant charge distribution is also investigated and it indicates that the charge within both heat exchangers and compressor ought to be reduced.

Systems and apparatus relating to reheat combustion turbine engines with exhaust gas recirculation

Abstract: A power plant configured to include a recirculation loop about which a working fluid is recirculated, the recirculation loop comprising a plurality of components configured to accept an outflow of working fluid from a neighboring upstream component and provide an inflow of working fluid to a neighboring downstream component. The recirculation loop may include: a recirculation compressor; an upstream combustor; a high-pressure turbine; a downstream combustor; a low-pressure turbine; and a recirculation conduit configured to direct the outflow of working fluid from the low-pressure turbine to the recirculation compressor. The power plant may include: an oxidant compressor configured to provide compressed oxidant to both the upstream combustor and the downstream combustor; and means for extracting a portion of the working fluid from an extraction point disposed on the recirculation loop.

Power plant and method of operation

Abstract: A power plant and method of operation is provided. The power plant comprises at least one main air compressor, an oxidizer unit configured to deliver a compressed oxygen-rich gas flow to at least one gas turbine assembly. Each assembly comprises a turbine combustor for mixing the compressed oxygen-rich gas flow with a recirculated gas flow and a fuel stream to burn a combustible mixture and form the recirculated gas flow. The assembly also comprises a recirculation loop for recirculating the recirculated gas flow from a turbine to a turbine compressor. The assembly further comprises a recirculated gas flow extraction path for extracting a portion of the recirculated gas flow from the assembly and delivering this to a gas separation system. The gas separation system separates the portion of the recirculated gas flow into a nitrogen portion and a carbon dioxide portion.

Hybrid vapor compression refrigeration system with an integrated ejector cooling cycle

Abstract: A refrigeration system was developed which combines a basic vapor compression refrigeration cycle with an ejector cooling cycle. The ejector cooling cycle is driven by the waste heat from the condenser in the vapor compression refrigeration cycle. The additional cooling capacity from the ejector cycle is directly input into the evaporator of the vapor compression refrigeration cycle. The governing equations are derived based on energy and mass conservation in each component including the compressor, ejector, generator, booster and heat exchangers. The system performance is first analyzed for the on-design conditions. The results show that the COP is improved by 9.1% for R22 system. The system is then compared with a basic refrigeration system for variations of five important variables. The system analysis shows that this refrigeration system can effectively improve the COP by the ejector cycle with the refrigerant which has high compressor discharge temperature.