Expander Inlet Temperature Research Articles

초소형 유기랭킨사이클용 스크롤팽창기 효율 특성 분석

본 연구에서는 자동차용 엔진 폐열 회수 유기랭킨사이클에 적용하기 위해 개발 중인 스크롤 팽창기의 효율을 상용 스크롤 팽창기와 비교 분석을 수행하였다. 팽창기 효율 특성 시험을 위해 유기랭킨사이클을 운전하면서 팽창기 출력, 팽창기 입구 온도, 압력 및 작동유체(냉매 R134a)의 유량을 측정하였으며, 개발 중인 스크롤 팽창기의 전효율은 상용 스크롤 팽창기의 전효율에 비해 매우 낮은 수준을 나타내었다. 특히 팽창기 내부의 작동유체 누설에 의한 체적효율 저하가 전효율 저하에 큰 영향을 주는 것으로 파악되었기 때문에 향후 팽창기 효율 향상을 위해 팽창기 내부의 누설문제를 필히 해결해야할 것으로 분석되었다. In this Study, efficiencies of the scroll expander under development for organic Rankine cycle using engine waste heat of vehicle have been analyzed and compared with the commercial scroll expander. While operating organic Rankine cycle for analysing expander efficiencies, power of expander, inlet temperature of expander, inlet pressure of expander and the flow rate of the working fluid(refrigerant R134a) have been measured. Overall efficiency of the expander has been shown the very low level compared with the overall efficiency of the commercial expander. Especially, because the low volumetric efficiency has much effect on overall efficiency, the working fluid leakage trouble of expander has to be solved surely for improvement of the expander overall efficiency.

Performance Analysis and Working Fluid Selection of a Supercritical Organic Rankine Cycle for Low Grade Waste Heat Recovery

The performance analysis of a supercritical organic Rankine cycle system driven by exhaust heat using 18 organic working fluids is presented. Several parameters, such as the net power output, exergy efficiency, expander size parameter (SP), and heat exchanger requirement of evaporator and the condenser, were used to evaluate the performance of this recovery cycle and screen the working fluids. The results reveal that in most cases, raising the expander inlet temperature is helpful to improve the net power output and the exergy efficiency. However, the effect of the expander inlet pressure on those parameters is related to the expander inlet temperature and working fluid used. Either lower expander inlet temperature and pressure, or higher expander inlet temperature and pressure, generally makes the net power output more. Lower expander inlet temperature results in larger total heat transfer requirement and expander size. According to the screening criteria of both the higher output and the lower investment, the following working fluids for the supercritical ORC system are recommended: R152a and R143a.

Performance analysis in near-critical conditions of organic Rankine cycle

According to fluid critical temperature and heat source temperature, organic Rankine cycle (ORC) is recognized in two categories: subcritical ORC and supercritical ORC. For a given heat source, some organic fluids not only can be used in subcritical ORC, but also can be used in supercritical ORC. For heat source with temperature of 90 °C, HFC125, HFC143a and HF218 can be used in both ORCs. Performance of the three substances in both cycles, especially in near-critical conditions is studied with expander inlet temperature of 85 °C and hot water mass flow rate of 1 kg/s. The results show that when fluids go in supercritical ORC from subcritical ORC, cycle thermal efficiency varies continuously, while mass flow rate and net power generation vary discontinuously. Maximum net power generation in near-critical conditions of subcritical ORC is higher than that of supercritical ORC. For HFC125 and HFC143a, outlet temperature of hot water decreases with the increase of heating pressure ratio. For HF218, outlet temperature of hot water increases firstly and decreases secondly with the increase of heating pressure ratio, which leads to an increase of net power generation with the increase of heating pressure ratio in high heating pressure ratio conditions.

Study on thermal efficiency of low- to medium-temperature organic Rankine cycles using HFO−1234yf

HFO−1234yf is a new refrigerant with a nearly zero global warming potential (GWP) and ozone depletion potential (ODP); it exhibits thermodynamic properties similar to HFC−134a. The potential of HFO−1234yf as a working fluid for organic Rankine cycles (ORC) is elucidated through a first-order simulation. A fundamental thermodynamic model of ORC with five types of cycles—trilateral, saturated, superheated, sub-critical, and supercritical—is used to compare the thermal efficiency of HFO−1234yf with that of other working fluids. HFO−1234yf was found to offer a thermal efficiency that was comparable to that of HFC−134a. This paper provides a useful map that clearly shows the best possible thermal efficiency among the five types of cycles for various expander inlet and condensation temperatures. The highest thermal efficiency range (8.8%–11.4%) was obtained when the supercritical ORC was used at an expander inlet temperature of 170 ± 10 °C and a condensation temperature range of 20–40 °C for the given pump and expander efficiency. It is concluded that HFO−1234yf is a potential working fluid for ORC applications, especially for those with low- to medium-temperature heat sources.

Analysis and Optimization of ORC for Low-Temperature Waste Heat Power Generation

This paper presents energy analysis, thermodynamic calculation and exergy analysis for waste heat power generation system of Organic Rankine Cycle based on the first and second laws of thermodynamics. In order to improve system performance, for low-temperature waste heat of 120°C and R245fa organic working fluid, using Aspen Plus software conducted simulation, optimization and improvement. Results from these analyses show that decreasing the expander inlet temperature, increasing inlet pressure of the expander, and adding regenerative heater can increase thermal and exergy efficiencies, at the same time reduce system irreversibility.

Influence of a non-condensable gas on the performance of a piston expander for use in carbon dioxide trans-critical heat pumps

Non-condensable gas is proved to accelerate the phase change process and improve the expander performance by experimental researches on the carbon dioxide trans-critical heat pump. Using expander instead of throttle valve in carbon dioxide trans-critical heat pump can recover energy and improve system efficiency. Accelerating phase change process is a main way to improve expander efficiency. The theoretical analysis indicates that a non-condensable gas can reduce the required molecule number to form critical cluster, and convert homogeneous nucleation process into heterogenic nucleation process, thus increase the number of gas nucleus. In order to investigate the influence of a non-condensable gas to expander performance, experiments on expander efficiency adding different mass ratios of nitrogen gas into system are carried out. The results indicate that when the inlet temperature of expander is 35 °C and the inlet pressure keeps at 8 MPa, the efficiency of expander used in the system with non-condensable gas is 25% higher on average. The results also show that the more the addition quantity of non-condensable gas is used in the system, the more the expander efficiency increases. Moreover, the non-condensable gas can improve the expander efficiency more when the inlet temperature of expander is higher.

Applicability of scroll expander and compressor to an external power engine: Conceptual design and performance analysis

A scroll expander and scroll compressor for a 10-kW class Ericsson engine utilizing solar energy as heat source has been suggested. Orbiting scroll members of the expander and compressor were designed to have a base plate with double-sided wrap structure for compact size and axial gas force cancellation. For axial compliance of the scroll machines, a back pressure chamber was created on each fixed scroll. In order to compensate for the thermal expansion, flexible coupling between the orbiting scroll base plate and the scroll plate holders and sliding keys between the fixed scroll and the supporting frame were designed. Common shafts were shared by the expander and compressor for direct power transmission. For high- and low-side pressures of 6 and 2.5 MPa, respectively, and expander inlet temperature of 700°C, the proposed engine efficiency was estimated to be 7.3%. The engine efficiency strongly depends on the expander and compressor efficiencies as well as on the regenerator efficiency. The shaft output of the designed scroll expander was calculated to be 38.84 kW, while the input power for the scroll compressor was 27.97 kW, yielding 10.87 kW for the engine output. Copyright © 2011 John Wiley & Sons, Ltd.

An integrated power generation system combining solid oxide fuel cell and oxy-fuel combustion for high performance and CO 2 capture

An integrated power generation system combining solid oxide fuel cell (SOFC) and oxy-fuel combustion technology is proposed. The system is revised from a pressurized SOFC-gas turbine hybrid system to capture CO 2 almost completely while maintaining high efficiency. The system consists of SOFC, gas turbine, oxy-combustion bottoming cycle, and CO 2 capture and compression process. An ion transport membrane (ITM) is used to separate oxygen from the cathode exit air. The fuel cell operates at an elevated pressure to facilitate the use of the ITM, which requires high pressure and temperature. The remaining fuel at the SOFC anode exit is completely burned with oxygen at the oxy-combustor. Almost all of the CO 2 generated during the reforming process of the SOFC and at the oxy-fuel combustor is extracted from the condenser of the oxy-combustion cycle. The oxygen-depleted high pressure air from the SOFC cathode expands at the gas turbine. Therefore, the expander of the oxy-combustion cycle and the gas turbine provides additional power output. The two major design variables (steam expander inlet temperature and condenser pressure) of the oxy-fuel combustion system are determined through parametric analysis. There exists an optimal condenser pressure (below atmospheric pressure) in terms of global energy efficiency considering both the system power output and CO 2 compression power consumption. It was shown that the integrated system can be designed to have almost equivalent system efficiency as the simple SOFC-gas turbine hybrid system. With the voltage of 0.752 V at the SOFC operating at 900 °C and 8 bar, system efficiency over 69.2% is predicted. Efficiency penalty due to the CO 2 capture and compression up to 150 bar is around 6.1%.

Study on expansion power recovery in CO 2 trans-critical cycle

Due to the ozone depletion potential and global warming potential of CFCs and HCFCs, CO 2 is considered as most potential alternative refrigerant. However, there are serious throttle losses and low system efficiency to CO 2 trans-critical cycle because of its low critical temperature and high operating pressure. The aim of this paper is to design an expander to recover expansion power in CO 2 trans-critical cycle. The theoretical analysis and calculation show that 14–23% of input power of compressor can be recovered. A prototype of rolling piston expander is designed and manufactured and its test facility is established. The test facility consists of CO 2 trans-critical cycle, the expander, the chilling water system and the cooling water system. The experimental results show that the recovery ratio and expander efficiency are affected by rotational speed, inlet temperature and mass flow of expander. The highest recovery ratio can reach to 0.145, which means 14.5% of input power of compressor can be recovered. The expander efficiency can reach to 45%.

Theoretical and experimental investigation of an organic Rankine cycle for a waste heat recovery system

This article describes and evaluates an organic Rankine cycle (ORC) for a waste heat recovery system by both theoretical and experimental studies. Theoretical analysis of several working fluids shows that cycle efficiency is very sensitive to evaporating pressure, but insensitive to expander inlet temperature. Second law analysis was carried out using R600a as a working fluid and a flow of hot air as a heat source, which is not isothermal, along the evaporator. The result discloses that the evaporator's internal and external entropy generation is the main source of total entropy generation. The effect of the heat source temperature, evaporating pressure, and evaporator size on the entropy generation rate is also presented. The obtained useful power is directly linked to the total entropy generation rate according to the Gouy—Stodola theorem. The ORC testing system was established and operated using R600a as a working fluid and hot water as a heat source. The maximum cycle efficiency of the testing system is 5.2 per cent, and the testing result also proves that cycle efficiency is insensitive to heat source temperature, but sensitive to evaporating pressure. The entropy result also shows that internal and external entropy of the evaporator is the main source of total entropy generation.

Numerical simulation on scroll expander–compressor unit for CO 2 trans-critical cycles

In a two-stage compression CO 2 trans-critical cycle, application of a combined scroll expander–compressor unit has been considered in order to improve the cycle COP. For the combined scroll expander–compressor unit, power was recovered from a scroll expander which replaced the expansion valve and transmitted to the first stage auxiliary compressor which was directly coupled to the expander through a common crankshaft. Numerical simulation on its performance showed that for the suction pressure of 3.5 MPa, discharge pressure of 10 MPa with expander inlet temperature of 35 °C, the main compressor input could be reduced by 12.1% by the expander output. Increase in the cooling capacity by the expander was 8.6%. As a consequence, COP improvement of the cycle was estimated to be 23.5% by the application of this expander–compressor unit. COP improvement increased with lowering the expander inlet temperature, but decreased with increasing the suction pressure. Performance of the scroll expander was relatively insensitive to changes of operating pressure ratio, whereas that of the scroll compressor decreased rapidly as the operating pressure ratio became far from the design pressure ratio.

00/00446 Comparison between IGCC and supercritical power plant processes

In recent years great deal of research work has been done to improve the efficiency of coal fired power plants. There are principally two different ways to increase the efficiency. The first is to increase the steam parameters in a conventional steam process and the other is to develop combined cycles for coal based on integrated gasification combined cycle (IGCC) or pressurized fluidized bed (PFBC) technology. For supercritical processes, the parameters of interest are turbine inlet pressure and temperature. Parameters that must be optimized are the number of reheaters, reheat pressure and temperature, the number of feed water preheaters and extraction pressure. In this work the future possibilities of supercritical and IGCC processes were studied. Both supercritical and IGCC processor were optimized by using a PROcess SIMulation program (PROSIM). Parameter values for both cases were chosen to meet future expectations that will be achieved by improving steam and gas turbines and as well as boiler materials. Results showed that the net plant efficiency is increased by raising the inlet steam temperatures and pressures in a supercritical process, also gas turbine expander inlet temperature and pressure ratio in an IGCC process. In order to reach efficiencies over 50 %, the processmore » parameter values must be increased beyond what is possible today. Interesting result has been obtained by increasing the gasification temperature in the IGCC process. The net plant efficiency decreased if the process used Cold Gas Clean Up, but increased if Hot Gas Clean up was used.« less

96/05421 HCFC22-based absorption cooling systems. Part III: Effects of different absorber and condenser temperatures

The aim of this study is to investigate the economic performance of the waste heat recovery (WHR) system for a marine diesel engine. Four waste heat sources, which are exhaust gas, cylinder cooling water, scavenge air cooling water and lubricating oil of a marine diesel engine, are first applied to drive the transcritical Rankine cycle (TRC). R1234yf, R1234ze, R134a, R152a, R236fa and R290 are employed in the system as working fluids. The effects of expander inlet pressure and temperature on net power output, thermal efficiency, total cost, mass flow rate, and available efficiency of the WHR system are analyzed. The levelized energy cost is used to evaluate the economic optimizations and their corresponding optimal parameters in the WHR system. The results show that the optimal levelized energy cost of R236fa is the most excellent and is lower than that of R1234ze, R134a, R152a, R1234yf or R290 by 5.07%, 6.25%, 7.42%, 9.77% or 12.11%, respectively. The payback period, fuel oil saving, and CO2 emission reduction are applied to assess the suitability of these working fluids. Furthermore, the economic optimization correlations in terms of dimensionless optimal pressures and temperature difference ratios are proposed for the system design of the optimal operating conditions.

Raising the efficiency of piston-drive helium expansion engines

Operating tests of a cryogenic helium installation show that, at normal operating-mode parameters, the temperature of the gas flowing out through the gap between the piston and cylinder of a piston-drive expansion machine is much higher than its inlet temperature to the machine. The fact that preheated gas enters the expansion engine in line with a reverse current increases the temperature differnce between the direct and and reverse streams in the heat exchanger, thereby lowering the refrigeration capacity and the efficiency of the installation's operation as a whole. Shown, is a diagram of the DPG-4-24/0.2 piston-drive expansion engine, and figures of the warmup of helium flowing out of the expander cylinder vs. inlet temperature to the expander, and heat flow to the helium flowing out of the cylinder vs. temperature at the inlet to the expander. It is concluded that the design of the cylinder piston unit widely used is not an optimal design since gas circulation that develops from the reciprocating motion of the rod results in an additional refrigeration loss for the entire cryogenic helium installation.

High-temperature testing and evaluation of graphite helical-screw expanders and compressors.

A graphite expander, utilizing intermeshing helical rotors and following concepts of Lysholm, was demonstrated for possible use with inert gas cycles. Two demonstration assemblies were tested. Each assembly consisted of a graphite expander and an identical compressor. They were operated in an argon atmosphere where the motor-driven compressor provided pressurized argon to drive the expander. The graphite-on-graphite sliding bearings used were adequate for demonstration but probably not for application. Work is under way on graphite roller and gas bearings. In the first assembly the compressor failed catastrophically because of rotor dragging. The second assembly ran for 274 hr at furnace temperatures between 2350° and 2730°F before voluntary shutdown. Expander inlet temperatures are estimated to have exceeded 2900°F. Speeds to 14,100 rpm in the compressor and efficiencies to 37% in the expander were achieved. Shaft power to the compressor exceeded 10 hp and from the expander approached 1 hp. Pressure ratios in excess of 1.5 were achieved.