Review of Organic Rankine Cycle experimental data trends

Organic Rankine cycle design and performance comparison based on experimental database

Optimisation of Organic Rankine Cycles (ORCs) for binary-cycle geothermal applications could play a major role in the competitiveness of low to moderate temperature geothermal resources. Part of this optimisation process is matching cycles to a given resource such that power output can be maximised. Two major and largely interrelated components of the cycle are the working fluid and the turbine. Both components need careful consideration. Due to the temperature differences in geothermal resources a one-size-fits-all approach to surface power infrastructure is not appropriate. Furthermore, the traditional use of steam as a working fluid does not seem practical due to the low temperatures of many resources. A variety of organic fluids with low boiling points may be utilised as ORC working fluids in binary power cycle loops. Due to differences in thermodynamic properties, certain fluids are able to extract more heat from a given resource than others over certain temperature and pressure ranges. This enables the tailoring of power cycle infrastructure to best match the geothermal resource through careful selection of the working fluid and turbine design optimisation to yield the optimum overall cycle performance. This paper presents the rationale for the use of radial-inflow turbines for ORC applications and the preliminary design of several radial-inflow turbines based on a selection of promising ORC cycles using five different high-density working fluids: R134a, R143a, R236fa, R245fa and n-Pentane at sub- or trans-critical conditions. Numerous studies published compare a variety of working fluids for various ORC configurations. However, there is little information specifically pertaining to the design and implementation of ORCs using realistic radial turbine designs in terms of pressure ratios, inlet pressure, rotor size and rotational speed. Preliminary 1D analysis leads to the generation of turbine designs for the various cycles with similar efficiencies (77%) but large differences in dimensions (139289 mm rotor diameter). The highest performing cycle (R134a) was found to produce 33% more net power from a 150°C resource flowing at 10 kg/s than the lowest performing cycle (n-Pentane).

Candidate radial-inflow turbines and high-density working fluids for geothermal power systems

In the literature, energetic and exergetic performance of Organic Rankine Cycle (ORC) were investigated by various researchers. The working parameters affecting the cycle's performance were determined but the impact weights and the order of importance of these parameters were not discussed with a statistical approach. In this context, nine fundamental process parameters such as working fluid type, pinch point temperature differences in the evaporator and condenser, superheating temperature, evaporation and condensation temperatures, heat exchanger effectiveness, turbine and pump efficiencies have been selected for the statistical evaluation. A comprehensive statistical analysis has been carried out to observe the effect of the parameters on the first and second law efficiencies of the ORC. The impact ratios and order of importance of these parameters on the system's performance indicators have been determined. While Taguchi method is performed to determine the optimum levels of each parameter, ANOVA method is used to obtain the impact weights of the parameters on objective functions. In addition to these methods, Grey Relational Analysis (GRA) method is used to optimize the multi-objective function. Evaporator temperature, turbine efficiency, effectiveness of heat exchanger, condenser temperature are obtained as main process parameters on the multiple performance characteristics of ORC and the impact ratios of these parameters are calculated as 31.37%, 19.53%, 16.64%, and 16.61%, respectively. The best condition for the multiple performance characteristics is determined as A1B1C3D3E3F3G1H3I3 and under these operating conditions, the first and second law efficiencies of the system are found as 18.1% and 65.52%, respectively.

Multi-objective optimization of parameters affecting Organic Rankine Cycle performance characteristics with Taguchi-Grey Relational Analysis

https://orbit.dtu.dk/files/130574487/Postprint_Zeotropic.pdf

A review of recent research on the use of zeotropic mixtures in power generation systems

Summary
An experimental study on the practical performance of organic Rankine cycle (ORC) system using zeotropic mixture is performed by using a small scale ORC power generation experimental setup. R601a/R600a is selected as the working fluid. The effects of mixture composition, heat source temperature, and working fluid flow rate on the performance of ORC system are investigated. The experimental results indicate that the net power output first increases and then decreases as the R600a concentration increases. The optimal mixture composition with the maximum net power output is 0.6/0.4 (mass fraction) at the heat source temperature of 115°C. The net power output of R601a/R600a (0.6/0.4) is higher than that of R601a by 25%, indicating that the performance of ORC system can be clearly improved by using the zeotropic mixture. For a fixed working fluid flow rate, both net power output and thermal efficiency first decrease slowly and then drop sharply with the decrease of the heat source temperature. The appropriate superheat degree of R601a/R600a is in the range of 15 to 20°C when the heat source temperature has a small variation. In addition, the optimal working fluid volume flow rates yielding the maximum net power output are obtained for different compositions of R601a/R600a. The experimental results in the study can be of great significance for the design and operation of ORC power system using zeotropic mixture. Copyright © 2016 John Wiley & Sons, Ltd.

Experimental investigation on the performance of ORC power system using zeotropic mixture R601a/R600a

Experimental Study of the Influence of Light Intensity on Solar Organic Rankine Cycle Power Generation System

This paper presents the experimental study of the small organic Rankine cycle power system performance under different heat source temperature and different load resistance,1kW experimental system was built using scroll expander with the working fluid R600a. Experimental results show that when heat source temperature does not exceed 120°C, the system has a maximum power for 1.05kW and power generation efficiency of up to 4.51%, the expander rotation speed and expansion ratio can reach 2922rpm and 3.03, respectively; Experiment obtained the variable condition operating characteristics of the scroll expander and permanent magnet generator and the relationship with the load resistance; There exist optimal load resistance to make power generation and unit power output and power generation efficiency maximum at the different heat temperature and different working fluid flow.The scroll expander should match permanent magnet generator and the load resistance when designing systems so that the system can get optimal performance.

Experiments of Low-Grade Heat Organic Rankine Cycle Power Generation Optimal Load Characteristics

In this paper, three typical working fluids were selected for the near-critical ORC and subcritical ORC. The difference of performance between the near-critical ORC and subcritical ORC was analyzed by establishing the thermodynamic model. The reason for difference was analyzed in terms of the thermophysical properties. The results indicate that the performance of the near-critical ORC is better than the subcritical ORC. The net absorbed heat, net power and efficiency of the near-critical ORC vary slowly with the vapor generation temperature, which means that the near-critical ORC has good off-design performance. The dry working fluid R236fa is best adapted for the near-critical ORC among the three working fluids. The singular performance of the near-critical ORC depends on the properties of latent heat and type of working fluid in near-critical region.

Performance Analysis of Near-Critical and Subcritical Organic Rankine Cycle

The present invention relates to a passive type low-temperature heat sources organic working fluid power generation method. The organic working fluid absorbs heat and evaporates in the first evaporator and the second in turn evaporator. When the pressure of organic working fluid reaches the set pressure, the self-operated pressure regulator valve at the outlet of the evaporator opens triggered by operating pressure. The organic working fluid vapor flows into the turbine and pushes the turbine to rotate with a high speed, driving the generator to provide output power. The low-temperature low-pressure exhaust gas flows into the condenser and condenses into liquid working fluid. Through the first and second evaporator in turn providing working steam, the turbine can maintain continuous work and provide output power. Compared with the prior technology, the present invention has reliable performance, relying on the evaporation of the working fluid in a closed space to achieve increased pressure.

Passive low temperature heat sources organic working fluid power generation method

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