scholarly journals Carnot cycle in practice: compensating inefficiencies of ORC expanders through thermal regeneration

2021 ◽  
Vol 238 ◽  
pp. 10005
Author(s):  
Lucie Lefebvre ◽  
Ward De Paepe ◽  
Mario L. Ferrari ◽  
Alberto Traverso
Keyword(s):  
Heat Extraction ◽  
Cycle Performance ◽  
Maximum Temperature ◽  
Working Fluid ◽  
Small Scale ◽  
Low Grade ◽  
Expansion Process ◽  
Turbine Efficiency ◽  
Wide Range ◽  
Isentropic Efficiency

The Organic Rankine Cycle (ORC) is a thermodynamic cycle that can operate with a hot source over a wide range of temperatures, especially with low-grade heat (below 200°C). One of the main limitations for the success of small-scale ORC cycles (few to 100 kWe) is the relatively low isentropic efficiency of the typically used turbomachinery. Low turbine efficiency leads to low ORC cycle performance. To increase the performance of the cycle, the turbine efficiency must be increase, however, this significantly increases the cost of the machinery, making the cycle less profitable. In this work, the performance evaluation of low-temperature ORC cycles (100-150°C) with heat extraction along the expansion process is investigated, in an attempt to overcome this limitation. The studied cycle works in the same way as a conventional ORC, except that during the expansion process, heat is extracted. This heat is re-used later in the cycle, just before the hot source, allowing to reduce its load. The different cycles presented in this paper, using pentane as working fluid, are compared based on their exergetic and energetic efficiencies. The influence of three parameters on the cycle performance is studied: the regeneration ratio, the maximum temperature of the cycle and the turbine isentropic efficiency. In the case of a cycle using pentane with a maximum temperature of 150 °C and an turbine isentropic efficiency of 65%, the energy efficiency increases from 6.2% to 16.3% when going from no regeneration to full regeneration, and the exergy efficiency increases from 21.1 to 45.8%.. Secondly, the influence of the maximum temperature of the cycle is studied. Using pentane as the working fluid, the higher the maximum temperature is, the larger the benefits of heat extraction. However, this temperature cannot exceed the critical temperature of the organic fluid to stay in the case of a subcritical cycle. Finally, considering the turbine isentropic efficiency, it is possible to demonstrate that using a less efficient turbine, for example in small ORC systems, the performance of a cycle with an ideal turbine isentropic efficiency (100%) can be achieved compensating at cycle level the turbine losses with the heat extraction along the expansion process.

Development of Efficient Small Scale Axial Turbine for Solar Driven Organic Rankine Cycle

2016 ◽  
Author(s):  
Ayad Al Jubori ◽  
Raya K. Al-Dadah ◽  
Saad Mahmoud ◽  
Khalil M. Khalil ◽  
A. S. Bahr Ennil
Keyword(s):  
Large Scale ◽  
Renewable Energy Sources ◽  
Cycle Performance ◽  
Working Fluid ◽  
Small Scale ◽  
Cfd Simulations ◽  
Axial Turbine ◽  
Working Fluids ◽  
Wide Range ◽  
Inlet Conditions

Recently, the increase in fossil fuel consumption and associated adverse impact on the environment led to significant interest in renewable energy sources like solar. This paper presents a new methodology that integrates the ORC cycle analysis with modeling of an efficient small scale subsonic axial turbine at low temperature heat sources using wide range of organic working fluids like R123, R134a, R141b, R152a, R245fa, R290 and isobutene. The work involves detailed turbine analysis including 1D mean line approach, extensive 3D CFD simulations and ORC cycle analysis at inlet total pressure ranging from 2–5 bar corresponding to temperature range from 275K–365K to achieve the best turbine and cycle performance. This work provides a more reliable data base for small scale organic working fluids instead of using the map of large scale gas turbine. The numerical simulation was performed using 3D RANS with SST turbulence model in ANSYS-CFX. Using iterative CFD simulations with various working fluids with subsonic inlet conditions, Mach number ranging from 0.6–0.65, results showed that using working fluid R123 for a turbine with mean diameter of 70mm, the maximum isentropic efficiency was 82% and power output 5.66 kW leading to cycle efficiency of 9.5%.

1-D Model Analysis of Tesla Turbine for Small Scale Organic Rankine Cycle (ORC) System

2017 ◽  
Author(s):  
Jian Song ◽  
Chun-wei Gu
Keyword(s):  
Large Scale ◽  
Low Cost ◽  
Organic Rankine Cycle ◽  
Axial Flow ◽  
Rankine Cycle ◽  
Expansion Ratio ◽  
Working Fluid ◽  
Small Scale ◽  
Low Grade ◽  
D Model

Energy shortage and environmental deterioration are two crucial issues that the developing world has to face. In order to solve these problems, conversion of low grade energy is attracting broad attention. Among all of the existing technologies, Organic Rankine Cycle (ORC) has been proven to be one of the most effective methods for the utilization of low grade heat sources. Turbine is a key component in ORC system and it plays an important role in system performance. Traditional turbine expanders, the axial flow turbine and the radial inflow turbine are typically selected in large scale ORC systems. However, in small and micro scale systems, traditional turbine expanders are not suitable due to large flow loss and high rotation speed. In this case, Tesla turbine allows a low-cost and reliable design for the organic expander that could be an attractive option for small scale ORC systems. A 1-D model of Tesla turbine is presented in this paper, which mainly focuses on the flow characteristics and the momentum transfer. This study improves the 1-D model, taking the nozzle limit expansion ratio into consideration, which is related to the installation angle of the nozzle and the specific heat ratio of the working fluid. The improved model is used to analyze Tesla turbine performance and predict turbine efficiency. Thermodynamic analysis is conducted for a small scale ORC system. The simulation results reveal that the ORC system can generate a considerable net power output. Therefore, Tesla turbine can be regarded as a potential choice to be applied in small scale ORC systems.

A Comparison Study for Off-Design Performance Prediction of a Supercritical CO2 Compressor With Similitude Analysis

2019 ◽  
Author(s):  
Yongju Jeong ◽  
Seongmin Son ◽  
Seong kuk Cho ◽  
Seungjoon Baik ◽  
Jeong Ik Lee
Keyword(s):  
Critical Point ◽  
Supercritical Co2 ◽  
Power Plants ◽  
Cycle Performance ◽  
Working Fluid ◽  
Brayton Cycle ◽  
Power Cycle ◽  
Design Performance ◽  
Wide Range ◽  
Phase Fluid

Abstract Most of the power plants operating nowadays mainly have adopted a steam Rankine cycle or a gas Brayton cycle. To devise a better power conversion cycle, various approaches were taken by researchers and one of the examples is an S-CO2 (supercritical CO2) power cycle. Over the past decades, the S-CO2 power cycle was invented and studied. Eventually the cycle was successful for attracting attentions from a wide range of applications. Basically, an S-CO2 power cycle is a variation of a gas Brayton cycle. In contrast to the fact that an ordinary Brayton cycle operates with a gas phase fluid, the S-CO2 power cycle operates with a supercritical phase fluid, where temperatures and pressures of working fluid are above the critical point. Many advantages of S-CO2 power cycle are rooted from its novel characteristics. Particularly, a compressor in an S-CO2 power cycle operates near the critical point, where the compressibility is greatly reduced. Since the S-CO2 power cycle greatly benefits from the reduced compression work, an S-CO2 compressor prediction under off-design condition has a huge impact on overall cycle performance. When off-design operations of a power cycle are considered, the compressor performance needs to be specified. One of the approaches for a compressor off-design performance evaluation is to use the correction methods based on similitude analysis. However, there are several approaches for deriving the equivalent conditions but none of the approaches has been thoroughly examined for S-CO2 conditions based on data. The purpose of this paper is comparing these correction models to identify the best fitted approach, in order to predict a compressor off-design operation performance more accurately from limited amount of information. Each correction method was applied to two sets of data, SCEIL experiment data and 1D turbomachinery code off-design prediction code generated data, and evaluated in this paper.

scholarly journals Efficient Thermal Cycle Undergoing Adiabatic Contraction Based Work by Releasing Heat

2019 ◽  
pp. 1-15
Author(s):  
Ramon Ferreiro Garcia
Keyword(s):  
Thermal Efficiency ◽  
High Performance ◽  
Mechanical Work ◽  
Heat Extraction ◽  
Working Fluid ◽  
Low Grade ◽  
Compression Process ◽  
Compression Phase ◽  
Heat Addition ◽  
Thermodynamic Transformations

By means of observational evidence it is shown that, among the vast amount of heat-work interactions occurring in closed process based transformations, there exists the possibility of doing a transformation characterized by doing useful mechanical work by contraction based compression, while increasing the internal energy. Such thermodynamic transformation has never been considered in processes. However, in reality closed contraction based compression process are physically possible in which net work is produced by contraction of a thermal working fluid while fulfilling the fundamental laws. Thus, the objective is therefore to analyze heat-work interaction modes in closed processes conducted by heat addition, heat extracting and net work done by the process. Therefore, this analysis focuses on the feasible thermodynamic transformations contributing to the achievement of efficient closed processes based thermal cycles. The proposed cycles are characterized by performing mechanical work both in the expansion phase due to heat addition, and in the compression phase due to heat releasing. The cycles achieved are characterized by operating with closed thermal processes in which both transformations with isochoric heat addition and isochoric heat extraction are associated with useful mechanical work at high performance. The analysis of the cycle between top working temperatures ranging from 350 to 700 K while botom temperature approaches 300 K has been carried out, corroborated by experimental validation for low temperatures, in the order of 350 degrees Kelvin through a test bench designed specifically for this task. It is also worth noting that the thermal efficiency is independent of the temperature ratio. Therefore the results indicate that for lower temperatures below 690 K, the thermal efficiency of the cycle exceeds the Carnot factor, which is an efficient means of recovering residual or low-grade heat efficiently.

A Study on the Combined Driven Refrigeration Cycle Using Ejector

2021 ◽  
pp. 2150004
Author(s):  
Waseem Raza ◽  
Gwang Soo Ko ◽  
Youn Cheol Park
Keyword(s):  
Air Conditioning ◽  
Waste Heat ◽  
Primary Source ◽  
Mechanical Efficiency ◽  
Coefficient Of Performance ◽  
Cycle Performance ◽  
Working Fluid ◽  
Low Grade ◽  
Refrigeration Cycle ◽  
R 134A

The rising need for thermal comfort has resulted in a rapid increase in refrigeration systems’ usage and, subsequently, the need for electricity for air-conditioning systems. The ejector system can be driven by a free or affordable low-temperature heat source such as waste heat as the primary source of energy instead of electricity. Heat-driven ejector refrigeration systems become a promising solution for reducing energy consumption to conventional compressor-based refrigeration technologies. An air-conditioning system that uses the ejector achieves better performance in terms of energy-saving. This paper presents a study on the combined driven refrigeration cycle based on ejectors to maximize cycle performance. The experimental setup is designed to determine the coefficient of performance (COP) with ejector nozzle sizes 1.8, 3.6, and 5.4[Formula: see text]mm, respectively. In this system, the R-134a refrigerant is considered as a working fluid. The results depict that the efficiency is higher than that of the conventional refrigeration method due to comparing the performance of the conventional refrigeration cycle and the combined driven refrigeration cycle. The modified cycle efficiency is better than the vapor compression cycle below 0∘C, which implies sustainability at low temperatures by using low-grade thermal energy. For the improvement of mechanical efficiency, proposed cycle can be easily used.

Working Fluid and Parametric Optimization of a Two-Stage ORC Utilizing LNG Cold Energy and Low Grade Heat of Different Temperatures

2017 ◽  
Author(s):  
Zhixin Sun ◽  
Shujia Wang ◽  
Fuquan Xu ◽  
Tielong Wang
Keyword(s):  
Heat Source ◽  
Organic Rankine Cycle ◽  
Rankine Cycle ◽  
Cycle Performance ◽  
Maximum Efficiency ◽  
Working Fluid ◽  
Low Grade ◽  
Two Stage ◽  
Cold Energy ◽  
Low Grade Heat

Natural gas is considered as a green fuel due to its low environmental impact. LNG contains a large amount of cold exergy and must be regasified before further utilization. ORC (Organic Rankine Cycle) has been proven to be a promising solution for both low grade heat utilization and LNG cold exergy recovery. Due to the great temperature difference between the heat source and LNG, the efficiency of one-stage ORC is relatively small. Hence, some researchers move forward to a two-stage Rankine cycle. Working fluid plays a quite important role in the cycle performance. Working fluid selection of a two-stage ORC is much more challenging than that of a single-stage ORC. In this paper, a two-stage ORC is studied. Heat source temperatures of 100,150 and 200°C are investigated. 20 substances are selected as potential candidates for both the high and low Rankine cycles. The evaporating, condensing and turbine inlet temperatures of both Rankine cycles are optimized by PSO (Particle Swarm Optimization). The results show that the best combination for heat source temperature of 100°C is R161/R218 with the maximum exergy efficiency of 35.27%. The best combination for 150°C is R161/RC318 with the maximum efficiency of 37.84% and ammonia/ammonia with the maximum efficiency of 39.15% for 200°C. Fluids with intermediate critical temperature, lower triple point temperature and lower normal boiling temperature are good candidates.

Design and Optimization of a Low Temperature Organic Rankine Cycle and Turbine

2013 ◽  
Author(s):  
Murat Erbas ◽  
Mehmet Alper Sofuoglu ◽  
Atilla Biyikoglu ◽  
Ibrahim Uslan
Keyword(s):  
Low Temperature ◽  
Organic Rankine Cycle ◽  
Rankine Cycle ◽  
Cycle Performance ◽  
Working Fluid ◽  
Design Criteria ◽  
Design And Optimization ◽  
Turbine Efficiency ◽  
Design Requirements ◽  
R 134A

In this study, low temperature Organic Rankine Cycle (ORC) systems with single and two-stage turbine are proposed for the production of electricity. The refrigerant R-134a is selected as working fluid based on peak temperature of the cycle for solar and geothermal applications. The design criteria of ORC system is introduced and explained in detail. The radial inflow turbine is selected to satisfy the design requirements. The cycle performance is taken as a key point in the design criteria. The system performance map is constructed based on both velocity triangles and approximate efficiency of turbine. The procedures for turbine and cycle design are introduced in detail. The components of cycle and turbine are modeled using baseline correlations via real gas tables and macros created on Excel for the refrigerant, R134a. Finally, the turbine geometry is optimized to attain maximum turbine efficiency via MATLAB optimization toolbox.

Investigation on Solar-Powered Turbines Using Refrigerant R-134A

2014 ◽  
Author(s):  
Jihad Rishmany ◽  
Michel Daaboul ◽  
Issam Tawk ◽  
Nicolas Saba
Keyword(s):  
Power Generation ◽  
Solar Energy ◽  
Fossil Fuels ◽  
Rankine Cycle ◽  
Working Fluid ◽  
Small Scale ◽  
Combustion Gases ◽  
Water Heaters ◽  
Wide Range ◽  
R 134A

Renewable energy has become a promising solution to substitute fossil fuels in power generation. In particular, the use of solar energy is stretched to a wide range of applications, e.g. photovoltaic cells, solar water heaters, solar space heating, solar thermal plants. However, the combination of solar energy with the Rankine cycle is limited to few applications only. In this context, this study aims in investigating the practicality of employing solar heaters to operate a Rankine cycle for small scale power generation. The working fluid in this study is refrigerant R-134a. Sizing and calculations of the various components of the system are carried out based on a net output power of 1 kW. In comparison with available electricity sources in Lebanon, it was found that the proposed system is currently more expensive than public electricity. However, it can compete with private generators that currently fill the gap in electricity shortage. The main advantage herein lies in the friendly environmental load due to the absence of combustion gases.

Towards a Highly Efficient Small Scale Turboshaft Engine: Part II — Aero-Mechanical Turbine Design and Optimization

2014 ◽  
Author(s):  
U. Siller ◽  
G. Kröger ◽  
T. Moser ◽  
S. Hediger
Keyword(s):  
Industrial Development ◽  
Mechanical Design ◽  
Cycle Performance ◽  
Design Parameters ◽  
Small Scale ◽  
Optimization Strategy ◽  
Highly Efficient ◽  
Acceleration Techniques ◽  
Wide Range ◽  
Turboshaft Engine

Aero-mechanical design of the turbine section of a small scale turboshaft engine is presented in this paper. A single stage high-pressure turbine (HPT) and the power turbine stage (PT), have been designed by means of automated optimization. This study demonstrates how multi-disciplinary optimization can be used effectively in today’s industrial development cycles with respect to timeframe and computational resources. Both, the aerodynamic performance and the mechanical blade behavior were subject to the optimization in a very high dimensional design space expressed by well above 100 free design parameters for the annular duct and the bladings of two axial stages. In the first part, this paper describes the design task and constraints in order to meet the requested thermodynamic cycle performance and fabricational requirements. In the second part, the optimization strategy is explained with focus on geometry parameterization, simulation setups for flow and structural analysis and acceleration techniques for the optimization itself. Finally, a very promising resulting design is reviewed in terms of a detailed aerodynamic and mechanical assessment and regarding to the overall engine concept. This work contributes to the development of a highly efficient, light-weight propulsion system powering, beside a wide range of other possible applications, for example small aerial systems such as helicopter drones. The engine prototype is expected to be tested the first time in 2014.

scholarly journals Dynamic Modeling and Preliminary Performance Analysis of a New Solar Thermal Reverse Osmosis Desalination Process

Energies ◽  
2019 ◽  
Vol 12 (20) ◽  
pp. 4015 ◽  
Author(s):  
Clément Lacroix ◽  
Maxime Perier-Muzet ◽  
Driss Stitou
Keyword(s):  
Energy Consumption ◽  
Reverse Osmosis ◽  
Dynamic Modeling ◽  
Thermal Energy ◽  
Thermal Power ◽  
Solar Thermal ◽  
Working Fluid ◽  
Small Scale ◽  
Low Grade ◽  
Solar Collectors

Reverse osmosis (RO) is a desalination technique that is commonly preferred because of its low energy consumption. In this paper, an innovative, thermally powered RO desalination process is presented. This new thermo-hydraulic process uses solar thermal energy in order to realize the pressurization of the saltwater beyond its osmotic pressure to allow its desalination. This pressurization is enabled thanks to a piston or a membrane set in motion in a reservoir by a working fluid that follows a thermodynamic cycle similar to an Organic Rankine Cycle. In this cycle, the evaporator is heated by low-grade heat, such as the one delivered by flat-plate solar collectors, while the condenser is cooled by the saltwater to be treated. Such an installation, designed for small-scale (1 to 10 m3·day−1) brackish water desalination, should enable an average daily production of 500 L of drinkable water per m² of solar collectors with a specific thermal energy consumption of about 6 kWhth·m−3. A dynamic modeling of the whole process has been developed in order to study its dynamic cyclic operating behavior under variable solar thermal power, to optimize its design, and to maximize its performances. This paper presents the preliminary performance results of such a solar-driven desalination process.

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