Design Of Organic Rankine Cycle System Research Articles

Turning Data Center Waste Heat into Energy: A Guide to Organic Rankine Cycle System Design and Performance Evaluation

This study delves into the adoption of the organic Rankine cycle (ORC) for recovering waste heat from data centers (DCs). Through a literature review, it examines energy reuse with a focus on electric power generation, the selection of working fluids, and system design principles. The objective is to develop a thorough framework for system design and analysis, beginning with a quantity and quality investigation of waste heat available. Air cooling systems, chosen often for their simplicity, account for about 70% of used cooling methods. Water cooling demonstrates greater effectiveness, albeit less commonly adopted. This study pays close attention to the selection of potential working fluids, meticulously considering the limitations presented by the available sources of heat and cold for vaporization and condensation, respectively. It reviews an ORC-based system setup, incorporating fluid streams for internal processes. The research includes a conceptual case study where the system is designed and simulations are conducted in the DWSIM environment. The simulation model considers hot air or hot liquid water returning from the data center cooling system for ORC working fluid evaporation. Ambient water serves for condensing, with pentane and isopentane identified as suitable organic fluids. Pentane assures ORC net electric efficiencies ranging between 3.1 and 7.1% when operating pressure ratios increase from 2.8 to 6.4. Isopentane systems, meanwhile, achieve efficiencies of 3.6–7.0% across pressure ratios of 2.7–6.0. Furthermore, the investigation provides key performance indicators for a reference data center in terms of power usage effectiveness (PUE), energy reuse factor (ERF), energy reuse effectiveness (ERE), and greenhouse gas (GHG) savings. This study concludes with guidelines for system analysis, including exergy considerations, and details the sizing process for evaporators and condensers.

The effect of organic Rankine cycle system design on energy-based agro-industrial symbiosis

The effect of organic Rankine cycle system design on energy-based agro-industrial symbiosis

An Investigation of Organic Rankine Cycle (ORC) System Application for Energy Efficiency of Smart Agriculture

Organic rankine cycle (ORC) system application on smart agriculture is rather energy efficient in terms of waste heat recovery supplied by ORC. The recovered waste heat, such as from agricultural wastes, changes into the electrical energy produced by the generator of ORC cycle. This energy efficiency supplied by ORC system is crucial for smart agriculture as being not only efficient but also environment friendly which is good for green world and nature. In this study, biogas based regenerative ORC system design is explained as more efficient than simple ORC design due to its better regenerator efficiency.

Influence of thermal stability on organic Rankine cycle systems using siloxanes as working fluids

• An off-design model with fluid decomposition parameters was established. • The influence of MM thermal decomposition on the ORC system was evaluated. • MM decomposition reduced the net power and efficiency of ORC system obviously. • MM decomposition may lead to incomplete evaporation and evaporator acid corrosion. The organic Rankine cycle (ORC) is an efficient power generation technology that has been widely used in renewable energy utilization and industrial waste heat recovery. The thermal stability of working fluids has a significant effect on the fluid selection and system design of ORC systems. In this study, an off-design model of an ORC system was established with hexamethyldisiloxane (MM) as the working fluid, and the effects of the MM thermal stability on the system were analyzed. The results showed that the effect of MM thermal decomposition on the cold source and working fluid pump was limited. The outlet temperature of the evaporator decreased with MM decomposition, which might lead to incomplete evaporation of working fluids and possible damage to the expander. The outlet temperature of the heat source also decreased with MM decomposition, which led to lower outlet temperatures than the acid dew point limit temperature. Both of these results can affect the safe operation of ORC systems. The net power and thermal efficiency of the system decreased with increasing thermal decomposition ratios of MM. The net power and thermal efficiency decreased by 7.48% and 10.72% respectively in the model of this study with a 10% decomposition ratio.

Investigation and optimization of a two-stage cascade ORC system for medium and low-grade waste heat recovery using liquefied natural gas cold energy

This study proposed a two-stage cascade organic Rankine cycle (ORC) to harvest the medium and low-temperature discharged heat from internal combustion engine (ICE), and a liquefied natural gas (LNG) cold energy system is integrated into the proposed cycle in order to realize the cascade utilization of ICE multi-grade waste heat more efficiently. The thermodynamic and economic models are developed to investigate the proposed system performance under steady-state conditions. The influence of the important thermodynamic parameters, e.g. the ORC turbine inlet temperature, the high pressure of first-stage ORC and the outlet temperature of condenser are investigated. The calculated results indicated that the thermal efficiency and the exergy efficiency achieved 27.31% and 33.73%, respectively. In addition, it was found that the total sum unit cost of system product was decreased by increasing turbine Ⅰ inlet pressure. Furthermore, to reach the conflicting compromise between the two aspects of thermodynamic and economic, the Non-dominated Sorting Genetic Algorithm (NSGA-II) is employed to carry out the multi-objective optimization study by which the external investment cost and the thermal efficiency are selected as the objective function. At the same time, the influence region of decision variables related to the optimization is determined according to the scatter distribution of decision variables. Moreover, the exergy destruction and the investment cost ratio of each component under the optimization conditions are analyzed to obtain the preferred performance of the key components. The findings could provide references for the ORC system design and operation driven by multi-grade waste heat.

Synthesis and simultaneous optimization of multi-heat source multi-pressure evaporation organic Rankine cycle with mixed working fluid

The organic Rankine cycle (ORC)’s performance relies on heat source properties, cycle structures, and working fluids. Influences of these factors, however, are often interdependent, making it difficult to determine the optimal design of ORC systems. To address this issue, we propose a mixed-integer nonlinear programming model for the multi-pressure evaporation ORCs driven by multiple heat sources that not only optimizes operating conditions, but also identifies the best working fluid composition and cycle structure. Results demonstrate that the proposed model is accurate and effective. The dual-pressure evaporation ORC driven by multi-heat source shows a 10.87% rise in the net power output (NPO) compared to the one with single pressure evaporation. In general, 0.9/0.1 n-pentane/n-heptane is the optimal mixed working fluid generating 2.71–12.11% more power than the pure working fluids for the numerical studies. Dual-pressure evaporation ORC is found to be a balanced design for the multi-heat source driven ORC in terms of its NPO and cycle complexity.

Performance Analysis of Solar-Powered Organic Rankine Cycle With Energy Storage in Different Climate Zones in the United States

Abstract Solar-powered organic Rankine cycle (ORC) is considered a promising technology and has the potential to provide clean electric energy. Extensive studies on the design of ORC systems have been conducted and reported in the literature. However, few studies have presented the influence of climate zones on the performance of a solar-powered ORC, especially for an integrated ORC and energy storage system. This paper presents an analysis to determine the performance of solar-powered ORCs with electric energy storage (EES) systems to supply electricity to buildings in different climate zones in the United States. The building type evaluated in this paper is a large office, and the energy consumption of the facility in each climate location was determined using EnergyPlus. The ORC-EES operational strategy used in this investigation is described as follows: when solar irradiation is adequate to produce power, the ORC charges the EES. Then, when there is no solar energy available, the EES provides power to the building. The ORC-EES is evaluated based on the potential to reduce the operational cost, the primary energy consumption, and the carbon dioxide emission. Furthermore, the influence of the number of solar collectors and the EES size on the performance of the ORC-EES system is investigated.

Thermodynamic analysis and optimization of organic Rankine cycles based on radial-inflow turbine design

In recent years, high-temperature organic Rankine cycle (ORC) with a heat source temperature over 300 °C has attracted interests, which has wide range of applications from industrial point of view. However, few researchers have focused on the coupled design and optimization of the high-temperature ORC system and radial-inflow turbine (RIT). In this work, a coupled design of the ORC system and RIT with the heat source inlet temperatures of 300, 350 and 400 °C is developed using non-dominated sorting genetic algorithm. The ORC thermal efficiency and turbine performance factor (PF) are introduced as optimization objectives. Two mixtures of siloxanes, seven pure siloxanes and nine pure hydrocarbons are considered as working fluid candidates. In addition, the thermodynamic comparison between mixtures of siloxanes and pure working fluids is presented. Moreover, the influences of the turbine inlet total temperature, total-to-static expansion ratio, and specific speed on the ORC thermal efficiency, turbine performance, and turbine size are investigated. The results show that the turbine power output and cycle thermal efficiency are more sensitive to the expansion ratio while turbine size is more sensitive to the turbine inlet total temperature and specific speed. In addition, PF increases with the rise of the turbine inlet total temperature, expansion ratio and specific speed. Moreover, compared with pure working fluids, mixtures of siloxanes have higher efficiencies, but larger turbine and heat exchanger size. Cyclohexane, toluene, m-xylene and hexane with higher PF and smaller size of turbine and heat exchanger are promising working fluids in applications where the compact turbine and heat exchanger is preferred, such as vehicle waste heat recovery.

Optimal design of organic Rankine cycles for exhaust heat recovery from light-duty vehicles in view of various exhaust gas conditions and negative aspects of mobile vehicles

The organic Rankine cycle (ORC) is a promising method of recovering the exhaust heat of the internal combustion engine (ICE). However, the off-design exhaust conditions and the negative effects (such as increased backpressure and added weight) of the ORC installation onto vehicles greatly deterioratetheperformanceof ORC applied on mobile vehicles. In this paper, the ORC thermodynamic model with an integrated plate heat exchanger model is developed to evaluate the effects of sizing the heat exchanger and designing the ORC operating conditions on the thermodynamic performance of the ORC system. Considering various major exhaust conditions and the negative impacts of ORC system installation on vehicles, an optimal ORC system design strategy is proposed to maximize the net output power. The optimum geometric parameters of heat exchangers and ORC operating conditions are simultaneously designed through a mixed integer nonlinear programming problem. The proposed design strategy is compared with the design method without considering negative effects and the design method only based on one major engine operating point. The comparison results indicate that the proposed design strategy increases the weighted net output power and the proposed design strategy can ensure that the ORC works normally in various exhaust conditions. Among all the operating parameters, the size of the heat exchanger (two geometric parameters) is the major factor affecting the performance of ORC. These findings highlight the importance of considering various exhaust conditions and the negative impacts of vehicle-mounted ORC during the design procedure.

Design and off-design optimisation of an organic Rankine cycle (ORC) system with an integrated radial turbine model

This paper investigates the design and thermodynamic optimisation of both sub- and transcritical organic Rankine cycle (ORC) power systems featuring radial turbines via performance calculations using mean-line models. The emphasis is on rapid performance predictions for a given turbine geometry, as well as geometric optimisation for a given heat source. From three specified quantities, which are the turbine inlet temperature, inlet pressure and mass flow rate, the other flow properties (e.g., outlet pressure and temperature) are computed, together with derived quantities which are required for cycle- or system-level assessments, such as the isentropic efficiency of the turbine. Experimental investigations from the open literature suitable for validation purposes are summarised and analysed with respect to their strengths and weaknesses. Similar computational fluid dynamic (CFD) simulations are also used to complement the available experimental data. The main contributions of this paper are that it provides a comprehensive overview of radial turbine performance modelling, and that it proposes a detailed framework that can be used for the improved development of efficient thermodynamic power systems based on a unified mean-line model that is validated against experimental data and supported by CFD results. Specifically, predictions from the mean-line model show good accuracy over a wide range of operating conditions for different turbine designs and fluids with compressibility factors from 0.6 to 1.0. Finally, in order to demonstrate its efficacy, the integrated radial turbine and ORC system design framework is used in a case study of a nominally 400-kW power system with propane as the working fluid in low-grade waste-heat application, where the turbine inlet temperature is fixed at 150 °C and the condenser temperature is fixed at 15 °C. The novelty of this work arises from the optimisation of the turbine nozzle vane position at off-design conditions. This feature, along with multi-stage radial turbine designs are shown to allow high-performance operation over a wide range of off-design conditions. Specifically, good efficiencies are demonstrated over a wide range of heat-source fluid flow rates when employing an adjustable nozzle geometry, as is the ability of radial turbines to achieve efficiencies that are not constrained by the pressure ratio across them by replacing single-stage designs with multi-stage designs.

Organic Rankine cycle systems for engine waste-heat recovery: Heat exchanger design in space-constrained applications

Organic Rankine cycle (ORC) systems are a promising solution for improving internal combustion engine efficiencies, however, conflicts between the pressure drops in the heat exchangers, overall thermodynamic performance and economic viability are acute in this space-constrained application. This paper focuses on the interaction of the heat exchanger pressure drop (HEPD) and the thermo-economic performance of ORC systems in engine waste-heat recovery applications. An iterative procedure is included in the thermo-economic analysis of such systems that quantifies the HEPD in each case, and uses this information to revise the cycle and to resize the components until convergence. The newly proposed approach is compared with conventional methods in which the heat exchangers are sized after thermodynamic cycle modelling and the pressure drops through them are ignored, in order to understand and quantify the effects of the HEPD on ORC system design and working fluid selection. Results demonstrate that neglecting the HEPD leads to significant overestimations of both the thermodynamic and the economic performance of ORC systems, which for some indicators can be as high as >80% in some cases, and that this can be effectively avoided with the improved approach that accounts for the HEPD. In such space-limited applications, the heat exchangers can be designed with a smaller cross-section in order to achieve a better compromise between packaging volume, heat transfer and ORC net power output. Furthermore, we identify differences in working fluid selection that arise from the fact that different working fluids give rise to different levels of HEPD. The optimized thermo-economic approach proposed here improves the accuracy and reliability of conventional early-stage engineering design and assessments, which can be extended to other similar thermal systems (i.e., CO2 cycle, Brayton cycle, etc.) that involve heat exchangers integration in similar applications.

Design and manufacturing of organic rankine cycle (orc) system using working fluid r-134a with helical evaporator and condenser

Waste heat from industries such as steam power plants can be utilized to meet the world’s electricity need. However, it cannot be converted efficiently to electric power by using conventional power generation methods as opposed to a technology called Organic Rankine Cycle (ORC). ORC is one of the power plant systems that is a modification of the Rankine Cycle using organic working fluid. In this research, ORC was designed and manufactured using R-134a as working fluid and helical heat exchanger as evaporator and condenser. The design of ORC systems based on simulation using Cycle Tempo 5.0 with evaporator temperature of 90°C, condenser temperature of 10°C, inlet pressure of pump of 0.55 MPa, and inlet pressure of turbine of 0.79 MPa. The results of this study showed the length of tube evaporator and condenser of 10.61 m and 10.56 m, respectively, with system efficiency achieved at 3.8%. Based on experiment, with evaporator temperature of 95°C, condenser temperature of 10°C, inlet pressure of pump of 0.48 MPa and inlet pressure of turbine of 0.52 MPa so resulted of system efficiency of 3.33%.

Design space exploration for waste heat recovery system in automotive application under driving cycle

Organic Rankine Cycle (ORC) systems have been recently considered for the promising application to Waste Heat Recovery (WHR) in automotive application. However, the design of ORC systems for highly transient operations typical of heavy-duty vehicles faces several challenges. This work extends the method of Design Space Exploration (DSE) to optimize the design of an ORC system for heavy-duty vehicle applications. The goal is to match the size of ORC system with the feature areas of driving cycle. Starting from drive cycle data, the feature areas are identified to represent the driving cycle. Then, a Weighted Least Square method is adopted to determine the initial design condition from feature areas, and based on the design condition, the initial ORC model is built for the further optimization. Particle Swarm Optimization (PSO) with parallel computation is adopted to optimize the performance of nonlinear ORC system with coupled constraints. The result shows that the optimal system can output 6.87% more power than the initial system and 20.08% more power than the inferior system over the feature areas of WHTC test. The analysis shown in this work also includes general design guidelines for optimizing the system architecture and optimally sizing the heat exchangers to improve the ORC thermal efficiency.

Robust optimization for the preliminary design of solar organic Rankine cycle (ORC) systems

Organic Rankine cycle (ORC) powered by solar energy is a viable and effective option for a high efficiency conversion of solar thermal energy into electricity at a distributed scale but recurring fluctuations of the thermal energy often force solar-based ORC systems to operate at part-load conditions.With the aim of including the effects of the expected variations of the heat source and heat sink characteristics, even during the design phase, a novel optimization approach for the preliminary design of ORC systems integrated with concentrating solar collectors is presented and analysed. In particular, the minimization of the expected levelized cost of energy (LCOE) of the ORC unit is chosen as an objective function, while the generation of various scenarios is proposed to face the expected fluctuations on the heat source mass flow rate and temperature and cooling inlet temperature. In this way, the expected off-design performances are involved during the design step, giving robustness to the optimal design solution.The proposed methodology is tested by referring to the solar ORC system configuration of the Ottana solar facility. Firstly, the effect of a robust optimization on the preliminary ORC design is investigated by considering an increased number of scenarios for each of the three most significant ORC input variables (heat source mass flow rate and temperature and ambient temperature). Subsequently, the proposed methodology was applied to an ORC design case by considering a concurrent variation of the three variables and three different working fluids.The results of this study demonstrate that a multi-scenario approach drives towards an ORC configuration with lower performance under design conditions, but less sensitive to the variation of the main inputs. Less expensive solutions are therefore achieved by the proposed methodology, but the annual energy production obtained is comparable with those achieved by adopting a single scenario approach, with a consequent reduction of the LCOE.

Computer-aided working-fluid design, thermodynamic optimisation and thermoeconomic assessment of ORC systems for waste-heat recovery

The wider adoption of organic Rankine cycle (ORC) technology for power generation or cogeneration from renewable or recovered waste-heat in many applications can be facilitated by improved thermodynamic performance, but also reduced investment costs. In this context, it is suggested that the further development of ORC power systems should be guided by combined thermoeconomic assessments that can capture directly the trade-offs between performace and cost with the aim of proposing solutions with high resource-use efficiency and, importantly, improved economic viability. This paper couples, for the first time, the computer-aided molecular design (CAMD) of the ORC working-fluid based on the statistical associating fluid theory (SAFT)-γ Mie equation of state with thermodynamic modelling and optimisation, in addition to heat-exchanger sizing models, component cost correlations and thermoeconomic assessments. The resulting CAMD-ORC framework presents a novel and powerful approach with extended capabilities that allows the thermodynamic optimisation of the ORC system and working fluid to be performed in a single step, thus removing subjective and pre-emptive screening criteria that exist in conventional approaches, while also extending to include cost considerations relating to the resulting optimal systems. Following validation, the proposed framework is used to identify optimal cycles and working fluids over a wide range of conditions characterised by three different heat-source cases with temperatures of 150 °C, 250 °C and 350 °C, corresponding to small- to medium-scale applications. In each case, the optimal combination of ORC system design and working fluid is identified, and the corresponding capital costs are evaluated. It is found that fluids with low specific-investment costs (SIC) are different to those that maximise the power output. The fluids with the lowest SIC are isoheptane, 2-pentene and 2-heptene, with SICs of £5620, £2760 and £2070 per kW respectively, and corresponding power outputs of 32.9 kW, 136.6 kW and 213.9 kW.

Recent trends in the development of heat exchangers for geothermal systems

The potential use of geothermal resources has been a remarkable driver for market players and companies operating in the field of geothermal energy conversion. For this reason, medium to low temperature geothermal resources have been the object of recent rise in consideration, with strong reference to the perspectives of development of Organic Rankine Cycle (ORC) technology.The main components of geothermal plants based on ORC cycle are surely the heat exchangers. A lot of different heat exchangers are required for the operation of ORC plants. Among those it is surely of major importance the Recovery Heat Exchanger (RHE, typically an evaporator), in which the operating fluid is evaporated. Also the Recuperator, in regenerative Organic Rankine Cycle, is of major interest in technology. Another important application of the heat exchangers is connected to the condensation, according to the possibility of liquid or air cooling media availability. The paper analyzes the importance of heat exchangers sizing and the connection with the operation of ORC power plants putting in evidence the real element of innovation: the consideration of the heat exchangers as central element for the optimum design of ORC systems.

An improved modeling for low-grade organic Rankine cycle coupled with optimization design of radial-inflow turbine

Organic Rankine cycle (ORC) has been proven to be an effective and promising technology to convert low-grade heat energy into power, attracting rapidly growing interest in recent years. As the key component of the ORC system, turbine significantly influences the overall cycle performance and its efficiency also varies with different working fluids as well as in different operating conditions. However, turbine efficiency is generally assumed to be constant in the conventional cycle design. Aiming at this issue, this paper couples the ORC system design with the radial-inflow turbine design to investigate the thermodynamic performance of the ORC system and the aerodynamic characteristics of radial-inflow turbine simultaneously. The constrained genetic algorithm (GA) is used to optimize the radial-inflow turbine with attention to six design parameters, including degree of reaction, velocity ratio, loading coefficient, flow coefficient, ratio of wheel diameter, and rotational speed. The influence of heat source outlet temperature on the performance of the radial-inflow turbine and the ORC system with constant mass flow rate of the heat source and constant heat source inlet temperature is investigated for four kinds of working fluids. The net electrical powers achieved are from few tens kWs to one hundred kWs. The results show that the turbine efficiency decreases with increasing heat source outlet temperature and that the decreasing rate of turbine efficiency becomes faster in the high temperature region. The optimized turbine efficiency varies from 88.06% (using pentane at the outlet temperature of 105°C) to 91.01% (using R245fa at the outlet temperature of 80°C), which appears much higher compared to common values reported in the literature. Furthermore, the cycle efficiency increases monotonously with the growth of the heat source outlet temperature, whereas the net power output has the opposite trend. R123 achieves the maximum cycle efficiency of 12.21% at the heat source outlet temperature of 110°C. Based on the optimized results, the recommended ranges of the key design parameters for ORC radial-inflow turbine are presented as well.

Iterative Approach for the Design of an Organic Rankine Cycle based on Thermodynamic Process Simulations and a Small-Scale Test Rig

Waste heat recovery from industrial processes may be a door opener for market penetration of Organic Rankine Cycle (ORC) systems. Within this study, an ORC for industrial waste heat recovery is designed by adopting an iterative approach. Therefore, experiments are performed in a thermal oil heated 1 kW test rig with internal recuperator and a maximum thermal efficiency of 10.6%. The results are iteratively implemented in thermodynamic process simulation. Thus, the simulation results of different stationary operating points can be compared to experimental measurements for different steps of the iterative design process. Results outline the importance of experimental results for the design of ORC systems. The simulation accuracy can be significantly improved with a single reimplementation of experimental data, which enables accurate sensitivity analysis on ORC waste heat recovery system performance. For two different representative operating points, the mean deviations between experiment and simulation decrease from 8.4% to 1.0% and 4.1% to 1.7% respectively, considering the enthalpy and pressure of all thermodynamic state points.

Thermo-economic comparison of air-cooled and cooling tower based Organic Rankine Cycle (ORC) with R245fa and R1233zde as candidate working fluids for different geographical climate conditions

This article compares the part-load operation of air cooled and cooling tower based low-medium temperature geothermal Organic Rankine Cycle (ORC) systems installed at different geographical locations. Working fluid R245fa was compared with a newer competitor R1233zde for thermo-economic performance, environment-friendly and efficient system integration. Monthly averaged, weather data is used to simulate ambient conditions of Ulsan, London, Vegas and Kuala Lumpur. Mathematical models for condenser part load operation were formulated for both air cooled and mechanical draft wet cooling tower based systems. Numerical study and experimental validation was performed for the condenser when wet cooling tower based system was investigated. The ORC system design was optimized for maximum power output to grid and operational control optimization was performed on the heat sink to achieve maximum power output at different ambient or off-design conditions. Economic analysis was performed by comparing the capital investment/kW and levelized cost of electricity (LCOE) over the lifetime of the system. Based on the economic analysis, the results reveal that R1233zde has potential to replace R245fa working fluid when the source temperature is higher (around 145 °C). Cooling tower based system are preferable for hot dry regions while air-cooled systems can be implemented with R1233zde for Ulsan and London.

Experimental and Numerical Analyses on the Rotary Vane Expander Operating Conditions in a Micro Organic Rankine Cycle System

Micro (0.5–10 kW) organic Rankine cycle (ORC) power systems are nowadays considered for domestic power generation. Selection of a suitable expander is one of the most important problems connected with the domestic ORC system design. Volumetric machines or micro-turbines can be adopted as an expander in domestic ORC systems. Scroll and screw expanders are a common choice and were successfully applied in different small- and micro-power applications. However, micro-turbines as well as scroll and screw expanders are mechanically complicated and expensive. An alternative are rotary-vane machines, which are simple and cheap compared to micro-turbines. This paper documents a study providing the experimental and numerical analyses on the rotary vane expander operating conditions in a micro-ORC system. A test-stand was designed and set up and a series of experiments was performed using the test-stand. Results of these experiments were further used as an input to numerical simulations of an expander operation. In order to simulate the expander operating conditions, a three-dimensional numerical model has been prepared. The analysis presented in this paper indicates that a properly designed multi-vane expander is a cheap and mechanically simple alternative to other expansion devices proposed for domestic ORC systems.