Organic Rankine Cycle Power Systems Research Articles

Dynamic behaviour and performance evaluation of a biomass-fired organic Rankine cycle combined heat and power (ORC-CHP) system under different control strategies

The dynamic behaviour and performance evaluation of a biomass-fired organic Rankine cycle combined heat and power (ORC-CHP) system under two different control strategies are investigated in this study. The dynamic model is established, while the dynamic characteristics of key operating parameters (superheat degree, evaporating pressure and mass flow rate) with the step change of heat source temperature are examined. The effects of controlled superheat degree and controlled expander shaft work on dynamic behaviours of thermodynamic, economic and environmental performance are discussed and compared under different control methods (feedforward active control, PID passive control and combined control). Results indicate that the superheat degree is significantly influenced by the heat source temperature under the without control strategy, with the variation reaching 8.4 K. The combined control method exhibits the best control performance with overshoot and control response times of 1.2 K and 12.3 s, respectively. Compared to without control, the expander shaft work and ORC thermal efficiency of the control strategy of superheat degree increase by 3.2 kW and 0.8 %, while that of the control strategy of expander shaft work increase by 1.0 kW and 0.3 %, respectively. The control strategy of superheat degree presents a significant improvement in the economic and environmental performance of the biomass-fired ORC-CHP system. This study is expected to provide better guidance for the practical operation and control of biomass-fired ORC-CHP systems.

Nonideal Compressible Fluid Dynamics of Dense Vapors and Supercritical Fluids

The gas dynamics of single-phase nonreacting fluids whose thermodynamic states are close to vapor-liquid saturation, close to the vapor-liquid critical point, or in supercritical conditions differs quantitatively and qualitatively from the textbook gas dynamics of dilute, ideal gases. Due to nonideal fluid thermodynamic properties, unconventional gas dynamic effects are possible, including nonclassical rarefaction shock waves and the nonmonotonic variation of the Mach number along steady isentropic expansions. This review provides a comprehensive theoretical framework of the fundamentals of nonideal compressible fluid dynamics (NICFD). The relation between nonideal gas dynamics and the complexity of the fluid molecules is clarified. The theoretical, numerical, and experimental tools currently employed to investigate NICFD flows and related applications are reviewed, followed by an overview of industrial processes involving NICFD, ranging from organic Rankine and supercritical CO2 cycle power systems to supercritical processes. The future challenges facing researchers in the field are briefly outlined.

Experimental Analysis of Partial Evaporation Micro-ORC for low-temperature Heat Recovery

In this paper, we present an experimental assessment of the performance of a partial evaporating organic Rankine cycle (PE-ORC) power system. The system converts low temperature heat into electrical energy, with a power size around 1 kW, thus suitable for micro-generation in the residential sector. Although the test bench was designed for operating with superheated vapour at the expander inlet, it has demonstrated to be able to work with the expansion occurring entirely in two-phase condition. Since the direct measurement of the vapour quality is not possible using the sensors installed in the test rig, the state of the fluid in the two-phase condition is estimated by means of the thermal balance at the heat exchangers, so the thermodynamic cycle can be evaluated. Temperatures of the heat source in the range between 40 °C and 75 °C have been tested, and for each temperature value the vapour quality at the expander inlet has been varied by regulating the feed-pump rotating speed. Experimental data are provided regarding the performance of the overall cycle, of the heat exchangers, of the expander and of the feed-pump. It was observed that the effectiveness of the evaporator and the efficiency of the pump are improved with respect to the operation with superheated vapour at the expander inlet. However, the overall performance is lower, especially due to the high ratio of the pump consumption over the expander produced power, commonly called back work ratio (BWR). The latter, under some boundary conditions, has resulted higher than the unit, meaning that the system is not able to produce net electrical power. The aim of the paper is to identify the design characteristics required by a micro-ORC energy system in order to enhance its performance in the PE operating mode.

Experimental Investigation Techniques for Non-Ideal Compressible Fluid Dynamics

The rising number of applications of the organic Rankine cycle (ORC) or supercritical CO2 (sCO2) power systems have shaped a new branch of fluid mechanics called non-ideal compressible fluid dynamics (NICFD). This field of fluid mechanics is concerned with flows of vapors or gases, which are characterized by substantial deviations from the perfect gas model. In extreme cases, even non-classical gas dynamic phenomena could occur. Although these non-ideal compressible flows are the subject of sophisticated numerical simulation studies today, there is also a growing need for experimental data for validating purposes. In the last couple of years, new experimental test rigs designed for investigating non-ideal compressible fluid dynamics have been developed and commissioned. Classical practical measurement techniques are currently being re-developed and applied to non-ideal compressible flows. Despite its substantial relevance, information about these measurement techniques and their differences from conventional methods in the open literature is scarce. The present review article is an attempt to reduce that gap. After briefly discussing the thermodynamics and fluid dynamics of non-ideal compressible flows, the currently available test rigs and their utilized measurement techniques are reviewed. This review discusses schlieren optical investigations, pneumatic and laser-optical methods, and hot-wire anemometry for non-ideal compressible flows.

Exergoeconomic analysis and multi-objective optimization of ORC configurations via Taguchi-Grey Relational Methods

Recovery of low-grade waste heat in industrial processes is an essential energy management topic. Yet, most low-temperature heat sources discharge their heat directly into the environment. The Organic Rankine Cycle (ORC), which has the benefits of being energy-efficient, enabling investment savings, and being ecologically friendly, is crucial in recycling energy from low-temperature waste heat. Both the application of the optimum cycle design and the provision of optimum working conditions are the issues that need to be focused on efficiently using energy. This study performs the energy, exergy, and exergoeconomic analysis of four different organic Rankine cycle configurations operating with renewable or low grade waste heat. The effect degrees and ratios of selected control factors are calculated using Taguchi and variance analysis methods to compare thermal and exergy efficiencies, total system cost, and unit cost of electricity produced by the system. The objective function of the multi-objective optimization problem is defined, and its solution is realized with the Taguchi-Grey Relational Analysis method. The best thermodynamic and exergoeconomic performance result is calculated for the configuration of ORC with Feed Fluid Heater-Internal Heat Exchanger (IHE–FFH–ORC). As a result of Taguchi and ANOVA analysis, the factors that most affect the thermal efficiency of the system, the exergy efficiency, the total system investment cost, and the unit cost of the electricity produced are, respectively, the evaporation temperature (∼50%), turbine efficiency (∼25%), working fluid (∼20%), subcooling (∼4%), pump efficiency (∼0.05%), and superheating (∼0.05%). As a result of the optimization process, the thermal and exergy efficiencies, the total system cost and the unit cost of produced electricity for the IHE–FFH–ORC power system are calculated as 22.6% and 73.5%, 1.06 $/h, 0.039 $/kWh and 2.9 years, respectively.

Innovations for organic Rankine cycle power systems: Current trends and future perspectives

Since the early 2000s, organic Rankine cycle (ORC) technology has experienced rapid development and market uptake. More than 4.5 GW of total ORC power plant capacity has been installed since then. Due to its flexibility, suitability for small- to medium-scale installations, its applicability to low- to medium-temperature heat sources, and compact design, ORC technology is already considered as state-of-the-art. However, to further increase the technical and economic potential of this technology, significant research is needed to further improve efficiency and other key performance indicators, as well as to address environmental and safety aspects. Therefore, it is important to research new technologies and to foster innovations for improving performance; but it is of similar importance to resolve operational challenges with applied research that focuses closer to the market, and the technology provider and user needs. This vision article outlines the current state-of-the-art and presents current research trends. Parts of this article summarize the research progress reported at the 6th International Seminar on ORC Power Systems (ORC2021) and accompanies the associated special issue published following this event. The article highlights research trends at the concept level, but also at the component and system levels and, therefore, provides a holistic overview for the interested reader regarding the current challenges and potential future research activities in this area. Beyond the variety of cycle concepts in Section 2.1, the different heat sources and applications in Section 2.2, rotating device and turbomachinery (pumps and expansion devices) options in Section 2.3, current R&D trends for working fluids are presented in Section 2.4. This editorial concludes with a more applied perspective on ORC systems, covering process control and a general perspective on the technology in Section 2.5. With an increasing number of ORC plants operating in the field, their integration within a wider energy system is also of increasing importance, and this is addressed in Section 2.6. All prior elements are levers toward the grand challenges in ORC technology: increasing efficiency, reducing investment costs, as well as increasing sustainability, environmental performance, and system compactness.

Design and commissioning of experiments for supersonic ORC nozzles in linear cascade configuration

In organic Rankine cycle (ORC) power systems, the turbo-expander involves the major technical challenges as the demand for compactness and flexibility of operation couples with severe compressibility and non-ideal gas effects. For these reasons the design of ORC turbines heavily relies on advanced aerodynamic models, whose validation is crucial but is still limited due to a lack of experimental data. To fill this gap, an experimental campaign on supersonic ORC nozzle cascades has been launched at Politecnico di Milano. This paper describes the conception and set-up of a novel class of experiments on linear cascades representative of stator nozzles of axial/radial ORC turbines, and aims at serving as a reference for future experimental investigations on ORC cascades. The paper also discusses the technical challenges of performing measurements on supersonic flows for a vapor at thermodynamic conditions close to saturation. Moreover, the paper reviews all steps required to design the campaign, discussing the blade design and the numerical simulations performed to assess the flow configuration in the linear cascade, with emphasis on the periodicity of the flow. The main objective of the experiments is to investigate the flow phenomena occurring in the blade trailing edge region and to retrieve the total pressure losses through the cascade with a relatively high spatial resolution, aiming at providing a benchmark for numerical simulations. To this end, the set of measurement techniques includes supersonic total pressure probes and wall pressure taps, as well as thermo-couples and schlieren visualizations. The main result of this preliminary work is the implementation of a relatively simple methodology to carry out experiments in blade cascade operated with organic vapors and aimed at evaluating cascade losses, without resorting to specifically calibrated instrumentation.

The organic Rankine cycle power systems market: Recent developments and future perspectives

This work presents an up-to-date overview on the recent developments in the Organic Rankine Cycle (ORC) industry. Information from more than 30 manufacturers, representing a total of almost 2900 projects have been collected and analyzed providing information on trends in the past and the market evolution during the last four years in terms of installed capacity and installed plants divided by application, macro region and manufacturer. At the end of 2020, the cumulated installed capacity of ORCs was 4.5 GW. Since 2016, the overall ORC market increased by 40 % (+1.18 GW) in terms of installed capacity and by 46.5 % (+859) in terms of installed plants. Regarding the capacity increase between 2016 and 2020, the largest increase is due to geothermal application (+972 MW, +45 %) with 74 new plants, while waste heat systems have the largest growth in terms of the number of installed systems (630 plants, +208 %) with an installed capacity of 125 MW. The installed capacity of biomass ORC systems increased by 20 % (69 MW), while the number of installed plants increased by 22 % (77 plants).Additionally, a market survey was conducted, and ten established ORC manufactures contributed their perspective on the ORC market. The results highlight that, despite COVID-19, the current market situation is in good shape and that the majority of the manufacturers have positive expectations concerning the future development. Central and Eastern Europe as well as the ASEAN region are rated as the regions with the highest growth potential. Geothermal energy and small waste heat installations are expected to be the most relevant heat sources for the coming years.

A study on the design of Waste Heat Recovery Unit (WHRU) for 30kW Organic Rankine Cycle (ORC) power system for ships

ABSTRACT As the improvement of ship energy efficiency is emphasized internationally, researches for this are being conducted in various ways. Accordingly, research is being conducted on the application of ORC power generation systems for ships using waste heat from the main engine exhaust gas generated during operation. The WHRU constituting the ORC system must be designed so that stable-phase change heat transfer occurs. In this study, a design study was conducted using the ANSYS CFX program for the production of a WHRU capable of generating ORC power generation output for a 30-kW ship using R134a refrigerant. A WHRU capable of achieving 30 kW generation output performance was designed while changing various design elements (shape, tube diameter, number of tubes, number of stages, etc.) of the WHRU. As a result, it was confirmed that the refrigerant (R134a) in a liquid state at a temperature of 14.8°C entered at a flow rate of 1.06 kg/s, evaporated by the exhaust gas, and was discharged from the outlet in a state of vapor fraction 1 at a temperature of 56.4°C. The heat transfer rate of the WHRU was 219.2 kW, the pressure during the evaporation process was constant at 13.9 bar in absolute pressure, and the enthalpy was 220 kJ/kg at the inlet and 426 kJ/kg at the outlet, respectively.

Thermodynamic analysis of exhaust heat recovery of marine ice using organic rankine cycle

The use of organic Rankine cycle power systems for waste heat recovery on marine internal combustion engines can help to mitigate the GHG and reduce the fuel consumption of the marine engine. In this paper, the internal combustion engine combined with an organic Rankine cycle system was developed to analyze the performance of waste heat recovery from the exhaust gas of a heavy-duty marine Diesel engine via five selected working fluids with low global warming potential and ozone depletion potential. The net output power and thermal efficiency for each of the selected working fluids were obtained. Results indicate that the working fluids of butane have the best performance among the selected working fluids with the power efficiency of the organic Rankine cycle subsystem of 12.27% under the power load of 100%. For the overall proposed system, the maximum net power output is 1048 kW and the power efficiency is 36.47%. Besides, the total thermal efficiency of the proposed system was 67.94% when considering the recovered waste energy from jacket water.

Optimal tuning of model predictive controllers for organic Rankine cycle systems recovering waste heat from heavy-duty vehicles

The organic Rankine cycle power system is an emerging technology, which is able to recover the waste heat from the diesel engine of heavy-duty trucks and thus increase the overall engine efficiency. One of the major technical challenges for the integration of the organic Rankine cycle unit on-board trucks are the broad and rapid fluctuations of the available waste heat, caused by the unsteady driving conditions of the truck. Model predictive control has shown to be a powerful tool to ensure safe operation and optimal performance of the organic Rankine cycle unit on-board trucks. This paper presents a novel systematic method for the tuning of model predictive controllers based on a multi-objective optimization routine using a fourth-order reduced linear model. The objectives of the optimization are the settling time due to a step change of the exhaust gas mass flow rate and the cumulative controller effort due to measurement noise. The results suggest that a trade-off exists between the two objectives. Among the controller design parameters, the input rate weight has the largest influence on the controller performance. Interestingly, the simplified optimization procedure based on the reduced-order linear model of the organic Rankine cycle unit can provide key information about the controller performance based on a more complex nonlinear model of the organic Rankine cycle unit when subjected to a realistic waste heat profile. The results indicate that the settling time due to a step change of the exhaust gas mass flow rate is a good indicator of the absolute mean square tracking error over the profile, and it should not exceed 15 s for an absolute mean square tracking error below 2 K. On the other hand, the cumulative controller effort due to measurement noise is strongly correlated to the cumulative controller effort over the profile, and it should stay below 0.5 %/s for a cumulative controller effort over the whole profile below 2 %/s. The presented method is a powerful tool to help the control designer to find the optimal design parameters of model predictive controllers in a systematic way, in contrast to the time-consuming, experience-based trial and error methods.

Experimental and numerical investigation of a micro-ORC system for heat recovery from data centers

In the effort to enhance the recovery of waste energy, data centers are drawing attention because of the huge amount of heat discharged from the computer racks. Organic Rankine cycle (ORC) power systems are a viable solution to exploit servers’ waste heat, as it is available at very low temperatures. The purpose of this study is to assess the feasibility of integrating a micro-ORC system into data centers cooling systems and its potential energy saving. An experimental analysis is carried out on a kW-scale ORC test bench, with R134a as working fluid. Heat is supplied at temperatures and flow rates in the range respectively 40-55 °C and 1.8-5 m3/h, consistently with typical values observed in data centers application, showing the second law efficiency varying between 5% and 13%. Furthermore, a steady-state model of the micro-ORC has been recalibrated and validated against experimental data; the built-in volume ratio of the reciprocating piston expander has been optimized to improve the filling performance of the machine. A parametric analysis, varying the boundary conditions within their range of interest for this application, and the working fluid (R1234yf and R1234ze(E)), shows that a maximum second law efficiency of 30% is achievable with R1234ze(E).

Study of the Performance Parameters in an Organic Rankine Cycle Power System Operating in Low Temperature Conditions

The working fluid normally used in Organic Rankine Cycle (ORC) systems is R245fa. However, due to stricter regulations for emission control, this type of fluid will be phased out. Due to the above, in this research, the performance parameters of ORC systems operating at low temperatures with different working fluids are analyzed. The research was carried out by numerical simulation using MATLAB® software and the CoolProp® database. The working fluids investigated were R245fa, R1233zd(E), and R1336mzz(Z), respectively. The analysis of the performance parameters involves the net power, thermal efficiency, and exergetic efficiency of the ORC system. From the results obtained, it was shown that the net power obtained with the working fluid R1233zd(E) and R1336mzz(Z) are 3.5% and 6% lower compared to R245fa. However, the higher evaporation temperature of R1233zd (E) allows achieving a higher thermal and exergetic efficiency of the thermal cycle. R1233zd(E) enables a 3.8% and 4.8% improvement in thermal and exergetic efficiency compared to R245fa working fluid. R1336mzz(Z) working fluid is not recommended as a replacement for R245fa. In general, R1233zd(E) has the potential to replace R245fa, which is one of the main working fluids used despite its high level of CO2 emissions.

A Study on the Refrigerant Characteristics of the Organic Rankine Cycle Power System Using the Waste Heat of the Main Propulsion Engine

A Study on the Refrigerant Characteristics of the Organic Rankine Cycle Power System Using the Waste Heat of the Main Propulsion Engine

Daily, monthly and annual thermal performance of a linear Fresnel reflector to drive an organic Rankine-cycle system

AbstractThe organic Rankine cycle (ORC) coupled with a linear Fresnel reflector (LFR) utilizes a low-grade heat source. This article presents the study of a small-scale LFR–ORC power-generation plant under the climatic conditions of Almatret, Spain. The mathematical modelling is performed using thermodynamic equations and simulations are conducted to evaluate the optical performance of the LFR system and thermal performance of the ORC plant. Therminol-62 is used as a heat-transfer fluid (HTF) in the solar field, whereas NOVECTM 649 is used as the working fluid in the ORC power system. The LFR is integrated with a thermal-storage unit based on a two-tank system and stores the solar thermal energy via a heat exchanger. The thermal-energy output of the receiver tube of the LFR system is 108 kW and thermal losses are 7.872 kW during the peak time operation of a day at 1:00 p.m. The mechanical power output of the ORC turbine is 7.296 kW using the specific design conditions and the two-tank thermal-storage system adds 4 operation hours to the power plant after sunset.

Efficiency based optimization of a Tesla turbine

Tesla turbine is a bladeless, radial turbine which might be suitable for the applications in various energy systems, e.g. in Organic Rankine Cycle or combined heat and power systems if its efficiency improves. The investigations presented in the paper concern efficiency based numerical optimization of a Tesla turbine. Parameters subjected to the optimization process are inlet nozzle height, inter-disc gap, nozzle angle, pressure and rotational velocity. The optimization was conducted using response surface methodology. The first stage of the optimization excluded pressure ratio as neutral to efficiency. The second stage of the optimization allowed determination of the most important parameters: tangential velocity ratio, partial admission coefficient, reaction degree and aspect ratio required for maximization of the turbine's efficiency. Efficiency was improved almost twice with the respect to the nominal model (from 9% to 17%) and validated experimentally. Performance characteristics of the optimized turbine model were calculated using computational fluid dynamics software.

Adjoint-Based Unsteady Optimization of Turbomachinery Operating with Nonideal Compressible Flows

The lack of established optimal design guidelines for turbomachinery operating in the nonideal flow regime (e.g., organic Rankine cycle turbines, compressors, compressors for refrigeration systems) demands for effective and efficient automated design methods. Past research work focused on gradient-free methods applied to computational fluid-dynamic simulations. The application of the adjoint method is a cost-effective alternative as it enables gradient-based optimization irrespective of the number of design variables. This paper presents the application of a fully turbulent unsteady adjoint method for the automated design of multirow turbomachinery partly operating in the nonideal flow regime. The method therefore allows for the solution of constrained unsteady fluid-dynamic optimization problems, in which the thermodynamic properties of the working fluid need to be modeled by means of complex equations of state. The optimal designs computed with unsteady simulations obtained with the harmonic balance method are then compared with optimal design resulting from mixing-plane simulations. The method is applied to the optimization of 1) a two-dimensional turbine cascade subject to time-varying inlet conditions, and 2) a two-dimensional turbine stage of an organic Rankine cycle power system. The results demonstrate the importance of computing fluid properties using accurate thermodynamic models and of using unsteady simulations for shape optimization of these machines.

Evaporation/Condensation Heat Transfer and Pressure Drop of R1336mzz (E) and Its Mixture Working Fluid for High-temperature inside Horizontal Microfin Tubes

Research is currently in progress on developing and improving efficiency of high-temperature heat pumps and organic Rankine cycle power systems, both of which generate high-temperature steam by effectively utilizing low-quality heat sources from ship engines and factories for industrial purposes. From an environmental point of view, development efforts are also underway to replace low-pressure working fluids used in these systems with new alternative working fluids with low global warming potentials (GWPs). The purpose of this study is to experimentally clarify the evaporation and condensation flow characteristics of alternative low-GWP working fluids inside two types of horizontal microfin tubes with outer diameters of 9.5 mm. The Hydrofluoroolefin (HFO) working fluids R1336mzz(E) and R1336mzz(Z), both of which are expected to replace the working fluid R245fa that is used widely at present, two pure components and their mixture were used as test fluids in this study. In this experiment, the authors measured the evaporation and condensation heat transfer coefficients and pressure drop under the conditions of 50-300 kg/(m2s) mass velocity, a saturated evaporation temperature of 40 °C and a saturated condensation temperature of 60 °C. The results of the experiment clarified the effects of mass velocity and fin geometries on the evaporation and condensation heat transfer and pressure drop characteristics of R1336mzz(E), R1336mzz(Z) and their mixture working fluid. In addition, comparisons were made between the evaporation and condensation heat transfer coefficients and pressure drop of these working fluids and those of R245fa to highlight differences in their performance. Furthermore, the measured values were correlated with previous correlations for evaporation and condensation heat transfer for microfin tubes to verify the applicability of these predicted correlations.

Techno-economic feasibility analysis of zeotropic mixtures and pure fluids for organic Rankine cycle systems

• Optimization of net present value of ORC units using mixtures and pure fluids. • Zeotropic mixture R1234yf/i-butane (53/47) reaches highest net present value. • Sensitivity analysis employed for comparing R1234yf/i-butane and R1234yf. • Result robust to variations in fluid cost, electricity price and cost models. In this paper the techno-economic feasibility of employing zeotropic mixtures as working fluids in organic Rankine cycle power systems is assessed. For an application case based on the utilization of low temperature geothermal heat at 135 °C, the net present value of the organic Rankine cycle system was maximized by optimizing the process variables and heat transfer equipment design parameters. Parametric studies detailing the effect of the assumed electricity price and the employed equipment cost estimation models were carried out. The working fluids propane, i-butane, i-pentane, R1234yf, and their mixtures were selected for investigation, since they have shown promising performance in previous studies. The results suggest that the highest net present value (43.1 M€) is reached by the mixture R1234yf/i-butane (53.3/46.7), which is 2.1 M€ higher compared to the most economically feasible pure fluid R1234yf for an electricity price of 0.252 €/kWh. The results of the sensitivity analyses suggest that the techno-economic benefit of using the mixture is robust to variations in the electricity price, the cost of the working fluid, and the equipment cost estimation models. In the comparison of R1234yf based mixtures to propane based mixtures, the inclusion of model for estimating the turbine efficiency is assessed to have a relevant influence on the results. The results also indicate that the R1234yf/propane, R1234yf/i-butane, and R1234yf/i-pentane result in lower cooling water flows and thereby lower cooling tower costs compared with R1234yf.

Sizing the thermal energy storage (TES) device for organic Rankine cycle (ORC) power systems

Thermal energy storage (TES) became one of the main research topics in modern power engineering. The design of TES devices and systems depend on their application. Different thermal energy storage materials (e.g., solids, liquids, or phase change materials) can be applied in TES devices. The selection of the thermal energy storage material depends mainly on the thermal power and operating temperature range of the TES device. These devices and systems are applied in different energy conversion systems, including solar power plants or combined heat and power (CHP) stations. The application of TES devices is also considered in the case of other industries, such as metallurgy. The possible application of TES devices is particularly promising in the case of organic Rankine cycle (ORC) systems. These systems are often utilizing floating heat sources such as solar energy, waste heat, etc. TES device can be therefore applied as the evaporator of the ORC system in order to stabilize these fluctuations. In this paper, the possible thermal energy storage materials used in TES devices applied in ORCs are discussed. Moreover, the modelling results are reported related to assessment parameters which can be applied to size the TES device for ORC system utilizing different low-boiling working fluids. The thermal properties of working fluids are taken from CoolProp. The function of heat capacity of different TES materials is also provided and the calculation is computed by employing MATLAB. The result shows that based on the simulation, the gradient of the natural characteristic of TES with working fluids (ζ(Tb)) tends to decrease. The presented result in this paper gives a new point of view which can be used by scientists and engineers during the design and implementation of TES evaporators dedicated to ORC power systems.