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On mixtures as working fluids of air-cooled ORC bottoming power plants of gas turbines

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Dabo Krempus and colleagues have recently released a publication in the journal “Applied Thermal Engineering.” The study centers on utilizing mixtures as working fluids within ORC cycles, and the titled piece is “Utilizing Mixtures as Working Fluids in Air-Cooled ORC Bottoming Power Plants for Gas Turbines.” For their calculations, they employed the Asimptote Cycle-Tempo and FluidProp software. Teus van der Stelt from Asimptote also played a role as a co-author in the development of this publication. The article is openly available and can be viewed through the following link.


The use of mixtures as working fluids of organic Rankine cycle (ORC) waste heat recovery (WHR) power plants has been proposed in the past to improve the matching between the temperature profile of the hot and the cold streams of condensers and evaporators, thus to possibly increase the energy conversion efficiency of the system. The goal of this study is to assess the benefits in terms of efficiency, environmental (GWP) and operational safety (flammability) that can be obtained by selecting optimal binary mixtures as working fluids of air-cooled ORC bottoming power plants of medium-capacity industrial gas turbines. Furthermore, two thermodynamic cycle configurations are analyzed, namely the simple recuperated cycle and the so-called splitcycle configurations. The benchmark case is a combined cycle power plant formed by an industrial gas turbine and an air-cooled recuperated ORC power unit with cyclopentane as the working fluid. The results of this study indicate that binary mixtures provide the designer with a wider choice of optimal working fluids, however, in the case of the recuperated-cycle configuration, no improvement in terms of combined cycle efficiency over the benchmark case can be achieved. The split-cycle configuration leads to an increase of combined cycle efficiency of the order of 1.5%, both in case of pure and blended working fluids. Furthermore, for this cycle configuration the use of Novec 649 as working fluid is advantageous because it is environmentally and operationally safe, and it does not involve any penalty in terms of combined cycle efficiency if compared to the benchmark case. Additionally, the use of this fluid would lead to a more compact turbine, as the corresponding thermodynamic cycle would determine a turbine volume flow ratio that is half of the value of the benchmark case and a specific enthalpy difference over the expansion that is one fifth.


Exergy Analysis of a CI Engine Operating on Ternary Biodiesel Blends

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Sreekanth Manavalla et al. have recently published an article in the Sustainability journal, focusing on IC engines titled “Exergy Analysis of a CI Engine Operating on Ternary Biodiesel Blends”. As part of their research, they utilized Cycle-Tempo for exergy calculations. The article is freely accessible and can be accessed via this link.


Exergy analysis is carried out on a single-cylinder CI engine fueled with biodiesel blends of palm, jatropha and cottonseed oils. This is to identify the blends with high exergy destruction. To this end, experimental and analytical methods were adopted. Three types of biodiesel blends incorporated in this study are primary, binary and ternary. The load was varied as an independent parameter, and mass flow rates of air and fuel, flue gas composition, etc., were measured during the study. Moreover, the chemical composition of the fuel blends and flue gas, as well as their flow rates, were used to determine the total exergy. The output parameters determined were 1st and 2nd law efficiency and fuel exergy destruction under all loading conditions. The inference obtained from the experiment suggests minutely higher 1st law efficiency for the biodiesel blends. Increasing the blending ratio led to an increase in efficiency indices.

Cycle-Tempo: historical perspective and a sneak preview of the upcoming version

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The development of the Cycle-Tempo software has been ongoing for a very long time and started in the late 1970s. Many different versions marked its evolution as Cycle-Tempo has been running on various computer types and several operating systems. A brief summary of this long story is provided and a sneak preview of the upcoming releases of Cycle-Tempo concludes this report.

1970’s to 1985

The oldest source code listing that resembles pieces code of Cycle-Tempo came to light in the early 1970’s. This first attempt at solving the mass and energy balances of a complex energy conversion systems was written in PL/1, which is an abbreviation of Programming Language 1, a programming language developed by IBM. PL/1 was meant to combine COBOL from the business world and FORTRAN from the scientific world, but it never became successful. Later, FORTRAN IV was used to develop the first official version, which was just called CYCLE at that time. CYCLE was succeeded by CYCLE II in 1976.

Cycle II allowed modelling water/steam cycles containing boilers, reheaters, steam turbines, feedwater heaters, condensers, contact heaters, pumps, and junctions/splitters. It ran on an IBM mainframe in batch-mode, meaning an input dataset had to be composed on punch cards containing the system configuration and design parameters (like pressures and temperatures). Together with the program code, this had to be submitted to the mainframe and, if you were lucky 😊, printed output containing the output of the calculation was ejected to your hands by the machine. In the most common situation, the output just contained a list of error messages and you had to correct your mistakes and resubmit your dataset.

In 1981, CYCLE III was born as a deliverable of a PhD project (J.A. Miedema, CYCLE: a general code for thermodynamic cycle computations, studies of cogeneration in district heating systems, 1981, Delft University of Technology). Among others, thermodynamic property calculations of ideal gas mixtures and models of a combustor, a valve, and a drum were added to CYCLE III, making it possible to model systems with combustion and gas turbines. At that time, also industrial companies became interested in the software and several copies of CYCLE III were purchased.

1985 to 2000

In the meantime, computer terminals made their appearance and replaced punch card machines, which was a great progress (and relief!). Computer terminals were devices consisting of a screen and a keyboard remotely connected to the mainframe that allow data to be entered, retrieved, and displayed. Around that time, 1986, the author started working as a computer science engineer at the Laboratory of Thermal Power Engineering of the Delft University of Technology (TU Delft) and was involved in the further development of CYCLE, a year or so later.

During that time, quite a few improvements were made to the software and many extensions of its capabilities were achieved. For example, the possibility of simulating open cycle systems was added, which greatly increased the flexibility of the software. In the Laboratory for Refrigeration and Climate control of the Mechanical Engineering faculty, facilities and components were added to make it possible to model refrigeration systems, e.g., absorption refrigeration. This was meant to be the new version of CYCLE, namely CYCLE IV. However, this work was not finalized at that time, probably due to a combination of lack of further interest and continuity of capable people who were able to carry on this work to good effect. The current Ziegler-Trepp NH3/H2O model for the calculation of the thermodynamic properties of ammonia/water mixtures is one of the remains of that work.

For several years there had been a close collaboration with TNO, a Dutch institute for applied research. Within the framework of this collaboration, the calculation of potassium cycle system was implemented. TNO became also responsible for the commercialization of CYCLE and took care of the marketing and distribution of the software.

At the same time, other important extensions were being worked on. Chemical equilibrium calculations were improved and already at that time a model of a reformer and a fuel cell were added. Modelling systems with molten-carbonate (MCFC) and solid oxide (SOFC) fuel cells became then possible. These models are still the base of the reformer and fuel cell models that are available in Cycle-Tempo nowadays. To give credit to the possibility of modeling open cycle systems, it was considered to change the name of the software from CYCLE to TEMPO, an acronym for Thermodynamic Energy systems, Mass flow calculation for POwer processes. However, the name CYCLE had already become widely known by then, and therefore it was decided to rename the software to CYCLE-TEMPO, which remained unchanged to this day, although now written as Cycle-Tempo.

The costs of using the mainframe were increasingly passed on to departments and laboratories. Consequently, and having earned some money from selling CYCLE, the Thermal Power Engineering laboratory bought their own computer system consisting of two mini computers. These systems were IBM RT systems running on the AIX operating system, an IBM UNIX dialect based on AT&T’s UNIX System V. The systems were originally connected to 5 terminals, and, over time, a significant number of personal computers were used as terminals as PC ownership became widespread and commonplace on desks.

CYCLE-TEMPO was ported from the main frame to the IBM RT and as a result CYCLE-TEMPO 2.0 was born. Also, the code itself was for a large part ported to FORTRAN 77, which allowed more structured programming by almost entirely eliminating the need of GO TO statements and many more relevant enhancements. Later, after the release of Fortran 90 and Fortran 95, more and more features of these modern programming languages were added to the code.

At that time CYCLE-TEMPO was still running in batch-mode and without graphical user interface (GUI). We thus built an AutoCAD library with component symbols and line types for component connections to create drawings of process schemes in AutoCAD, and spent much time making these drawings and keep them synchronized with the calculations that were carried out. Would not it be much simpler if required data could be entered directly from the process diagram and the configuration of the energy system could be retrieved from the process flow diagram? Yes, of course! Investigations were started to figure out if and how a GUI could be realized in such manner. A first attempt to create a GUI was carried out on the IBM RT system by TU Delft students of the Mathematics & Computer Science faculty. They employed CGE (Configurable Graphical Editor), an inhouse software of TNO, but the attempt was unsuccessful.

Building on the experience of this first attempt, in 1993 a GUI was coded using Borland C++ such that it could run on a Windows 3.1 PC. The OWL library in Borland C++ gave the GUI a full Windows 3.1 look and feel, which was nice because many people were already used to it. In the end we were able to develop a basic version of a GUI that met the minimum requirements for process flow diagrams of energy conversion systems, and that allowed to enter the desired process data to carry out the calculations. With the help of a master student of the Mathematics & Computer Science faculty department, the GUI, internally known as GUIDE (Graphical User Interface for Designing Energy systems) was developed further.

A problem was that the calculations itself could not be carried out on a PC, because at that time Fortran programs and compilers required more RAM memory than commonly possible on 16-bits computer systems. A first solution was to have GUIDE create a dataset for a CYCLE-TEMPO batch run on the RT system. The dataset was then sent from the PC to the RT using Kermit, a file-transfer and -management protocol, which in turn sent the output of the batch calculation back to the PC.

In the 90’s of the previous century, many developments were going on in parallel. Aside from what is mentioned above, in the meantime many new energy system component models were added to the program, such as a type of gasifier, the compressor, the chemical reactor, components for gas treatment (cleaning, drying, saturating), fuel cells (alkaline – AFC, phosphor-acid – PAFC, proton exchange membrane fuel cell – PEMFC, also named solid polymer fuel cell – SPFC), an extended condenser model with advanced off-design features, etc. Exergy analysis became possible by adding the feature that allows to calculate all exergy flows in a system and the exergy efficiencies of the components. A team of several scientists, PhD students, software scientific software engineers, and master students were all working together doing research and extending Cycle-Tempo to fulfill their research requirements.

Finally, also during the 90’s, TNO improved the modeling capabilities for refrigeration systems, like vapor compression cycles, absorption refrigeration cycles, and heat pumps. An early version of REFPROP (version 4), a library for the estimation of fluid thermodynamic properties, was added by TNO, with data for a large number of refrigerants. Thus, evolving through CYCLE-TEMPO 3.0, the last century ended with Cycle-Tempo 4.1, showcasing a modern graphical user interface and even a gas turbine library.


In the early 2000s, the GUI was ported to a 32-bit system, therefore making the software suitable for use on a Windows NT platform, later followed by Windows 2000, XP, Vista, Windows 7, 8, and 10. Currently, Cycle-Tempo 5 runs on all Windows 11 platforms, including 64-bits and the latest Windows Server systems such as Windows Server 2019.

In the meantime, the collaboration with TNO had ended and support, marketing and distribution had returned to the developers at TU Delft. Existing models were continuously improved and a model of a Direct Carbon Fuel Cell (DCFC) was added. Aside from that, driven by research needs, these years were focused on developing capabilities for working fluids of organic Rankine cycle systems.

FluidProp, a software package for the calculation of thermodynamic and transport properties of fluids was developed at TU Delft separately from Cycle-Tempo. FluidProp is in fact an encapsulation of different existing packages for the calculation of thermodynamic properties with a number of additional features. Packages like TPSI, StanMix, GasMix, PCP-SAFT and IF97 became all available through the common FluidProp interface such that the user would not need to learn anything particular to any of the various fluid property modules. NIST REFPROP was also added to FluidProp. In turn, FluidProp was coupled to Cycle-Tempo and as such all fluids and fluid models / equations of state implemented in FluidProp became available to Cycle-Tempo within a typical client server architecture.

A new website was developed and released and it included a web shop for direct purchase and payment of software products and professional licensing software was incorporated into both Cycle-Tempo and FluidProp. Meanwhile, in 2022, the website has been renovated and the licensing system was replaced with a modern license key system for Cycle-Tempo.

The innovative and superior textbook Thermodynamics: fundamentals and engineering applications by William C. Reynolds and Piero Colonna, was developed by leveraging on a close collaboration with Asimptote as far as many of the illustrations, exercises and more are concerned. It was released in 2018 and can be purchased from, among others, the web site of Cambridge University Press and FluidProp and Cycle-Tempo allowed to generate the majority of the useful tables, wonderful figures, calculation examples, and exercises that are sprinkled throughout the entire book.


Solar and wind energy play a significant role in the transition to a cleaner, more sustainable global energy system. Both solar and wind energy are considered renewable sources of energy because they can be replenished naturally. However, their availability can vary significantly over short periods of time, which can make it challenging to rely on them as the primary source of electricity.

To address storing excess solar and wind energy, one of the potential developments, next to batteries or pumped hydroelectric storage, is electrolysis. An electrolyser or a reversible fuel cell produces hydrogen gas out of electricity, which can be stored and reused to generate electricity (with a fuel cell) or burned to produced heat.

In order to satisfy the need to calculate the mass and energy balances of electrolysis systems, an electrolyser model for Cycle-Tempo is under development. As a first step, this model is limited to high temperature solid oxide cells (SOFC’s). It covers steam electrolysis, CO2-electrolysis and co-electrolysis.

What’s next? For the foreseeable future, we consider Software as a Service (SaaS) as an attractive addition to our software portfolio. SaaS is a software delivery model in which a software application is hosted by a third-party provider and made available to customers over the internet. SaaS providers typically host and maintain the infrastructure, security, and maintenance of the software, while customers pay a subscription fee to access and use the software on a monthly or annual basis. One of the main benefits of SaaS is that it allows customers to access software applications and data from any device with an internet connection, without the need to install and maintain software on their own computers or servers. This makes it an attractive option for companies and universities, as it reduces the upfront cost and technical expertise required to run software applications. Another advantage of SaaS is that it allows for frequent updates and new features to be rolled out to customers without requiring them to manually update their software. This means that SaaS customers can always access the latest version of the software, with new features and improvements being made available on a regular basis. Overall, SaaS is a popular and convenient way for companies and universities to access and use software applications, without the need for upfront costs and ongoing maintenance.

What could this mean for Asimptote? A kind of online version of Cycle-Tempo? Yes, indeed!! We are working on it already for quite some time (Hojo Cycle project) and soon a demo/trial version will be released.

Keep an eye on the news items on our website and the on Facebook, Instagram, and LinkedIn posts. The user interface has been written in JavaScript and resides with an NodeJS server and the famous Fortran calculation kernel on a Linux server. On your side, Hojo Cycle runs in your browser (e.g., Safari, Google Chrome, Firefox, Windows Edge). Can you imagine running Cycle-Tempo on your tablet, or even on your smartphone?  STAY TUNED!


Teus van der Stelt

February, 2023

Scientific publications, PCP-SAFT, and Novec 649™

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FluidProp and Novec 649TM

Novec 649TM is a relatively recently invented fluid, brought forward by the company 3M. The chemical formula is C6F12O and the chemical name dodecafluoromethylpentanone. This Novec molecule belongs to the so-called fluoroketones family, a family of chemical compounds consisting of a fluorinated carbon backbone and a double bonded oxygen atom (carbonyl group). Figure 1 shows a 3D model image of the molecule, in which the green dots represent the fluorine atoms and the red dot the double bonded oxygen atom.

Novec 649TM is a clear, colorless and low odor fluid. It has a low toxicity, high thermal stability and a low flammability and is an effective heat transfer fluid with a normal boiling point of 49 °C. When fluoroketones are dissolved in liquid water, they usually hydrolyze and form an organic acid, but they are very stable in the absence of water. In contrast with greenhouse gases like perfluorocarbons and hydrofluorocarbons, Novec 649TM has a very low global warming potential (GWP = 1) and a short atmospheric life time of about 5 days. For instance, the hydrofluorocarbon HFC-134a (C2H2F4), frequently used as, amongst others, refrigerant in automotive air conditioning systems, has a GWP of 1300 and an atmospheric life of about 140 years.

Figure 1: 3D model image of the Novec 649TM molecule

Other examples are the hydrofluorocarbon refrigerant R245fa (C3H3F5), inter alia used as a working fluid in organic Rankine cycles (ORC) systems, with a GWP of 1030 and an atmospheric lifetime of 7.6 years and world’s strongest greenhouse gas sulphur hexafluoride (SF6) with a GWP of 32000 and a life time of 3200 years. In addition to other new fluids in general and refrigerants in particular (like the hydrofluoroolefins R1234yf, R1336mzz-Z, etc.), Novec 649TM has been developed as a greenhouse-friendly alternative to these substances. Novec 649 TM can be used, for example, as a working fluid in ORC systems, fire protection fluid, electronics cooling and as computer/data center cooling.

Novec 649TM is available in the Extended Fluid Set Add-on of FluidProp, our software for the calculation of thermophysical properties of fluids and can be used with the (free)StanMix, PCP-SAFT, and REFPROP libraries (REFPROP is a product of NIST, the National Institute of Standards and Technology, part of the U.S. Department of Commerce, but also available as add-on for FluidProp). Cycle-Tempo, our steady state flow sheeting software for the thermodynamic analysis and optimization of energy conversion systems, in turn, connects to FluidProp. As a result, the fluid is also available in Cycle-Tempo to, for example, design and analyze ORC systems. Figure 2 and figure 3 present a process scheme of such an ORC system made with Cycle-Tempo and a temperature-entropy diagram of the process, created with Microsoft Excel and data imported from Cycle-Tempo. For more information about the system, see the news item of June, 2022, a model example of an ORC system. Both systems are similar, except that in this example  a lower turbine inlet temperature and pressure has been chosen (160 °C and 15 bar, respectively), because the critical temperature and pressure of Novec 649TM are less than that of pentane, applied in the previous example.

Figure 2: Process scheme of an organic Rankine cycle system with recuperation and Novec 649TM as working fluid.

Figure 3: Thermodynamic process of the system presented in figure 2 in a T-s diagram.

Scientific publications

A scientific paper and letter of correspondence have recently been published by Georgios Kasapis, et al. 1) and Shangze Yang, et al. 2) from the University of Edinburgh. In the paper, the PCP-SAFT equation of state of our FluidProp software is used to perform the calculations of the thermodynamic properties of state of mixtures of Novec 649TM and nitrogen. The PCP-SAFT equation of state is based on statistical mechanics. As a consequence, it incorporates information at molecular level, thus reducing the need for fluid measurement data (which hardly exists for mixtures of Novec 649TM and nitrogen) for the development an accurate fluid model. Because of the strong physical background, it is robust, consistent, and predictive when calculating vapor–liquid equilibria and single-phase properties of complex fluids and of mixtures in general.

The paper of Kasapis, et al.1) describes laser imaging experiments on laminar jets to observe the interface between an injected liquid and the surrounding gas under subcritical, transcritical and supercritical conditions. To do this, a stream of the fluoroketone Novec 649TM is injected into a chamber with nitrogen under high pressure and temperature and is examined as it evolves with the flow time. To define test cases for the entire range from subcritical to supercritical states, vapor-liquid equilibrium calculations were performed using the PCP-SAFT equation of state in FluidProp to identify the critical locus for mixtures of nitrogen and Novec 649TM. Planar laser-induced fluorescence and planar elastic light scattering imaging were applied to the jets to simultaneously image the mixing fraction with interface strength detection. The article presents and discusses evidence for interface evolution and supercritical states.

The image of figure 4 presents a P-xy chart of the Novec 649TM/nitrogen mixture for isotherms T = 360, 390, and 420 K calculated with PCP-SAFT. The results may slightly differ from the paper, because in the paper for Novec 649TM molecular parameters were applied that were published by Linnemann and Vrabec3), which were obtained by fitting to a only a subset of experimental data that were used to fit the molecular parameters in the present version of FluidProp. Note that for T = 390 K, close to the critical point, PCP-SAFT was not able to compute all the points of the curve because of convergence difficulties in this area. Figure 5 shows the phase envelope of a Novec 649TM/nitrogen mixture with 70 mole-% Novec 649TM. It is remarkable that for this mixture the cricondenbar (» 76 bar) is much larger than the critical pressure (» 46 bar).

Figure 4: P-xy chart of Novec 649TM/nitrogen mixtures.

Figure 5: Phase envelope of the Novec 649TM/nitrogen 70/30% mixture.

In the letter of correspondence of Yang, et al.2), evidence is evaluated for interface scattering that can occur even when the interface is assumed to have broken down in a supercritical jet. To evaluate this phenomenon, estimates are reported of the optical reflectivity for a diffuse, transcritical interface, including various liquids of current interest. Reliance is placed on prior work to explain the phenomenon and to estimate how strong it is for the cases of interest to the community. NIST REFPROP and the PCP-SAFT equation of state in our FluidProp software were used to calculate densities of various mixtures: dodecane/nitrogen, acetone/nitrogen, hexane/nitrogen, pentane/nitrogen, and fluoroketone/nitrogen.

If you need more information about our products in general or about PCP-SAFT and Novec 649TM in particular, please contact us. Furthermore, you can find more information about Cycle-Tempo and FluidProp on this website.


1) Georgios Kasapis, Shangze Yang, Zachary Falgout, Mark Linne, A study of Novec 649TM fluid jets injected into sub-, trans- and super-critical thermodynamic conditions using planar laser induced fluorescence and elastic light scattering diagnostics, Physics of Fluids, 2022-09-13, DOI:

2) Shangze Yang, Georgios Kasapis, Mark Linne, Reflectivity of diffuse, transcritical interfaces, Experiments in Fluids (2022) 63:137, DOI:

3) Linnemann, M., & Vrabec, J. (2017). Vapor–Liquid Equilibria of Nitrogen + Diethyl Ether and Nitrogen + 1,1,1,2,2,4,5,5,5-Nonafluoro-4-(trifluoromethyl)-3-pentanone by Experiment, Peng–Robinson and PCSAFT Equations of State. Journal of Chemical & Engineering Data, 62(7), 2110–2114. DOI:

FluidProp online Calculator

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Have you ever tried the FluidProp online calculator? It is a demonstration of a small fraction of the features of FluidProp. You can calculate freely several thermodynamic properties as function of two other independent properties of various common fluids with this calculator. The considered thermodynamic properties are, for instance, pressure, temperature, density, enthalpy, entropy, and vapor quality.

The online calculator also works very well on smartphones and tablets.

FluidProp has much more features, such as other thermodynamic properties (isobaric and isochoric specific heat capacities, speed of sound), transport properties (dynamic viscosity, thermal conductivity, surface tension), partial derivatives, etc.

Also, more fluids are available in the basic version of FluidProp and in specific fluid add-on packages, e.g. Extended Fluid Set Add-on, Siloxanes Add-on, Hydrofluoroolefins Add-on, etc.  Both pure fluids and mixtures are available. Click here for an overview the available fluids.

FluidProp is very well suited to be linked to other software, like Microsoft Excel, Matlab, and Python. It can also be linked to your own developed software, almost regardless the programming language.

If sufficient interest the on-line calculator will be extended with other features of which FluidProp is capable.

You are welcome to give it a try,

please click here!

Online calculator

Workshop thermo-chemical energy systems using Cycle-Tempo

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On July 23 – 24, 2022, Vellore Institute of Technology (VIT) Chennai will host the third international conference on sustainable energy solutions for a better tomorrow (SESBT).

Prior to this conference there will be a hands-on training on simulating and optimizing thermochemical energy systems using Cycle-Tempo.

Date: 22nd July 2022 Friday

Time: Forenoon – 9:00 a.m. to 11:00 a.m. & Afternoon – 2:00 p.m. to 4:00 p.m. (Indian Standard Time)

Thermo-Chemical Energy Conversion Technologies play a major role in meeting our day-to-day energy requirement. Since their efficiency is limited by the 2nd law of thermodynamics, any improvement in performance achieved by modifying and optimizing an existing system would be greatly welcome. A creative mind is needed to conceive new configurations involving traditional as well as hybrid energy systems. However, before building the prototype, ascertaining the performance using simulations would give tremendous confidence to the engineer.

The pre-conference workshop intends to provide hands-on training on simulating energy systems involving steam turbine power plants, gas turbine power plants, gasifiers, fuel cells etc. Our Cycle-Tempo flow-sheeting software for the thermodynamic analysis and optimization of energy conversion systems will be used for this purpose. It is one of the few software packages capable of carrying out exergy analysis. The software has a large user community, including energy companies, consultancy firms and R&D organizations. The software along with license valid for one month will be provided to the participants.

If you would like to join, complete your registration here! It is FREE for SESBT 2022 participants.

A model example of an ORC system

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A new series of model examples has been added to the Cycle-Tempo model examples on the website, consisting of a simple organic subcritical Rankine cycle system and a recuperated one. No effort has been done to present optimal systems in terms of efficiency, performance, and costs; this example is just to show how you can model ORC system in Cycle-Tempo.

Assumptions are an energy supply by hot flue gases: pressure = 2 bar, temperature = 400 °C, mass flow = 3 kg/s, turbine inlet conditions temperature = 180 °C and pressure = 20 bar, and a water-cooled super atmospheric condenser with cooling water inlet temperature of 20 °C.

As working fluid, the hydrocarbon n-pentane is selected because it has an evaporation temperature of 162.7 °C at 20 bar and a condensation temperature of about 38.6 °C at 1.1 bar. The critical temperature is 196.6 °C and the critical pressure 33.7 bar. All fluid data are according to the freeStanMix model in FluidProp.

A Cycle-Tempo process scheme is presented in the figure below.

Cycle-Tempo does not support state diagrams for other fluids than water/steam (yet). Therefore, we used an Excel spreadsheet to visualize the system behavior in a temperature-entropy (T-s) chart. It is easy to draw the saturation lines and some isobars of a fluid in a T-s chart using FluidProp. Next, it is little bit more work, we copy the data of the table “Data for all pipes” in the Cycle-Tempo output and paste it directly in Excel and making use of these data we connect the state points in the T-s chart. Once setup, next time, data for different conditions can be copied and pasted and the results are immediately visible in Excel.

In the figure above, a T-s chart created in this way is depicted. From this figure one can notice that the condenser has to do quite some cooling before condensation takes place. Therefore, it can be concluded that the use of recuperator (regenerator) might be justified (in terms of performance and efficiency). In the figure below a Cycle-Tempo scheme is presented of a similar system but then including a recuperator.

Immediately it is clear that the performance of the system increases from 166 kW to 175 kW, which is almost 5.5 %. An Excel sheet is created for this system by copying the previous one and extending the data with data for the recuperator. In the following figure, the T-s chart is presented.

The green lines of the process in the T-s chart indicate the amount of heat the recuperator regenerates. As a result, the boiler/evaporator now just has to heat the working fluid only from 80 °C instead of 40 °C in case of the first version, the simple ORC system.

As stated before, this example is just to present a way to model an ORC system in Cycle-Tempo and to show a way to visualize some of the results in a T-s chart in Excel. Although n-pentane is relatively greenhouse-friendly working fluid, other fluids are also possible, probably even performing better in terms of power output. In FluidProp and as a consequence also in Cycle-Tempo, several refrigerants (also modern ones with a with a low global warming potential, for example) are available to potentially do the same job, overcoming the issue of flammability of hydrocarbons. Furthermore, mixtures of working fluids are also possible.

In Cycle-Tempo, ORC systems can be developed for several temperature levels, for example lower temperature geothermal systems, systems for automotive applications, and solar powered systems. For condensers an air-cooled type might be a choice. Higher working fluid temperatures are possible using siloxanes, which are usually more stable at higher temperatures than hydrocarbons (like n-pentane) and refrigerants. At last, aside from subcritical systems as in this example, also supercritical systems are possible.

You can download the Cycle-Tempo files of these ORC systems here.

KCORC white paper energy harvesting

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The Thermal Energy Harvesting Advocacy Group (TEHAG) of the Knowledge Centrum Organic Rankine Cycle (KCORC) is in charge of actions aimed and fostering general public knowledge / awareness and policy and regulation regarding the enormous potential of waste-heat-to-power technologies, and therefore the use of ORC power plants and systems for both stationary and mobile applications. As a consequence, TEHAG announced it is extremely pleased with the release of the white paper titled “Thermal Energy Harvesting – the Path to Tapping into a Large CO2-free European Power Source”.

KCORC recently completed a major effort by publishing this white paper. It is very important context and background for everyone in the field of energy technology and it is really suggested to everybody to consider reading it, as it is very important that the general public and especially young professionals become more aware of the huge potential of these technologies and of the “thermodynamic crime” of wasting resources. Furthermore, taking into account the recent, latest Sixth Assessment Report, April 2022 of The Intergovernmental Panel on Climate Change (IPCC), it is five minutes until midnight and every possibility should be addressed to prevent a disastrous global warming of our planet.

The document takes a position on ORC technology and aims to capture information and ideas put forward by an enthusiastic and knowledgeable group of volunteers (academics, corporate professionals, researchers in government agencies), supported by various ORC- companies. The ultimate goal is to make a substantial contribution to solving the global climate problem and improving society in general.

The paper can be download here.

New Asimptote website launched!

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If you read this, the new website of Asimptote has been launched. We proudly present the result!

At Asimptote we never stand still and we are always working on development and improvement. We have been very busy behind the scenes with our new website and after almost 10 years of use, we have had a thorough overhaul of our website.

A beautiful new website, meeting all the requirements of modern times, has been set up in no time and we now are completely up-to-date and prepared for the future. The new website is responsive, which means that it adjusts for different screen sizes and viewports. As a result, it looks good on all devices!

HTTPS (Hyper Text Transfer Protocol Secure) appears in the URL as the website is secured by an SSL certificate. The details of the certificate, including the issuing authority and the corporate name of the website owner, can be viewed by clicking on the lock symbol on the browser bar.

A series of news items will now be visible on the homepage. Frequently new articles will appear about product innovations, developments in the energy market and technical treatises. Keep an eye on the news!

In the near future, some fine-tuning will be done to the texts and images and, of course, we are going for expansions of the product portfolio. Video tutorials have been started for our software to help novice users get started.

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Hydrofluoroolefins package extended

By News

In recent years, new fluids with a low global warming potential have been developed. These fluids are called hydrofluoro- and hydrochlorofluoroolefins (HFO and HCFO’s, respectively) and are developed as foam blowing agents, fire distinguishers, and working fluids for refrigeration, air conditioning, and heat pump systems. Furthermore, they are also suited for low temperature organic Rankine system machinery.

Hydro(chloro)fluoroolefins are unsaturated organofluorine compounds composed of hydrogen, fluorine, (chlorine) and carbon atoms. Some of the new fluids are just different isomers of the already existing ones. The isomers can differ in the orientation of hydrogen atoms and the trifluoromethyl groups. Although the difference between the isomers is subtle, their thermodynamic properties differ significantly. For example, the normal boiling points of HFO-1336mzz-Z and HFO-1336mzz-E are 33.4 °C and 7.5 °C and the critical temperatures 171.4 °C and 130.2 °C, respectively. In this case, the difference in thermodynamic properties of these isomers is mainly due to the difference in the polarity of the two molecules; the trans-isomer has a dipole moment close to 0 and thus is hardly polar, while the cis-isomer has a dipole moment of 3.2 Debye, which is well above the threshold whereby polar forces become significant.

Now the Hydrofluoroolefins Add-on of FluidProp has been updated and extended with new fluids. The new fluid package consists of the following fluids:

FluidProp name IUPAC name CAS Nr. Chemical formula
HCFO-1224yd-Z cis-2,3,3,3-tetrafluoro- 1-chloro-1-propene 111512-60-8 (Z)CF3-CF=CHCl NEW!
HCFO-1233zd-E trans-1-chloro-3,3,3-trifluoro-1-propene 102687-65-0 (E)CF3-CH=CHCl
HCFO-1233zd-Z cis-1-chloro-3,3,3-trifluoro-1-propene 99728-16-2 CF3-CH=CHCl NEW!
HCFO-1233xf 2-chloro-3,3,3-fluoro-1-propene 2730-62-3 CF3-CCl=CH2 NEW!
HFO-1234yf 2,3,3,3-tetrafluoro-1-propene 754-12-1 CF3-CF=CH2
HFO-1234ze-Z cis-1,3,3,3-tetrafluoro-1-propene 29118-25-0 (Z)CF3-CH=CHF NEW!
HFO-1234ze-E trans-1,3,3,3-tetrafluoro-1-propene 29118-24-9 (E)CF3-CH=CHF
HFO-1243zf 3,3,3-trifluoropropene 677-21-4 CF3-CH=CH2
HFO-1336mzz-Z cis-1,1,1,4,4,4-hexafluoro-2-butene 692-49-9 (Z)CF3-CH=CH-CF3
HFO-1336mzz-E trans-1,1,1,4,4,4-hexafluoro-2-butene 66711-86-2 (E)CF3-CH=CH-CF3 NEW!

The hydro(chloro)fluoroolefines are available for the freeStanMix, StanMix, and PCP-SAFT thermodynamic models in FluidProp. A limited set of these fluids are also available in the RefProp 10 Add-on (see overview of fluids on the FluidProp page).