Broad use base and number of users both in industry and academia

Friendly, prompt and professional support

Continuously developed in cooperation with leading institutes

All Posts By

Teus van der Stelt

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

By News

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

By News

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.

Scientific publications, PCP-SAFT, and Novec 649™

By News

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:

Workshop thermo-chemical energy systems using Cycle-Tempo

By News

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

By News

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

By News

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!

By News

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.

We believe that we will be able to continue to serve our customers well in the future with our new website and hope that they can continue to find their way to us. And, of course: we would like to hear comments from our visitors and whether there are any other wishes in what we can offer.