Teus van der Stelt

Novec 649^TM 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 649^TM are less than that of pentane, applied in the previous example.

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 649^TM 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 649^TM 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 649^TM 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 649^TM. 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 649^TM/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 649^TM 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 649^TM/nitrogen mixture with 70 mole-% Novec 649^TM. 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 649^TM/nitrogen mixtures.

Figure 5: Phase envelope of the Novec 649^TM/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 649^TM in particular, please contact us. Furthermore, you can find more information about Cycle-Tempo and FluidProp on this website.

References

¹⁾ Georgios Kasapis, Shangze Yang, Zachary Falgout, Mark Linne, A study of Novec 649^TM 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: https://doi.org/10.1063/5.0106473

²⁾ Shangze Yang, Georgios Kasapis, Mark Linne, Reflectivity of diffuse, transcritical interfaces, Experiments in Fluids (2022) 63:137, DOI: https://doi.org/10.1007/s00348-022-03492-9

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: https://doi.org/10.1021/acs.jced.7b00217

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 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.