SpinOffs

In the chiller industry, the evolution of centrifugal compressor chiller cycles has led to an interesting and powerful cycle and related compressor configuration which involves reinjection of refrigerant between stages. Such systems are thermodynamically identified broadly as cascade cycle options and have the common objective of improving the Coefficient of Performance (COP) of the standard refrigeration cycle.

Super critical carbon dioxide power (sCO₂) cycles are attracting a lot of interest these days all over the world. Many initiatives using various levels of private and public funding are in progress in several countries right now. Preliminary testing on small scale units have shown that such systems are technically viable. The next round of larger scale testing under way now will determine if the concepts are financially viable as well.

Turbomachinery is used in a very wide variety of industries and applications.   While applications like aerospace ‘jet engines’ or powerplant steam turbines are the applications that come to mind for a lot of people, turbomachinery is integrated with or buried in a huge range of other equipment, and often transparent to the user.   I give a talk to local middle school sciences classes on what turbomachinery is, and give a quiz at the end of the talk where I ask them to list every piece of turbomachinery in their home. The students have surprised me with their understanding and reasoning ability, and I now have a list of 20 to 30 examples of turbomachinery running in their homes.

When designing a turbomachine, the best analytical approach is not necessarily the most accurate method possible, but the one that will generate the best candidate design in the time and budget available.  It makes little sense to do analytical work down to a 1/10% accuracy,  while ignoring candidate designs that might yield improvements 20 times that amount if they were considered in the first place.  Mastering the art of modern engineering requires an intuitive sense for the cost and accuracy of a given analytical method, and knowing when to move between them. 

In many instances, the design of new turbofan engine is an iterative process of optimizing engine cycle parameters (i.e. thermodynamics) and executing  preliminary design geometry of engine components (i.e. aero design, constrained with structural, manufacturing, fitting in engine layout, size, weight  & other requirements) for the best performing  realizable  solution.  Consideration of the preliminary design of the engine in the totality of these requirements seems to be an interesting topic to address.

 Coupling cycle calculations with detailed preliminary design of turbomachinery components for getting optimized turbofan engine is the topic of this article. Detailed preliminary design means generating geometry and getting flow data and performance for each component of the multistage geometry of the engine, sufficient in the scope to move design process to 2D and 3D considerations.

Why supercritical CO₂?

Super critical carbon dioxide (sCO₂) is one of the hottest topics in the turbomachinery world right now.  From my own experience, I remember when the subject occupied a few sleepy sessions at the ASME Turbo Expo several years back.  Today, its possible to spend the entire week at the conference and never leave a well-attended session dedicated specifically to sCO₂.