SpinOffs

In my last blog I wrote about visiting a local middle school to give a talk on ‘What is Turbomachinery, and How Does It Work?’   The quiz at the end of the talk was for the students to list all the turbomachinery in their home. I had a few examples in mind to get the list started but was impressed with how long of a list we were able to generate after the students thought about it for a while. Since then the list has grown to include 40 items.   I will present those 40 below, but first let me repeat the assignment and the ground rules to see if you can think of more:

1. List every piece of turbomachinery in your home.
2. Inside and outside (in your yard is OK).
3. Positive displacement equipment is OK to list.
4. Don’t include turbomachinery in your cars or any vehicle or wheeled yard equipment (that’s another list…)

On occasion I’m invited to a local middle school to give a talk to one of the science classes about ‘What Is Turbomachinery, and How Does It Work?’.   I teach in several of the turbomachinery design courses we give at Concepts NREC, and while I’m comfortable in those courses, presenting at this level was different. I originally found it a challenge to come up with a good presentation that would keep the students' attention, while still providing some science education as requested by the science teacher that invited me. Derivation of the Euler turbomachinery equation was probably out. The attention getters that seemed to work best to get the conversation going included bringing our turbocharger cut-away (definitely the biggest hit of anything I brought), along with other interesting impeller samples. From there getting into the purpose of various types of turbomachinery (compressor vs turbine vs pump) and a very high level discussion of energy transfer to/from a fluid, seemed to flow. Getting them thinking about some of the physical aspects of turbomachinery operation (Just how fast is 100,000 rpm?) also seemed to keep their attention.

Here at Concepts NREC, we work on a wide range of turbomachinery components designed for fluids ranging from gases to liquids, including supercritical fluids like supercritical CO₂ which have properties of both gases and liquids.   We do a lot of pump design, consulting work and education. In fact our annual course on Centrifugal and Axial Pump Design is consistently one of the most popular.   Many engineers in the gas compressor industries consider pump design plain vanilla, without the added complexities of Mach number effects, but there are reasons why our pump course is so popular – pump design can indeed be very difficult, with a number of complicating factors that are unique or especially critical to the pump industry.

A small turbine (for ORC, air liquification processes) , operating with low volumetric flows at inlet and significant pressure ratio in a single stage configuration (to reduce costs) is often associated with flow of media with transition from liquid to gas-liquid state, with operating levels of Mach numbers above 1.8 at nozzle exit, that assumes convergent-divergent nozzle geometry, and may require partial admission.

This blog article is a follow up for the earlier blog “Coupled Optimization of Preliminary Design Geometry of Low Flow  Steam Turbine with Curtis Stage Layout and Rankine Cycle Parameters”, which considers more complicated case  of coupled optimization of regenerative Rankine cycle and 2 stage turbine geometry with change from partial to full admission flow.

Designing turbines for low flow Rankine Cycle for steam is challenging due to their small size, manufacturing restrictions, clearances and cost constraints. Such turbines operate at significant pressure ratios that require use of partial admission and are likely to operate in choked supersonic flow mode due to reduced stage count (controlled by cost).