Tuesday, 10 May

This Week's Seminar was on Scroll Expanders

The QGECE seminar of this week was from Braden Twomey. Braden's Post-Graduate research topic is modelling of the dynamic behaviour of the QGECE/Verdicorp Portable Test Plant. The QGECE/Verdicorp Portable Test Plant is expected to be ready for testing by the ned of the yuear. In the meantime, Braden has been developing his modelling and testing skills using a scroll expander.

Scroll compressors are used in small air conditioning systems. They are mass-produced and therefore are relatively inexpensive. Running a scroll compressor in reverse, one gets a cheap expander. In fact, if one has access to a hot spring and a pond for cooling the condensers, it is easy to build a small homemade geothermal power plant using a second-hand scroll compressor and heat exchangers. Scroll expanders are positive displacement expanders and the fluid is expanded by being passed from one chamber to another as one scroll rotates within a fixed scroll. This is shown in the following figure, which is the reverse animation of a scroll compressor.

As an introduction to his Thesis, Braden Twomey has been modelling a scroll expander for the last several months and recently he ran some tests to compare against his modelling. Today he talked about his results. His first series of runs was with compressed air to expeirmentally identify a number of geometric variables about his particular scroll expander. He wil be running a refrigerant loop next in a true simulation of a small geothermal power plant.

 

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