Isothermal Models comparison

Discussion on Stirling or "hot air" engines (all types)
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Joined: Thu Apr 12, 2018 4:01 am

Isothermal Models comparison

Post by omblauman » Wed May 09, 2018 9:10 am

I was curious to see what a simple isothermal model would predict for my S engine, i am talking about the often called Schmidt analysis
Looking on the web I found a few web page, or spreadsheet, calculators which have the machinery in place to calculate all relevant parameters and are free:
1) Herzog - ... index.html#
2 )Solar Heat Engines - ... simulator/
3) Urieli - ... ermal.html which I will not consider since it doesn't give a result in closed form but only in terms of integrals
4) van Dormael worksheet
5) K.Hirata - ... implee.htm

First question: does anybody know of others? Have their reliability/ease-of-use been tested?

Second question: how to enter certain parameters

In model 1 it's not clear to me where does the work cylinder volume enters
these were my input data for an output of 6.5J per cycle
Engine Type gamma
Type of gas air
T heater 500.00 [ K ]
T kooler 300.00 [ K ]
Phase Lag 90.00 [ ° ]
Aver P 78.00 [ kPa ]
Clear comp sp 15.00 [ cm³ ]
Swept comp sp 78.00 [ cm³ ]
Clear expan sp 10.00 [ cm³ ]
Swept exp sp 750.00 [ cm³ ]
Vol kooler 50.00 [ cm³ ]
Vol reg 50.00 [ cm³ ]
Vol heater 50.00 [ cm³ ]

In model 2 the input /output table for the same parameters is the following
Screen Shot 2018-05-09 at 17.39.28.jpg
Screen Shot 2018-05-09 at 17.39.28.jpg (90.73 KiB) Viewed 3815 times
engine energy /cycle 2.1 J

In model 4 the same input seems to yield 4.25 J
Untitled.jpg (322.46 KiB) Viewed 3815 times
In model 5 one doesn't even enter the work cylinder volume! anyway with the same parameters as above I got 3 J/cycle

Model 1 was particularly obscure to me as far as volume definitions and I certainly misunderstood how to enter the work piston volume since at this large ratio of displacer to work volume I would expect the pressure dynamic to be independent from the work volume and the energy output proportional.

Lot's of other questions of course but the bottom line is to find out if there is a reliable calculator for such a simple case
Thanks, Oskar

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