[Gasification] tesla turbine

[Kevin Chisholm]

Dear Ken

Ken Boak wrote:
> Gents,
>
> I started reading Schmidt's paper and got to the bottom of page 2.
>
> I think I need an explanation of the term Isoentropic efficiency.  
Isotropic efficiency isthe efficiency at constant entropy. Entropy is a 
measure of disorder. The maximum efficiency you can get is when a heat 
engine runs under isotropic conditions. If a gas was at a pressure of 
550', and you had a flow of 1 pound per second, the the power you could 
generate would be 550 foot-lbs/second, or 1.0 HP. When you put it 
through your turbine, if you extracted .8 HP, then you would have 80% 
Isotropic efficiency. (Assuming no heat losses from teh system. Well 
designed expansion turbines are typically in the range of 80% to 90% 
Isotropic efficiency.
> Page 15 
> states
>
> Isoentropic turbine efficiency = shaft power / energy in the heated 
> compressed gas  entering the turbine relative to ambient conditions.
>
> Further to the report on page 7, it states that compressed air was available 
> at up to 290 psig at 500cfm, and a head of 80psi was maintained so as to run 
> the combustor at 40 psig. Running a compressor to meet these requirements 
> consumes considerable energy in its own right.   During test runs, between 
> 9600 and 15,000 standard cu ft /hr of air was consumed at above 40psig - all 
> this has to be deducted from the efficiency figures.  A rough estimate 
> suggests that a 16kW compressor would be needed to supply the lower of these 
> two figures at only 40psig!   The tesla turbine would probably spin on the 
> airflow alone without introducing gaseous fuel !
>   
If there were no compressor or combustion chamber losses, the work 
required to compress the air is fully recovered by the work turbine. For 
example, in this case, we could have a 100 HP net output power turbine, 
that actually generated 140 HP, of which 40 HP was used for driving the 
air compressor.
>
> Two cases stated:
>
> (1) Running on natural gas with a firing rate of 173,000 BTU/hr   Power = 
> 4.6hp
>
> (2) Running on biomas at 192,600 BTU/hr Power = 4.3 hp
>
> 1 hp/ hr  = 2544.43 BTU
>
> So efficiency (1)  = (4.6 x 2544.43)/ 173000   = 6.765%    ( Isoentropic 
> eff. 12.25% quoted)
>
> So efficiency (2)  = (4.3 x 2544.43)/ 192600   = 5.68%      ( Isoentropic 
> 11% quoted)
>   
The Isotropic efficiency of the turbine is one thing... it could perhaps 
expand teh gases at say 80% efficiency. However, there are other losses 
and inefficiencies. For one, the system is not adiabatic... there are 
heat losses from the system. For another, there are the carnot cycle 
limitations
> Whilst Schmidt concludes that the isoentropic efficiency needs to rise,  I 
> cannot see any startling results with the thermo-mechanical efficiency that 
> would get me excited over this device in its current state.
>   
It is hard to get enthused about 6% efficiency.
> However to its merit is its simplicity and the reduced requirement for gas 
> treatment following a gasifier.
>   
Small turbines are a real snot to operate... they need very high speeds. 
The problem with high speed is blade erosion, so it is important that 
ash and particulate matter levels be low.

Best wishes,

Kevin
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> Ken
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