This is done in "Thermal Mass Flow Controllers". It think 
they are quite accurate and are used in applications that 
cannot have the fluid flow disrupted by the measuring device 
(f.e., rotameters).

Hope this helps,
Mohit.
www.BioZen.co.in.

Dario Greggio wrote:
> We've been considering measuring air flow (at some 1-2 bar) by using a 
> temperature sensor (possibly a I2C one such as MCP9800) and maybe a 
> heater coupled to it.
> 
> Do you think it's doable with some good precision? Of course the other 
> method would be using a fan or alike and an encoder but it's quite more 
> complicated... :)
> 
> thanks for any tip!
> 
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