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SUMMARY:The impact of internal heat transfer on the performance of air bre
 athing cycles - Rob Miller\, Cambridge
DTSTART:20150507T110000Z
DTEND:20150507T120000Z
UID:TALK58675@talks.cam.ac.uk
CONTACT:Catherine Pearson
DESCRIPTION:This presentation considers the effect of heat transfer betwee
 n fluid streams on the efficiency of air breathing cycles\, such as gas tu
 rbines.  To correctly characterize the effect of heat transfer requires th
 e definition of a new property\, ‘mechanical work potential’\, which i
 s a measure of the maximum useful work that can be extracted from a fluid 
 by an isentropic turbine exhausting to a fixed exit static pressure.  A ba
 lance equation for the property is developed.  The equation shows the surp
 rising result that entropy creation through thermal mixing has no effect o
 n cycle efficiency.  It does\, however\, show that a second heat transfer 
 term\, ‘thermal creation’\, does alter cycle efficiency.  Thermal crea
 tion occurs in regions of the turbine where heat transfer occurs across a 
 finite pressure difference.  The term is the non-linear version of the aco
 ustic energy creation term proposed by Lord Rayleigh in 1878\, and formali
 zed mathematically by Putnam and Dennis in 1954\, in their thermo-acoustic
  criterion.  The new method is used to examine the impact of heat transfer
  within a high pressure turbine\, of a gas turbine cycle\, on the cycles o
 verall efficiency.  It is shown heat transfer within the freestream\, betw
 een coolant and combustion products\, causes a negligible change in effici
 ency and therefore can be ignored in the design process.  The method also 
 shows that heat transfer from the freestream\, through the walls of the tu
 rbine blade and into the blade coolant passages\, results in ~0.5% rise in
  stage efficiency.  This is a significant and should be accounted for in t
 he design process.  The new property and balance equation offers a method 
 of analysing a broader range of air breathing problems.   
LOCATION:Open Plan Area\, BP Institute\, Madingley Rise CB3 0EZ
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