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Color of GT inlet duct : impact on performance on hot summer days ?

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alcor30

Mechanical
Jun 15, 2007
4
Dear all,

my colleagues and myself are in charge of detailed engineering a gas turbine project. The gas turbine will be located oudoor, in a hot and sunny region.

A this stage of the project, we will have to specify the painting color expected on the inlet and filtration duct.

Based on previous field experience, some people suggest that a white color is the best choice from a performance perspective. Because of its low radiation absorption coefficient, a white inlet duct is less sensitive to solar radiations.

According to some former operators, an inlet duct painted in white would slightly reduce the temperture of the air ingested by the compressor. On hot summer days, the benefit on compressor inlet temperature could reach up to -1°C, which would also mean addtional power output.

I am personnally not convinced that external color of the duct may really influence compressor inlet temperature... but it is not easy to bring a clear and convincing demonstration.

Any comment and operating feedback on this matter would be helpful.

Thanks to all of you.
 
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I'm not going to get too detailed, but you could make a few calculations based on solar emissivity of the inlet and how it affects air temperature and, subsequently, power output of the turbine.

Personal opinion, having a white inlet actually allows for easier damage identification of the housing (black car, white car example). Black shows dusts (which you probably don't care) and white offers higher contrast for visual inspection. Also, having a white painted body lowers thermal fatigue of the material being in a hot & sunny area, like Arizona. The Air Force Graveyard frequently uses white paint on the planes to keep them from experiencing such harsh thermal cycles, making the plane more worthy for reintroduction into an air wing if need be. Just a thought...

Kyle

Kyle Chandler

"To the Pessimist, the glass is half-empty. To the Optimist, the glass is half-full. To the Engineer, the glass is twice as large as it needs to be!"
 
Well, it will influence the inlet temperature-dark vs. light that is, but the question is; how much and is it really quantifiable. The theory is there and it is undeniable. Ever owned a black car? Ever owned a white car? But, considering the huge volume of air that a CT ingests and the poor heat transfer characteristics of flat plate, it is doubtful that you could even detect the increase in temperature of the inlet air stream.

All that said, I would go with the lighter color if it were my decision to make. Sorry, but any increase in inlet air temperature is too much increase in inlet air temperature in the case of a CT-especially one in a warm and sunny climate.

rmw
 
A light heat shield structure will help avoid concerns on this question.
 
I too seriously doubt that you could actually measure the difference in compressor inlet temp (CIT), between a black painted intake vs. a white painted intake, while running. However, we may wish to consider other variables, such as what effect the inlet duct inside temperature could be on unit shutdown, and subsequent re-starting. During those times, when airflow is low, a hotter inlet air temp could potentially upset the light-off fuel schedule, which seems to be particularily fussy, on the newer low-emissions type combustors. If the choice is yours to make, I suggest painting a lighter colour, but inlet restriction will have a bigger effect on the performance of the turbine. A couple inches of water column depression across the inlet system will have much greater effect on output than a dark coloured intake might have. Best thing you can do for your turbine unit is to verify adequate inlet system capacity.

j79guy
 
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