SPOautos

Anyone know how much energy is required to raise the temperature of air? Lets say ambient is 75F and the temps at the outlet of the turbo are say 375F. How many Joules did it take to increase the temps that high?

The reason I'm needing to know is I'm working on a air/liquid IC and I need a good idea of the heat capacity it needs to be designed around.

Also, does anyone have any good information regaurding the IC inlet temps? I've heard as hot at 400F but the inlet pipe on a IC system is never anywhere close to that. They are usually less than 200F on the hot side so I can't imagine the charge air gets as hot as 400F. Whats your opinion?

Thanks,
STEPHEN

KevinK2

btu per lbm: Q = Cp(T2-T1), for const mass

T= degF
Cp air =.24 btu/lbm/degF

so for 75->375, Q= 72 btu/lbm

eng hp ~ fuel mass flow / bsfc

air mass flow = afr x fuel mass flow
= afr x enghp x bsfc

for afr=11.5, bsfc =.6 :

so air mass flow = 7 x eng hp, in lbm/hr

heat flow = Q' = btu/lbm x lbm/hr = btu/hr
= 72 x 7 x enghp
= 500 x enghp, in btu/hr
or
= .2 x enghp, in hp

mabe

SPOautos

Thanks for that info Kevin

anyone have any fairly solid infomation about the turbo outlet temps? To determine the BTU's or Joules in the charge air I really need to know the temperature differential. Say its 100F going into the turbo anyone have any idea of the temps at the outlet. Consider a large frame turbo within its efficiency range.

Also, would the actual weight of air go up as pressure goes up? I know the weight of 1000cfm of air at 175F is about 62lbs BUT thats at 1atm pressure, anyone know if it would double at 2atm pressure? I know the "force" would but is that the same? I need to know this cause to figure the BTU's that it took to raise the temperature of the air depends on the weight, like I said I have the weight at atm pressure but wondering if it goes up with pressure. Prob so since its more dense with molecules but does it double with atm pressure doubles?

Maybe I should have paid more attention in science class LOL

STEPHEN

maxcooper

Here's a thread about compressor outlet temps, including a spreadsheet I made to calculate them:
https://www.rx7club.com/showthread.p...hreadid=285228

-Max

SPOautos

Hey great Max, thanks a ton!!! I found some info online and some equations, ect and my numbers came out real close to what your showing. Looks like I need to figure about a 200-220F differential.

So anyone want to take a wager on how many BTU's or Joules it takes to increase the temp of air 200-220F? Keep in mind I'm designing this around 1000cfm of compressed air with a differential of 200F and a over all temp before the IC of 300F which obviously means 100F turbo inlet temps.

I think I have a close answer but it just seems SOOOO damn high that its almost unbelievable. My answer came out to be about 4000 BTU/MIN on average depending on the heat differential used. I think using 200F diff it was right around 3300BTU/MIN which is scary if you ask me. I dont know how a IC could exchange that much heat....guess it just takes a REAL big one LOL

STEPHEN

KevinK2

1000 cfm ingested into turbo implies about 700 hp. For 200F temp rise, thats 2/3 x .2 x 700 = 93 hp heat flow. Note that engine radiator would be shedding about 700 hp, so 93 doesn't seem so big.

Better reconsider cfm goal, or consider big mouth front and V-mount with vented hood and mega oil coolers, or ... very brief use of full hp.

SPOautos

Yep, thats real close. 93hp heat flow/hr would = right at 3900BTU/minute which is pretty much what I came up with as well.

The problem is with a a/l IC your heat exchanger core really needs to be about 4x larger than your IC core. About the most I've been able to come up with is about 2x the IC core and thats not going to be enough for long periods of on off boost. I might need to start getting more creative haha

STEPHEN

dubulup

What are dangerous air temps for our little engines? (at the stock location air intake temp sensor)