[Author Prev][Author Next][Thread Prev][Thread Next][Author Index][Thread Index]

*To*: quattro <quattro@coimbra.ans.net>*Subject*: I/C Temperature Math - update*From*: "David G. Lawson" <dbldmnd@compuserve.com>*Date*: Sun, 23 Nov 1997 01:15:44 -0500*Sender*: owner-quattro@coimbra.ans.net

A few days ago I went through the baseline MC case which DeWitt throughly covered in his 'search for a baseline' post. But one thing caught my eye, both Scott M. and I got 80-82% efficiency numbers where DeWitt was showing 73-75% efficiency numbers. Scott and I used degrees F for our calculations and DeWitt used degrees C. Keep in mind that the data published in the SAE report 860103 which we have all mentioned is in degrees C. I think I found out the reason for the difference. Myself, and I think Scott, took the intake manifold temp and converted it to degF and then took the delta temp which the intercooler produced and converted it to deg F and then added them together to get the turbo outlet temp. I have included both the degC and degF calculations below. If you use deg C Tm = intake manifold temp = 38 degC (published Audi data) Dic = intercooler delta temp = 52 degC (published Audi data) Tco = turbo compressor outlet temp = Tm + Dic = 38 + 52 = 90 deg C = 194 degF If you use deg F Tm = intake manifold temp = 100.4 degF Dic = intercooler delta temp = 125.6 degF Tco = turbo compressor outlet temp = Tm + Dic = 100.4 + 125.6 = 226 degF Obviously different answers which vary by 32 degF. The difference comes about because when working with the i/c delta temp, we shouldn't be adding in the 32 degrees which you would normally do when converting from degC to degF, i.e. degF = degC*1.8 + 32 So if we choose to do our math in degF, we should only multiply the intercooler delta temp by 1.8 but not add 32. So the degF example becomes Tm = intake manifold temp = 100.4 degF Dic = intercooler delta temp = 93.6 degF Tco = turbo compressoroutlet temp = Tm + Dic = 100.4 + 93.6 = 194 degF For the tests Audi performed the ambient temp was 20 degC = 68 degF So the intercooler efficiency calculation becomes Eic = (Tco-Tm)/(Tco - Ta) = (194 - 100.4)/(194-68) = .743 = 74.3% efficiency This difference only manifested itself when the intercooler delta temp was converted from degC to degF like it is usually done. If Audi had published compressor outlet temps, we would not have noticed this difference. Now with Scott M.s data for his 1.8 bar modification which he presented last wed, his temps were actual numbers before and after the intercooler so the efficiency for his data shows Tm = intake manifold temp = 85 degF Tco = turbo compressor outlet temp = 210 degF Dic = intercooler delta temp = 210-85 = 125 degF Ta = ambient temp = 43 degF Eic = (Tco-Tm)/(Tco - Ta) = (210-85)/(210-43) = .749 = 74.9% efficiency So we now have some baseline numbers for the stock 2 pass intercoolers, in the stock system with 1.42bar, the intercooler is 74.3% efficient and in a 1.8bar modified system, the same intercooler is 74.9% efficient. Real data producing real efficiency numbers here. We are on the way to building a database of the stock 2 pass intercooler efficiency relative to increased boost pressure mods. Now if Scott M. could swap the 1.8 prom with a 1.95 prom and run the same set of tests, we could see if this real world in car test data would match the other numbers presented by Eric F. I'm taking some time off, keep these tech discussions moving and play nice. - Dave Lawson

- Prev by Author:
**ur-q vacuum brake conversion** - Next by Author:
**Re: ur-q vacuum brake conversion** - Prev by thread:
**Peter Fraser??** - Next by thread:
**I/C Temperature Math - update** - Index(es):