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Specific Heat (Cp) Density Specific Gravity Specific Heat (Cp) Temp. Pressure Temp. Pressure Density
Substance Chemical
Symbol Mol.
Weight ° F BTU/lb Air = 1 BTU/lb °F lb/cu. ft Water = 1 BTU/lb °F °F psia °F psia lb/cu ft
Air -- 28.98 -317.8 88.2 1 0.241 0.08018
You are correct Bob, I always use the cp for BTU/LBm/F which as you and the chart point out is 0.241 BTU/Lbm/F(for 32F), and just assumed that's the units that Al was using. Should have read it more carefully Al's use of BTU/CubicFoot/F
I use BTU/LBM/F as that gives me the opportunity to throw in the air density (via the Lbm) to determine the heat transferred at various altitudes.
Ed
----- Original Message ----- From: "Bob White" <bob@bob-white.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Friday, October 21, 2005 9:25 PM
Subject: [FlyRotary] Re: specific heat of air
Hi Ed,
Al's number was .02 BTU/cu-ft. - F and your number is 0.241 BTU/lb - F.
Per the web site you mentioned, density is given as 0.08018 lb/cu-ft.
So if I'm doing the conversion in the right direction:
0.241 X 0.08= 0.019 which is about 0.02.
Are both numbers correct?
Bob W.
On Fri, 21 Oct 2005 20:46:02 -0400
"Ed Anderson" <eanderson@carolina.rr.com> wrote:
Al, I went back to some of my spreadsheets and I have for constant pressure (Cp) as
0.25 BTU/Lbm/F
Here is web site which gives it as 0.241 BTU/LBM/F at 32F Sea Level
http://www.uigi.com/physical_prop_e.html
So looks like you have the decimal off a bit.
Sorry, it took me so long, been out at the aircraft all day putting on the new right gear leg, and brakes, etc.
Ed A
----- Original Message ----- From: Al Gietzen
To: Rotary motors in aircraft
Sent: Friday, October 21, 2005 2:59 PM
Subject: [FlyRotary] specific heat of air
Ed, or Bill, or somebody; help me out here. I was reviewing my calcs for air flow requirements, and find I used 0.02 Btu/cu. ft -F for the specific heat of air. I don't know where that came from, and can only find it in joules/Kg - K. By the time I do all the conversions to British units and mass to volume I now get quite a different number.
What is a good number for air at about 1 atmosphere and, say 90F; in Btu per cu ft per degree F?
Thanks,
Al
-- http://www.bob-white.com
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