Re: [Phys-l] Insulation R-value

[Ludwik Kowalski <kowalskil@mail.montclair.edu>]

On Feb 17, 2006, at 11:57 AM, ALVIN BACHMAN wrote:

> R is related to the reciprocal of k.
>
>    dQ/dt= k A (T1-T0) / L  = A (T1-T0) / R
>
> For a set of slabs (same R) , of conductivity Ki and thickness Xi, R = 
> SUM(
> 1/KiXi )
>
> Units of k are  W/(mK)  and common units of R are BTU per sq-ft per 
> hour per
> F-deg,
> which is why everyone drops the units and says  R-19 or R-30, etc. )

Thanks Al, I was not aware that R is defined differently from k. 
Perhaps k should be called thermal konductivity and R should be called 
thermal Resistivity. We want house walls to be made from materials that 
have large R and small k. Right?

Ludwik Kowalski
Let the perfect not be the enemy of the good.