A hollow cylinder has length L, inner radius r1, outer radius r2, and thermal conductivity k. The thermal resistance of the cylinder for radius conduction is
1
\(\frac{{\ln\;\left( {{r_2}/r_1} \right)}}{{2\pi kL}}\)
2
\(\frac{{\ln\;\left( {{r_1}/{r_2}} \right)}}{{2\pi kL}}\)
3
\(\frac{{2\pi kL}}{{\ln\;\left( {{r_2}/{r_1}} \right)}}\)
4
\(\frac{{2\pi kL}}{{\ln\;\left( {{r_1}/{r_2}} \right)}}\)