The heat transfer by conduction through a thick cylinder of inner radius r1, outer radius r2, Higher temperature T1, lower temperature T2, length of cylinder l and thermal conductivity k is given by

• A. \(\frac{{2\pi \;lk\;\left( {{T_1} - {T_2}} \right)}}{{2.3\log \left( {\frac{{{r_2}}}{{{r_1}}}} \right)}}\)
• B. \(\frac{{2.3\log \left( {\frac{{{r_2}}}{{{r_1}}}} \right)}}{{2\pi \;lk\left( {{T_1} - {T_2}} \right)}}v\)
• C. \(\frac{{2\pi \left( {{T_1} - {T_2}} \right)}}{{2.3\;lk\log \left( {\frac{{{r_2}}}{{{r_1}}}} \right)\;}}\)
• D. \(\frac{{2\pi \;lk}}{{2.3\;\left( {{T_1} - {T_2}} \right)\log \left( {\frac{{{r_2}}}{{{r_1}}}} \right)}}\)