railway RRB JE (CBT I + CBT II) Mock Test 2024 Heat Transfer Conduction Critical Thickness of Insulation
The critical radius of insulation for a spherical shell is
1
\(\frac{{{\rm{thermal\;conductivity\;of\;insulating\;material}}}}{{{\rm{heat\;transfer\;coefficient\;at\;the\;outer\;surface}}}}\)
2
\(\frac{{{2\times \rm{thermal\;conductivity\;of\;insulating\;material}}}}{{{\rm{heat\;transfer\;coefficient\;at\;the\;outer\;surface}}}}\)
3
\(\frac{{{\rm{thermal\;conductivity\;of\;insulating\;material}}}}{{{\rm{2 \times heat\;transfer\;coefficient\;at\;the\;outer\;surface}}}}\)
4
\(\frac{{{\rm{heat\;transfer\;coefficient\;at\;the\;outer\;surface}}}}{{{\rm{thermal\;conductivity\;of\;insulating\;material}}}}\)