In a thin walled heat exchanger with no fouling, the overall heat transfer coefficient is
1
\(A{\left( {h_i^{ - 1} + h_o^{ - 1}} \right)^{ - 1}}\)
2
\({\left( {h_i^{ - 1} + h_o^{ - 1}} \right)^{ - 1}}\)
3
\(A\left( {h_i^{ - 1} + h_o^{ - 1}} \right)\)
4
\(\left( {h_i^{ - 1} + h_o^{ - 1}} \right)\)