In industrial heat exchanger design, the overall heat transfer coefficient $U$ is estimated from the equation
$$ \frac{1}{U}=\frac{1}{h_{i}}+\frac{1}{h_{o}}$$
where $h_{i}$ and $h_{o}$ are the convective heat transfer coefficients on the inner and outer side of the tube, respectively. This is valid for ___(i)___ tube of _____(ii)____ thermal conductivity.
Which one of the following is the CORRECT option to fill in the gaps (i) and (ii)?
- (i) thick-walled, (ii) high
- (i) thin-walled, (ii) high
- (i) thin-walled, (ii) low
- (i) thick-walled, (ii) low
