The overall heat transfer coefficient based on the outside surface area of a tubular heat exchanger decreased due to fouling during operation from $1000 \mathrm{~W} \mathrm{~m}^{-2} \mathrm{~K}^{-1}$ to $800 \mathrm{~W} \mathrm{~m}^{-2} \mathrm{~K}^{-1}$. The fouling film coefficient of the heat exchanger in $\mathrm{W} \mathrm{m}^{-2} \mathrm{~K}^{-1}$ is_____________

The overall heat transfer coefficient based on the outside surface area of a tubular heat exchanger decreased due to fouling during operation from $1000 \mathrm{~W} \mathrm{~m}^{-2} \mathrm{~K}^{-1}$ to $800 \mathrm{~W} \mathrm{~m}^{-2} \mathrm{~K}^{-1}$. The fouling film coefficient of the heat exchanger in $\mathrm{W} \mathrm{m}^{-2} \mathrm{~K}^{-1}$ is_____________

127