For a shell-and-tube heat exchanger, the clean overall heat transfer coefficient is calculated as $\text{250 W m$^{-2}$ K}^{-1}$ for a specific process condition. It is expected that the heat exchanger may be fouled during the operation, and fouling resistance of $0.001 \text{ m$^2$ K W}^{-1}$ is prescribed. The dirt overall heat transfer coefficient is __________ $(\text{W m$^{-2}$ K}^{-1})$.
- $100$
- $150$
- $200$
- $250$