ANS:A - keeping the heat transfer surface clean.

Keeping the heat transfer surface clean in a heat exchanger is crucial for maintaining high heat transfer efficiency and achieving energy conservation. Here's why:

1. Minimizing Fouling: Over time, heat transfer surfaces can accumulate deposits, such as scale, sediment, biological growth, or other contaminants. This accumulation, known as fouling, acts as an insulating layer that impedes heat transfer between the fluid and the surface. By keeping the surface clean, fouling is minimized, allowing for more efficient heat transfer.
2. Reducing Thermal Resistance: Fouling increases the thermal resistance at the surface-fluid interface, thereby reducing the overall heat transfer coefficient. This means that for a given temperature difference between the fluid and the surface, less heat is transferred across the surface. By keeping the surface clean, the thermal resistance is minimized, and heat transfer efficiency is improved.
3. Optimizing Performance: A clean heat transfer surface ensures that the heat exchanger operates at its designed capacity and performance levels. It helps maintain the desired temperature profiles, flow rates, and pressure drops within the system. This optimization leads to energy conservation by ensuring that the heat exchanger operates efficiently without unnecessary energy losses.
4. Preventing Corrosion: In addition to fouling, corrosion of the heat transfer surface can also degrade heat transfer efficiency. Corrosion creates rough surfaces or pits, which disrupt the fluid flow and reduce the effective surface area available for heat transfer. Keeping the surface clean helps prevent corrosion and maintain the integrity of the heat exchanger.

Overall, by keeping the heat transfer surface clean, heat exchangers can operate more efficiently, leading to energy conservation, reduced operating costs, and prolonged equipment life. Regular maintenance practices, such as cleaning and inspection, are essential for ensuring optimal heat exchanger performance and achieving energy efficiency goals.