Final answer:
Shell and tube and Double tube evaporators commonly require chemical treatment to prevent problems like scaling and corrosion, which can affect heat transfer and equipment lifespan.
Step-by-step explanation:
The question,"Which design of evaporators must be chemically treated?" relates to the engineering and maintenance practices of evaporators used in various industrial processes. The two designs of evaporators that typically require chemical treatment are the Shell and tube and Double tube designs. Chemical treatment is necessary to prevent scaling, corrosion, and fouling, which can impair heat transfer, reduce efficiency, and potentially lead to equipment failure.
The Shell and tube evaporators are widely used in many industries due to their robustness and efficiency in handling large volumes of vapors or liquids. They often contain many tubes which can accumulate deposits and require cleaning. The Double tube design, while less common, consists of two concentric tubes and can also face similar issues. Both designs demand routine chemical treatment to maintain optimal performance and prolong equipment lifespan.