Which of the following is NOT one of the five fundamental requirements for boiler design?

In the context of boiler design, the five fundamental requirements typically emphasize aspects that directly impact the performance, functionality, and safety of the boiler system. Reliability, safety, and cost are critical considerations that engineers prioritize to ensure that a boiler operates efficiently, maintains structural integrity, and remains safe for operation.

Reliability is essential because a boiler must consistently perform its intended function without failure, ensuring that it can withstand various operational stresses. Safety is paramount, as boilers operate under high pressures and temperatures, necessitating design features that prevent accidents and protect users. Cost is also a significant factor, as budget constraints influence the design decisions that affect material selection, manufacturing processes, and overall lifecycle expenses.

Appearance, while it may hold some importance in aesthetic considerations for specific installations, does not fall under the fundamental requirements fundamentally related to the safe and efficient operation of a boiler. Instead, the primary focus for engineers is on performance, reliability, safety, and economy, thereby making appearance a secondary concern in the boiler design process. This distinction underscores why appearance is considered the option that does not align with the core requirements of boiler design.