What role does a tube sheet play in a boiler?

A tube sheet is an essential component of a boiler, playing a critical role in its design and operation. Its primary function is to securely hold the tubes in place, providing structural support and helping to facilitate the flow of water and steam within the boiler system.

The correct choice emphasizes that the tube sheet holds the tubes but does not directly come into contact with the fire. This is significant because the tubes themselves are where the water is heated and turned into steam, and they must withstand high temperatures and pressures. The tube sheet must maintain the integrity of these tubes while remaining insulated from the extreme heat that could compromise its structure and the safety of the boiler.

In contrast, options suggesting that the tube sheet is exposed to fire or secrete steam do not accurately reflect its role. The tube sheet's design focuses on providing a barrier that prevents the heat from affecting its material while ensuring the tubes are well-aligned and securely attached for effective operation.