Final answer:
Draft on a boiler is the difference in pressure between the atmosphere and the firebox or furnace, which allows for the flow of gases and enables combustion and exhaust processes.
Step-by-step explanation:
The term draft on a boiler refers to the flow of gases through the boiler during operation, and more specifically, the difference in pressure that enables this flow. In essence, draft is the difference in pressure between the atmosphere and the firebox or furnace, which causes air to flow into the firebox for combustion and flue gases to flow out of the chimney. This draft can be facilitated by temperature differences (natural draft) or mechanical equipment such as fans (forced or induced draft).
In the context of steam turbines, dramatic changes in pressure can significantly affect operational efficiency, as highlighted in the challenge problems. Specifically, a significant pressure difference, such as between the turbine chamber and the steam condenser, is necessary for the steam to pass through and turn the turbine, which is key for effective energy conversion.