Which of the following is a method of heat transfer?

Convection is a method of heat transfer that occurs through the movement of fluids (liquids or gases). It involves the transfer of heat by the physical motion of the fluid itself. When a fluid is heated, it becomes less dense and rises, while cooler, denser fluid sinks. This creates a circulation pattern that effectively transports heat. For instance, in a boiler system, water is heated, becomes less dense, and rises, allowing cooler water to move in and be heated as well, ensuring efficient energy transfer.

The other options, while related to thermal processes, do not describe methods of heat transfer. Condensation involves the change of state from gas to liquid and is typically a consequence of temperature changes rather than a means of transferring heat. Compression refers to the increase in density of a substance, usually through mechanical means, and does not directly denote a heat transfer method. Centrifugation is a technique used to separate substances of different densities using centrifugal force and is not a means of transferring heat. Understanding convection and its role in heat transfer is crucial for effective boiler operation and system efficiency.