Final answer:
The chimney's T-shape and crosspiece exploit Bernoulli's principle to draw up gases, augmented by convection from heating.
Step-by-step explanation:
The upward movement of air within the chimney is due to Bernoulli's principle and the phenomenon of convection. Chimney pipes with a T-shape feature a crosspiece that creates faster-moving air over the top when there is a breeze, leading to a decrease in pressure above the chimney due to Bernoulli's principle. This pressure difference between the bottom and top of the chimney aids in drawing the gases upwards as it generates an upward force on the air inside the chimney. Additionally, as the air within the chimney is heated by a source, like a furnace or fire, its volume increases and density decreases according to Charles's law, which causes the warmer, less dense air to rise naturally.
In the case of the T-shaped chimney pipe, the crosspiece on top creates a constriction that accelerates the air passing through it. This increase in velocity results in a decrease in pressure above the crosspiece. As a result, the pressure inside the main chimney pipe becomes higher than above the crosspiece, creating an upward force that draws up the gases.