Final answer:
The chimney cap is the top element of a masonry chimney, with roles including improving draft and protecting the chimney. Bernoulli's principle explains how a T-shaped chimney cap can help draw up gases by creating a pressure difference when the wind blows over it.
Step-by-step explanation:
The chimney cap is the top element of a masonry chimney. In terms of functionality, a chimney cap serves several purposes such as preventing rainwater from entering the chimney, blocking downdrafts, and keeping animals out. Additionally, when designed with certain shapes such as a T-shape, a chimney cap can help improve the chimney's draft. This is explained by Bernoulli's principle, which states that an increase in the speed of a fluid occurs simultaneously with a decrease in pressure or a decrease in the fluid's potential energy.
When a breeze passes over the crosspiece of a T-shaped chimney pipe, it causes the air speed above the chimney to increase, which decreases the air pressure above the exit of the chimney. This pressure difference between the higher pressure inside the chimney and the lower pressure outside encourages the fireplace gases and smoke to move upwards and out. Such a design can enhance the performance of a chimney, ensuring a more efficient removal of combustion gases, and works well with modern wood stoves or other efficient devices that aim to prevent heat from just escaping through the chimney.