Final answer:
An exhaust fan positioned close to the ceiling, like B's, will be more effective than one positioned on a window lower down, like A's. This is because hot air rises to the ceiling, and having a fan in that location will directly expel the hot air and increase ventilation.
Step-by-step explanation:
The effectiveness of an exhaust fan in expelling hot air is primarily dependent on the location and movement of air within the space. Hot air naturally rises due to its lower density compared to cooler air. Therefore, an exhaust fan positioned near the ceiling, as in B's kitchen, will be more effective in expelling hot air because it is closer to where the hot air accumulates. This aligns with the principle of convection, which is the transfer of heat by the movement of a fluid (including air) where the warmer part of the mass will rise and the cooler portions will sink.
Additionally, it is important to increase ventilation in order to reduce the levels of pollutants and to bring in cooler air from the outside. This is where positioning plays a crucial role. Since hot air collects near the ceiling, B's exhaust fan will more effectively remove the hot air and consequently draw in cooler air from lower points of the kitchen, such as windows or open doors, or from air conditioned parts of the building.
Understanding that warm air rises and that an exhaust fan's primary function is to remove this warm air will also help in knowing why we feel refreshed when using a fan. The fan aids in moving warm air away from our body, replacing it with cooler air and enhancing evaporation, which makes us perceive a cooling effect.