Final answer:
Proper air supply is essential for the combustion in gas-fired appliances, and entrainment devices help in mixing air with natural gas for efficient and safe operation. Examples include the gas nozzle in a Bunsen burner and the chimney in a water heater.
Step-by-step explanation:
Air supply to a gas-fired appliance is crucial for ensuring proper combustion and safety. In the context of such appliances, entrainment is a common method used to introduce air into the combustion system. Figure 12.5 presents examples of entrainment devices, which use increased fluid speed to create low pressures, thereby drawing one fluid into another. Examples include the adjustable gas nozzle of a Bunsen burner and the chimney of a water heater. Air is an essential component for the combustion of natural gas, where it combines with the gas to produce a controllable flame for heating purposes. Proper air supply is also necessary to prevent the incomplete combustion of gas, which can lead to the production of carbon monoxide, a dangerous gas. Hence, it's imperative to always ventilate and follow the manufacturer's instructions when using gas-fired appliances.