What method is used to reduce the temperature of gases leaving a furnace?

In the context of reducing the temperature of gases exiting a furnace, all of the listed methods are viable and commonly used techniques. Spraying with water effectively lowers gas temperature through the process of evaporative cooling, as the heat from the gases is absorbed by the water, turning it into vapor. This method is particularly effective as it can significantly reduce the temperature quickly and is often employed in various industrial applications.

Dilution with cool air is another method wherein cooler air is mixed with the hot gases, which decreases the overall temperature of the gas mixture. This approach is straightforward and can be easily implemented in systems designed to manage emissions and heat.

Passing through heat exchangers is a more mechanized technique where hot gases are transferred through a system that captures the heat. This captured heat can sometimes be used for preheating combustion air or process fluids, thereby improving overall energy efficiency while reducing the temperature of the exiting gases.

Since each method plays a role in temperature reduction, the correct answer acknowledges that all of these techniques can be utilized either individually or in combination to achieve effective temperature management of gases from a furnace. This understanding highlights the importance of thermodynamic principles and technology in industrial processes.