What type of water system is commonly used in water-tube boilers?

Water-tube boilers typically utilize a closed-loop water system. This system circulates water through the tubes that absorb heat from the combustion of fuel in the boiler. The water in this system is heated to high pressures and temperatures, producing steam that can then be used for various applications, such as heating or powering turbines.

A closed-loop system is advantageous because it prevents the loss of water and minimizes the risk of contamination. It allows for controlled conditions, which enhances efficiency and safety. The closed nature means that once the water circulates through the system, it is continuously reused, making it an efficient choice for industrial and marine applications where water resources and system reliability are critical.

The other types of systems mentioned, like open-loop systems and evaporative systems, operate differently and would not provide the same efficiency or effectiveness in a boiler context. An open-loop system, for example, would introduce fresh water and discharge wastewater, which is less efficient and can be problematic in terms of water quality management.