Water-tube boiler is the one, in which

ANS:A - water passes through tubes and flue gases around it.

A water-tube boiler is a type of boiler where water flows inside the tubes that are surrounded by hot combustion gases. This design is in contrast to fire-tube boilers, where the hot gases flow inside the tubes and the water surrounds them. Water-tube boilers are known for several advantages:

1. Efficient Heat Transfer: Water-tube boilers offer efficient heat transfer due to their design, which allows for a large surface area of water to be exposed to the heat from combustion gases. This leads to faster heating and higher steam production rates.
2. Higher Pressure Capability: Water-tube boilers are capable of operating at higher pressures compared to fire-tube boilers. This makes them suitable for applications where high-pressure steam is required, such as power generation and industrial processes.
3. Reduced Risk of Explosion: Water-tube boilers have a lower risk of catastrophic failure compared to fire-tube boilers, as the water contained within the tubes acts as a natural barrier between the combustion gases and the surrounding environment.
4. Flexibility in Design: Water-tube boilers come in various designs and configurations, allowing for flexibility to meet specific application requirements. They can be designed for various fuel types, capacities, and operating conditions.
5. Ease of Maintenance: Water-tube boilers generally have easier access for inspection and maintenance compared to fire-tube boilers. This facilitates routine maintenance tasks and reduces downtime.