ANS:A - natural

When the temperature and humidity of the air are low, it indicates that the air has a lower moisture content and is generally cooler. In such conditions, the use of a natural draft cooling tower is often preferred. Here's why:

1. Natural Draft Cooling Tower:
   • Natural draft cooling towers rely on the natural buoyancy of air to induce airflow through the tower.
   • They typically have a tall chimney-like structure that allows warm air to rise and draw in cooler air from the surroundings.
   • The airflow in a natural draft cooling tower is driven by the temperature difference between the warm air inside the tower and the cooler air outside.
   • In low temperature and humidity conditions, the natural buoyancy effect is still effective in inducing airflow, making natural draft cooling towers suitable for use.
2. Forced Draft Cooling Tower:
   • Forced draft cooling towers use mechanical fans or blowers to force air through the tower.
   • They are more commonly used in situations where natural draft is not sufficient to provide the required airflow rate, such as in high-temperature or high-humidity environments.
   • While forced draft cooling towers can provide precise control over airflow, they require energy to operate the fans, making them less energy-efficient compared to natural draft cooling towers.
3. Induced Draft Cooling Tower:
   • Induced draft cooling towers use mechanical fans to draw air through the tower from the top, creating a negative pressure or suction effect.
   • They are commonly used in various temperature and humidity conditions and offer advantages such as compact design and flexibility in placement.
   • However, induced draft cooling towers may still require energy for fan operation, similar to forced draft cooling towers.