Question

In summer, an air cooler is used in a room. To achieve maximum cooling efficiency, which of the following setups is best?

• A. Cooler fan facing the window, no salt in water
• B. Cooler fan facing away from window, no salt
• C. Cooler fan facing window, salt added to water
• D. Cooler fan facing away from window, salt added

Hint:

Think of an air cooler as a device that 'trades' air temperature for air humidity. To keep this trade going efficiently, you need a constant source of 'low-humidity' currency (fresh outdoor air) and a way to get rid of the 'high-humidity' product (by venting the room). Adding salt is like a tax on the transaction, making it less efficient.

Answer 1

The Correct Option is A

Step 1: Understanding the Question: This question asks for the best setup for an air cooler to maximize its cooling performance. This is a repeated concept from earlier questions (Q11, Q21).

Step 2: Detailed Explanation: To achieve maximum cooling efficiency with an evaporative cooler, we need to maximize the rate of water evaporation. This depends on two primary factors: 1. Ventilation: The cooler needs a constant supply of hot, dry air.
• Placing the cooler at an open window (fan facing the window) allows it to draw in fresh air from outside. This is the correct approach.
• Placing it away from a window (fan facing away from window) in a closed or poorly ventilated room causes it to recirculate the same air. This air quickly becomes humid, which dramatically slows down evaporation and cooling. 2. Evaporation Rate of Water: The properties of the water affect how easily it evaporates.
• Using pure water (no salt) allows for the maximum natural rate of evaporation.
• Adding salt (salt added to water) lowers the vapor pressure of the water. A lower vapor pressure leads to a slower rate of evaporation, which in turn reduces the cooling effect.

Step 3: Final Answer: The best setup combines both optimal conditions: placing the cooler at a window for fresh air intake and using pure water without salt.