Question

To increase cooling efficiency of an air cooler, which setup is best?

• A. Fan towards open window, no salt in water
• B. Fan away from window, no salt
• C. Fan towards window, salt added
• D. Fan away from window, salt added

Hint:

For air cooler efficiency questions, remember two rules: 1. Maximize Ventilation: Always bring in fresh, dry air from outside. 2. Maximize Evaporation Rate: Use pure water. Avoid adding solutes like salt.

Answer 1

The Correct Option is A

Step 1: Understanding the Question: The question asks for the optimal setup to maximize the efficiency of an air cooler, considering ventilation and water properties. This is a rephrasing of Q-11.

Step 2: Detailed Explanation: Two main factors determine the efficiency of an evaporative cooler: 1. Air Supply (Ventilation): The cooling effect is proportional to the amount of water that can be evaporated. Evaporation is most effective when the incoming air is dry (low humidity).
• Fan towards open window: This phrasing implies the cooler is placed at an open window, drawing in fresh, dry air from outside and blowing cool air into the room. This continuous supply of fresh air is essential for sustained evaporation and cooling.
• Fan away from window: This implies the cooler is placed inside the room, merely recirculating the air. The room air will quickly become saturated with humidity, stopping the evaporation process and rendering the cooler ineffective. Therefore, proper ventilation by placing the cooler at a window is crucial. 2. Water Properties (Effect of Salt): The goal is to have the water evaporate as quickly as possible.
• Adding salt (a non-volatile solute) to water lowers its vapor pressure.
• A lower vapor pressure means a slower rate of evaporation.
• Slower evaporation means less heat is drawn from the air per unit time, leading to reduced cooling efficiency. Therefore, using pure water (no salt) is best.

Step 3: Final Answer: Combining these two points, the best setup is to place the cooler at an open window (fan towards open window) and use water with no salt added. This matches option (A).