Rapid cooling is achieved by maximizing the rate of heat transfer from the rice to the surroundings. Putting the bowl in a water bath (option C and D) allows for efficient heat transfer by conduction from the rice through the bowl to the water. Operating a fan (option B and C) increases the rate of convection of air over the surface, enhancing cooling. The combination of placing the bowl in water and using a fan is the most effective because the water bath provides good conductive heat transfer, and the fan significantly increases the rate of evaporation from the water's surface (which cools the water and thus the rice) and also enhances convective cooling of the rice itself.
On a day when I am in hurry to go to office, I have a fixed quantity of rice which was just cooked and kept in a bowl. In order to cool it quickly, which one of the following is the best option?
Asked in UPSC CDS 1 2024 · Topic: Heat and Thermodynamics (Modes of Heat Transfer (Conduction, Convection, Radiation))
Show answer
Answer: C. Let it be kept in a bowl of water (at room temperature) and operating a ceiling fan (or table fan) at full speed
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