Phase change technology is used to absorb heat during cooling by using which medium?

• A. Use dry ice
• B. Use cool packs as the cooling medium
• C. Use liquid nitrogen
• D. Use ambient air

Answer: (B)

Phase change materials absorb heat most effectively when they melt, because they store a large amount of energy as latent heat while the temperature stays near the material’s melting point. Cool packs are designed with these phase-change substances, so as they absorb heat from a warmer object, they melt and pull heat away without a big temperature swing. This makes them a practical, portable, and reusable cooling medium.

Dry ice relies on sublimation (solid turning directly into gas), which is a different heat-transfer mechanism. Liquid nitrogen boils at extremely low temperatures, also a different approach and not as practical for routine cooling with stable, moderate temperatures. Ambient air provides no phase-change cooling. So the packs containing phase-change material are the best fit for absorbent, controlled cooling.