Using waste heat effectively In which refrigeration system can waste heat be productively used to drive the cycle?

Introduction / Context:
Industrial plants often have low-grade waste heat that can be harnessed to drive cooling. The selection of a refrigeration cycle that uses heat rather than mechanical work is the key to improving overall plant efficiency.

Given Data / Assumptions:

• Waste heat is available as hot water, steam, or exhaust gases.
• Goal: use this heat to produce refrigeration.
• Systems compared: vapour compression, vapour absorption, and air cycles.

Concept / Approach:
Vapour absorption refrigeration (e.g., ammonia–water or lithium bromide–water) uses a thermal compressor (generator, absorber, solution pump) driven primarily by heat input. In contrast, vapour compression relies on mechanical compressors driven by shaft work. Air cycles (reverse Brayton) also require mechanical compression and are not heat-driven.

Step-by-Step Solution:
Identify the driver for each cycle: absorption → heat; compression/air → mechanical work.Where waste heat exists, absorption cycles can convert that into cooling effect by powering the generator.Hence, the correct choice is vapour absorption cycle.

Verification / Alternative check:
Combined heat and power (CHP) systems often integrate absorption chillers to utilize waste heat for chilled water production.

Why Other Options Are Wrong:
Vapour compression and air cycles require mechanical power; waste heat does not directly drive them. Thermoelectric systems are powered electrically, not by heat input.

Common Pitfalls:
Assuming that any “refrigeration system” can accept waste heat; in practice only absorption (and adsorption) systems are designed to be heat-driven.

Final Answer:
Vapour absorption cycle