Electrolux (ammonia–water–hydrogen) refrigerator Why is hydrogen circulated in the Electrolux absorption refrigerator?

Introduction / Context:
The Electrolux absorption refrigerator uses ammonia as the refrigerant, water as the absorbent, and hydrogen as an inert gas. Understanding hydrogen’s role clarifies how cooling is achieved without a mechanical compressor.

Given Data / Assumptions:

• Evaporator contains liquid ammonia.
• Hydrogen is essentially insoluble in ammonia and water and acts as an inert gas.
• Total pressure in the low-pressure side is nearly constant.

Concept / Approach:
Hydrogen reduces the partial pressure of ammonia in the evaporator while keeping the total pressure nearly constant. Lower ammonia partial pressure reduces its saturation temperature, allowing it to evaporate rapidly at a very low temperature, thus absorbing heat from the refrigerated space.

Step-by-Step Solution:
Total pressure = p_total = p_NH3 + p_H2 (approximately).Introduce H2 → p_NH3 drops for the same p_total.Lower p_NH3 → lower saturation temperature → faster evaporation → more cooling.

Verification / Alternative check:
Dalton’s law in gas mixtures explains the partition of total pressure; reducing ammonia’s partial pressure directly lowers its boiling point at the evaporator.

Why Other Options Are Wrong:
(a) Equalising pressures is not the purpose; the system already operates near uniform low-side pressure. (b) Opposite to the actual effect. (d) No moving parts in the low-side that need hydrogen lubrication. (e) Hydrogen does not raise condenser pressure.

Common Pitfalls:
Confusing total system pressure with ammonia’s partial pressure; it is the latter that sets the evaporation temperature.

Final Answer:
to increase the rate of ammonia evaporation in the evaporator