Psychrometric process — specific humidity during sensible cooling During sensible cooling of air (no condensation occurs), how does the specific humidity (humidity ratio) change?

Introduction / Context:Sensible cooling reduces air temperature without removing moisture. It is common when air is cooled but kept above its dew point, such as pre-cooling before dehumidification.

Given Data / Assumptions:

• No moisture is condensed; coil surface temperature remains above the air’s dew point.
• Process is steady and adiabatic with respect to mass transfer of water.

Concept / Approach:Specific humidity w equals the mass of water vapour per mass of dry air. If no condensation occurs and no water is added, the mass of water vapour remains unchanged, so w is constant. On a psychrometric chart, the process line moves horizontally to the left (lower dry-bulb) at the same w.

Step-by-Step Solution:

Verification / Alternative check:Compare with cooling and dehumidification: when the coil is below dew point, the process line descends leftward, reducing w as condensate is removed.

Why Other Options Are Wrong:Any change in w implies mass transfer of water; that does not occur in pure sensible cooling.

Common Pitfalls:Assuming relative humidity constant; it actually increases as temperature drops at constant w, potentially approaching saturation if cooling continues.

Final Answer:

remains constant