In Regnault’s app

Regnault’s apparatus is an excellent apparatus to measure the amount of heat energy required to change the temperature of a solid body by a known amount.

In Regnault’s apparatus the inlet is near the top and the outlet is near the bottom as steam enters at inlet and leaves in liquid phase at outlet.

When the steam enters at inlet, it loses heat, in which a part of steam condenses back to water.

On the other hand, the part of hot steam after losing heat gets denser and moves down towards the bottom.

So outlet must be in bottom as liquid lies below the steam.