Steam bath physics In the steam bath at the health club, why is the "steam" thicker first thing in the morning before it has been used all day and the walls are "hotter"?
 A: When you say it's "thicker" in the morning, do you mean it seems more foggy/cloudy when the bath is first turned on? I suspect someone more well-versed in steam-bath design can refine this, but here is a guess:
When the steam bath is first turned on in the morning, steam is vented into a room whose air and walls are initially at ambient temperature. As steam vents into the room for the first few minutes, nucleation occurs in the air and condensation occurs against the walls, warming both. The thermal mass of the air in a steam bath room is considerably less than the thermal mass of the walls, so the air will probably approach thermal equilibrium on the timescale of 10 minutes or so, whereas the walls will probably take a couple hours to approach their steady-state temperature. So, in the morning, you have a room full of hot steam with cool walls, and later in the day, you have a room full of hot steam with hot walls.
In the morning, the steam-laden room air supplies heat to the walls via two routes, condensation and convective cooling. Condensation against the walls removes water from the air, and the thermal energy of condensation mostly goes into the walls. Convective cooling, however, does not reduce the water content of the air, but it reduces its temperature. Water is then forced to nucleate slowly (in order to equalize its chemical potential between phases), forming the fog present in the mornings.
In the afternoon, the walls will have more closely approached thermal equilibrium, and so the cooling of the air due to convective heat transfer will be reduced. As a result, there will be less nucleation, and the room air will not have as many microscopic water droplets floating around, making it seem "thinner".
