# Water, humity, temperature questions

## Main Question or Discussion Point

say there is a room 30 square meters by 2.5 meters high, completely insulated. if the room is at 25 degrees Celsius and 30% relative humidity then suddenly you bring in 10 liters of water at the same temperature and pour it on the floor; question is will the temperature of the room increase due to more energy being put in the room, decrease due to water evaporating and cooling the air, or stay the same as water is at same temperature as the air.

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russ_watters
Mentor
Sounds like homework. What do you think the answer is and why?

Sounds like homework. What do you think the answer is and why?
it actually isnt homework, i have completed a BE in mechanical about a year ago, i was just thinking about humidity and how it works.

i guess temperature would go up as you are adding more energy to the room, thats if the water has more energy at 25 degrees than air. thats what i think.

K^2
And how did that energy flow from 25°C fluid to 25°C air? Heat spontaneously flows from hot to cold. Always. No exceptions.

On the other hand, humidity is the rate of evaporation vs rate of condensation. At 100%, they are equal. Bellow that, evaporation is faster. Water at 25°C won't stay at that temperature in a 30% room. Work out what happens to the water, and you'll have your answer.

it actually isnt homework, i have completed a BE in mechanical about a year ago, i was just thinking about humidity and how it works.

i guess temperature would go up as you are adding more energy to the room, thats if the water has more energy at 25 degrees than air. thats what i think.
If you have completed a degree and ME and still can't figure this out, it is sad.

Temp. will decrease, that is the answer.

And how did that energy flow from 25°C fluid to 25°C air? Heat spontaneously flows from hot to cold. Always. No exceptions.

On the other hand, humidity is the rate of evaporation vs rate of condensation. At 100%, they are equal. Bellow that, evaporation is faster. Water at 25°C won't stay at that temperature in a 30% room. Work out what happens to the water, and you'll have your answer.
the water would evaporate and reduce the air temperature, floor temperature. but since this is a closed system when you are adding the water to that system which is at the same air temperature inside wouldnt the energy in that system increase? and there fore the room temperature would increase? if im wrong then im wrong, asking questions is how you learn

russ_watters
Mentor
but since this is a closed system when you are adding the water to that system which is at the same air temperature inside wouldnt the energy in that system increase? and there fore the room temperature would increase? if im wrong then im wrong, asking questions is how you learn
You're adding energy but you're also adding mass so the average energy doesn't change. Temperature is a function of average energy, not total energy - otherwise a big house would always be warmer than a small house.

the water would evaporate and reduce the air temperature, floor temperature. but since this is a closed system when you are adding the water to that system which is at the same air temperature inside wouldnt the energy in that system increase? and there fore the room temperature would increase? if im wrong then im wrong, asking questions is how you learn
Adding "energy" doesn't mean you have higher temperature. You have also changed the heat capacity of the system by adding water. Your reasoning is fallacious.

but since this is a closed system when you are adding the water to that system which is at the same air temperature inside wouldnt the energy in that system increase?
What is your definition of a closed system?