Relative Humidity and Temperature Changes when adding Heat

[john ryan]

Homework Statement

Can anyone help me with this?

-How much heat must be added to 3.5 m3 /s of moist air with a dry bulb temperature of 10°C and a relative humidity of 60% to raise the temperature of the air by 17°C?

• What will be the relative humidity of the air once this heat is added?

• What is the power required in the heating unit?

Relevant Equations

LIT

Can anyone help me with this?

-How much heat must be added to 3.5 m3 /s of moist air with a dry bulb temperature of 10°C and a relative humidity of 60% to raise the temperature of the air by 17°C?

• What will be the relative humidity of the air once this heat is added?

• What is the power required in the heating unit?

 

[phyzguy]

As stated in the forum rules, you must show some effort on the problem before we can help. What have you learned about heat capacity and how would you approach the problem? Also, note that the 3rd question cannot be answered unless there is some mention of how much time is allowed to raise the temperature.

 

[russ_watters]

This looks like HVAC/mechanical engineering homework to me. Have you learned how to use a psychrometric chart?

 

[hmmm27]

Once the temperature is up, steady power influx is needed to balance thermal losses to the environment. Not sure that's what they want though : there's no context given.

 

[mjc123]

This looks like HVAC/mechanical engineering homework to me. Have you learned how to use a psychometric chart?

That's presumably a psychrometric chart?

 

[russ_watters]

That's presumably a psychrometric chart?

Typo, yep, fixed.

 

[rude man]

As others have said, you need a psychrometric chart (or e.g. a p_V diagram) for water.

I would interpret part 1 as 3.5m^3 of water and ignore part 3.

 

[haruspex]

I would interpret part 1 as 3.5m^3 of water and ignore part 3.

Alternatively, read part 3 as "how much power ... if this to be done once a second?"

 

[rude man]

Alternatively, read part 3 as "how much power ... if this to be done once a second?"

See post 4.

 

[haruspex]

See post 4.

I don't see the problem. It is reasonably clear that the author intends this as an ongoing process. Moist air is coming in at $3.5m^3/s$ and has to be raised from 10C to 17C, and the last part asks for the power. It's just worded poorly, so it is unclear whether the first part is asking for a quantity of energy or power.

 

[rude man]

I don't see the problem. It is reasonably clear that the author intends this as an ongoing process. Moist air is coming in at $3.5m^3/s$ and has to be raised from 10C to 17C, and the last part asks for the power. It's just worded poorly, so it is unclear whether the first part is asking for a quantity of energy or power.

OK the air is moving at 3.5m^3/sec. Then asking for heat is meaningless; it's power that makes sense. I went with 3.5m^3 of air; then asking for heat made sense. Poorly stated but not as bad as what I thought.

 

[phyzguy]

I don't see the problem. It is reasonably clear that the author intends this as an ongoing process. Moist air is coming in at $3.5m^3/s$ and has to be raised from 10C to 17C, and the last part asks for the power. It's just worded poorly, so it is unclear whether the first part is asking for a quantity of energy or power.

This makes sense. When I made my comment in Post #2, I didn't see the "/s". I just read 3.5 m^3. Thanks for clarifying.