heat flow of dry vs. moist air.

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chuckdonaldson
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Joined: Mon Jan 03, 2011 6:45 pm

heat flow of dry vs. moist air.

Post by chuckdonaldson »

Given: I am heating ambient air from 60 F. to 130 F. then transporting the air about 20 ft. through a 4" duct to my basement.

Questions:
1. How can I increase the heat carrying ability of the air such that I could use a smaller duct (less flow) and still move the same amount of energy?
2. What are the consequences of injecting water into the heater and increasing the relative humidity to near 100%?

I get conflicting answers and am not versed in the science enough to figure it out. It seems that the Heat of Evaporation and Condensation would increase the amount of energy per unit volume transported. But water vapor is lighter than air, so less mass would be moved through the duct thus decreasing the heat flow.

Thank you, please feel free to call.
Chuck Donaldson
(617) 942-3242
admin
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Re: heat flow of dry vs. moist air.

Post by admin »

Here you have equation for heat power in relation to flow rate and temperature difference:
http://www.pipeflowcalculations.com/pip ... ansfer.php

There you can see that in order to reduce flow rate q, for same thermal power P - you should make bigger temperature difference Delta t.

If you add water to air duct and it evaporate it will take the heat power from air to evaporate making the air cooler.

BUT if you add water with higher temperature than air, than its heat power is added to the air - as at the end mixture of water and air will have the same temperature.
Pipe flow calculations - since 2000
chuckdonaldson
Posts: 2
Joined: Mon Jan 03, 2011 6:45 pm

Re: heat flow of dry vs. moist air.

Post by chuckdonaldson »

Thank you for the insight but I want to increase the heat density instead of increaseing the temp. deference.
admin
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Posts: 375
Joined: Mon Feb 08, 2010 7:47 pm

Re: heat flow of dry vs. moist air.

Post by admin »

As water has much higher spec. volume than air, if you have more water in air you will have more heat power, but the mass of water in 100% saturated air is not to much.
Pipe flow calculations - since 2000
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