Heat Exchanger Thermal Effectiveness

[wilsonudevil]

Hi all,

Ok quick question about heat exchangers.

I'm using a finned tube heat exchanger similar to the one below:

http://i35.tinypic.com/eaqn49.jpg

Water is circulating through the tube and air is being passed over the tube.

If I heat the water I can warm the air passing over the tube. Similarly if I chill the water I can cool the air passing over the tube.

Now my question is about the Thermal Effectiveness (E) of the heat exchanger.

Using E = (t1-t2)/(tw-t1)

where:
t1 = air temp before heat exchanger
t2 = air temp after heat exchanger
tw = inlet water temp

Will the thermal effectiveness of the heat exchanger be the same for cooling as it is for heating? (for constant air and water flow rates)

I have an average experimental effectiveness for cooling (around 0.8), but want to know if I can use this same effectiveness for the heating condition. ;)

Or will I have to do another experiment?! :mad:

Many thanks.

[nike123]

Hi all,

Ok quick question about heat exchangers.

I'm using a finned tube heat exchanger similar to the one below:

http://i35.tinypic.com/eaqn49.jpg

Water is circulating through the tube and air is being passed over the tube.

If I heat the water I can warm the air passing over the tube. Similarly if I chill the water I can cool the air passing over the tube.

Now my question is about the Thermal Effectiveness (E) of the heat exchanger.

Using E = (t1-t2)/(tw-t1)

where:
t1 = air temp before heat exchanger
t2 = air temp after heat exchanger
tw = inlet water temp

Will the thermal effectiveness of the heat exchanger be the same for cooling as it is for heating? (for constant air and water flow rates)

I have an average experimental effectiveness for cooling (around 0.8), but want to know if I can use this same effectiveness for the heating condition. ;)

Or will I have to do another experiment?! :mad:

Many thanks.

In cooling you have sensible and latent heat. In heating you have only sensible heat. Difference between cooling and heating is in that latent heat.
If you are not considering that in calculations you could have different "effectiveness".