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# Heat exchanger

Experimenter

Hello,

I am using AMESim only recently.

I try to simulate a heat exchanger with 2 halves (see picture).

I would like to use a thermotric efficiency value, but it is not taken into account. I probably do something wrong...

Please, can someone tell me the way to use halves heat exchangers ?

Thanks.

Christophe

7 REPLIES

# Re: Heat exchanger

Siemens Creator

Hi Chris75,

On the simple halves heat exchanges, the thermometric efficiency is defined as follows:

The efficiency is then calculated with a ratio of the hot side heat capacity rate and the minimal heat capacity rate. You can find the proper equation in Fundamentals of Heat and Mass Transfer, Incorpera & De Witt (p660, eq 11.21 of the fifth edition). The efficiency value is then limited to 1 as greater values can lead to non physical results.

Regards,

# Re: Heat exchanger

Experimenter

Hi NCY,

Unfortunatly, when I recalculate the thermotric efficiency, I can't find the value I filled.

Moreover :

-  the thermal power exchanged between hot and cold sides is always the same,

-  the thermal power recalculated for cold side and hot side are different.

The picture below show the results and the calculation for 3 cases : efficiency = 100 %, 50 % and 25 %.

Regards.

# Re: Heat exchanger

Siemens Creator

After looking at your inputs, as you have the mass flow rate of both sides, i advice you to use following sketch:

I guess your effectiveness correspond to the Amesim thermal effectiveness, so i've calculated following thermometric efficiencies:

• eff=100% --> th_eff = 0.186
• eff=50% --> th_eff = 0.093
• eff=25% --> th_eff = 0.046

I launched the Amesim calculation with these values and i obtained the expected efficiencies:

And the heat flow rate evolution is consistent:

Is this proposition ok for you?

Regards

# Re: Heat exchanger

Experimenter

Thanks for the sketch.

My aim is to impose the thermometric efficiency (Batch Parameters.jpg).

I understand that the maximum value is 18,6 % : why (it seems to be a very little value) ? When I increase the flow rates, this efficiency increases too (a little bit). So, what are the limiting parameters ?

Regards.

# Re: Heat exchanger

Siemens Creator

Below, you can find the temperature evolution at eff= 100%:

The inlet hot temperature is the limiting factor of the heat exchange otherwise non physical values would be reached. The cold temperature reaches this value when the efficiency is set to 100%. The low value of thermometric efficiency is due to the difference between the cold side inlet and the hot side outlet.

# Re: Heat exchanger

Experimenter

Hi,

Thanks.

I totally agree with you.

I think I do something wrong because, with my model, T Cold Outlet never reaches T Hot Inlet.

# Re: Heat exchanger

Siemens Creator

May'be the boundary conditions are not correctly set. Here are mine:

The other parameters are set with default values.