[TRNSYS-users] Heat Exchanger & Units

[Sasa Pantic <usrobotics011@yahoo.com>]

Hello,

 

I am modelling the simple project similar to the "begin" example included in the TRNSYS.  The difference is that instead  of the Auxiliary Heater, I am using the Type 91 Heat Exchanger (air to water) with constant effectiveness of 0.8 .

The inlet conditions are as follows:

cold side: water, inlet temperature 20degC, 0.09 kg/s

hot side: air, inlet=outlet of the solar collector (Temperature is varying over the time), 0.162 kg/s

As a result, I am getting that the outlet temperature on the cold side is almost  constant(20degC) over the August 1st for Madison (USA). Around noon there is a slight increase (cca 1degC)  and then decrease. The curve shape is similar that of the the hot side outlet.

 

I would kindly ask for  clarifications please.

My concerns are as follows:

 

1) Regarding the heat exchanger performance with the constant effectiveness...

  a)Why does  the outlet temperature on the cold side  decrease or stay flat?  What seems to be the problem?

b) If the inlet temperature condition on the cold side is constant, the outlet temperature on the cold side will always decrease. Therefore, how can  change that condition to have temperature  inlet on the cold side as a function of time.

 

2) Regarding the units ...

 How can I change the units to be e.g. W/m2 when I plot the results on the on-line ploter?

 

Thank you for your time and consideration.

Regards Sasa Pantic

 

 

 

 

 

 

 

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