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Anas,<br>
It isn't quite as simple as introducing a new formula. You would
need to modify the Fortran source code of all of the affected
models. For one thing, you would need to change those input
variables (such as specific heat and density) from TRNSYS parameters
to inputs because parameters are set once at the beginning of the
simulation and are not updated after that. However, the problem goes
far deeper than that. The assumption of constant properties is
implicit in the Types' algorithms in many cases. When we write the
equation q = m*Cp*dT/dt, we are writing a simplification of the
actual energy balance of q = d(m*Cp*T)/dt which expands to: q =
m*Cp*dT/dt + m*T*dCp/dt + T*Cp*dm/dt. The simplification comes from
assuming that dCp/dt and dm/dt are both zero over a time step. You
would need to rederive all of the algorithms in the affected Types
and then recode them in order to allow all of the properties to vary
with time. Fortunately most of the fluids that we deal with have
relatively constant properties over the temperature range at which
they are used. One exception is the working fluids in high
temperature solar thermal applications and you will find some
components available in the High Temperature Solar TESS Library that
do not make the simplifying assumptions above.<br>
regards,<br>
David<br>
<br>
<br>
<div class="moz-cite-prefix">On 4/27/2015 3:44 AM, Anas Majdouli
wrote:<br>
</div>
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<div dir="ltr">Hi TRNsys community, <br>
<br>
I hope you are doing very well.<br>
<br>
For TRNsys simulations, usually when we are using types, density
and/or Fluid Specific Heat are among the parameters to specify.
The problem is sometimes, these parameters vary and depend on
temperature, pression... <br>
<br>
So I looked for a polynomial equation that gives for example
density=f(Temperature) and I found one [formula 1 in <a
moz-do-not-send="true"
href="http://metgen.pagesperso-orange.fr/metrologiefr19.htm%5d."
target="_blank">http://metgen.pagesperso-orange.fr/metrologiefr19.htm].</a>
My question is : how to introduce this formula in TRNsys so that
this latter will use it automatically ? I don't want to create
an 'Assembly/Insert new equation' component each time...<br>
<br>
Thank you in advance,<br>
<br>
Anas MAJDOULI </div>
<br>
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<pre class="moz-signature" cols="72">--
***************************
David BRADLEY
Principal
Thermal Energy Systems Specialists, LLC
22 North Carroll Street - suite 370
Madison, WI 53703 USA
P:+1.608.274.2577
F:+1.608.278.1475
<a class="moz-txt-link-abbreviated" href="mailto:d.bradley@tess-inc.com">d.bradley@tess-inc.com</a>
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