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Anas, 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. regards, David On 4/27/2015 3:44 AM, Anas Majdouli
wrote:
-- *************************** 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 d.bradley@tess-inc.com http://www.tess-inc.com http://www.trnsys.com |