Isothermal or Adiabatic

Question

Regarding to this wiki ,what does happen for Temperature during transient analysis in Hydripneumatic tank? Does temperature assume to be fixed during transient (isothermal) or is not fixed but adiabatic? If HAMMER assumes it as an adiabatic process, how is temperature interfered in calculations? I mean what is role of air temperature in HAMMER? 
 H.

Jesse Dringoli · Answer

A transient analysis occurs over a relatively short duration, on the order of 30 seconds - 5 minutes typically. As the article mentions, the isothermal gas law is used for hydropneumatic tanks and temperature is assumed to be constant.

Regards,

Jesse Dringoli
Technical Support Manager, OpenFlows
Bentley Communities Site Administrator
Bentley Systems, Inc.

Jesse Dringoli · Answer

Apologies, I misunderstood the question. 
 
Yes, as the article states, during the transient simulation it is more appropriate to assume that the process is adiabatic, and HAMMER uses the gas law coefficient that you enter in the hydropneumatic tank properties. 
 
The normal ideal gas law is PV=nRT, where "T" is the temperature. However, a constant number of moles / mass of gas in the tank and constant temperature is assumed, so the 'nRT' term in the gas law equation is replaced by a constant, K (PV=K). 
 
See Transient Simulation Behavior > Without a Bladder in this article: 
 
Modeling Reference - Hydropneumatic Tanks [TN] 
 
 communities.bentley.com/.../modeling-reference-_2D00_-hydropneumatic-tanks 
 
So in other words, the temperature "T" is considered to be constant. 
 
As far as the "heat is lost or gained" part - I believe you could say that the exact temperature change isn't directly used but rather is accounted for by way of the gas law exponent.