Pete McGrail

Thank you Daniel - catching and correcting bugs in the simulator are the key reason for posting on this forum. I will download the the latest update. Thanks again, Pete McGrail

Hi Salvador, When I ran your simulation with the default ODE Solver Volume Step of 0.1, selecting the adiabatic PFR did not converge. However, try reducing that setting down to 0.01 (under the PFR's Advanced tab). The Runge-Kutta solver converged for me after about 10 sec compute time after changing that setting. Best, Pete McGrail Leapfrog Technical Services

In several simulations I have set up recently, there is a very large change in the mass flow rate of one fluid entering a heat exchanger from the value of the discharge. In the attached file, an Outdoor Air stream is specified as entering the heat exchanger (Condenser) at 1055 kg/h but the discharge air mass flow inexplicably drops to 332 kg/h. I have seen a change exceeding 10^6 kg/h in one of my other flow sheets. The simulations run fine and don't report any errors so I only caught this by accident....

Thanks Daniel. I was not aware of the issues with phase change in most of the HX calculation modes. First thing that was important is to uncheck was the "Ignore LMTD Error" box. Doing that immediately generates an error message so alerts the user that there is a problem. After that, I switched the Calculation Type to Calculate Outlet Temperatures and now the outlet temperatures are reasonable with computed heat transfer efficiency of 70%. Because phase change in heat exchangers is an extremely common...

Frank - thanks but I know the simulation converges and your changes did not affect the result significantly. What I don't understand is how it is physically possible for the glycol-water fluid that is being cooled to be discharged from the HX at a lower temperature than the water vapor that is discharged (plus minor liquid) that is the heat sink via phase change in the HX. The temperature profile shows no temperatures below 14.5°C that would be required to cool the glycol solution to the discharge...

I have a relatively simple simulation of a vapor compression cooling loop using only water at low pressure. In the evaporator heat exchanger, the liquid water is vaporized at low pressure to derive cooling. When looking at the discharge temperatures, the temperature of the fluid being cooled goes below the temperature of the water-side discharge, which is mostly vapor. That is not possible unless a colder temperature was achieved somewhere in the heat exchanger profile. However, when looking at the...