# How to I simulate only heat exchanger outlet conditions?

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TiffyEng on 10 Jan 2021
Commented: TiffyEng on 13 Jan 2021
I want to simulate the outlet temperature of a shell and tube heat exchanger with a fixed mass flow rate of fluid on the tube side and variable mass flow rate of thermal liquid on the shell side. I built the model shown below but I get an error. I believe it is because I don't have port B of the mass flow rate source connected to anything but how do I resolve this? I am not interested in the downstream conditions. I'm curious to know why this same error doesn't apply to the thermal liquid side?
The error is:
An error occurred while running the simulation and the simulation was terminated
Caused by:
• ['Fuel_Gas_Process/Solver Configuration']: Steady state solve failed to converge.
• The model may not give enough information to make it possible to solve for values of some of its variables. Specific advice is given below.
Cannot solve for one or more variables:
Equations of one or more components may be dependent or inconsistent. This can cause problems in transient initialization. Here is the set of components involved:
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### Accepted Answer

Juan Sagarduy on 12 Jan 2021
Hello Tiffy
What happens underneath is that the model has got too many state variables in relation to equations.
In order to solve the mathematical problem, simscape needs constraints on both outlet ports in G and TL. Reservoirs or pressure sources are the options u have.
Hope this helps. Regards / Juan
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TiffyEng on 13 Jan 2021
I used the reservoir to specify the downstream pressure and note the properties of the reservoir block state that the reservoir temperature is based on the direction of flow which in this case is into the reservoir from the heat exchanger.
Thank you for your help.

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R2020b

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