How can I simulate my models better and more specifically?

[KieranF <kieran.fung@…>]

I started modeling subsystems of the Rankine Power Cycle in an attempt to verify each component works individually as well as how each component works with others.

The model I have been working on has been a simple Heat Exchanger model. It only involves the HX, and (2) MassSourceFlow for the water and gas and (2) SinkSourceflow for the water and gas respectively. Finally, temperature sensors (SensT) were given to the inlet and outlets of each fluid for the Heat Exchanger for a total of (4) temperature sensors.

This model was created using the ThermoPower Library where all of the components are from and located within this library.

The model is able to be checked, it instantiates and it simulates consistently as well. The issue I am having is that the simulation does not describe the physics or desired results an ideal Heat Exchanger that one would expect.

What's happening for me in my simulation is that the 700 [K] FlueGas is going through the Heat Exchanger and at the outlet is reading 372 [K]. These are the readings of sensT1 and sensT2 components for the inlet and outlet temperatures of the working fluid (FlueGas).

These initial results are great and all at first inspection but looking into it more, its obvious that something is off and something is not working the way it should. Allow me to go into greater detail:

The outlet sensT2 reads 372 [K]. But clicking on the tab in the simulation window shows the plot of temperature vs. time. In the plot, the temperature starts at 300 [K] and linearly increases over the interval of 30 [sec] to the temperature of 372 [K] by the time t=20 [s]. Here, at the outlet of the working fluid (FlueGas), it is increasing in temperature instead of transferring the heat to the other fluid, water, as a heat exchanger should.

Looking at the water inlet and outlet sensT sensors show good results. The inlet reads 298 [K] and the outlet reads 372 [K]. It can be observed that the outlet starts increasing in temperature over the interval 0<t<10 [s] to where Tfinal of the outlet = 372 [K].

Does anyone understand why the working fluid FlueGas is increasing in temperature at the outlet? It should be decreasing in temperature the entire time it goes in and out of the heat exchanger being the working fluid that is supposed to deliver the energy for the system.

Feel free to leave a comment below with any advice or insight you have. I have also attached my files as well in case you want to see the visualized simulations as well instead of reading about it. Cheers.

[KieranF <kieran.fung@…>]

Heat Exchanger Working Model

[anonymous]

Does anyone understand why the working fluid FlueGas is increasing in temperature at the outlet?

The heat exchanger uses cocurrent flow of both fluids. So both fluids have the same temperature at their outlet. You can see this with a look into the heat exchanger model.
The metal in heat exchanger heats up due to the incoming heat from the gas. You see this by the increasing temperature of the heat exchanger wall.
What seems to be missing is the temperature difference for the heat transfer itself. But this is a totally different topic.

So from my understanding there is nothing wrong here.

Ulrich