Centrifugal Pump doesnt increase pressure in Simscape for 2P-Fluid

Hello friends,

In my system I want to increase the 2P-liquid taken from the reservoir,its pressure from 5 bar to 15 bar and then send it to the heat exchanger to evaporate it. for this I used the centrifugal pump. I did the necessary calculations, adjusted all the parameters for the desired pressure, but I couldn't get the pressure of the liquid to the desired pressure. At first I only did it with the flow rate source, but when I connect another component to this flow rate source (e.g. a heat exchanger and then an ejector), the system pressure increases by itself and this prevents vaporization.

Is it not possible to increase this pressure with a centrifugal pump or which pump can I use instead of this centrifugal pump ?

Thank you in advance for your help. I have uploaded the system, you can get suggestions there.

[Yifeng Tang]

Hi Omer,

It looks to me there are many things that needs to get fixed.

let's start with a few simple ones:

• 2P inlet reservoir at 5 bar & 52 degC, on P-H diagram, this appears to be vapor. You can't move vapor with a pump, nor can a vapor evaporate. Check and correct this.
• 2P outlet reservoir should be set at the desired outlet pressure (15bar). The temperature matters less but it's best to set at a vapor temperature.
• make sure your nominal head at the pump can overcome the expected pressure difference (15-5=10bar).

And, definitely set up a P-H diagram to understand the states change, and set up flow rate sensor to understand the direction of 2P flow. There is a chance that without correct parameters, the 2P flow may go backwards.

Please provides an update once you fix these and we can look deeper.

[ÖMER]

Hello Yifeng

I applied what you said, but if the reservoir is at the desired pressure in that way, won't it give an error in the process? (because that's what the pump has to do, which is to raise the pressure to that level) I say this because if I already set both the inlet and outlet reservoir to those pressures, how will we determine that the pump is working under the conditions I want. What I have formulated here is the simple part of the system, normally the system is more complex and detailed. For this, the pressure really has to reach the levels I want, otherwise the system gives an error.

I also did the calculation for sufficient height to increase the pressure by 10 bar as follows

(P1-P2)*10^5/(density_rho*gravity_g)

Answer 1

[Yifeng Tang]

Hi ÖMER,

Two things I did to make the "Comminityfrage.slx" model to produce reasonable results.

1. At the pump, make the max head twice of the nominal head. Otherwise, if the max head is less than the nominal head, the block throws an error.
2. Assign unit "rpm" to the Simulink-PS converter. The default unit "1" will be interpreted as rad/s for angular velocity and it's WAY too fast.

With these two changes, I'm seeing the volumetric flow rate at ~4e-5 m^3/s, which is the correct order of magnitude given in the pump block.

At the heat exchanger, I'm seeing 5.5kW of heat transfer at steady state. The water temperature drops from 363.15K to 356.66K, while the butane goes from liquid at 326.68K to a mixture at 358.54K and quality 0.71. You may need to further parametrize the heat exchanger block if the performance isn't what you expect.

Another piece of suggestion: set up some sensors and a P-H diagram to understand the states of the 2P side. You may find usage of the P-H diagram in many examples in the Fluids library. For instances:

https://www.mathworks.com/help/hydro/ug/residential-refrigeration-unit.html

https://www.mathworks.com/help/hydro/ug/refrigerator.html

https://www.mathworks.com/help/hydro/ug/residential-air-source-heat-pump.html

Hope this helps.

Yifeng