volume flow rate problem

[volamminhtriet96]

I used centrifugal fan to set the flow rate in AHU but the outlet anh inlet flow rate was not as I expected. Please can you check my design for me to see what I did wrong ? Thank you very much for your help!!!

[Jon.Wilde]

For some reason, I cannot open this file. Did you follow everything in the guide here?

[volamminhtriet96]

Dear Mr.Jon,

I am sorry about the file, the reason you can't open it because I'm using CFD 2018 and i can't get the file until monday as it is in my friend's laptop.

Instead of using rotating region, i used centrifugal pump/blower material and assigned it as a plug fan with constant volume flow rate (Fan1:3319 l/s, Fan 2: 2688 l/s) and rotation speed 2900 rpm. 

Cooling coil (heat exchanged material) volume flow rate:2688 l/s; dehumidification: 11oC 100%

Heating coil (heat exchanged material) volume flow rate:2688 l/s; dehumidification: 18oC 63%

Inlet(2): Tem=23oC Humidity:0.52 Pressure: -250 Pa

exhaust air oulet(3) : Tem=23oC Humidity:0.52 Pressure: 700 Pa

oulet : Pressure(1): 750 Pa

I use moist air(variable) as the fluid. The heat rate of both cooling coil and heating coil are correct but the flow rate of the inlet, exhaust air outlet and the outlet is not right. Their sum is not equal to 0.I also used Advection Scheme 5. So should i use rotating region as your recomended or i have done something wrong. Hope for your respond!

[Jon.Wilde]

Heat Exchanger materials are not designed to be embedded internally like this - you can make it work with a flag though.

Internal heat exhanger flag.

That should really help you out, might even be the solution.

Thanks,

Jon

[volamminhtriet96]

That might be the solution, I will tell the result as soon as possible.  Thank you very much for your help!

[volamminhtriet96]

Dear Mr Jon,

Here are the results:

1. The pressure between 2 heat exchanger is <0 which must be 500-600 Pa as expected

2. The inlet anh air exhaust outlet volume flow rate are seem correct but the outlet is not ( I think because of the heat exchanger in series with the plug fan but I don't know how to make it right)

Here is the file in CFD 2017, I hope you can open it

[Jon.Wilde · Accepted solution]

My initial guess would be that you have no possibility for mathematical error, so this is probably over constrained on flow.

Do you need the fans at all? If you know the flow rate, why not just use it at the inlet to the entire system? (No pressure assigned at the inlet then)

Maybe then, if you need the fans for flow distribution, you could give them a curve so they have some 'float'?

[volamminhtriet96]

I want to solve all the problems in just 1 design but it seems not possible. When I solved the design without the heat exchangers, the volume flow rate and the pressure distribution were correct but when I added the heat exchangers, things went wrong. Now, I see what my problem is.

Thank you very much for your help!!