in - pressure, out pressure, is that make sense?
Hi everyone,
I want to simulate a flow through Bosch Rexroth directional valve. I modeled geometry. I want to obtain nominal flow rate through valve. I have found how companies determine it. This quotation from Bosch rexroth documentation from their website. " No norm exists for the term “nominal flow rate”. To obtain a clear numerical value, Rexroth has defined the following: Inlet pressure: pabs = 7 bar Differential pressure: ∆p = 1 bar Medium temperature: TM = 293 K (20 °C) Humidity: Φ ≅ 0 % Flow rates are indicated in volumes per time unit. The volume refers to a normal state valid for pneumatics according to ISO 8778, and this is as follows: Pressure: p0 = 100 kPa (1 bar) Temperature: T0 = 20 °C Relative humidity: Φ ≅ 65 % In order to identify the flow rate q as a slack volume, the acronym ANR (Atmosphère Normale de Référence) can be added after the unit. Example: q = 12 dm3/s (ANR)" According to this documentation, I have asssumed reference pressure 1bar, 6 bar pressure at inlet, and 5 bar at outlet. Ansys CFX gave me mass flow at outlet q = 0.00743 kg/s and i divided it by 1,18kg/s (density in nominal state) and I multiplied it by 1000 and 60 to determine nominal flow in dm^3/min. But unfortunately results are about 4 times less than from technical card about this directional valve. Did I simulate this valve in proper way? Why there is so big difference? Thank you for your help Mateusz K. |
1) I didnt understand what you meant about the operating conditions that valve was tested. until thats clear (at least to you) i dont think you will ever find the solution
2) you said many words but nothing on how you modeled the valve in cfx (however find the answer to (1) first ) i presume it was steady state? did you assumed an isothermal state ? 3) read the "recommended configurations of boundary conditions" in the cfx manual. |
1) operating conditions, They assumed 6bar at inlet and 5bar at outlet
2) yes it is steady state analysis, and I applied compressibility of flow by assuming Ideal Gas |
Hi Sir,
is it possible to do an experimental analysis (only one Sir) with this valve? After that, u can do your (several) simulations with these CFD tools. Rogerio. :rolleyes: |
Defining pressure BC on both inlet/outlets does not make sense to me. You need some other BC conditions to make the problem closed.
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Total pressure in, static pressure out is fine...
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Quote:
http://www.abcm.org.br/symposiumSeri...SSM3_IV_05.pdf especially at the end of section 2.3 and look how they apply bc. I aware that static pressure at in and out is not appropriate. |
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