# how to incorporate the temperature of fluid in pressure based cavitation model

 Register Blogs Members List Search Today's Posts Mark Forums Read

 September 23, 2014, 10:51 how to incorporate the temperature of fluid in pressure based cavitation model #1 New Member   Join Date: Aug 2014 Posts: 22 Rep Power: 10 I want to simulate a cavitation model in a converging-diverging nozzle. I use the mixture model where the primary phase is water liquid & the secondary phase is water vapour. the inlet pressure is 248 kpa & the outlet pressure is 101 kpa. the mass flow is 8.78 kg per sec. the temp of the fluid at inlet is 370k. due to heat is not absorbed or released by the fluid throughout the system. we can assume the temp is constant throughout the system, that is 400 k. but I can not incorporate the temp in this model. because there is no option to give the temp in pressure inlet & pressure outlet based cavitation model. So I want to know, how I can incorporate the temp of the fluid in this cavitation model

 September 23, 2014, 11:16 #2 Senior Member     Daniele Join Date: Oct 2010 Location: Italy Posts: 1,016 Rep Power: 25 Hi, I don't understand your question...you are stating that: - we can assume the temp is constant throughout the system, that is 400 k - So I want to know, how I can incorporate the temp of the fluid in this cavitation mode If you want to simulate at constant temperature all you need to do is to specify the fluid properties at that temperature, you don't need to set temperature in fluent; this means you have to set constant density, viscosity, vaporization pressure and surface tension (for Singhal et al model), which are unique values at that operating temperature. thermal energy likes this.

September 24, 2014, 03:08
#3
New Member

Join Date: Aug 2014
Posts: 22
Rep Power: 10
Quote:
 Originally Posted by ghost82 Hi, I don't understand your question...you are stating that: - we can assume the temp is constant throughout the system, that is 400 k - So I want to know, how I can incorporate the temp of the fluid in this cavitation mode If you want to simulate at constant temperature all you need to do is to specify the fluid properties at that temperature, you don't need to set temperature in fluent; this means you have to set constant density, viscosity, vaporization pressure and surface tension (for Singhal et al model), which are unique values at that operating temperature.
thank you sir for your kind information.
sorry, I give the wrong temp. the right temp is 370k. I get the constant density, viscosity, vaporization pressure and surface tension at this temp for water liquid. but how I can get the density & viscosity of water vapour at this temp? please specify the equation from where I can get the density & viscosity for water vapour at specific temp.

 September 24, 2014, 04:07 #4 Senior Member     Daniele Join Date: Oct 2010 Location: Italy Posts: 1,016 Rep Power: 25 You need to calculate saturated steam properties at that vapor pressure/temperature (370 K). You can use for example this calculator: http://www.peacesoftware.de/einigewe...r_dampf_e.html Input the temperature (370 K) in the box "Calculation of thermodynamic properties of saturated steam". You will have: vaporization pressure: 90535,51 Pa Water: density: 960,59 kg/m3 dynamic viscosity: 0,00029 Pa*s surface tension: 0,05987 N/m (ref. http://www.nist.gov/data/PDFfiles/jpcrd231.pdf) Steam: density: 0,538 kg/m3 dynamic viscosity: 1,216E-05 Pa*s

 September 24, 2014, 05:33 #5 New Member   Join Date: Aug 2014 Posts: 22 Rep Power: 10 thank you sir, I got your answer. But I want to know the relation or equation from where I can solve manually the value of the density & viscosity of water vapor at a specific temp

September 24, 2014, 05:34
#6
New Member

Join Date: Aug 2014
Posts: 22
Rep Power: 10
Quote:
 Originally Posted by ghost82 You need to calculate saturated steam properties at that vapor pressure/temperature (370 K). You can use for example this calculator: http://www.peacesoftware.de/einigewe...r_dampf_e.html Input the temperature (370 K) in the box "Calculation of thermodynamic properties of saturated steam". You will have: vaporization pressure: 90535,51 Pa Water: density: 960,59 kg/m3 dynamic viscosity: 0,00029 Pa*s surface tension: 0,05987 N/m (ref. http://www.nist.gov/data/PDFfiles/jpcrd231.pdf) Steam: density: 0,538 kg/m3 dynamic viscosity: 1,216E-05 Pa*s
thank you sir, I got your answer. But I want to know the relation or equation from where I can solve manually the value of the density & viscosity of water vapor at a specific temp

 September 24, 2014, 05:45 #7 Senior Member     Daniele Join Date: Oct 2010 Location: Italy Posts: 1,016 Rep Power: 25 If you treat steam as ideal gas, ideal gas equation for density and Sutherland equation for viscosity (for example).

October 17, 2014, 01:00
#8
New Member

Join Date: Aug 2014
Posts: 22
Rep Power: 10
Quote:
 Originally Posted by ghost82 If you treat steam as ideal gas, ideal gas equation for density and Sutherland equation for viscosity (for example).
ideal gas equation is pv=nRT. In this problem pressure is varying throughout from inlet to outlet. so, what pressure value I have to choose to solve the ideal gas equation to get the vapour density.

what is the formula for this case to calculate the turbulent intensity percentage.

Last edited by wyldckat; November 1, 2014 at 07:53. Reason: posted few minutes apart

 October 17, 2014, 03:38 #9 Senior Member     Daniele Join Date: Oct 2010 Location: Italy Posts: 1,016 Rep Power: 25 As I wrote some posts above, the vapor is saturated; so pressure in the ideal gas equation is the vapor pressure at the calculated temperature. Turbulent intensity is defined as the ratio of the root mean square of the velocity fluctuations, to the mean free stream velocity.

 October 17, 2014, 06:29 #10 New Member   Join Date: Aug 2014 Posts: 22 Rep Power: 10 thank you sir

October 30, 2014, 09:58
#11
New Member

Join Date: Aug 2014
Posts: 22
Rep Power: 10
Quote:
 Originally Posted by ghost82 As I wrote some posts above, the vapor is saturated; so pressure in the ideal gas equation is the vapor pressure at the calculated temperature. Turbulent intensity is defined as the ratio of the root mean square of the velocity fluctuations, to the mean free stream velocity.
the inlet & outlet diameter of converging-diverging nozzle is 51.2 mm. the throat diameter is 25.6 mm. mass flow at inlet is 8.75 kg/sec. the density of water at 373 k is 958.462. so the velocity of water at inlet is calculated as 4.4341 m/sec. Reynolds number at inlet is calculated as 771095.9264 by taking kinematic viscosity at 373 k is 0.2944198 x 10^-6 & hydraulic diameter 51.2 mm.
Is the reynolds number calculation is right ?

& can I use this formula for turbulent intensity calculation?
I= 0.16 x (Re)^(-1/8)

 October 30, 2014, 10:35 #12 Senior Member     Daniele Join Date: Oct 2010 Location: Italy Posts: 1,016 Rep Power: 25 If these are the data for inlet Re number is correct. But I don't think the input data are correct..have you boiling water at venturi exit??

October 30, 2014, 13:20
#13
New Member

Join Date: Aug 2014
Posts: 22
Rep Power: 10
Quote:
 Originally Posted by ghost82 If these are the data for inlet Re number is correct. But I don't think the input data are correct..have you boiling water at venturi exit??
in this case the pressure inlet is 555 kpa & outlet pressure is 378 kpa.
so then the input data are correct or not?

Quote:
 Originally Posted by ghost82 If these are the data for inlet Re number is correct. But I don't think the input data are correct..have you boiling water at venturi exit??
if the reynolds number calculation is right, then please specify that the above turbulent intensity percentage calculation formula is applicable or not ?

Last edited by wyldckat; November 1, 2014 at 07:53. Reason: posted few minutes apart

 October 30, 2014, 13:29 #14 Senior Member     Daniele Join Date: Oct 2010 Location: Italy Posts: 1,016 Rep Power: 25 That formula refers to internal duct fully developed flow so if this is the case it is correct. __________________ Google is your friend and the same for the search button!

October 30, 2014, 14:34
#15
New Member

Join Date: Aug 2014
Posts: 22
Rep Power: 10
Quote:
 Originally Posted by ghost82 That formula refers to internal duct fully developed flow so if this is the case it is correct.
what is the momentum equation for this case?

 October 30, 2014, 14:38 #16 Senior Member     Daniele Join Date: Oct 2010 Location: Italy Posts: 1,016 Rep Power: 25 Refer to fluent user guide. __________________ Google is your friend and the same for the search button!

October 31, 2014, 07:00
#17
New Member

Join Date: Aug 2014
Posts: 22
Rep Power: 10
Quote:
 Originally Posted by arindamsantra7 in this case the pressure inlet is 555 kpa & outlet pressure is 378 kpa. so then the input data are correct or not?
I give all the data as per I told previously. but the calculation show that divergence occurs. which I have to adjust now to converge the solution.

November 3, 2014, 03:41
#18
New Member

Join Date: Aug 2014
Posts: 22
Rep Power: 10
Quote:
 Originally Posted by arindamsantra7 in this case the pressure inlet is 555 kpa & outlet pressure is 378 kpa. so then the input data are correct or not? if the reynolds number calculation is right, then please specify that the above turbulent intensity percentage calculation formula is applicable or not ?
In this calculation I get the reversed flow in several faces & it is still after the 3000 iterations. what adjustment I have to do.

November 6, 2014, 11:31
#19
New Member

Join Date: Aug 2014
Posts: 22
Rep Power: 10
Quote:
 Originally Posted by ghost82 You need to calculate saturated steam properties at that vapor pressure/temperature (370 K). You can use for example this calculator: http://www.peacesoftware.de/einigewe...r_dampf_e.html Input the temperature (370 K) in the box "Calculation of thermodynamic properties of saturated steam". You will have: vaporization pressure: 90535,51 Pa Water: density: 960,59 kg/m3 dynamic viscosity: 0,00029 Pa*s surface tension: 0,05987 N/m (ref. http://www.nist.gov/data/PDFfiles/jpcrd231.pdf) Steam: density: 0,538 kg/m3 dynamic viscosity: 1,216E-05 Pa*s
what is the uses of residual factors?

November 11, 2014, 23:36
#20
New Member

Join Date: Aug 2014
Posts: 22
Rep Power: 10
Quote:
 Originally Posted by ghost82 You need to calculate saturated steam properties at that vapor pressure/temperature (370 K). You can use for example this calculator: http://www.peacesoftware.de/einigewe...r_dampf_e.html Input the temperature (370 K) in the box "Calculation of thermodynamic properties of saturated steam". You will have: vaporization pressure: 90535,51 Pa Water: density: 960,59 kg/m3 dynamic viscosity: 0,00029 Pa*s surface tension: 0,05987 N/m (ref. http://www.nist.gov/data/PDFfiles/jpcrd231.pdf) Steam: density: 0,538 kg/m3 dynamic viscosity: 1,216E-05 Pa*s
Respected sir,
I have done the simulation by taking the water as working fluid. But now I want to do the simulation by taking the diesel fuel as working fluid. So, please tell how I can get the properties of diesel fuel at 300 k & at other temperature.