[arindamsantra7]

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

[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.

[arindamsantra7]

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.

[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

[arindamsantra7]

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

[arindamsantra7]

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

[ghost82]

If you treat steam as ideal gas, ideal gas equation for density and Sutherland equation for viscosity (for example).

[arindamsantra7]

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.

[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.

[arindamsantra7]

thank you sir

[arindamsantra7]

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)

[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??

[arindamsantra7]

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?

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 ?

[ghost82]

That formula refers to internal duct fully developed flow so if this is the case it is correct.

[arindamsantra7]

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?

[ghost82]

Refer to fluent user guide.

[arindamsantra7]

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.

[arindamsantra7]

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.

[arindamsantra7]

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?

[arindamsantra7]

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.