- #1
nanunath
- 70
- 0
Hello...
Reynold's Number is given by:
where:
is the mean fluid velocity (SI units: m/s)
L is a length of the object that the flow is going through or around (m)
μ is the dynamic viscosity of the fluid (Pa·s or N·s/m² or kg/m/s)
ν is the kinematic viscosity (ν = μ / ρ) (m²/s)
is the density of the fluid (kg/m³)
Q is the volumetric flow rate (m³/s)
A is the pipe cross-sectional area (m²)
{Taken from wikipedia:http://en.wikipedia.org/wiki/Reynolds_number" [Broken]}
What I don't get is "Characteristic Length"...how do I decide it for a particular flow??
Wikipedia says its just conventionally taken..diff people can take diff chacteristic lengths...
Why??How?
-----------------------------------------------------------------------------------------
Also...does choice of characteristic length have any connection with the nature of viscous forces...if yes how?
Plz help me on this ... I have bee through few boooks ... but unable to understnd how to decide the "Characteristic length"...I mean why we should take "diameter" only for a tube...why not radius??..and if I take radius[the non-conventional way]...what is the effect...what am I exactly doin?
-----------------------------------------------------------------------------------------
Thirdly...
For a shell and tube heat exchanger ...how do I decide the characteristic length...because I had been through a paper on Shell and tube Heat exchangers..in which the Reynold's number[Shell side flow!] is given by:
Re=[density]*[mean velocity of flow]*[outer diameter of tubes!{not the shell!...why?}]/[mu]
Why is that the tubes outer diameter is considered for the shell side flow??
----------------------------------------------------------------------------------------
In short my main question is : "How to decide the most suitable Characteristic Length"...
Plz help me on Heat exchanget question also...
Lastly:
Any views are most welcome...waiting for your relpies...
Thankssss in advance!
Reynold's Number is given by:
where:
is the mean fluid velocity (SI units: m/s)
L is a length of the object that the flow is going through or around (m)
μ is the dynamic viscosity of the fluid (Pa·s or N·s/m² or kg/m/s)
ν is the kinematic viscosity (ν = μ / ρ) (m²/s)
is the density of the fluid (kg/m³)
Q is the volumetric flow rate (m³/s)
A is the pipe cross-sectional area (m²)
{Taken from wikipedia:http://en.wikipedia.org/wiki/Reynolds_number" [Broken]}
What I don't get is "Characteristic Length"...how do I decide it for a particular flow??
Wikipedia says its just conventionally taken..diff people can take diff chacteristic lengths...
Why??How?
-----------------------------------------------------------------------------------------
Also...does choice of characteristic length have any connection with the nature of viscous forces...if yes how?
Plz help me on this ... I have bee through few boooks ... but unable to understnd how to decide the "Characteristic length"...I mean why we should take "diameter" only for a tube...why not radius??..and if I take radius[the non-conventional way]...what is the effect...what am I exactly doin?
-----------------------------------------------------------------------------------------
Thirdly...
For a shell and tube heat exchanger ...how do I decide the characteristic length...because I had been through a paper on Shell and tube Heat exchangers..in which the Reynold's number[Shell side flow!] is given by:
Re=[density]*[mean velocity of flow]*[outer diameter of tubes!{not the shell!...why?}]/[mu]
Why is that the tubes outer diameter is considered for the shell side flow??
----------------------------------------------------------------------------------------
In short my main question is : "How to decide the most suitable Characteristic Length"...
Plz help me on Heat exchanget question also...
Lastly:
Any views are most welcome...waiting for your relpies...
Thankssss in advance!
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