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 dev.... September 3, 2008 02:32

ItsVery Urgent:Pressure,Heat Convection coeficient

Hi all, I have a question about Heat Transfer (NATURAL CONVECTION) & Air conditioning system. I have a gaseus environment of CO2 gas over a FLAT PLATE. Now Initial conditions are:

1. CO2 gas condition:- Pressure = 1.4 Bar(WHICH IS GREATER THAN ATMOSPHERIC PRESSURE), Temperature = 30 Celcius, Relative Humidity = 80%

2. Flate Plate is at tempetareture of 10 C(Celcius)

Now I want to get value of Heat-Transfer Coefficient (h). Is there any relation to calculate this Heat transfer coefficient for NATURAL CONVECTION PROBLEM ?

yours help/suggestions would be appreciable.

Thank you

 JAY September 3, 2008 03:49

Re: ItsVery Urgent:Pressure,Heat Convection coefic

Hi dev,

Please let me know whether the flat plate is vertical or horizontal.

Because it makes a difference in natural convection flow and thermal set-up.

 dev.... September 3, 2008 07:23

Re: ItsVery Urgent:Pressure,Heat Convection coefic

Hi Jay,

This is Vertical Plate. If you need any more data, your most welcome & thanks for ur responce

 JAY September 4, 2008 08:11

Re: ItsVery Urgent:Pressure,Heat Convection coefic

hi dev...

here it is... let us assume that the vertical plate is isothermal (in your case, it is 10 C)

Find the material properties (Density, specific heat ,dynamic viscosity, thermal conductivity ,Prandtl number) of CO2 at film temperature ((Twall+Tinfinity)/2) at 1 ATM

Using ideal gas law, PV=mRT, find the density at 1.4 bar and subsequently viscosity too... (CO2 can easily be considered as ideal gas law)

Find thermal expansion co-efficient (beta) = 1/Tinfinity where T is in kelvin

Find Grahs-hoff number = (gravity*beta*del T*length of plate along the vertical direction^3)/(kinematic viscosity^2)

find Rayleigh number = Gr*Pr

if it is <10^9, flow is laminar otherwise it is turbulent

Nusselt number = (0.678*Ra^0.25) (Pr/(Pr+0.952))^0.25

Nu = hL/k so h = Nu*k/L

Regards, Jayaveera

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