Find the convective heat transfer coefficient

In summary, the conversation involves a first year chemical engineering student seeking help with finding the convective heat transfer coefficient for petrol. The student provides information on the dimensions and properties of the petrol, and others chime in to provide assistance and verify calculations. The final calculated convective heat transfer coefficient is found to be 30,950 W/m^2*K.
  • #1
Carlo09
15
0
Ok it's my first time here and I was hoping to get some help on some questions I have been given. I am a first year chem eng and I'm finding the work pretty hard so any help at all will be useful, thanks.

I need to find the convective heat transfer coefficient, h for petrol using this equation:

hD/Lamdaf = 0.37 Re^0.6

so using information I am given:

D = 3mm = 0.003m
Lamdaf (thermal conductivity) = 0.145 w/m k
(M)=viscosity = 0.0006 Pa s
u=Velocity of petrol = 19.2 m/s
P=density of petrol = 737.22 kg/m^3

Ok so to calculate Re I am using: Dup/(M) = (0.003*19.2*737.22)/0.0006 = 70773.12

Is this correct so far?

Then I put this back into the equation and rearrange for h which I get to be =14533.475! w/m^2 k

Is this correct because it seems very big to me! if not please can someone point me into the right direction... thank you very much!
 
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  • #2
I'm assuming this is flow through a pipe? You seem to have run the numbers correctly, and that convective coefficient doesn't seem out of the realm of possibility to me.

Your Reynold's number does seem a bit low, I caluclated 126,500 but I might have used some fuzzy numbers in there.
 
  • #3
It says the temperature of petrol is monitored by a thermocouple in the flow, so I'm guessing pipes?

How did you get your Re at that value? Have i used the wrong values to calculate it?

Thank you for your help
 
  • #4
I calculated the Reynold's number using the equation:

[tex]Re_{D}=\frac{\rho*u_{m}*D}{\mu}[/tex]

where
[tex]\rho=719\frac{kg}{m^{3}}[/tex]
[tex]u_{m}=19.2\frac{m}{s}[/tex]
[tex]D=3mm[/tex]
[tex]\mu=3.3*10^{-4}Pa*s[/tex]

With these inputs the Reynold's number works out to 125,200.
 
  • #5
So since I was a third of the way there anyway, I went ahead and tried calculating the convective heat transfer coefficient. The equations I used are out of my heat transfer textbook, "Introduction to Heat Transfer" by Incropera and DeWitt.

The answer I got was h= 30,950 W/m^2*K

I attached the MathCAD sheet I used to calculate it rather than trying to type it out in Latex.
 

Attachments

  • Mathcad - Gasoline flowing in a tube.pdf
    18.4 KB · Views: 452

1. What is the convective heat transfer coefficient?

The convective heat transfer coefficient is a measure of the ability of a fluid to transfer heat by convection. It is defined as the ratio of the convective heat transfer rate to the temperature difference between the surface and the bulk fluid.

2. How is the convective heat transfer coefficient calculated?

The convective heat transfer coefficient can be calculated using the following formula: h = q/(A(Ts-T∞)), where h is the convective heat transfer coefficient, q is the heat transfer rate, A is the surface area, Ts is the surface temperature, and T∞ is the bulk fluid temperature.

3. What factors affect the convective heat transfer coefficient?

The convective heat transfer coefficient is affected by several factors, including fluid properties (such as viscosity and density), fluid velocity, surface roughness, and the geometry of the surface.

4. Why is the convective heat transfer coefficient important?

The convective heat transfer coefficient is important because it determines the rate at which heat can be transferred between a surface and a fluid. This is crucial in many engineering applications, such as in heat exchangers, cooling systems, and thermal insulation.

5. How can the convective heat transfer coefficient be increased?

The convective heat transfer coefficient can be increased by increasing the fluid velocity, using a more efficient heat transfer fluid, and increasing the surface area or using surface enhancements such as fins or turbulators. Additionally, improving the thermal conductivity of the surface material can also increase the convective heat transfer coefficient.

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