Convective heat transfer coefficient


by Carlo09
Tags: coefficient, convective, heat, transfer
Carlo09
Carlo09 is offline
#1
Nov13-09, 04:53 PM
P: 15
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!
Phys.Org News Partner Engineering news on Phys.org
SensaBubble: It's a bubble, but not as we know it (w/ video)
WSU innovation improves drowsy driver detection
Faster computation of electromagnetic interference on an electronic circuit board
Mech_Engineer
Mech_Engineer is offline
#2
Nov13-09, 06:02 PM
Sci Advisor
PF Gold
Mech_Engineer's Avatar
P: 2,234
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.
Carlo09
Carlo09 is offline
#3
Nov14-09, 07:52 AM
P: 15
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

Mech_Engineer
Mech_Engineer is offline
#4
Nov16-09, 09:04 AM
Sci Advisor
PF Gold
Mech_Engineer's Avatar
P: 2,234

Convective heat transfer coefficient


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.
Mech_Engineer
Mech_Engineer is offline
#5
Nov16-09, 09:26 AM
Sci Advisor
PF Gold
Mech_Engineer's Avatar
P: 2,234
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 text book, "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.
Attached Files
File Type: pdf Mathcad - Gasoline flowing in a tube.pdf (18.4 KB, 33 views)


Register to reply

Related Discussions
heat transfer coefficient of bare wire in still air Electrical Engineering 9
calculating heat transfer coefficient from experimental data Classical Physics 6
coupled conductive-convective heat transfer using FDM Engineering, Comp Sci, & Technology Homework 1
heat transfer coefficient General Physics 2