# Heat transfer help please

1. Apr 29, 2008

### JMorris

I am working on my first heat transfer design and I have almost all of my data, but I do not know what to do with it.

I know the following for the material on each side of a wall:
specific heat
viscosity
thermal conductivity
density
velocity

for the wall in between them I know the following:
thickness
mean surface area
thermal conductivity

i understand all about Reynalds, Nusselts, and Prandtl number as well.

i also know the temperature that both substances will initially be.

i am trying to figure out how long in time it will take to get one substance (nylon in solid pellet form) to drop from 350 F to 100 F. this nylon will be in a tube with an auger inside moving at a slow rate to transport through the system. On the other side of the wall in the tube will be cold water around 40 F that will be circulating in order to draw the heat out of the nylon.

if I can figure out the temperature of either side of the wall, I can solve for how long my tube needs to be through lump mass approx method.
Here are some values I have if I attempt to solve for the wall temp assuming it is convective heat transfer:

For Nylon
Cp specific heat capacity 1670 J/kg-K
k thermal conductivity 0.25 W/m-K
v velocity 1.524 m/hr (rate of auger)
p density 560.645 kg/m^3
R resistance 102317.0565
u viscosity ?? it is around for 1E+12 kg/m-s for solids but this gives me a "h" that doesnt make sense when i solve for it using the Nusselt number.

so that didnt seem to work so instead i assume it is conductive heat transfer and use the following:

k thermal conductivity 0.25 W/m-K
x thickness 0.889 m
A Surface Area 17.01674016 m^2
R resistance 0.208970694

but again this does not make sense cause i end up getting a temperature on the S.S. wall of less than 41 F when it is next to 350 F, and the water temp on the other side of the wall is 40 F.

what gives?

and thanx.

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Can you offer guidance or do you also need help?
Draft saved Draft deleted