the heat transfer coefficient of water

[5286]

can i know whether the inside heat transfer coefficient, hi and the outside heat transfer coeffcient of water flows inthe pipe, ho is how much ? Is it must lie between the range of 1000 to 2000 W/m2.oC?

 

[MortenA]

Im not quite sure if i got the question but yes: You can calculate the heat transfer coefficient. For water as for any liquid or gas you need:

-Thermal conductivity of liquid, k (water 0.59 kW/m C)
-Heat capacity, Cp (water: 4190 J/kg C)
-Viscosity, visc (water 0.001 kg/m s)
-Density, den (water 1000 kg/m3)
- Pipe diameter, D (m)
- Flow, V (m3/s)

1) Calculate Reynolds no.
Re= V*D*den/visc
2) Calculate Prandtls no:
Pr=Cp*visc/k
Use the correlation by Nussel:
Nu=0.023*Re^.8*Pr^.33

and

Nu=h*D/k

where h er the inside/ouside heat trabsfer coefficient.

When calculating from the outside (assuming the problem conserns pipe in pipe HX) use hydraulic diameter for D and calculate liquid velocity based on free area between pipes.

This is 100% standard heat transfer theory and any text book on the subject should tell you this.

Best Regards

Morten

 

[5286]

yes, i did the calculation as u show to me. But the problem is the values of hi and ho are very high, hi=5024 W/m20C and ho = 3800 W/m20C.

My design is actually an agitated reactor with immersed cooling coils. Cooling water is flowing inside the coils while glucose solution is outside the coil. My task now is to determine the number of coils used. At first, I need to calculate the heat transfer area. Therefore I need to calculate the heat transfer coefficient inside and outside the coils.

From the Coulson & Richardson (1993, Volume 6), hi for an agitated vessel is

hi x k /D = 1.10 Re(0.62) Pr (0.33)

and ho = hi x ID/OD

and Ud= 1/Uc + Rd where Rd is the fouling factor which i used 0.0003 m2oC/W.

After calculation, the result is hi around 5024 W/m2oC
ho around 3800 W/m2oC
Ud aroung 2000 W/m2oC

Do u know the overall heat transfer coefficient for a system consists of glucose solution (hot fluid) and cooling water (Cold fluid) in a heat exchanger system?