overall heat transfer coefficient

[JohnWeal]

Hello

For a stainless steel tube, 168mm OD and 2mm wall, carrying digested sludge at 36 deg C and the outer annulus carrying teated water at 70 deg C Counter-current flow and both flows are turbulant, is there a 'rule of thumb' practical overall heat transfer 'U' value used in calculations?

I have an old standard from the 1980's but suspect since there are better manufacturing techniques nowadays, (ie the use of rippled or suaged tubes to create even more turbulance / improved heat transfer), the value given as 0.9 kW/m2.deg C could be a little low.

Can anyone state an alternative fairly well proven value from modern design criteria?

Regards
John

 

[srfish]

I don't have an practical overall heat transfer but for sludge type materials, the tube velocity should be at least 4 ft/sec.

 

[jrrocks]

Here, you can calculate U value as per following steps -
1. Calculate heat transfer rate using Q = m X Cp X dT
2. Now, you can calculated U-value as per Q = U.A.LMTD, so U = Q/A.LMTD