Editing Heat transfer coefficient (section)

====Internal flow, turbulent flow====
{{See also|Dittus-Boelter equation}}
The Dittus-Bölter correlation (1930) is a common and particularly simple correlation useful for many applications. This correlation is applicable when forced convection is the only mode of heat transfer; i.e., there is no boiling, condensation, significant radiation, etc. The accuracy of this correlation is anticipated to be ±15%.

For a fluid flowing in a straight circular pipe with a [[Reynolds number]] between 10,000 and 120,000 (in the [[turbulent]] pipe flow range), when the fluid's [[Prandtl number]] is between 0.7 and 120, for a location far from the pipe entrance (more than 10 pipe diameters; more than 50 diameters according to many authors<ref>{{cite book |author1=S. S. Kutateladze |author2=V. M. Borishanskii |title=A Concise Encyclopedia of Heat Transfer |publisher=Pergamon Press |year=1966}}</ref>) or other flow disturbances, and when the pipe surface is hydraulically smooth, the heat transfer coefficient between the bulk of the fluid and the pipe surface can be expressed explicitly as:

:<math>{h d \over k}= {0.023} \, \left({j d \over \mu}\right)^{0.8} \, \left({\mu c_p \over k}\right)^n</math>

where:
:<math>d</math> is the [[hydraulic diameter]]
:<math>k</math> is the [[thermal conductivity]] of the bulk fluid
:<math>\mu</math> is the fluid [[viscosity]]
:<math>j</math> is the [[mass flux]]
:<math>c_p</math> is the isobaric [[heat capacity]] of the fluid
:<math>n</math> is 0.4 for heating (wall hotter than the bulk fluid) and 0.33 for cooling (wall cooler than the bulk fluid).<ref>{{cite book |editor=F. Kreith |editor-link=Frank Kreith |title=The CRC Handbook of Thermal Engineering |url=https://archive.org/details/crchandbookofthe00krei |url-access=registration |publisher=CRC Press |year=2000}}</ref>

The fluid properties necessary for the application of this equation are evaluated at the [[bulk temperature]] thus avoiding iteration.