Almost all convection calculations hinge on the ability to choose the correctNusselt number correlation. The Nusselt number is defined as

Nu = |
hLchr |

k |

wherehis the convective heat transfer coefficient,Lis the appropriate characteristic length and_{chr}kis the fluid thermal conductivity.The

physicalinterpretation of Nusselt number is the enhancement of heat transfer due to convection over conduction alone. IfNu=1, then, than your fluid is stationary and all heat transfer is by conduction. WithNu>1, the fluid motion enhances heat transfer byadvection.The Nusselt number is of paramount importance because it contains the heat transfer coefficient information. Indeed, one interpretation of Nusselt number is simply that of dimesionless heat transfer coefficient. In simplest terms, Nu is simply a dimensionless ehat transfer coefficient.