Convection

Convection is the mechanism of heat transfer through a fluid in the presence of bulk fluid motion. It is classified as natural (or free) and forced convection depending on how the fluid motion is initiated. In forced convection, fluid is forced to flow by external means such as pump or fan. Natural convection is caused by natural means such as buoyancy effects.

Nusselt Number The larger the Nusselt number, the more effective the convection

Film temperature

The average Nusselt number over the entire plate is:

The average heat transfer coefficient is:

Example

film 210

Example (2) :

Example Engine oil at 60 ºC flows over the upper surface of a 5-m-long flat plate whose temperature is 20 ºC with a velocity of 2 m/s. Determine the rate of heat transfer per unit width of the entire plate.

The average Nusselt number for cylindrical and non-cylindrical pipes is expressed as: C, m, and n are constants evaluated from the following table. All fluid properties are evaluated at film temperature.

Next week (Sunday) you will have a quiz in the material covered so far.