- 1). Define the Nusselt number as NuL = Convective heat transfer / Conductive heat transfer where NuL is the Nusselt number for the characteristic length of the test object. For example, in the case of a vertical plate, this would be the plate's length.
- 2). Calculate the convective heat transfer as hL where h is the convective heat transfer coefficient of the test material and L is the characteristic length. The conductive heat transfer kf is equal to the thermal conductivity.
- 3). Use the heat transfer values obtained in step 2 to calculate the Nusselt number from observed values. From NuL = Convective heat transfer / Conductive heat transfer = hL/kf, we therefore have NuL = hL/kf.
- 4). Observe that the Nusselt number is a dimensionless number without units. The Nusselt number is a ratio of heat transfer quantities and will therefore have no units, so long as the heat transfer quantities are measured in equal units.
- 5). Interpret the Nusselt number. A value near 1 where the convection and conduction heat transfers are approximately equal is known as laminar flow. A large Nusselt number indicates more active convection, such that a turbulent fluid flow can produce Nusselt numbers in the range of 100 to 1000.
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