Final answer:
The Nusselt number is a dimensionless parameter represented by hD/K, which is used in most correlations for natural convection heat transfer coefficient calculations. It relates convective to conductive heat transfer and is pivotal in simplifying and analyzing heat transfer scenarios.
Step-by-step explanation:
The dimensionless Nusselt number is most commonly used for correlations in natural convection heat transfer coefficient calculations. The correct definition of the Nusselt number for this scenario is hD/K, where 'h' represents the heat transfer coefficient, 'D' is a characteristic dimension (such as diameter in case of a cylinder), and 'K' denotes the thermal conductivity of the fluid. The Nusselt number essentially relates the convective to conductive heat transfer across a fluid layer.
In the context of heat transfer analysis, the Nusselt number is essential in most correlations as it simplifies complex physical situations into a form that can be more easily analyzed and compared. It plays a key role in assessing the efficacy of the convective process under different physical situations.