![]() ![]() Where h is the convective heat transfer coefficient of the flow, L is the characteristic length, k is the thermal conductivity of the fluid. ![]() The convection and conduction heat flows are parallel to each other and to the surface normal of the boundary surface, and are all perpendicular to the mean fluid flow in the simple case. A larger Nusselt number corresponds to more active convection, with turbulent flow typically in the 100–1000 range. A similar non-dimensional parameter is Biot Number, with the difference that the thermal conductivity is of the solid body and not the fluid.Ī Nusselt number close to one, namely convection and conduction of similar magnitude, is characteristic of " slug flow" or laminar flow. The conductive component is measured under the same conditions as the heat convection but with a (hypothetically) stagnant (or motionless) fluid. Named after Wilhelm Nusselt, it is a dimensionless number. In this context, convection includes both advection and diffusion. The results show that the proposed correlations are more practical and they can predict the developing, fully developed, and average Nusselt numbers with very good accuracy across a wider range of flow conditions.In heat transfer at a boundary (surface) within a fluid, the Nusselt number ( Nu) is the ratio of convective to conductive heat transfer across ( normal to) the boundary. Moreover, the maximum and average differences for average Nusselt numbers are 4.59% and 2.01%, respectively. The maximum and average differences between the local Nusselt numbers predicted by the proposed correlations and the analytical data are respectively 2.04% and 0.38% for fully developed flows and 9.97% and 1.35% for developing flows. The correlations use exponential and power law functions of dimensionless axial and radial lengths they are more accurate, easier to use, more similar to fundamental analytical solutions, and require fewer terms. The correlations are developed based on the results of available series solutions for four fundamental boundary conditions. This study proposes new correlations for the local and average Nusselt numbers in hydrodynamically fully developed and thermally developing or fully developed regions of laminar flows. ![]() There are many problems involving heat transfer in concentric annuli which require accurate heat transfer coefficients for laminar and turbulent flows. ![]() Concentric circular annular ducts are common and important elements in fluid flow and heat transfer equipment, including chemical mixing devices and heat exchangers. ![]()
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