What is Nusselt number: Definition and 13 Discussions

In fluid dynamics, the Nusselt number (Nu) is the ratio of convective to conductive heat transfer at a boundary in a fluid. Convection includes both advection (fluid motion) and diffusion (conduction). The conductive component is measured under the same conditions as the convective but for a hypothetically motionless fluid. It is a dimensionless number, closely related to the fluid's Rayleigh number.A Nusselt number of value one represents heat transfer by pure conduction. A value between one and 10 is characteristic of slug flow or laminar flow. A larger Nusselt number corresponds to more active convection, with turbulent flow typically in the 100–1000 range. The Nusselt number is named after Wilhelm Nusselt, who made significant contributions to the science of convective heat transfer.A similar non-dimensional property is the Biot number, which concerns thermal conductivity for a solid body rather than a fluid. The mass transfer analogue of the Nusselt number is the Sherwood number,

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  1. bardia sepehrnia

    Engineering Average heat transfer coefficient (forced convection)

    So firstly, I don't understand if the mass flow rate is for steam or for water. If it is for water, I know I can find the heat transfer rate using equation:Q=mcdeltaT. But then I don't know how to find h (the average heat transfer coefficient) because I don't know the surface area (As). I can...
  2. G

    Laminar flow in a tube, heat transfer coefficient-sanity check

    Hi there, Hopefully this is a very easy question and you all can just confirm this for me. When calculating heat transfer into a fluid from a heated tube, is it correct to say that the heat transfer coefficient is *not* dependent on the tube diameter? So, if we solve for T_{out}, we get...
  3. R

    Fluid mechanics/heat transfer - meaning of Nusselt number

    The Nusselt number represents the ratio of heat transfer by convection relative to conduction. At the onset of convection does this correspond to a Nusselt number of 1?
  4. F

    Nusselt number for a developing turbulent flow in the entrance region

    Anyone knows if i can calculated Nusselt number for a developing turbulent flow in the entrance region for a duct/ tube?
  5. C

    Nusselt Number Correlation

    I am looking for a Nusselt number correlation that will work for a shell & tube heat exchanger in the Re < 3000 region, i.e. extremely laminar flow (for a lab experiment). I've been searching for a while now, but can only find empirical correlations for Re > 3000, and was thus hoping that...
  6. M

    Heat and mass transfer analogy to find average Nusselt no.

    I am trying to find an expression for the average Nusselt number corresponding to heat transfer from an isothermal disk. Given: ShD≡hm(r)D/DAB=Sho[1 + a (r/ro)n] (1) Sho=hm(r=0)D/DAB=0.814ReD1/2Sc0.36 (2) Relevant equations: Average nusselt number is defined as Nuav=havD/k where k...
  7. M

    Nusselt Number for Flat Plate: Laminar vs Turbulent

    The Nusselt number for an entire flat plate in the turbulent region has two different equations: One for Turbulent and one for Combined Laminar and Turbulent. How do I know when to use one or the other?
  8. J

    Nusselt Number dimension question

    So, in Nu=\frac{hD}{k} h is the heat transfer coefficient, and D is the diameter of the pipe in which heat transfer takes place... ..but what are the dimensions of k in terms of mass (M), length (L), time (T) and temperature (\theta)? So far, I've worked out that the units for h...
  9. J

    Dimensions of k in Nusselt Number

    Homework Statement A common dimensionless group used in heat transfer calculations is defined as: Nu=\frac{hD}{k} where h is the heat transfer coefficient, and D is the diameter of the pipe in which heat transfer takes place. Please determine the dimensions of the quantity k in...
  10. A

    How can I extract the Nusselt number over time in Ansys for a cavity model?

    Hi everybody I built a cavity model in Ansys in order to modelling natural convection heat transfer inside a heat exchanger. But I do not know how to export Nusselt number over time. I need to see how it varies while time passing. Please help me. I know that from Reports part of software I can...
  11. D

    Nusselt Number Equation Simplification?

    Homework Statement See the picture for the homework problem: http://i41.tinypic.com/2drk2x.png Homework Equations I'm having trouble converting between the first equation and the second one. I understand that Nu_x=h_x*x/k Re = rho*v*x/visc Pr = c_p*visc/k But how the heck do I...
  12. A

    How to Calculate Nusselt Number for Air Flow in a Pipe with ANSYS?

    Hi i need to calculate nusselt number for stimulation of air flow in a pipe with 5mm diameter and the pressure is 5atm. it should be in the form: Nu = N1 + N2 Re^N3*Pr^N4 and i want to calculate N1,N2,N3,N4. but i don't know how? can anyone Help?
  13. S

    How to calculate Nusselt number

    Hello I need to calculate the Nusselt number for liquid sodium in a pipeline. Length of the pipeline is 3 meter. Diameter of the pipeline is 0.3 meter. Heat flux through outer surface of the pipeline is equal zero. Temperature on the right side and left side of the pipeline is 573 K and 773 K...