# Fully developed flow

All fluid flow is classified into one of two broad categories. The fluid flow can be either laminar or turbulent and therefore these two categories are:. The turbulent fluid does not flow in parallel layers, the lateral mixing is very high, and there is a disruption between the layers. Heat transfer through the fluid layer will be by convection when the fluid involves some motion and by conduction when the fluid layer is motionless.

Taking their ratio gives:. The preceding equation defines the Nusselt number. Therefore, the Nusselt number represents the enhancement of heat transfer through a fluid layer as a result of convection relative to conduction across the same fluid layer.

The larger the Nusselt numberthe more effective the convection. A larger Nusselt number corresponds to more effective convection, with turbulent flow typically in the — range. For turbulent flow, the Nusselt number is usually a function of the Reynolds number and the Prandtl number. The term streamline flow is descriptive of the flow because, in laminar flow, layers of water flowing over one another at different speeds with virtually no mixing between layers, fluid particles move in definite and observable paths or streamlines.

On the other hand turbulent flow tends to occur at higher velocities and low viscosity. Since laminar flow is common only in cases in which the flow channel is relatively small, the fluid is moving slowly, and its viscosity is relatively high, laminar flow is not common in industrial processes. Most industrial flows, especially those in nuclear engineering are turbulent. See also: Reynolds Number.

The average Nusselt number over the entire plate is determined by:. This relation gives the average heat transfer coefficient for the entire plate when the flow is laminar over the entire plate. In laminar flow in a tube with constant surface temperature, both the friction factor and the heat transfer coefficient remain constant in the fully developed region.

Therefore, for fully developed laminar flow in a circular tube subjected to constant surface heat fluxthe Nusselt number is a constant. There is no dependence on the Reynolds or the Prandtl numbers. In turbulent flow the speed of the fluid at a point is continuously undergoing changes in both magnitude and direction.

CFD is a branch of fluid mechanics that uses numerical analysis and algorithms to solve and analyze problems that involve turbulent fluid flows. This relation gives the average heat transfer coefficient for the entire plate only when the flow is turbulent over the entire plate, or when the laminar flow region of the plate is too small relative to the turbulent flow region.

See also: Dittus-Boelter Equation. For flows characterized by large property variations, the corrections e. The Nusselt number for the forced convection inside the fuel channel is then equal to:. Nusselt Number. The Nusselt number is a dimensionless number, named after a German engineer Wilhelm Nusselt. Nusselt number is equal to the dimensionless temperature gradient at the surface, and it provides a measure of the convection heat transfer occurring at the surface.

The conductive component is measured under the same conditions as the heat convection but with a stagnant fluid. The Nusselt number is to the thermal boundary layer what the friction coefficient is to the velocity boundary layer.

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## Laminar vs Turbulent – Nusselt Number

Forums Engineering Mechanical Engineering. Fully developed flow. Thread starter hanson Start date Oct 7, Hi all! What actually does a "fully developed flow" mean? Is it equivalent to saying the the velocity is uniform along the directon of flow?

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FredGarvin Science Advisor. Shawnzyoo said:. Last edited by a moderator: May 2, This website uses cookies to function and to improve your experience. By continuing to use our site, you agree to our use of cookies.

Discussion Closed This discussion was created more than 6 months ago and has been closed. To start a new discussion with a link back to this one, click here. I want to create a pipe which has fully developed flow through in it. Unfortunately, I am very new in comsol and I cannot find that fully developed choice in the program. Also I am not sure that there is that fully developed fluid flow choice in the program but I hope that.

Please inform me about my problem. Prior to v5. The outlet of that sacrificial solution could then be used as an inlet boundary condition for the "real" problem.

You could solve the sacrificial component with each solution of the real problem, or more efficiently, solve it once, and use it again thereafter. Now with v5.

You should carefully decide if it is sufficient for your problem; desired turbulence model, fluid properties, turbulent intensity, etc. Thanks for your answer.

Fully Developed Laminar Flow (Using Force Balance)

Unfortunately, I cannot understand what you suggest me : I am not sure that I can create a "sacrificial" solution for my real problem. By sacrifical solution, create a separate model that is geometrically an extrusion of your inlet boundary perhaps this is a pipe, square duct, etc.

Make this long enough to generate a fully developed flow. Solve for the sacrificial geometry. The outlet of this component would be a fully developed turbulent flow. Extract or couple this outlet flow and use that as the inlet boundary condition for your real problem. You can do this with a separate model or separate component within your same model, or combine it and have one larger component and model. Alternative 1: Find a correlation or curve fit for fully developed flow and generate a velocity profile.

Use this result as your inlet BC. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' or the latest version listed if standards is not an option. North America. Log Out Log In Contact. OK Learn More. Discussion Forum.A fluid flow need some length to fully develop the velocity profile after passing through components like bends, valves, pumps, turbines or similar. The entrance length can be expressed with the dimensionless Entrance Length Number as.

The Entrance length number correlation with the Reynolds Number for turbulent flow can be expressed as:. Add standard and customized parametric components - like flange beams, lumbers, piping, stairs and more - to your Sketchup model with the Engineering ToolBox - SketchUp Extension - enabled for use with the amazing, fun and free SketchUp Make and SketchUp Pro.

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Entrance Length and Developed Flow The entrance length is the length in a tube or duct after an obstruction - until the flow velocity profile is fully developed Sponsored Links. Tag Search en: entrance length developed flow velocity profile tube duct obstruction.

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### Fully Developed Flow

Citation This page can be cited as Engineering ToolBox, Entrance Length and Developed Flow. Modify access date. Scientific Online Calculator. Make Shortcut to Home Screen?Hot Threads.

Hi, For my experiment I was asked to determine the length of the tube for a fully developed flow to occur Entrance length as shown in the attachmentwith the following flow parameters.

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My question How do I find out the length of the tube required to have a fully developed flow at its end. A valve is connected to the end, so the flow should be fully developed at the end when it hits the valve. The length of the tube is unknown. How would one use reynolds number to calculate this when I have both the length and the reynolds number not known. Last edited: Apr 13, Chestermiller Mentor.

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What evidence will I need to submit along with my disability claim? Are there any risks to using the Fully Developed Claims program? What should the evidence show to support my disability claim? Can VA help me gather evidence? We can help you through the Fully Developed Claims program. When should I turn in my evidence? How do I turn in my information and evidence?November 9,what is the fully developed fluid flow? Hi all, I want to know that what are physical characteristics of fully developed fluid flows?

November 10,Re: what is the fully developed fluid flow? Hi charles A fully developed fluid flow through a pipe is one in which the boundary layer extends to the centreline. Hence the maximum velocity of the boundary layer is the same as the centreline velocity of the pipe. Hi Luke, If I understood that flow occurs in the narrow canal flow otherwise boundary layer can not extend to the centerline.

Thanks for help. Best regards. Fully developed flow is an ideal case and does not occur in reality as a laminar Bl cannot extend to the centreline, it will turn turbulent long before that happens Are you sure about this???? As long as the boundary layer velocity profile will not change along flow direction, this flow is called fully developed flow.

November 12,Re: what is the fully developed fluid flow? I agree with Bian. Fully developed flow was when you have zero gradients in the streamwise direction. November 13,Re: what is the fully developed fluid flow? I would add that zero gradients is for velocity, not for pressure in the streamwise direction.