Nusselt flat

Returns the Nusselt number for a fluid going over a flat surface.

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Interface
Nusselt Flat
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Interface

C++

Excel

Nusselt Flat

doubleNusselt_flat(	double	`Pr`
	double	`Re`	)[inline]

This module calculates the Nusselt number for a fluid which flows over a flat surface, the flow being either laminar or turbulent. The fluid must keep its state of matter during the heat transfer process.

The formulae for each case are given by

${\rm Nu} = 0.335 {\rm Re}^{0.5} {\rm Pr}^{0.5} \qquad \mbox{(laminar case)}$

(2)

and

${\rm Nu} = 0.36 {\rm Re}^{0.8} {\rm Pr}^{0.75} \qquad \mbox{(turbulent case)}$

(3)

where $\inline {\rm Re}$ is the Reynolds number and $\inline {\rm Pr}$ is the Prandtl number of the fluid. If the Reynolds number is less than 2000 the flow is considered laminar, while if it is greater than 4000 the flow is considered turbulent.

In the diagram below the relation between the velocity of the fluid and its corresponding Reynolds number is shown, as well as the unit heat flow in the laminar, unpredictable and turbulent cases.

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Example 1

The following code calculates the Nusselt number for Ethylene Glycol at 17 degrees Celsius, considering both the laminar and turbulent cases.

#include <codecogs/engineering/heat_transfer/convection/nusselt_flat.h>
#include <stdio.h>
 
int main()
{
  double Pr = 233.7745380139, Re1 = 1700, Re2 = 4200;
 
  printf("\nEthylene Glycol at 17 deg. Celsius\n\n");
 
  printf("Re = %.2lf (laminar flow)\n", Re1);
  printf("Nu = %.4lf\n\n", 
  Engineering::Heat_Transfer::Convection::Nusselt_flat(Pr, Re1));
 
  printf("Re = %.2lf (turbulent flow)\n", Re2);
  printf("Nu = %.4lf\n\n", 
  Engineering::Heat_Transfer::Convection::Nusselt_flat(Pr, Re2));
 
  return 0;
}

Output

Ethylene Glycol at 17 deg. Celsius
 
Re = 1700.00 (laminar flow)
Nu = 211.1873
 
Re = 4200.00 (turbulent flow)
Nu = 17041.1869

References

Dan Stefanescu, Mircea Marinescu - "Termotehnica"

Parameters

Pr	the Prandtl number of the fluid
Re	the Reynolds number of the fluid

Returns

the Nusselt number of the fluid with given parameters

Authors

Grigore Bentea, Lucian Bentea (November 2006)

Source Code

Source code is available when you buy a Commercial licence.

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