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flow shield

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Interface

#include <codecogs/engineering/heat_transfer/radiation/flow_shield.h>

using namespace Engineering::Heat_Transfer::Radiation;

	double	`flow_shield` (double T1, double T2, double e1, double e2, int n, double es)[inline]* Computes the radiative heat flow between two plane surfaces that are separated by a number of absorptive thin shields.
	Real	cc_flow_shield (Real T1, Real T2, Real e1, Real e2, Integer n, Range es) This function is available as a Microsoft Excel add-in.

Function Documentation

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doubleflow_shield(	double	`T1`
	double	`T2`
	double	`e1`
	double	`e2`
	int	`n`
	double*	`es`	)[inline]

This module calculates the radiative heat flow per unit surface between two plane surfaces, considering the case when these are separated by a number of absorptive thin shields.

On account of the Stefan-Boltzmann law, the unit radiative heat flow between the two surfaces separated by

shields is given by

(1)

$\displaystyle q = e_{1, S_1, S_2, \ldots, S_n, 2} \,\, C_0 \left[\left(\frac{T_1}{100}\right)^4 - \left(\frac{T_2}{100}\right)^4\right] \qquad \left[\frac{W}{m^2}\right]$

where

(2)

$\displaystyle e_{1, S_1, S_2, \ldots, S_n, 2} = \left(\frac{1}{e_{1,S_1}} + \frac{1}{e_{S_1,S_2}} + \frac{1}{e_{S_2,S_3}} + \ldots + \frac{1}{e_{S_{n-1},S_n}} + \frac{1}{e_{S_n,2}} \right)^{-1}$

and

(3)

$\displaystyle e_{1, S_1} = \left(\frac{1}{e_1} + \frac{1}{e_{S_1}} - 1\right)^{-1} \qquad e_{S_n, 2} = \left(\frac{1}{e_2} + \frac{1}{e_{S_n}} - 1\right)^{-1}$

(4)

$\displaystyle e_{S_i, S_{i+1}} = \left(\frac{1}{e_{S_i}} + \frac{1}{e_{S_{i+1}}} - 1\right)^{-1} \qquad i = 1, 2, \ldots, n - 1$

with

the emissivity factors of the first and second surface $(0 < e_1, e_2 \leq 1)$ , $e_{S_i}$ the emissivity factor of the

-th shield $(0 < e_{S_i} \leq 1)$ ,

the emissivity constant of the black body $\displaystyle \left(C_0 \approx 5.669 \left[\frac{W}{m^2 K^4}\right]\right)$ and

the corresponding absolute temperatures of the two plane surfaces.

The above expression of the unit heat flow can be further simplified to the following formula

(5)

$\displaystyle q = C_0 \left[\left(\frac{T_1}{100}\right)^4 - \left(\frac{T_2}{100}\right)^4\right] \left[\frac{1}{e_1} + \frac{1}{e_2} - (n + 1) + 2 \sum_{i=1}^n \frac{1}{e_{S_i}} \right]^{-1} \qquad \left[\frac{W}{m^2}\right].$

In the diagram below is shown the radiative heat transfer between two plane surfaces, separated by

shields

, $\ldots$ ,

Example:

The example below computes the unit radiative heat flow between an oxidated aluminium plane surface at 873.16 degrees Kelvin and an oxidated copper plane surface at 403.16 degrees Kelvin, separated by two thin shields. The first shield is made of zinc-covered iron at 297.16 degrees Kelvin, while the second is made of brass at 323.16 degrees Kelvin. You may notice that in the presence of these two thin shields, the heat flow between the given plane surfaces decreases by a factor of 72% than in the case of a non-absorptive medium, as calculated in the Engineering/Heat_Transfer/Radiation/flow_noshield module.

#include <codecogs/engineering/heat_transfer/radiation/flow_shield.h>
#include <stdio.h>
 
int main()
{
  // the temperature of the oxidated aluminium surface
  double T1 = 873.16;
 
  // the temperature of the oxidated copper surface
  double T2 = 403.16;
 
  // the emission factor of the aluminium surface
  double e1 = 0.19;
 
  // the emission factor of the copper surface
  double e2 = 0.76;
 
  // the number of shields
  int n = 2;
 
  // the emission factors of the iron and brass shields
  double es[3] = {0.276, 0.22};
 
  // display radiative heat flow between the two plane surfaces
  printf("Radiative heat flow = %.5lf W per sq. meter\n",
  Engineering::Heat_Transfer::Radiation::flow_shield
  (T1, T2, e1, e2, n, es));
 
  return 0;
}

Output:

Radiative heat flow = 1579.33128 W per sq. meter

Parameters:

T1	the absolute temperature of the first surface (Kelvin)
T2	the absolute temperature of the second surface (Kelvin)
e1	the emissivity factor of the first surface
e2	the emissivity factor of the second surface
n	the number of shields
es	an array with the emissivity factors of the shields

Returns:

the radiative heat flow between the two plane surfaces (Watt per square meter)

Note:

A table with the emissivity factors of various materials at different temperatures can be found at the following link http://www.monarchserver.com/TableofEmissivity.pdf

References:

Dan Stefanescu, Mircea Marinescu - "Termotehnica"

Authors:

Grigore Bentea, Lucian Bentea (November 2006)

Source Code:

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Last Modified: 18 Oct 07 @ 17:07 Page Rendered: 2008-05-08 16:27:15

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