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/* gas-model.c */
/* gas compressibility model */
#include <stdio.h>
#include <stdlib.h>
#include "dive.h"
/* "Virial minus one" - the virial cubic form without the initial 1.0 */
#define virial_m1(C, x1, x2, x3) (C[0]*x1+C[1]*x2+C[2]*x3)
/*
* Cubic virial least-square coefficients for O2/N2/He based on data from
*
* PERRY’S CHEMICAL ENGINEERS’ HANDBOOK SEVENTH EDITION
*
* with the lookup and curve fitting by Lubomir.
*
* The "virial" form of the compression factor polynomial is
*
* Z = 1.0 + C[0]*P + C[1]*P^2 + C[2]*P^3 ...
*
* and these tables do not contain the initial 1.0 term.
*
* NOTE! Helium coefficients are a linear mix operation between the
* 323K and one for 273K isotherms, to make everything be at 300K.
*/
double gas_compressibility_factor(struct gasmix *gas, double bar)
{
static const double o2_coefficients[3] = {
-0.00071809207370164567,
+0.00000281852572807643,
-0.00000000150290620491
};
static const double n2_coefficients[3] = {
-0.00021926035329221337,
+0.00000292844845531647,
-0.00000000207613482075
};
static const double he_coefficients[3] = {
+0.00047961098687979363,
-0.00000004077670019935,
+0.00000000000077707035
};
double o2, he;
double x1, x2, x3;
double Z;
o2 = get_o2(gas) / 1000.0;
he = get_he(gas) / 1000.0;
x1 = bar; x2 = x1*x1; x3 = x2*x1;
Z = virial_m1(o2_coefficients, x1, x2, x3) * o2 +
virial_m1(he_coefficients, x1, x2, x3) * he +
virial_m1(n2_coefficients, x1, x2, x3) * (1.0 - o2 - he);
/*
* We add the 1.0 at the very end - the linear mixing of the
* three 1.0 terms is still 1.0 regardless of the gas mix.
*/
return Z + 1.0;
}
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