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741099bdbb
When collecting the data for the infobox, we have already computed the current partial pressures of the breathing gas taking into accoutn the divemode. Use those rather than fractions (which for CCR mode are those of diluent) to compute the gas density. Reported-by: Pietro Tranquillini <p.tranquillini@gmail.com> Signed-off-by: Robert C. Helling <helling@atdotde.de>
85 lines
2.2 KiB
C
85 lines
2.2 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/* gas-model.c */
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/* gas compressibility model */
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#include <stdio.h>
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#include <stdlib.h>
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#include "dive.h"
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/* "Virial minus one" - the virial cubic form without the initial 1.0 */
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static double virial_m1(const double coeff[], double x)
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{
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return x*coeff[0] + x*x*coeff[1] + x*x*x*coeff[2];
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}
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/*
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* Z = pV/nRT
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*
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* Cubic virial least-square coefficients for O2/N2/He based on data from
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*
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* PERRY’S CHEMICAL ENGINEERS’ HANDBOOK SEVENTH EDITION
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*
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* with the lookup and curve fitting by Lubomir.
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*
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* The "virial" form of the compression factor polynomial is
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*
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* Z = 1.0 + C[0]*P + C[1]*P^2 + C[2]*P^3 ...
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*
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* and these tables do not contain the initial 1.0 term.
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*
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* NOTE! Helium coefficients are a linear mix operation between the
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* 323K and one for 273K isotherms, to make everything be at 300K.
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*/
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double gas_compressibility_factor(struct gasmix gas, double bar)
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{
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static const double o2_coefficients[3] = {
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-7.18092073703e-04,
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+2.81852572808e-06,
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-1.50290620492e-09
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};
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static const double n2_coefficients[3] = {
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-2.19260353292e-04,
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+2.92844845532e-06,
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-2.07613482075e-09
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};
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static const double he_coefficients[3] = {
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+4.87320026468e-04,
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-8.83632921053e-08,
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+5.33304543646e-11
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};
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int o2, he;
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double Z;
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/*
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* The curve fitting range is only [0,500] bar.
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* Anything else is way out of range for cylinder
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* pressures.
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*/
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if (bar < 0) bar = 0;
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if (bar > 500) bar = 500;
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o2 = get_o2(gas);
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he = get_he(gas);
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Z = virial_m1(o2_coefficients, bar) * o2 +
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virial_m1(he_coefficients, bar) * he +
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virial_m1(n2_coefficients, bar) * (1000 - o2 - he);
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/*
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* We add the 1.0 at the very end - the linear mixing of the
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* three 1.0 terms is still 1.0 regardless of the gas mix.
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*
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* The * 0.001 is because we did the linear mixing using the
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* raw permille gas values.
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*/
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return Z * 0.001 + 1.0;
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}
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/* Compute the new pressure when compressing (expanding) volome v1 at pressure p1 bar to volume v2
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* taking into account the compressebility (to first order) */
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double isothermal_pressure(struct gasmix gas, double p1, int volume1, int volume2)
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{
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double p_ideal = p1 * volume1 / volume2 / gas_compressibility_factor(gas, p1);
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return p_ideal * gas_compressibility_factor(gas, p_ideal);
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}
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