diff options
Diffstat (limited to 'subsurface-core/gas-model.c')
| -rw-r--r-- | subsurface-core/gas-model.c | 48 |
1 files changed, 48 insertions, 0 deletions
diff --git a/subsurface-core/gas-model.c b/subsurface-core/gas-model.c new file mode 100644 index 000000000..9cffd5e47 --- /dev/null +++ b/subsurface-core/gas-model.c @@ -0,0 +1,48 @@ +/* gas-model.c */ +/* gas compressibility model */ +#include <stdio.h> +#include <stdlib.h> +#include "dive.h" + +/* + * This gives an interative solution of hte Redlich-Kwong equation for the compressibility factor + * according to https://en.wikipedia.org/wiki/Redlich–Kwong_equation_of_state + * in terms of the reduced temperature T/T_crit and pressure p/p_crit. + * + * Iterate this three times for good results in our pressur range. + * + */ + +double redlich_kwong_equation(double t_red, double p_red, double z_init) +{ + return (1.0/(1.0 - 0.08664*p_red/(t_red * z_init)) - + 0.42748/(sqrt(t_red * t_red * t_red) * ((t_red*z_init/p_red + 0.08664)))); +} + +/* + * At high pressures air becomes less compressible, and + * does not follow the ideal gas law any more. + */ +#define STANDARD_TEMPERATURE 293.0 + +double gas_compressibility_factor(struct gasmix *gas, double bar) +{ + /* Critical points according to https://en.wikipedia.org/wiki/Critical_point_(thermodynamics) */ + + double tcn2 = 126.2; + double tco2 = 154.6; + double tche = 5.19; + + double pcn2 = 33.9; + double pco2 = 50.5; + double pche = 2.27; + + double tc, pc; + + tc = (tco2 * get_o2(gas) + tche * get_he(gas) + tcn2 * (1000 - get_o2(gas) - get_he(gas))) / 1000.0; + pc = (pco2 * get_o2(gas) + pche * get_he(gas) + pcn2 * (1000 - get_o2(gas) - get_he(gas))) / 1000.0; + + return (redlich_kwong_equation(STANDARD_TEMPERATURE/tc, bar/pc, + redlich_kwong_equation(STANDARD_TEMPERATURE/tc, bar/pc, + redlich_kwong_equation(STANDARD_TEMPERATURE/tc, bar/pc,1.0)))); +} |