From: Linus Torvalds <[email protected]> Date: Wed, 2 Mar 2016 13:49:59 -0800 Subject: [PATCH 1/2] gas model: split up gas compressibility into a file of its own
The gas compressibility is such a specialized thing that I really prefer having it separate. This keeps Robert's Redlich-Kwong equation as-is, but let's experiment with other models soon... Signed-off-by: Linus Torvalds <[email protected]> --- subsurface-core/CMakeLists.txt | 1 + subsurface-core/dive.c | 43 ------------------------------------- subsurface-core/gas-model.c | 48 ++++++++++++++++++++++++++++++++++++++++++ 3 files changed, 49 insertions(+), 43 deletions(-) create mode 100644 subsurface-core/gas-model.c diff --git a/subsurface-core/CMakeLists.txt b/subsurface-core/CMakeLists.txt index 703864ad0b22..d9b1d3421a6a 100644 --- a/subsurface-core/CMakeLists.txt +++ b/subsurface-core/CMakeLists.txt @@ -36,6 +36,7 @@ set(SUBSURFACE_CORE_LIB_SRCS divelist.c equipment.c file.c + gas-model.c git-access.c libdivecomputer.c liquivision.c diff --git a/subsurface-core/dive.c b/subsurface-core/dive.c index 4108c0942711..0837675826d9 100644 --- a/subsurface-core/dive.c +++ b/subsurface-core/dive.c @@ -846,49 +846,6 @@ static void update_min_max_temperatures(struct dive *dive, temperature_t tempera } } -/* - * 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)))); -} - int gas_volume(cylinder_t *cyl, pressure_t p) { double bar = p.mbar / 1000.0; diff --git a/subsurface-core/gas-model.c b/subsurface-core/gas-model.c new file mode 100644 index 000000000000..9cffd5e470e0 --- /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)))); +} -- 2.7.2.334.g7c0da37 _______________________________________________ subsurface mailing list [email protected] http://lists.subsurface-divelog.org/cgi-bin/mailman/listinfo/subsurface
