From bb6ceba4ac0310c504f931674a71e9e77c0afa1c Mon Sep 17 00:00:00 2001
From: "Robert C. Helling" <helling@atdotde.de>
Date: Fri, 12 May 2017 15:36:24 +0200
Subject: [PATCH] Compute and display gas density
This appears to be critical for work of breathing so it might be
worthwhile to compute. So far only in infobox.
For background, see
https://www.youtube.com/watch?v=QBajM3xmOtc
Signed-off-by: Robert C. Helling <helling@atdotde.de>
---
core/dive.h | 2 ++
core/gas-model.c | 8 ++++++++
core/profile.c | 6 +++++-
core/profile.h | 1 +
core/units.h | 2 +-
5 files changed, 17 insertions(+), 2 deletions(-)
diff --git a/core/dive.h b/core/dive.h
index fa89edc44..c2ae1e36d 100644
--- a/core/dive.h
+++ b/core/dive.h
@@ -139,6 +139,8 @@ extern int units_to_sac(double volume);
extern int gas_volume(cylinder_t *cyl, pressure_t p);
extern double gas_compressibility_factor(struct gasmix *gas, double bar);
extern double isothermal_pressure(struct gasmix *gas, double p1, int volume1, int volume2);
+extern double gas_density(struct gasmix *gas, int pressure);
+
static inline int get_o2(const struct gasmix *mix)
diff --git a/core/gas-model.c b/core/gas-model.c
index dd84e9b9d..49c677967 100644
--- a/core/gas-model.c
+++ b/core/gas-model.c
@@ -9,6 +9,8 @@
#define virial_m1(C, x1, x2, x3) (C[0]*x1+C[1]*x2+C[2]*x3)
/*
+ * Z = pV/nRT
+ *
* Cubic virial least-square coefficients for O2/N2/He based on data from
*
* PERRY’S CHEMICAL ENGINEERS’ HANDBOOK SEVENTH EDITION
@@ -73,3 +75,9 @@ double isothermal_pressure(struct gasmix *gas, double p1, int volume1, int volum
return p_ideal * gas_compressibility_factor(gas, p_ideal);
}
+
+inline double gas_density(struct gasmix *gas, int pressure) {
+ int density = gas->he.permille * HE_DENSITY + gas->o2.permille * O2_DENSITY + (1000 - gas->he.permille - gas->o2.permille) * N2_DENSITY;
+
+ return density * (double) pressure / gas_compressibility_factor(gas, pressure / 1000.0) / SURFACE_PRESSURE / 1000000.0;
+}
diff --git a/core/profile.c b/core/profile.c
index 86bc974b8..d46904cbe 100644
--- a/core/profile.c
+++ b/core/profile.c
@@ -1151,6 +1151,7 @@ static void calculate_gas_information_new(struct dive *dive, struct plot_info *p
entry->pressures.n2 / amb_pressure * N2_DENSITY +
entry->pressures.he / amb_pressure * HE_DENSITY) /
(O2_IN_AIR * O2_DENSITY + N2_IN_AIR * N2_DENSITY) * 1000 - 10000;
+ entry->density = gas_density(&dive->cylinder[cylinderindex].gasmix, depth_to_mbar(entry->depth, dive));
if (entry->mod < 0)
entry->mod = 0;
if (entry->ead < 0)
@@ -1292,7 +1293,7 @@ static void plot_string(struct plot_info *pi, struct plot_data *entry, struct me
{
int pressurevalue, mod, ead, end, eadd;
const char *depth_unit, *pressure_unit, *temp_unit, *vertical_speed_unit;
- double depthvalue, tempvalue, speedvalue, sacvalue;
+ double depthvalue, tempvalue, speedvalue, sacvalue, density;
int decimals;
const char *unit;
@@ -1327,15 +1328,18 @@ static void plot_string(struct plot_info *pi, struct plot_data *entry, struct me
put_format(b, translate("gettextFromC", "MOD: %d%s\n"), mod, depth_unit);
}
eadd = lrint(get_depth_units(lrint(entry->eadd), NULL, &depth_unit));
+
if (prefs.ead) {
switch (pi->dive_type) {
case NITROX:
ead = lrint(get_depth_units(lrint(entry->ead), NULL, &depth_unit));
put_format(b, translate("gettextFromC", "EAD: %d%s\nEADD: %d%s\n"), ead, depth_unit, eadd, depth_unit);
+ put_format(b, translate("gettextFromC", "density: %.1fg/l\n"), entry->density);
break;
case TRIMIX:
end = lrint(get_depth_units(lrint(entry->end), NULL, &depth_unit));
put_format(b, translate("gettextFromC", "END: %d%s\nEADD: %d%s\n"), end, depth_unit, eadd, depth_unit);
+ put_format(b, translate("gettextFromC", "density: %.1fg/l\n"), entry->density);
break;
case AIR:
case FREEDIVING:
diff --git a/core/profile.h b/core/profile.h
index 0fd284d47..079aaa1db 100644
--- a/core/profile.h
+++ b/core/profile.h
@@ -64,6 +64,7 @@ struct plot_data {
int bearing;
double ambpressure;
double gfline;
+ double density;
};
struct ev_select {
diff --git a/core/units.h b/core/units.h
index 7e4c2e7d2..df63dba49 100644
--- a/core/units.h
+++ b/core/units.h
@@ -14,7 +14,7 @@ extern "C" {
#define O2_IN_AIR 209 // permille
#define N2_IN_AIR 781
#define O2_DENSITY 1429 // mg/Liter
-#define N2_DENSITY 1251
+#define N2_DENSITY 1165
#define HE_DENSITY 179
#define SURFACE_PRESSURE 1013 // mbar
#define SURFACE_PRESSURE_STRING "1013"