1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
|
/* gas-model.c */
/* gas compressibility model */
#include <stdio.h>
#include <stdlib.h>
#include "dive.h"
/*
* Generic cubic polynomial
*/
static double cubic(double bar, const double coefficient[])
{
double x0 = 1.0,
x1 = bar,
x2 = x1*x1,
x3 = x2*x1;
return x0 * coefficient[0] +
x1 * coefficient[1] +
x2 * coefficient[2] +
x3 * coefficient[3];
}
/*
* Cubic 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.
*
* NOTE! Helium coefficients are a linear mix operation between the
* 323K and one for 273K isotherms, to make everything be at 300K.
*/
static const double o2_coefficients[4] = {
+1.00117935180448264158,
-0.00074149079841471884,
+0.00000291901111247509,
-0.00000000162092217461
};
static const double n2_coefficients[4] = {
+1.00030344355797817778,
-0.00022528077251905598,
+0.00000295430303276288,
-0.00000000210649996337
};
static const double he_coefficients[4] = {
+1.00000137322788319261,
+0.000488393024887620665,
-0.000000054210166760015,
+0.000000000010908069275
};
static double o2_compressibility_factor(double bar) { return cubic(bar, o2_coefficients); }
static double n2_compressibility_factor(double bar) { return cubic(bar, n2_coefficients); }
static double he_compressibility_factor(double bar) { return cubic(bar, he_coefficients); }
/*
* We end up using a simple linear mix of the gas-specific functions.
*/
double gas_compressibility_factor(struct gasmix *gas, double bar)
{
double o2, n2, he; // Z factors
double of, nf, hf; // gas fractions ("partial pressures")
o2 = o2_compressibility_factor(bar);
n2 = n2_compressibility_factor(bar);
he = he_compressibility_factor(bar);
of = get_o2(gas) / 1000.0;
hf = get_he(gas) / 1000.0;
nf = 1.0 - of - nf;
return o2*of + n2*nf + he*hf;
}
|
