unitproc/python/bkt-humidity

   1 #!/usr/bin/env python3
   2 # Desc: Humidity conversion functions from EVA-2020-02-2
   3 # Ref/Attrib: https://gitlab.com/baltakatei/ninfacyzga-01
   4
   5 def rel_to_abs(T,P,RH):
   6     """Returns absolute humidity given relative humidity.
   7
   8     Inputs:
   9     --------
  10     T : float
  11         Absolute temperature in units Kelvin (K).
  12     P : float
  13         Total pressure in units Pascals (Pa).
  14     RH : float
  15         Relative humidity in units percent (%).
  16
  17     Output:
  18     --------
  19     absolute_humidity : float
  20         Absolute humidity in units [kg water vapor / kg dry air].
  21
  22     References:
  23     --------
  24     1. Sonntag, D. "Advancements in the field of hygrometry". 1994. https://doi.org/10.1127/metz/3/1994/51
  25     2. Green, D. "Perry's Chemical Engineers' Handbook" (8th Edition). Page "12-4". McGraw-Hill Professional Publishing. 2007.
  26
  27     Version: 0.0.1
  28     Author: Steven Baltakatei Sandoval
  29     License: GPLv3+
  30     """
  31
  32     import math;
  33
  34     # Check input types
  35     T = float(T);
  36     P = float(P);
  37     RH = float(RH);
  38
  39     #debug
  40     # print('DEBUG:Input Temperature   (K)  :' + str(T));
  41     # print('DEBUG:Input Pressure      (Pa) :' + str(P));
  42     # print('DEBUG:Input Rel. Humidity (%)  :' + str(RH));
  43
  44     # Set constants and initial conversions
  45     epsilon = 0.62198 # (molar mass of water vapor) / (molar mass of dry air)
  46     t = T - 273.15; # Celsius from Kelvin
  47     P_hpa = P / 100; # hectoPascals (hPa) from Pascals (Pa)
  48
  49     # Calculate e_w(T), saturation vapor pressure of water in a pure phase, in Pascals
  50     ln_e_w = -6096*T**-1 + 21.2409642 - 2.711193*10**-2*T + 1.673952*10**-5*T**2 + 2.433502*math.log(T); # Sonntag-1994 eq 7; e_w in Pascals
  51     e_w = math.exp(ln_e_w);
  52     e_w_hpa = e_w / 100; # also save e_w in hectoPascals (hPa)
  53     # print('DEBUG:ln_e_w:' + str(ln_e_w)); # debug
  54     # print('DEBUG:e_w:' + str(e_w)); # debug
  55
  56     # Calculate f_w(P,T), enhancement factor for water
  57     f_w = 1 + (10**-4*e_w_hpa)/(273 + t)*(((38 + 173*math.exp(-t/43))*(1 - (e_w_hpa / P_hpa))) + ((6.39 + 4.28*math.exp(-t / 107))*((P_hpa / e_w_hpa) - 1))); # Sonntag-1994 eq 22.
  58     # print('DEBUG:f_w:' + str(f_w)); # debug
  59
  60     # Calculate e_prime_w(P,T), saturation vapor pressure of water in air-water mixture, in Pascals
  61     e_prime_w = f_w * e_w; # Sonntag-1994 eq 18
  62     # print('DEBUG:e_prime_w:' + str(e_prime_w)); # debug
  63
  64     # Calculate e_prime, vapor pressure of water in air, in Pascals
  65     e_prime = (RH / 100) * e_prime_w;
  66     # print('DEBUG:e_prime:' + str(e_prime)); # debug
  67
  68     # Calculate r, the absolute humidity, in [kg water vapor / kg dry air]
  69     r = (epsilon * e_prime) / (P - e_prime);
  70     # print('DEBUG:r:' + str(r)); # debug
  71
  72     return float(r);
  73
  74 def rel_to_dpt(T,P,RH):
  75     """Returns dew point temperature given relative humidity.
  76
  77     Inputs:
  78     --------
  79     T : float
  80         Absolute temperature in units Kelvin (K).
  81     P : float
  82         Total pressure in units Pascals (Pa).
  83     RH : float
  84         Relative humidity in units percent (%).
  85
  86     Output:
  87     --------
  88     T_d : float
  89         Dew point temperature in units Kelvin (K).
  90
  91     References:
  92     --------
  93     1. Sonntag, D. "Advancements in the field of hygrometry". 1994. https://doi.org/10.1127/metz/3/1994/51
  94     2. Green, D. "Perry's Chemical Engineers' Handbook" (8th Edition). Page "12-4". McGraw-Hill Professional Publishing. 2007.
  95
  96     Version: 0.0.1
  97     Author: Steven Baltakatei Sandoval
  98     License: GPLv3+
  99     """
 100
 101     import math;
 102
 103     # Check input types
 104     T = float(T);
 105     P = float(P);
 106     RH = float(RH);
 107
 108     #debug
 109     # print('DEBUG:Input Temperature   (K)  :' + str(T));
 110     # print('DEBUG:Input Pressure      (Pa) :' + str(P));
 111     # print('DEBUG:Input Rel. Humidity (%)  :' + str(RH));
 112
 113     # Set constants and initial conversions
 114     epsilon = 0.62198 # (molar mass of water vapor) / (molar mass of dry air)
 115     t = T - 273.15; # Celsius from Kelvin
 116     P_hpa = P / 100; # hectoPascals (hPa) from Pascals (Pa)
 117
 118     # Calculate e_w(T), saturation vapor pressure of water in a pure phase, in Pascals
 119     ln_e_w = -6096*T**-1 + 21.2409642 - 2.711193*10**-2*T + 1.673952*10**-5*T**2 + 2.433502*math.log(T); # Sonntag-1994 eq 7; e_w in Pascals
 120     e_w = math.exp(ln_e_w);
 121     e_w_hpa = e_w / 100; # also save e_w in hectoPascals (hPa)
 122     # print('DEBUG:ln_e_w:' + str(ln_e_w)); # debug
 123     # print('DEBUG:e_w:' + str(e_w)); # debug
 124
 125     # Calculate f_w(P,T), enhancement factor for water
 126     f_w = 1 + (10**-4*e_w_hpa)/(273 + t)*(((38 + 173*math.exp(-t/43))*(1 - (e_w_hpa / P_hpa))) + ((6.39 + 4.28*math.exp(-t / 107))*((P_hpa / e_w_hpa) - 1))); # Sonntag-1994 eq 22.
 127     # print('DEBUG:f_w:' + str(f_w)); # debug
 128
 129     # Calculate e_prime_w(P,T), saturation vapor pressure of water in air-water mixture, in Pascals
 130     e_prime_w = f_w * e_w; # Sonntag-1994 eq 18
 131     # print('DEBUG:e_prime_w:' + str(e_prime_w)); # debug
 132
 133     # Calculate e_prime, vapor pressure of water in air, in Pascals
 134     e_prime = (RH / 100) * e_prime_w;
 135     # print('DEBUG:e_prime:' + str(e_prime)); # debug
 136
 137     n = 0; repeat_flag = True;
 138     while repeat_flag == True:
 139         # print('DEBUG:n:' + str(n)); # debug
 140
 141         # Calculate f_w_td, the enhancement factor for water at dew point temperature.
 142         if n == 0:
 143             f = 1.0016 + 3.15*10**-6*P_hpa - (0.074 / P_hpa); # Sonntag-1994 eq 24
 144             f_w_td = f; # initial approximation
 145         elif n > 0:
 146             t_d_prev = float(t_d); # save previous t_d value for later comparison
 147             f_w_td = 1 + (10**-4*e_w_hpa)/(273 + t_d)*(((38 + 173*math.exp(-t_d/43))*(1 - (e_w_hpa / P_hpa))) + ((6.39 + 4.28*math.exp(-t_d / 107))*((P_hpa / e_w_hpa) - 1))); # Sonntag-1994 eq 22.
 148         # print('DEBUG:f_w_td:' + str(f_w_td)); # debug
 149
 150         # Calculate e, the vapor pressure of water in the pure phase, in Pascals
 151         e = (e_prime / f_w_td); # Sonntag-1994 eq 9 and 20
 152         # print('DEBUG:e:' + str(e)); # debug
 153
 154         # Calculate y, an intermediate dew point calculation variable
 155         y = math.log(e / 611.213);
 156         # print('DEBUG:y:' + str(y)); # debug
 157
 158         # Calculate t_d, the dew point temperature in degrees Celsius
 159         t_d = 13.715*y + 8.4262*10**-1*y**2 + 1.9048*10**-2*y**3 + 7.8158*10**-3*y**4;# Sonntag-1994 eq 10
 160         # print('DEBUG:t_d:' + str(t_d)); # debug
 161
 162         if n == 0:
 163             # First run
 164             repeat_flag = True;
 165         else:
 166             # Test t_d accuracy
 167             t_d_diff = math.fabs(t_d - t_d_prev);
 168             # print('DEBUG:t_d     :' + str(t_d)); # debug
 169             # print('DEBUG:t_d_prev:' + str(t_d_prev)); # debug
 170             # print('DEBUG:t_d_diff:' + str(t_d_diff)); # debug
 171             if t_d_diff < 0.01:
 172                 repeat_flag = False;
 173             else:
 174                 repeat_flag = True;
 175
 176         # Calculate T_d, the dew point temperature in Kelvin
 177         T_d = 273.15 + t_d;
 178         # print('DEBUG:T_d:' + str(T_d)); # debug
 179
 180         if n > 100:
 181             return T_d; # good enough
 182
 183         # update loop counter
 184         n += 1;
 185     return T_d;