projects / BK-2020-03.git / blame
| Commit | Line | Data |
|---|---|---|
| b9f7f618 SBS |
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; |