ASHRAE FUNDAMENTALS SI CH 1-2017 Psychrometrics.pdf

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1、1.1CHAPTER 1PSYCHROMETRICSComposition of Dry and Moist Air 1.1U.S. Standard Atmosphere. 1.1Thermodynamic Properties of Moist Air . 1.2Thermodynamic Properties of Water at Saturation. 1.4Humidity Parameters. 1.8Perfect Gas Relationships for Dry and Moist Air 1.8Thermodynamic Wet-Bulb and Dew-Point Te

2、mperature. 1.9Numerical Calculation of Moist Air Properties. 1.10Psychrometric Charts. 1.10Typical Air-Conditioning Processes 1.12Transport Properties of Moist Air 1.15Symbols 1.15SYCHROMETRICS uses thermodynamic properties to ana-Plyze conditions and processes involving moist air. This chapterdiscu

3、sses perfect gas relations and their use in common heating,cooling, and humidity control problems. Formulas developed byHerrmann et al. (2009) may be used where greater precision isrequired.Herrmann et al. (2009), Hyland and Wexler (1983a, 1983b), andNelson and Sauer (2002) developed formulas for th

4、ermodynamicproperties of moist air and water modeled as real gases. However,perfect gas relations can be substituted in most air-conditioningproblems. Kuehn et al. (1998) showed that errors are less than 0.7%in calculating humidity ratio, enthalpy, and specific volume of satu-rated air at standard a

5、tmospheric pressure for a temperature range of50 to 50C. Furthermore, these errors decrease with decreasingpressure.1. COMPOSITION OF DRY AND MOIST AIRAtmospheric air contains many gaseous components as well aswater vapor and miscellaneous contaminants (e.g., smoke, pollen,and gaseous pollutants not

6、 normally present in free air far from pol-lution sources).Dry air is atmospheric air with all water vapor and contaminantsremoved. Its composition is relatively constant, but small variationsin the amounts of individual components occur with time, geo-graphic location, and altitude. Harrison (1965)

7、 lists the approximatepercentage composition of dry air by volume as: nitrogen, 78.084;oxygen, 20.9476; argon, 0.934; neon, 0.001818; helium, 0.000524;methane, 0.00015; sulfur dioxide, 0 to 0.0001; hydrogen, 0.00005;and minor components such as krypton, xenon, and ozone, 0.0002.Harrison (1965) and H

8、yland and Wexler (1983a) used a value 0.0314(circa 1955) for carbon dioxide. Carbon dioxide reached 0.0379 in2005, is currently increasing by 0.00019 percent per year and is pro-jected to reach 0.0438 in 2036 (Gatley et al. 2008; Keeling andWhorf 2005a, 2005b). Increases in carbon dioxide are offset

9、 bydecreases in oxygen; consequently, the oxygen percentage in 2036 isprojected to be 20.9352. Using the projected changes, the relativemolecular mass for dry air for at least the first half of the 21st centuryis 28.966, based on the carbon-12 scale. The gas constant for dry airusing the current Moh

10、r and Taylor (2005) value for the universal gasconstant isRda= 8314.472/28.966 = 287.042 J/(kgdaK) (1)Moist air is a binary (two-component) mixture of dry air andwater vapor. The amount of water vapor varies from zero (dry air) toa maximum that depends on temperature and pressure. Saturation isa sta

11、te of neutral equilibrium between moist air and the condensedwater phase (liquid or solid); unless otherwise stated, it assumes aflat interface surface between moist air and the condensed phase.Saturation conditions change when the interface radius is very small(e.g., with ultrafine water droplets).

12、 The relative molecular mass ofwater is 18.015 268 on the carbon-12 scale. The gas constant forwater vapor isRw= 8314.472/18.015 268 = 461.524 J/(kgwK) (2)2. U.S. STANDARD ATMOSPHEREThe temperature and barometric pressure of atmospheric air varyconsiderably with altitude as well as with local geogra

13、phic andweather conditions. The standard atmosphere gives a standard of ref-erence for estimating properties at various altitudes. At sea level,standard temperature is 15C; standard barometric pressure is101.325 kPa. Temperature is assumed to decrease linearly with in-creasing altitude throughout th

14、e troposphere (lower atmosphere), andto be constant in the lower reaches of the stratosphere. The lower at-mosphere is assumed to consist of dry air that behaves as a perfect gas.Gravity is also assumed constant at the standard value, 9.806 65 m/s2.Table 1 summarizes property data for altitudes to 1

15、0 000 m.Pressure values in Table 1 may be calculated fromp = 101.325(1 2.25577 105Z)5.2559(3)The equation for temperature as a function of altitude ist =15 0.0065Z (4)whereZ = altitude, mp = barometric pressure, kPat =temperature, CThe preparation of this chapter is assigned to TC 1.1, Thermodynamic

16、s andPsychrometrics.Table 1 Standard Atmospheric Data for Altitudes to 10 000 mAltitude, m Temperature, C Pressure, kPa500 18.2 107.4780 15.0 101.325500 11.8 95.4611000 8.5 89.8751500 5.2 84.5562000 2.0 79.4952500 1.2 74.6823000 4.5 70.1084000 11.0 61.6405000 17.5 54.0206000 24.0 47.1817000 30.5 41.

17、0618000 37.0 35.6009000 43.5 30.74210 000 50 26.436Source: Adapted from NASA (1976).1.2 2017 ASHRAE HandbookFundamentals (SI)Equations (3) and (4) are accurate from 5000 m to 11 000 m.For higher altitudes, comprehensive tables of barometric pressureand other physical properties of the standard atmos

18、phere, in both SIand I-P units, can be found in NASA (1976).3. THERMODYNAMIC PROPERTIES OF MOIST AIRTable 2, developed from formulas by Herrmann et al. (2009),shows values of thermodynamic properties of moist air based on theInternational Temperature Scale of 1990 (ITS-90). This ideal scalediffers s

19、lightly from practical temperature scales used for physicalmeasurements. For example, the standard boiling point for water (at101.325 kPa) occurs at 99.97C on this scale rather than at the tra-ditional 100C. Most measurements are currently based on ITS-90(Preston-Thomas 1990).The following propertie

20、s are shown in Table 2:t = Celsius temperature, based on the ITS-90 and expressed relativeto absolute temperature T in kelvins (K) by the followingrelation:T = t + 273.15Ws= humidity ratio at saturation; gaseous phase (moist air) exists inequilibrium with condensed phase (liquid or solid) at givente

21、mperature and pressure (standard atmospheric pressure). Atgiven values of temperature and pressure, humidity ratio W canhave any value from zero to Ws.vda= specific volume of dry air, m3/kgda.vas= vs vda, difference between specific volume of moist air at saturation and that of dry air, m3/kgda, at

22、same pressure and temperature.vs= specific volume of moist air at saturation, m3/kgda.hda= specific enthalpy of dry air, kJ/kgda. In Table 2, hdais assigned avalue of 0 at 0C and standard atmospheric pressure.has= hs hda, difference between specific enthalpy of moist air atsaturation and that of dry

23、 air, kJ/kgda, at same pressure andtemperature.hs= specific enthalpy of moist air at saturation, kJ/kgda.sda= specific entropy of dry air, kJ/(kgdaK). In Table 2, sdaisassigned a value of 0 at 0C and standard atmospheric pressure.ss= specific entropy of moist air at saturation kJ/(kgdaK).Table 2 The

24、rmodynamic Properties of Moist Air at Standard Atmospheric Pressure, 101.325 kPaTemp., CtHumidity RatioWs, kgw/kgdaSpecific Volume, m3/kgdaSpecific Enthalpy, kJ/kgdaSpecific Entropy, kJ/(kgdaK)Temp., Ctvdavasvshdahashssdass60 0.0000067 0.6027 0.0000 0.6027 60.341 0.016 60.325 0.2494 0.2494 6059 0.00

25、00076 0.6055 0.0000 0.6055 59.335 0.018 59.317 0.2447 0.2446 5958 0.0000087 0.6084 0.0000 0.6084 58.329 0.021 58.308 0.2400 0.2399 5857 0.0000100 0.6112 0.0000 0.6112 57.323 0.024 57.299 0.2354 0.2353 5756 0.0000114 0.6141 0.0000 0.6141 56.317 0.027 56.289 0.2307 0.2306 5655 0.0000129 0.6169 0.0000

26、0.6169 55.311 0.031 55.280 0.2261 0.2260 5554 0.0000147 0.6198 0.0000 0.6198 54.305 0.035 54.269 0.2215 0.2213 5453 0.0000167 0.6226 0.0000 0.6226 53.299 0.040 53.258 0.2169 0.2167 5352 0.0000190 0.6255 0.0000 0.6255 52.293 0.046 52.247 0.2124 0.2121 5251 0.0000215 0.6283 0.0000 0.6283 51.287 0.052

27、51.235 0.2078 0.2076 5150 0.0000243 0.6312 0.0000 0.6312 50.281 0.059 50.222 0.2033 0.2030 5049 0.0000275 0.6340 0.0000 0.6340 49.275 0.066 49.209 0.1988 0.1985 4948 0.0000311 0.6369 0.0000 0.6369 48.269 0.075 48.194 0.1943 0.1940 4847 0.0000350 0.6397 0.0000 0.6397 47.263 0.085 47.179 0.1899 0.1895

28、 4746 0.0000395 0.6425 0.0000 0.6426 46.257 0.095 46.162 0.1854 0.1850 4645 0.0000445 0.6454 0.0000 0.6454 45.252 0.107 45.144 0.1810 0.1805 4544 0.0000500 0.6482 0.0001 0.6483 44.246 0.121 44.125 0.1766 0.1761 4443 0.0000562 0.6511 0.0001 0.6511 43.240 0.136 43.104 0.1722 0.1716 4342 0.0000631 0.65

29、39 0.0001 0.6540 42.234 0.153 42.081 0.1679 0.1672 4241 0.0000708 0.6568 0.0001 0.6568 41.229 0.172 41.057 0.1635 0.1628 4140 0.0000793 0.6596 0.0001 0.6597 40.223 0.192 40.031 0.1592 0.1583 4039 0.0000887 0.6625 0.0001 0.6626 39.217 0.215 39.002 0.1549 0.1539 3938 0.0000992 0.6653 0.0001 0.6654 38.

30、211 0.241 37.970 0.1506 0.1495 3837 0.0001108 0.6682 0.0001 0.6683 37.206 0.269 36.936 0.1464 0.1451 3736 0.0001237 0.6710 0.0001 0.6711 36.200 0.301 35.899 0.1421 0.1408 3635 0.0001379 0.6738 0.0001 0.6740 35.195 0.336 34.859 0.1379 0.1364 3534 0.0001536 0.6767 0.0002 0.6769 34.189 0.374 33.815 0.1

31、337 0.1320 3433 0.0001710 0.6795 0.0002 0.6797 33.183 0.417 32.766 0.1295 0.1276 3332 0.0001902 0.6824 0.0002 0.6826 32.178 0.464 31.714 0.1253 0.1232 3231 0.0002113 0.6852 0.0002 0.6855 31.172 0.516 30.656 0.1211 0.1189 3130 0.0002345 0.6881 0.0003 0.6883 30.167 0.573 29.593 0.1170 0.1145 3029 0.00

32、02602 0.6909 0.0003 0.6912 29.161 0.636 28.525 0.1129 0.1101 2928 0.0002883 0.6938 0.0003 0.6941 28.156 0.706 27.450 0.1088 0.1057 2827 0.0003193 0.6966 0.0004 0.6970 27.150 0.782 26.368 0.1047 0.1013 2726 0.0003532 0.6994 0.0004 0.6998 26.144 0.866 25.278 0.1006 0.0969 2625 0.0003905 0.7023 0.0004

33、0.7027 25.139 0.958 24.181 0.0965 0.0924 2524 0.0004314 0.7051 0.0005 0.7056 24.133 1.059 23.074 0.0925 0.0880 2423 0.0004761 0.7080 0.0005 0.7085 23.128 1.170 21.958 0.0884 0.0835 2322 0.0005251 0.7108 0.0006 0.7114 22.122 1.291 20.831 0.0844 0.0790 2221 0.0005787 0.7137 0.0007 0.7143 21.117 1.424

34、19.693 0.0804 0.0745 2120 0.0006373 0.7165 0.0007 0.7172 20.111 1.570 18.542 0.0765 0.0699 20Psychrometrics 1.319 0.0007013 0.7193 0.0008 0.7201 19.106 1.728 17.377 0.0725 0.0653 1918 0.0007711 0.7222 0.0009 0.7231 18.100 1.902 16.198 0.0685 0.0607 1817 0.0008473 0.7250 0.0010 0.7260 17.095 2.091 15

35、.003 0.0646 0.0560 1716 0.0009303 0.7279 0.0011 0.7290 16.089 2.298 13.791 0.0607 0.0513 1615 0.0010207 0.7307 0.0012 0.7319 15.084 2.523 12.560 0.0568 0.0465 1514 0.0011191 0.7336 0.0013 0.7349 14.078 2.769 11.310 0.0529 0.0416 1413 0.0012261 0.7364 0.0014 0.7378 13.073 3.036 10.037 0.0490 0.0367 1

36、312 0.0013425 0.7392 0.0016 0.7408 12.067 3.326 8.741 0.0452 0.0317 1211 0.0014689 0.7421 0.0017 0.7438 11.062 3.642 7.419 0.0413 0.0267 1110 0.0016062 0.7449 0.0019 0.7468 10.056 3.986 6.070 0.0375 0.0215 109 0.0017551 0.7478 0.0021 0.7499 9.050 4.358 4.692 0.0337 0.0163 98 0.0019166 0.7506 0.0023

37、0.7529 8.045 4.763 3.282 0.0299 0.0110 87 0.0020916 0.7534 0.0025 0.7560 7.039 5.202 1.838 0.0261 0.0055 76 0.0022812 0.7563 0.0028 0.7591 6.034 5.677 0.356 0.0223 0.0000 65 0.0024863 0.7591 0.0030 0.7622 5.028 6.192 1.164 0.0186 0.0057 54 0.0027083 0.7620 0.0033 0.7653 4.023 6.750 2.728 0.0148 0.01

38、15 43 0.0029482 0.7648 0.0036 0.7684 3.017 7.354 4.337 0.0111 0.0175 32 0.0032076 0.7677 0.0039 0.7716 2.011 8.007 5.995 0.0074 0.0236 21 0.0034877 0.7705 0.0043 0.7748 1.006 8.712 7.707 0.0037 0.0299 10 0.003790 0.7733 0.0047 0.7780 0.000 9.475 9.475 0.0000 0.0364 01 0.004076 0.7762 0.0051 0.7813 1

39、.006 10.198 11.203 0.0037 0.0427 12 0.004382 0.7790 0.0055 0.7845 2.011 10.970 12.981 0.0073 0.0492 23 0.004708 0.7819 0.0059 0.7878 3.017 11.794 14.811 0.0110 0.0559 34 0.005055 0.7847 0.0064 0.7911 4.023 12.673 16.696 0.0146 0.0627 45 0.005425 0.7875 0.0068 0.7944 5.029 13.611 18.639 0.0182 0.0697

40、 56 0.005819 0.7904 0.0074 0.7978 6.034 14.610 20.644 0.0219 0.0769 67 0.006238 0.7932 0.0079 0.8012 7.040 15.674 22.714 0.0254 0.0843 78 0.006684 0.7961 0.0085 0.8046 8.046 16.807 24.853 0.0290 0.0919 89 0.007158 0.7989 0.0092 0.8081 9.052 18.013 27.065 0.0326 0.0997 910 0.007663 0.8017 0.0098 0.81

41、16 10.058 19.297 29.354 0.0362 0.1078 1011 0.008199 0.8046 0.0106 0.8152 11.063 20.661 31.724 0.0397 0.1162 1112 0.008768 0.8074 0.0113 0.8188 12.069 22.111 34.181 0.0432 0.1248 1213 0.009372 0.8103 0.0122 0.8224 13.075 23.653 36.728 0.0468 0.1338 1314 0.010013 0.8131 0.0131 0.8262 14.081 25.290 39.

42、371 0.0503 0.1430 1415 0.010694 0.8159 0.0140 0.8299 15.087 27.028 42.115 0.0538 0.1525 1516 0.011415 0.8188 0.0150 0.8338 16.093 28.873 44.966 0.0573 0.1624 1617 0.012181 0.8216 0.0160 0.8377 17.099 30.830 47.929 0.0607 0.1726 1718 0.012991 0.8245 0.0172 0.8416 18.105 32.906 51.011 0.0642 0.1832 18

43、19 0.013851 0.8273 0.0184 0.8457 19.111 35.108 54.219 0.0676 0.1942 1920 0.014761 0.8301 0.0196 0.8498 20.117 37.441 57.559 0.0711 0.2057 2021 0.015724 0.8330 0.0210 0.8540 21.124 39.914 61.038 0.0745 0.2175 2122 0.016744 0.8358 0.0224 0.8583 22.130 42.534 64.663 0.0779 0.2298 2223 0.017823 0.8387 0

44、.0240 0.8626 23.136 45.308 68.444 0.0813 0.2426 2324 0.018965 0.8415 0.0256 0.8671 24.142 48.246 72.388 0.0847 0.2560 2425 0.020173 0.8443 0.0273 0.8716 25.148 51.355 76.504 0.0881 0.2698 2526 0.021451 0.8472 0.0291 0.8763 26.155 54.647 80.801 0.0915 0.2842 2627 0.022802 0.8500 0.0311 0.8811 27.161

45、58.129 85.290 0.0948 0.2992 2728 0.024229 0.8529 0.0331 0.8860 28.167 61.813 89.980 0.0982 0.3148 2829 0.025738 0.8557 0.0353 0.8910 29.174 65.709 94.883 0.1015 0.3311 2930 0.027333 0.8585 0.0376 0.8961 30.180 69.829 100.010 0.1048 0.3481 3031 0.029018 0.8614 0.0400 0.9014 31.187 74.186 105.373 0.10

46、81 0.3658 3132 0.030797 0.8642 0.0426 0.9069 32.193 78.792 110.986 0.1115 0.3843 3233 0.032677 0.8671 0.0454 0.9124 33.200 83.661 116.861 0.1147 0.4035 3334 0.034663 0.8699 0.0483 0.9182 34.207 88.807 123.014 0.1180 0.4236 3435 0.036760 0.8727 0.0514 0.9241 35.213 94.247 129.460 0.1213 0.4447 3536 0

47、.038975 0.8756 0.0546 0.9302 36.220 99.995 136.215 0.1246 0.4666 3637 0.041313 0.8784 0.0581 0.9365 37.227 106.069 143.296 0.1278 0.4895 3738 0.043783 0.8813 0.0618 0.9430 38.233 112.488 150.722 0.1311 0.5135 3839 0.046391 0.8841 0.0657 0.9498 39.240 119.272 158.512 0.1343 0.5386 3940 0.049145 0.886

48、9 0.0698 0.9567 40.247 126.440 166.687 0.1375 0.5649 4041 0.052053 0.8898 0.0741 0.9639 41.254 134.016 175.270 0.1407 0.5923 4142 0.055124 0.8926 0.0788 0.9714 42.261 142.023 184.284 0.1439 0.6211 42Table 2 Thermodynamic Properties of Moist Air at Standard Atmospheric Pressure, 101.325 kPa (Continued)Temp., CtHumidity RatioWs, kgw/kgdaSpecific Volume, m3/kgdaSpecific Enthalpy, kJ/kgdaSpecific Entropy, kJ/(kgdaK)Temp., Ctvdavasvshdahashssdass1.4 2017 ASHRAE HandbookFundamentals (SI)4. THERMODYNAMIC PROP