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. 1.6Humidity Parameters. 1.12Perfect Gas Relationships for Dry and Moist Air 1.12Thermodynamic Wet-Bulb and Dew-Point
2、Temperature. 1.13Numerical Calculation of Moist Air Properties. 1.14Psychrometric Charts. 1.14Typical Air-Conditioning Processes 1.16Transport Properties of Moist Air 1.19Symbols 1.19SYCHROMETRICS uses thermodynamic properties to ana-Plyze conditions and processes involving moist air. This chapterdi
3、scusses 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
4、 thermodynamicproperties 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 standar
5、d atmospheric pressure for a temperature range of60 to 120F. 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
6、 not 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 (1
7、965) 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) a
8、nd Hyland 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 of
9、fset 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
10、 Mohr and Taylor (2005) value for the universal gasconstant isRda= 1545.349/28.966 = 53.350 ftlbf/lbdaR (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 is
11、a state 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 dropl
12、ets). The relative molecular mass ofwater is 18.015268 on the carbon-12 scale. The gas constant forwater vapor isRw= 1545.349/18.015268 = 85.780 ftlbf/lbwR (2)2. U.S. STANDARD ATMOSPHEREThe temperature and barometric pressure of atmospheric air varyconsiderably with altitude as well as with local ge
13、ographic andweather conditions. The standard atmosphere gives a standard of ref-erence for estimating properties at various altitudes. At sea level,standard temperature is 59F; standard barometric pressure is14.696 psia or 29.921 in. Hg. Temperature is assumed to decreaselinearly with increasing alt
14、itude throughout the troposphere (loweratmosphere), and to be constant in the lower reaches of the strato-sphere. The lower atmosphere is assumed to consist of dry air thatbehaves as a perfect gas. Gravity is also assumed constant at the stan-dard value, 32.1740 ft/s2. Table 1 summarizes property da
15、ta for alti-tudes to 30,000 ft.Pressure values in Table 1 may be calculated fromp = 14.696(1 6.8754 106Z)5.2559(3)The equation for temperature as a function of altitude ist = 59 0.00356620Z (4)whereZ = altitude, ftp = barometric pressure, psiat =temperature, FThe preparation of this chapter is assig
16、ned to TC 1.1, Thermodynamics andPsychrometrics.Table 1 Standard Atmospheric Data for Altitudes to 30,000 ftAltitude, ft Temperature, F Pressure, psia1000 62.6 15.236500 60.8 14.9660 59.0 14.696500 57.2 14.4301,000 55.4 14.1752,000 51.9 13.6643,000 48.3 13.1734,000 44.7 12.6825,000 41.2 12.2306,000
17、37.6 11.7787,000 34.0 11.3418,000 30.5 10.9149,000 26.9 10.50610,000 23.4 10.10815,000 5.5 8.29620,000 12.3 6.75830,000 47.8 4.371Source: Adapted from NASA (1976).1.2 2017 ASHRAE HandbookFundamentals Equations (3) and (4) are accurate from 16,500 ft to 36,000 ft.For higher altitudes, comprehensive t
18、ables of barometric pressureand other physical properties of the standard atmosphere, 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
19、 theInternational Temperature Scale of 1990 (ITS-90). This ideal scalediffers slightly from practical temperature scales used for physicalmeasurements. For example, the standard boiling point for water (at14.696 psia) occurs at 211.95F on this scale rather than at the tra-ditional 212F. Most measure
20、ments are currently based on ITS-90(Preston-Thomas 1990).The following properties are shown in Table 2: t = Fahrenheit temperature, based on the ITS-90 and expressedrelative to absolute temperature T in degrees Rankine (R) by thefollowing relation:T = t + 459.67Ws= humidity ratio at saturation; gase
21、ous phase (moist air) exists inequilibrium with condensed phase (liquid or solid) at giventemperature 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, ft3/lbda.vas= vs vda, di
22、fference between specific volume of moist air at saturation and that of dry air, ft3/lbda, at same pressure and temperature.vs= specific volume of moist air at saturation, ft3/lbda.hda= specific enthalpy of dry air, Btu/lbda. In Table 2, hdais assigned avalue of 0 at 0F and standard atmospheric pres
23、sure.has= hs hda, difference between specific enthalpy of moist air atsaturation and that of dry air, Btu/lbda, at same pressure andtemperature.hs= specific enthalpy of moist air at saturation, Btu/lbda.sda= specific entropy of dry air, Btu/lbda R. In Table 2, sdaisassigned a value of 0 at 0F and st
24、andard atmospheric pressure.ss= specific entropy of moist air at saturation Btu/lbdaR.Table 2 Thermodynamic Properties of Moist Air at Standard Atmospheric Pressure, 14.696 psiaTemp., FtHumidity RatioWs, lbw/lbdaSpecific Volume, ft3/lbdaSpecific Enthalpy, Btu/lbdaSpecific Entropy, Btu/lbdaFTemp., Ft
25、vdavasvshdahashssdass80 0.0000049 9.553 0.000 9.553 19.218 0.005 19.213 0.04593 0.04592 8079 0.0000053 9.578 0.000 9.578 18.977 0.005 18.972 0.04530 0.04529 7978 0.0000057 9.603 0.000 9.604 18.737 0.006 18.731 0.04467 0.04465 7877 0.0000062 9.629 0.000 9.629 18.497 0.006 18.490 0.04404 0.04402 7776
26、0.0000067 9.654 0.000 9.654 18.256 0.007 18.250 0.04341 0.04339 7675 0.0000072 9.680 0.000 9.680 18.016 0.007 18.009 0.04279 0.04277 7574 0.0000078 9.705 0.000 9.705 17.776 0.008 17.768 0.04216 0.04214 7473 0.0000084 9.730 0.000 9.730 17.535 0.009 17.527 0.04154 0.04152 7372 0.0000090 9.756 0.000 9.
27、756 17.295 0.009 17.286 0.04092 0.04090 7271 0.0000097 9.781 0.000 9.781 17.055 0.010 17.045 0.04030 0.04027 7170 0.0000104 9.806 0.000 9.806 16.814 0.011 16.804 0.03968 0.03966 7069 0.0000112 9.832 0.000 9.832 16.574 0.012 16.563 0.03907 0.03904 6968 0.0000120 9.857 0.000 9.857 16.334 0.012 16.321
28、0.03845 0.03842 6867 0.0000129 9.882 0.000 9.882 16.094 0.013 16.080 0.03784 0.03781 6766 0.0000139 9.908 0.000 9.908 15.853 0.014 15.839 0.03723 0.03719 6665 0.0000149 9.933 0.000 9.933 15.613 0.015 15.598 0.03662 0.03658 6564 0.0000160 9.958 0.000 9.959 15.373 0.017 15.356 0.03601 0.03597 6463 0.0
29、000172 9.984 0.000 9.984 15.132 0.018 15.115 0.03541 0.03536 6362 0.0000184 10.009 0.000 10.009 14.892 0.019 14.873 0.03480 0.03475 6261 0.0000198 10.034 0.000 10.035 14.652 0.020 14.632 0.03420 0.03414 6160 0.0000212 10.060 0.000 10.060 14.412 0.022 14.390 0.03360 0.03354 6059 0.0000227 10.085 0.00
30、0 10.085 14.171 0.023 14.148 0.03300 0.03293 5958 0.0000243 10.110 0.000 10.111 13.931 0.025 13.906 0.03240 0.03233 5857 0.0000260 10.136 0.000 10.136 13.691 0.027 13.664 0.03180 0.03173 5756 0.0000279 10.161 0.000 10.161 13.451 0.029 13.422 0.03120 0.03113 5655 0.0000298 10.186 0.000 10.187 13.210
31、0.031 13.179 0.03061 0.03053 5554 0.0000319 10.212 0.001 10.212 12.970 0.033 12.937 0.03002 0.02993 5453 0.0000341 10.237 0.001 10.237 12.730 0.035 12.695 0.02942 0.02933 5352 0.0000365 10.262 0.001 10.263 12.490 0.038 12.452 0.02883 0.02874 5251 0.0000390 10.288 0.001 10.288 12.249 0.040 12.209 0.0
32、2825 0.02814 5150 0.0000416 10.313 0.001 10.314 12.009 0.043 11.966 0.02766 0.02755 5049 0.0000445 10.338 0.001 10.339 11.769 0.046 11.723 0.02707 0.02695 4948 0.0000475 10.364 0.001 10.364 11.529 0.049 11.479 0.02649 0.02636 4847 0.0000507 10.389 0.001 10.390 11.289 0.053 11.236 0.02591 0.02577 474
33、6 0.0000541 10.414 0.001 10.415 11.048 0.056 10.992 0.02532 0.02518 4645 0.0000577 10.439 0.001 10.440 10.808 0.060 10.748 0.02474 0.02459 4544 0.0000615 10.465 0.001 10.466 10.568 0.064 10.504 0.02417 0.02400 4443 0.0000656 10.490 0.001 10.491 10.328 0.068 10.259 0.02359 0.02341 4342 0.0000699 10.5
34、15 0.001 10.517 10.087 0.073 10.015 0.02301 0.02283 4241 0.0000744 10.541 0.001 10.542 9.847 0.078 9.770 0.02244 0.02224 4140 0.0000793 10.566 0.001 10.567 9.607 0.083 9.524 0.02187 0.02166 40Psychrometrics 1.339 0.0000844 10.591 0.001 10.593 9.367 0.088 9.279 0.02129 0.02107 3938 0.0000898 10.617 0
35、.002 10.618 9.127 0.094 9.033 0.02072 0.02049 3837 0.0000956 10.642 0.002 10.644 8.886 0.100 8.787 0.02015 0.01990 3736 0.0001017 10.667 0.002 10.669 8.646 0.106 8.540 0.01959 0.01932 3635 0.0001081 10.693 0.002 10.695 8.406 0.113 8.293 0.01902 0.01874 3534 0.0001150 10.718 0.002 10.720 8.166 0.120
36、8.046 0.01846 0.01816 3433 0.0001222 10.743 0.002 10.745 7.926 0.128 7.798 0.01789 0.01757 3332 0.0001298 10.769 0.002 10.771 7.685 0.136 7.550 0.01733 0.01699 3231 0.0001379 10.794 0.002 10.796 7.445 0.144 7.301 0.01677 0.01641 3130 0.0001465 10.819 0.003 10.822 7.205 0.153 7.052 0.01621 0.01583 30
37、29 0.0001555 10.845 0.003 10.847 6.965 0.163 6.802 0.01565 0.01525 2928 0.0001650 10.870 0.003 10.873 6.725 0.173 6.552 0.01509 0.01467 2827 0.0001751 10.895 0.003 10.898 6.485 0.184 6.301 0.01454 0.01409 2726 0.0001857 10.920 0.003 10.924 6.244 0.195 6.050 0.01398 0.01351 2625 0.0001970 10.946 0.00
38、3 10.949 6.004 0.207 5.797 0.01343 0.01293 2524 0.0002088 10.971 0.004 10.975 5.764 0.219 5.545 0.01288 0.01234 2423 0.0002213 10.996 0.004 11.000 5.524 0.233 5.291 0.01233 0.01176 2322 0.0002345 11.022 0.004 11.026 5.284 0.246 5.037 0.01178 0.01118 2221 0.0002485 11.047 0.004 11.051 5.043 0.261 4.7
39、82 0.01123 0.01060 2120 0.0002632 11.072 0.005 11.077 4.803 0.277 4.527 0.01068 0.01002 2019 0.0002786 11.098 0.005 11.103 4.563 0.293 4.270 0.01014 0.00943 1918 0.0002949 11.123 0.005 11.128 4.323 0.310 4.013 0.00959 0.00885 1817 0.0003121 11.148 0.006 11.154 4.083 0.329 3.754 0.00905 0.00826 1716
40、0.0003302 11.174 0.006 11.179 3.843 0.348 3.495 0.00851 0.00768 1615 0.0003493 11.199 0.006 11.205 3.602 0.368 3.234 0.00797 0.00709 1514 0.0003694 11.224 0.007 11.231 3.362 0.389 2.973 0.00743 0.00650 1413 0.0003905 11.249 0.007 11.257 3.122 0.412 2.710 0.00689 0.00591 1312 0.0004127 11.275 0.007 1
41、1.282 2.882 0.436 2.446 0.00635 0.00532 1211 0.0004361 11.300 0.008 11.308 2.642 0.460 2.181 0.00582 0.00473 1110 0.0004607 11.325 0.008 11.334 2.402 0.487 1.915 0.00528 0.00414 109 0.0004866 11.351 0.009 11.360 2.161 0.514 1.647 0.00475 0.00354 98 0.0005138 11.376 0.009 11.385 1.921 0.543 1.378 0.0
42、0422 0.00294 87 0.0005425 11.401 0.010 11.411 1.681 0.574 1.108 0.00369 0.00234 76 0.0005725 11.427 0.010 11.437 1.441 0.606 0.835 0.00316 0.00174 65 0.0006041 11.452 0.011 11.463 1.201 0.639 0.561 0.00263 0.00114 54 0.0006373 11.477 0.012 11.489 0.961 0.675 0.286 0.00210 0.00053 43 0.0006721 11.502
43、 0.012 11.515 0.720 0.712 0.009 0.00157 0.00008 32 0.0007087 11.528 0.013 11.541 0.480 0.751 0.271 0.00105 0.00069 21 0.0007471 11.553 0.014 11.567 0.240 0.792 0.552 0.00052 0.00130 10 0.0007875 11.578 0.015 11.593 0.000 0.835 0.835 0.00000 0.00192 01 0.0008298 11.604 0.015 11.619 0.240 0.880 1.121
44、0.00052 0.00254 12 0.0008741 11.629 0.016 11.645 0.480 0.928 1.408 0.00104 0.00317 23 0.0009207 11.654 0.017 11.671 0.720 0.978 1.698 0.00156 0.00379 34 0.0009695 11.680 0.018 11.698 0.961 1.030 1.991 0.00208 0.00443 45 0.0010207 11.705 0.019 11.724 1.201 1.085 2.286 0.00260 0.00506 56 0.0010743 11.
45、730 0.020 11.750 1.441 1.142 2.583 0.00311 0.00570 67 0.0011306 11.755 0.021 11.777 1.681 1.203 2.884 0.00363 0.00635 78 0.0011895 11.781 0.022 11.803 1.921 1.266 3.187 0.00414 0.00700 89 0.0012512 11.806 0.024 11.830 2.161 1.332 3.493 0.00466 0.00765 910 0.0013158 11.831 0.025 11.856 2.402 1.401 3.
46、803 0.00517 0.00832 1011 0.0013835 11.857 0.026 11.883 2.642 1.474 4.116 0.00568 0.00898 1112 0.0014544 11.882 0.028 11.910 2.882 1.550 4.432 0.00619 0.00965 1213 0.0015286 11.907 0.029 11.936 3.122 1.630 4.752 0.00670 0.01033 1314 0.0016062 11.933 0.031 11.963 3.362 1.714 5.076 0.00721 0.01102 1415
47、 0.0016874 11.958 0.032 11.990 3.603 1.801 5.403 0.00771 0.01171 1516 0.0017724 11.983 0.034 12.017 3.843 1.892 5.735 0.00822 0.01241 1617 0.0018613 12.008 0.036 12.044 4.083 1.988 6.071 0.00872 0.01311 1718 0.0019543 12.034 0.038 12.071 4.323 2.088 6.411 0.00922 0.01383 1819 0.0020515 12.059 0.040
48、12.099 4.563 2.193 6.756 0.00973 0.01455 1920 0.0021531 12.084 0.042 12.126 4.803 2.303 7.106 0.01023 0.01528 2021 0.0022593 12.110 0.044 12.153 5.044 2.417 7.461 0.01073 0.01602 2122 0.0023703 12.135 0.046 12.181 5.284 2.537 7.821 0.01123 0.01677 22Table 2 Thermodynamic Properties of Moist Air at Standard Atmospheric Pressure, 14.696 psia (Continued)Temp., FtHumidity RatioWs, lb
