Physical Chemistry , 1st ed.

the pressure drops the temperature goes up: it gets hotter upon expansion! At
some lower temperature, the Joule-Thomson coefficient becomes positive, and
then as pressure drops, the temperature of the gas drops as well. The temper-
ature at which the Joule-Thomson coefficient goes from negative to positive is
called the inversion temperature.In order to cool gases down using the Joule-
Thomson method, a gas must be below its inversion temperature.
The Joule-Thomson effect is used to liquefy gases, since one can engineer a
system where a gas is repeatedly compressed and expanded, decreasing its

2.7 Joule-Thomson Coefficients 45

Table 2.2 Joule-Thomson coefficients of various gases (K/atm)

p(atm) T150°C 100°C 50°C 0°C 50°C 100°C 150°C 200°C

Air, no water or carbon dioxide

1 — 0.5895 0.3910 0.2745 0.1956 0.1355 0.0961 0.0645

20 — 0.5700 0.3690 0.2580 0.1830 0.1258 0.0883 0.0580

60 0.0450 0.4820 0.3195 0.2200 0.1571 0.1062 0.0732 0.0453

100 0.0185 0.2775 0.2505 0.1820 0.1310 0.0884 0.0600 0.0343

140 0.0070 0.1360 0.1825 0.1450 0.1070 0.0726 0.0482 0.0250

180 0.0255 0.0655 0.1270 0.1100 0.0829 0.0580 0.0376 0.0174

200 0.0330 0.0440 0.1065 0.1090 0.0950 — — —

Argon

1 1.812 0.8605 0.5960 0.4307 0.3220 0.2413 0.1845 0.1377

20 — 0.8485 0.5720 0.4080 0.3015 0.2277 0.1720 0.1280

60 0.0025 0.6900 0.4963 0.3600 0.2650 0.1975 0.1485 0.1102

100 0.0277 0.2820 0.3970 0.3010 0.2297 0.1715 0.1285 0.0950

140 0.0403 0.1137 0.2840 0.2505 0.1947 0.1490 0.1123 0.0823

180 0.0595 0.0560 0.2037 0.2050 0.1700 0.1320 0.0998 0.0715

200 0.0640 0.0395 0.1860 0.1883 0.1580 0.1255 0.0945 0.0675

Carbon dioxide

1 — — 2.4130 1.2900 0.8950 0.6490 0.4890 0.3770

20 — — 0.0140 1.4020 0.8950 0.6375 0.4695 0.3575

60 — — 0.0150 0.0370 0.8800 0.6080 0.4430 0.3400

100 — — 0.0160 0.0215 0.5570 0.5405 0.4155 0.3150

140 — — 0.0183 0.0115 0.1720 0.4320 0.3760 0.2890

180 — — 0.0228 0.0085 0.1025 0.3000 0.3102 0.2600

200 — — 0.2480 0.0045 0.0930 0.2555 0.2910 0.2455

Nitrogen

1 1.2659 0.6490 0.3968 0.2656 0.1855 0.1292 0.0868 0.0558

20 1.1246 0.5958 0.3734 0.2494 0.1709 0.1173 0.0776 0.0472

60 0.0601 0.4506 0.3059 0.2088 0.1449 0.0975 0.0628 0.0372

100 0.0202 0.2754 0.2332 0.1679 0.1164 0.0768 0.0482 0.0262

140 0.0056 0.1373 0.1676 0.1316 0.0915 0.0582 0.0348 0.0168

180 0.0211 0.0765 0.1120 0.1015 0.0732 0.0462 0.0248 0.0094

200 0.0284 0.0587 0.0906 0.0891 0.0666 0.0419 0.0228 0.0070

Heliuma

p(atm) 160 K 200 K 240 K 280 K 320 K 360 K 400 K 440 K

 200 0.0574 0.0594 0.0608 0.0619 0.0629 0.0637 0.0643 0.0645

Source:a R. H. Perry and D. W. Green,Perry’s Chemical Engineers’ Handbook, 6th ed., McGraw-Hill, New York, 1984.

Below 200 atm, there is little variation in the value ofJTfor helium. (Also note that the helium data use Kelvin

temperatures.)