Joule-Thomson refrigerator

He is remembered for Joule s Law lhat describes the rale at which heal is produced by an electric current. Joule s work showed there were different kinds or energy, which can be changed into each other. He established the mechanical equivalence of heat. His work led to the law of conservation of energy. Alsu, he collaborated with William Thomson (Lord Kelvin) and verified experimentally the Joule-Thomson refrigeration effect. 

Refrigeration systems based on the Joule-Thomson effect have lower thermodynamic efficiencies than those based on refrigeration systems with expansion engines. Most small laboratory and commercial hydrogen liquefiers, however, (not including those depending upon helium expansion cycles) utilize Joule-Thomson refrigeration because of simplicity and compactness [5],... 

J. M. Geist and P. K. Lashmet, "Miniature Joule-Thomson Refrigeration Systems," Advances in Cryogenic Engineering, Vol. 5, K.D. Timerhaus (ed.), Plenum Press, Inc., New York (1960). 

Expanders The primary function of cryogenic expansion equipment is the reduction of the temperature of the gas being expanded to provide needed refrigeration. The expansion of a fluid to produce refrigeration may be carried out in two distinct ways (1) in an expander where mechanical work is produced, and (2) in a Joule-Thomson valve where no work is produced. 

Jotile-Thomson Valves The principal function of a J-T valve is to obtain isenthalpic coohng of the gas flowing through the valve. These valves generally are needle-type valves modified for cryogenic operation. They are an important component in most refrigeration systems, particularly in the last stage of the liquefac tion process. Joule-Thomson valves also offer an attractive alternative to turboexpanders for small-scale gas-recovery applications. 

Gas can be condensed by (a) mechanically refrigerating it, (b) compressing and expanding it, using turboexpanders, or, (c) pressure effects such as by Joule-Thomson cooling and overcoming the vapor pressure. The liquefaction of methane can involve all three of these effects. These effects can be separately evaluated to show the effectiveness of each in producing liquid. 

In summary, starting with 105°F gas at atmospheric pressure, the theoretical work necessary to liquify one pound of methane is 510.8 Btu or 352 hp/MMcfd. The simplified liquefaction process, as illustrated, uses a turboexpander/compressor and a small propane refrigeration unit. The 41.25% efficiency breaks down as follows one-fourth contributed by the turboexpander/compressor at 35.8% efficiency one-sixteenth contributed by the mechanical propane refrigeration unit at 43% efficiency, at a moderate temperature where its efficiency is high and a large fraction—eleven-sixteenths—contributed at 58.2% efficiency by compression and Joule-Thomson condensation energy. 

Hydroearbon dew point eontrol is aehieved by eooling the gas. There are three eooling alternatives free expansion or Joule-Thomson expansion, external refrigeration, and using a turboexpander. Joule-Thomson expansion does not always produee the needed refrigeration over the life of the plant and, henee, is not eonsidered as a viable... 

Fig. 6.12. Simplified scheme of a Joule-Thomson heat exchanger for dilution refrigerator.

Fig. 6.14. A recent Joule-Thomson dilution refrigerator (courtesy of Leiden Cryogenics).

Fig. 6.16. Cross-cut of Uhlig s cryostat with pulse tube refrigerator, dilution unit and Joule-Thomson... 

The third law is concerned with the nature of entropy (Sidebars 5.10-5.13) and thermodynamic behavior in the limiting approach toward T = OK. Although Joule-Thomson expansion (Section 3.6.3) is a useful refrigeration technique down to about 20K (7J for H2), more specialized cryogenic techniques are required to approach the sub-microkelvin (around 10 6K) domain of extreme low temperatures. The most important such technique, adiabatic demagnetization, is described in Sidebar 5.16. 

The temperatures on the envelope where pn = 0 are called inversion temperatures, Tt. At any given pressure, up to a maximum pressure, a given gas exhibits two inversion temperatures. The Joule-Thomson effect is important in refrigeration and in the liquefaction of gases. Modern refrigeration uses the larger effect of the evaporation of working fluids such as the chlorofluorocarbons. 

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