Joule-Thompson expansion

The flow through the sampling valve is a true Joule-Thompson expansion. 

When any vapor expands, due to a pressure reduction (other than H2 and C02), it cools off. This is called a Joule-Thompson expansion. The reduction in temperature of the steam is called a reduction in sensible-heat content. The sensible heat of the steam is converted to latent heat of condensation. Does this mean that the latent heat of condensation of 10-psig steam is much higher than that of 450 psig steam Let s see ... 

Fig. 8.2. Schematic cartoons illustrating various types of adiabatic volume changes. In each case the points on the PV diagram correspond to those in Figure 8.1. (a) Reversible, Isentropic. (b) Joule Expansion, (c) Joule-Thompson Expansion.

Calculate i Vo — for the Joule-Thompson expansion considered in the text, and verify that the result is the same as Ud — U. ... 

The air feed is first compressed and heat of compression is removed from the stream by intercooling, aftercooling and direct water quench. The elevated pressure airstream is purified to remove water and other impurities and it is then expanded to a lower pressure to generate the reduced temperature necessary for liquefaction. Expansion takes place either across a valve (Joule-Thompson expansion) or through a turboexpander producing useful work. The compression, cooling and subsequent expansion of the air feed stream constitutes the refrigeration cycle. 

A schematic of the system and the corresponding temperature-entropy diagram are shown in Figure 3. A schematic of the system is shown on the left side of the diagram. The equipment in this system are a gas compressor, compressor aftercooler, plate-fin heat exchanger, Joule-Thompson expansion valve and liquid-vapor separator. 

The expander cycle and its corresponding temperature-entropy diagram are shown in Figure 4. Notice that the expander cycle is similar to the simplified Joule-Thompson cycle, except that the Joule-Thompson expansion valve has been replaced by an expansion turbine. The performance of this cycle differs in several ways. The expansion of the gas is no longer isenthalpic, but with the expansion turbine, it is isentropic that is, there is a change in... 

Isothermal compression and heat rejection take place between points 1 and 2. A portion of the compressed gas is diverted from the plate-fin heat exchanger and expanded through an expansion turbine to lower the temperature and produce mechanical work. The expanded and cooled gas (point 11) reenters the heat exchanger between point 9 and point 10. The balance of the feed gas is further cooled and expanded through a Joule-Thompson expansion valve from point 5 to point 6. Liquid is formed in the Joule-Thompson expansion. 

This cycle is a variation of the Claude cycle. If air is the working fluid, the compressor discharge pressure is 200 bars (2885 psig) and the liquid fraction produced in the Joule-Thompson expansion is about 0.6, then the optimum temperature for the inlet to the expansion turbine is about ambi-... 

The part of the feed nitrogen that passes through the second plate-fin exchanger is expanded through a Joule-Thompson expansion valve and the two phase mixture enters a medium pressure vapor-liquid separator. The vapor from this vessel is mixed with the discharge from the turboexpander... 

John Brown Corporation, 172, 206 Johnson Matthey, 257, 258 Joule-Thompson expansion for air liquefaction, 5... 

Many relief valves leak hydrocarbons to the flare. If the vessel with a leaking relief valve is operating at a substantial pressure (about 30 or 40 psig), then the line downstream of the relief valve will be noticeably (perhaps 10°F) colder than the relief valve connection itself, due to a Joule-Thompson expansion. 

If the vessel with the leaking relief valve is liquid full with light hydrocarbons (ethane, propane, or butane), then a leaking relief valve will be quite obvious. The line downstream of the faulty pressure relief valve will be covered with ice. The ice is atmospheric moisture freezing on the line to the flare. This is not due to a Joule-Thompson expansion, but due to the auto-refrigeration of the volatile hydrocarbon liquid as it flashes to a vapor in the flare header piping. 

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