Nitrogen precooling with

After being precooled with product oxygen in exchanger E-l and with product nitrogen in E-2, the air serves as the heating medium in reboiler E-3 of column T-2. Its pressure then is reduced to 100 psig, and it is fed to the middle of column T-2. Bottoms of T-2 is fed to the middle of column T-3. This stream contains 40% oxygen. 

FIGURE 23.6 The simplest JT liquefier cycle (1) gas compression with a mechanical work W, (2) cooling in the heat exchanger, and (3) liquefying in the isenthalpic expansion valve to produce some liquid. In the case of hydrogen precooling with liquid nitrogen is needed. 

For operation at low temperature, the furnace may be surrounded by a Dewar flask and precooled with liquid nitrogen. The furnace is then heated by the furnace element using a heating-mode program. Another method is to use a gas as a heat exchange medium, such as is illustrated in Figure 6.12 (31). Most temperature programmers do not function efficiently unless a... 

With leads wired to the gauges and the current and voltage terminals, the test ring was mounted on the loading cones. After all the instruments were assembled, the test ring and loading cones were attached to the actuator, sealed into the helium dewar, precooled with liquid nitrogen, and immersed in liquid helium. 

The Claude cycle may be used without modification to liquefy hydrogen or neon, since this system does not primarily depend on the expansion valve to produce low temperatures. However, by using a liquid nitrogen precooling bath with the Claude system (see Fig. 4.13), a figure of merit 50-70% higher than that for the precooled Linde system may be obtained. 

Still another extension of the Claude cycle is the Collins helium liquefier, schematically represented in Fig. 4.18 with a typical set of operating conditions. Depending upon the helium inlet pressure, from two to five expansion engines are used in this system. The addition of a liquid nitrogen precoolant bath to this system results in a two- to threefold increase in liquefaction performance. 

Androst-4-ene-3,17,19-trione (0.23g) is added to a precooled solution of 0.23 g of potassium hydroxide in a mixture of 1 ml of water and 5 ml of methanol. The reaction mixture is stirred at 5-10° under nitrogen for 3 hr, diluted with benzene (30 ml) and washed with water (2 x 10 ml). The aqueous layer is reextracted with benzene and the benzene solution dried and evaporated. The crude crystalline product is filtered through 8 g of Merck silicagel and eluted with benzene-ethyl acetate (9 1) to yield 0.19 g of 19-norandrostenedione (88%) mp 169-171° 141° (CHCI3). 

A precooling of dewar with liquid nitrogen (LN2) from 300 to 77 K saves a large amount of LHe liquid N2 has a vaporization heat 60 times that of LHe and a cost 20 times less. Moreover, the enthalpy of materials (es. A1) between 77 and 300 K (162 J/g) is much higher than that between 4 and 77 K (9 J/g). 

Semicontinuous polymerization experiments were carried out in a stainless steel enclosure (dry box) under a dry nitrogen atmosphere in three neck flasks (11) equipped with overhead stirrer and an inlet for the continuous introduction of precooled inifer/isobutylene/ solvent feeds to stirred, dilute BCI3/solvent charges. Experiments with binifer were performed at -80°C by the use of CH3Cl/n-hexane solvent mixtures (80/20 v/v), with trinifer at -40°C using CH3CI... 

Cryoelectron microscopy makes it possible to have a direct view into the frozen sample without additional preparation [100]. With the aid of a cryogen (e.g., liquid nitrogen-cooled liquid ethane), the sample is plunge frozen as a very thin aqueous film prepared on a microscopic grid. Subsequently, the vitrified specimen is directly transferred into a precooled electron microscope. Because the specimens are usually ) 2005 by CRC Press LLC... 

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