Receiver dewar

FIGURE 5.4 Receiver Dewar for Low Pressure Liquid Hydrogen and Nitrogen Bubble Point Tests. 

Prior to insertion of the transfer tube into the supply and receiver dewars, the transfer tube and receiver dewar are filled with helium. This precaution eliminates the possibility that water or air may freeze in the pressure taps. After the transfer tube is in position, the weight of the supply dewar is put onto the cantilever beam by rotating a turnbuckle (see Figure 2). 

Flow through the system is started by pressurizing the supply dewar to a value which produces a pre-selected pressure upstream of the orifice this pressure is maintained constant throughout the run. After the transfer tube has cooled down, the pressure (or vacuum) in the receiver dewar is adjusted to... 

The liquid hydrogen was transferred from the pressurized supply dewar through the vacuum-insulated lines, the orifice flow meter, the test section, and into the receiving dewar. Data were taken after steady state, as indicated by a steady orifice reading, was attained the data consisted of pressures, temperatures, flow rates, time of day, and ambient conditions (i.e., atmospheric temperature and pressure, humidity, and wind velocity). Two wind velocities were used in these tests a steady wind velocity of 15mph supplied by two 24-in. fans, and zero wind velocity. 

The receiving dewar had a capacity of 500 gal. It was foam-insulated and suspended in the air by two load cells so that the increase in weight due to the quantity of liquid hydrogen transferred could be measured. 

A vent stack extended from the receiving dewar to a gas flowmeter and terminated above the test house. The main purpose of this vent in addition to exhausting the gas was to measure the quantity of vaporized liquid, since this is a factor in determining the total transfer rate of liquid hydrogen. 

Rowland Pettit (1927-19811 was born in Port Lincoln, Australia. He received two doctoral degrees, one from the University of Adelaide in 1952 and the second from the University of London in 1956, working with Michael Dewar. He then became professor of chemistry at the University of Texas, Austin (1957-1981). 

Figure 1. Diagram of the apparatus used in the s3mthesis and isolation of V(CO)g. Components (A) round-bottom flask, 500 mL (B) connecting tube, (C) specially adapted Schlenk tube receiver (D) stopcock (E) Dewar flask (F) water bath (G) butyl rubber vacuum tubing connection to vacuum/argon manifold. Dimensions a =165 mm b = 130 mm c = 170 mm d = 75 mm e = 20mm od.

Specifically, the glass connection between the Schlenk tube receiver (C) and stopcock (D) should extend about 130 mm below the top of the 24/40 standard taper inner joint and approximately 50 mm into Dewar flask (E) to prevent loss of the especially volatile V(CO)e to the vacuum line during the reaction and sublimation. The Schlenk tube receiver is cooled to about —70°C with dry ice/acetone or dry ice/isopropyl alcohol. The level of coolant should be near the top of the Dewar so that the glass connection between the stopcock (D) and the Schlenk tube is entirely covered. The apparatus is evacuated very slowly and cautiously... 

Chris Ramsden was born in Manchester, UK in 1946. He is a graduate of Sheffield University and received his PhD (W. D. Ollis) in 1970 and DSc in 1990. After post-doctoral work at the University of Texas (M. J. S. Dewar)(1971-3) and University of East Anglia (A. R. Katritzky)(1973-6), he worked in the pharmaceutical industry. He moved to Keele University as Professor of Organic Chemistry in 1992. His research interests are heterocycles, ortho-quinones and three-centre bonds, and applications of their chemistry to biological problems. 

Dewar s method has received considerable criticism, and has not been used in all-valence electrons calculations. 

Dewar s landmark contribution [32] did not receive much attention at the time it was published, possibly because the author did not seek to establish the experimental evidence for his model in subsequent publications. He seemed not to be very interested in the field of transition metal chemistry and was probably not aware that his description of the bonding in olefin silver complexes was supported by Raman studies reported a decade previously. In 1941, Harvey Taufen and coworkers had found that the olefin remained largely unchanged in its coordination to Ag+ and that the C=C bond was weakened only slightly by the formation of the olefin silver complex [36]. In contrast to Dewar, Joseph Chatt knew this paper and mentioned the results in a review on the mercuration of olefins, which like Dewar s article was also published in 1951 [37], In his paper, Chatt made a clear distinction between the olefin silver and olefin platinum complexes and argued that, in contrast to the ionized olefin silver(I) salts, in the olefin platinum(II) compounds the metal is present in a covalent state and not as an ion. He also believed that for Ag+ the d-shell was core like and not available in the manner necessary to stabilize the olefin-platinum bond [37]2. 

About 20 g of 2-butyne may be collected in an ice-cooled receiver if the dried solution is concentrated by distillation through a 25-cm Vi-greux column rather than by evaporation. The checkers do not recommend this mode of work-up, nor did they use a column for distilling the Dewar benzene, to avoid prolonged heating of the bicyclic system. 

Another receiver, consisting of a 3 by 30 cm. side-arm test tube, may be used. It is immersed in a Dewar flask and cooled with Dry Ice-methanol. Only a small amount of material is collected in this receiver. 

Note 5) the second is immersed in a Dry Ice-methanol mixture contained in a Dewar flask. The exit tube of the second receiver is connected to a manometer (Note 6) and to a water pump. 

The [n]cyclophanes are the archetypal small cyclophanes and, within this area, it is the [n]paracyclophanes (Fig. 1) that have received by far the most attention. A detailed computational study of [4]paracyclophane [1], which has only been prepared as a transient species via matrix isolation [2], was recently reported. An energy difference of 9 kcal mol between it and its Dewar benzene isomer was predicted. This paper also provides a comprehensive summary of the literature of the [n]paracylophanes. 

Figure 12.4. Block diagram of a modem NMR spectrometer. These systems use superconducting magnets that are based on a solenoid of a suitable alloy (e.g., niobium/titanium or niobium/tin) immersed in a dewar of liquid helium. The extremely low temperature of the magnet itself (4.2 K) is well insulated from the sample chamber in the center of the magnet bore. The probe in which the sample is housed usually incorporates accurate temperature control over the range typically of 4 to 40°C for biological samples. The rf coil in the probe is connected in turn to a preamplifier, receiver circuitry, analog-to-digital converter (ADC), and a computer for data collection.

The importance of products of intermediate volatility has received attention in recent investigations, and it has been found that photoisomerization plays an important role with substituted benzenes. Van Tamelen and Pappas showed that a medium-pressure mercury lamp converted 1,2,4-tri-t-butylbenzene in ether solution to a Dewar benzene, l,2,5-tri-t-butylbicyclo[2.2.0]hexa-2,5-diene. Burg-stahler and Chien found that, in ether solution, o-di-t-butylbenzene, when photolysed with a mercury lamp, was converted entirely to a 4 1 mixture of /> w-di-/-butylbenzene while either the meta or para compound was converted to the same mixture. Wilzbach and Kaplan have conducted a thorough investiga-... 

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