Helium, thermodynamic data

This reaction results in an equilibrium potassium vapor pressure (calculated from thermodynamic data) of 0.714 torr above the LiCl-KCl eutectic at 427°C (700°K). Metallic lithium is rapidly lost, by Reaction 1, from the lithium electrode in open cells exposed to an inert atmosphere of helium (3). However, this reaction has not been evident in hermetically sealed cells. 

Dye fixation on modified celluloses depended on the pH, temperature, time of thermofixation, type and concentration of the dye used. Diffusion data have been obtained for helium, nitrogen, oxygen, and carbon dioxide gases through membranes of the acetate derivative of cellulose. The thermodynamic data have been evaluated and the mechanism of diffusion was discussed. 

Figure 3 gives the parallel GT-ST-MHTGR system. The difference is that the GT cycle and ST are parallelly arranged in the second side. The high temperature helium is partly used for the GT cycle, and the rest for ST cycle. The thermodynamic data are shown in... 

For infinite dilution operation the carrier gas flows directly to the column which is inserted into a thermostated oil bath (to get a more precise temperature control than in a conventional GLC oven). The output of the column is measured with a flame ionization detector or alternately with a thermal conductivity detector. Helium is used today as carrier gas (nitrogen in earlier work). From the difference between the retention time of the injected solvent sample and the retention time of a non-interacting gas (marker gas), the thermodynamic equilibrium behavior can be obtained (equations see below). Most experiments were made up to now with packed columns, but capillary columns were used, too. The experimental conditions must be chosen so that real thermodynamic data can be obtained, i.e., equilibrium bulk absorption conditions. Errors caused by unsuitable gas flow rates, unsuitable polymer loading percentages on the solid support material and support surface effects as well as any interactions between the injected sample and the solid support in packed columns, unsuitable sample size of the injected probes, carrier gas effects, and imprecise knowledge of the real amount of polymer in the column, can be sources of problems, whether data are nominally measured under real thermodynamic equilibrium conditions or not, and have to be eliminated. The sizeable pressure drop through the column must be measured and accounted for. 

Recently, in the Thermodynamic Data Center of Moscow Power Institute, a database on thermodynamic properties of gaseous and vapor-liquid binary mixtures was created on the basis of results of experimental investigations carried out in this institute. Freons of the methane series, carbon dioxide and sulphur hexafluoride are the first component of these mixtures, with nitrogen, hydrogen and helium as the second component. The corresponding software product was developed for the information system (Baibuz 1990). 

There are presently several database programs of thermodynamic properties data developed specifically for fluids commonly associated with low temperature processing including helium, hydrogen, neon. 

The values in these tables were generated from the NIST REFPROP software (Lemmon, E.W., McLinden, M.O., and Huber, M.L., NIST Standard Reference Database 23 Reference Fluid Thermodynamic and Transport Properties—REFPROP, National Institute of Standards and Technology, Standard Reference Data Program, Gaithersburg, Md., 2002, Version 7.1). The primary source for the thermodynamic properties is McCarty, R.D., and Arp, V D., A New Wide Range Equation of State for Helium, Ado. Cryo. Eng. 35 1465-1475,1990. The source for viscosity is Arp, V. D., McCarty, R. D., and Friend, D. G., Thermophysical Properties of Helium-4 from 0.8 to 1500 K with Pressures to 2000 MPa, NIST Technical Note 1334, Boulder, Colo., 1998. The source for thermal conductivity is Hands, B. A., and Arp, V. D., A Correlation of Thermal Conductivity Data for Helium, Cryogenics, 21(12) 697-703,1981. 

Liquid helium can be regarded as an ordinary liquid however, its physical properties are modified somewhat compared to other liquids. The superheat data of Karagounis P ] correspond to reduced values larger than 1.5 ATp/Tc, whereas results from a vertical heater [- ] obtained at a very low power level, are small, as to be expected. In spite of the low temperature, there are no drastic deviations from thermodynamic similitude in the range 0.6 < T/Tc < 1, where equation (1) permits reasonable superheat estimates. 

Operating data for the 1-kw refrigerator indicate a value of i , the work input per unit of refrigeration, of 70 with a conventional nonlubricated compressor. The average refrigeration effect per pound of circulated gas, J5, is 12.0. This compares to calculated values of 58 and 16 for E and B, respectively. These differences in the theoretical and measured parameters are due to reduced performance by the compressor, expander, and heat exchanger. The comparison is also affected by the values assumed for the thermodynamic properties of the helium. 

Admolecules diffuse within the pore system of a solid sorbent. This process can last many hours, days, and even weeks, as has been observed for adsorption of helium in activated carbon (NORIT Rl), [1.23]. As a consequence it can take the same time till thermodynamic equilibrium between the sorptive gas phase and the adsorbate is realized. In view of practical and industrial needs it is therefore necessary to introduce the concept of technical equilibrium defined as a state in which the relative uptake (Am/m) of mass at total mass (m) due to adsorption is less than a given value (e) typically e = 10 , within a certain time interval (At), typically At = 30 . These data will allow, together with cycle periods (tc) of an industrial process, one to define characteristic Deborah numbers... 

Lick and Emmons publication on the thermodynamic properties of helium at temperatures up to 50 000 K does not include data for the liquid... 

Brooks, J.S., Donnelly, R.J., 1977. The calculated thermodynamic properties of superfluid helium-4. J. Phys. Chem. Ref. Data 6, 51-104. 

---