Helium viscosity

Figure 4. Graph of Helium Viscosity against Temperature...

Figure 1 graphically represents the results of the helitrm viscosity comparison and shows the deviation of the semi-empirical method of calculating helium viscosity from the empirically derived DIPPR crave fit recommended in this paper. Figtrre 1 shows that NIST results track well with DIPPR results. Helium semi-empirical values deviate from DIPPR values by as much as 10.4% at 1400 K (fuel clad strrface temperatures in contact with HeXe may approach 1400 K). 

Seven isotopes of helium are known Liquid helium (He4) exists in two forms He41 and He411, with a sharp transition point at 2.174K. He41 (above this temperature) is a normal liquid, but He411 (below it) is unlike any other known substance. It expands on cooling its conductivity for heat is enormous and neither its heat conduction nor viscosity obeys normal rules. 

Gaseous helium is commonly used as the working fluid ia closed-cycle cryogenic refrigerators because of chemical iaertness, nearly ideal behavior at all but the lowest temperatures, high heat capacity per unit mass, low viscosity, and high thermal conductivity. 

Liquid helium-4 can exist in two different liquid phases liquid helium I, the normal liquid, and liquid helium II, the superfluid, since under certain conditions the latter fluid ac4s as if it had no viscosity. The phase transition between the two hquid phases is identified as the lambda line and where this transition intersects the vapor-pressure curve is designated as the lambda point. Thus, there is no triple point for this fluia as for other fluids. In fact, sohd helium can only exist under a pressure of 2.5 MPa or more. 

Values for the viscosity of helium were calculated from the following equation given in Ref.l ... 

Helium is an interesting example of the application of the Third Law. At low temperatures, normal liquid helium converts to a superfluid with zero viscosity. This superfluid persists to 0 Kelvin without solidifying. Figure 4.12 shows how the entropy of He changes with temperature. The conversion from normal to superfluid occurs at what is known as the A transition temperature. Figure 4.12 indicates that at 0 Kelvin, superfluid He with zero viscosity has zero entropy, a condition that is hard to imagine.v... 

The fluidizing gas is usually methane, helium, or another non-reactive gas. Factors to consider to obtain proper fluidization are the density and size of the particles to be coated, and the velocity, density, and viscosity of the gases.If the velocity is too low, the particles will fall into the gas inlet if it is too high, they... 

The 1996 Nobel Prize in physics went to three researchers who studied liquid helium at a temperature of 0.002 K, discovering superfluid helium. A superfluid behaves completely unlike conventional liquids. Liquids normally are viscous because their molecules interact with one another to reduce fluid motion. Superfluid helium has zero viscosity, because all of its atoms move together like a single superatom. This collective behavior also causes superfluid liquid helium to conduct heat perfectly, so heating a sample at one particular spot results in an immediate and equal increase in temperature throughout the entire volume. A superfluid also flows extremely easily, so it can form a fountain, shown in the photo, in apparent defiance of gravity. 

The viscosity of the carrier gas determines the column pressure drop for a given velocity. For hydrogen, helium, and nitrogen it can be approximated by equations (1.53 to 1.55) in the temperature range of interest for gas [Pg.545]

The density of He I at the boiling point at 1 atm is 125 kg m 3 and the viscosity is 3 x 10 6 Pa s. As we would anticipate, cooling increases the viscosity until He II is formed. Cooling this form reduces the viscosity so that close to 0 K a liquid with zero viscosity is produced. The vibrational motion of the helium atoms is about the same or a little larger than the mean interatomic spacing and the flow properties cannot be considered in classical terms. Only a quantum mechanical description is satisfactory. We can consider this condition to give the limit of De-+ 0 because we have difficulty in defining a relaxation when we have the positional uncertainty for the structural components. 

It is seen that we are comparing kinematic viscosity, thermal diffusivity, and diffu-sivity of the medium for both air and water. In air, these numbers are all of the same order of magnitude, meaning that air provides a similar resistance to the transport of momentum, heat, and mass. In fact, there are two dimensionless numbers that will tell us these ratios the Prandtl number (Pr = pCpv/kj = v/a) and the Schmidt number (Sc = v/D). The Prandtl number for air at 20°C is 0.7. The Schmidt number for air is between 0.2 and 2 for helium and hexane, respectively. The magnitude of both of these numbers are on the order of 1, meaning that whether it is momentum transport, heat transport, or mass transport that we are concerned with, the results will be on the same order once the boundary conditions have been made dimensionless. 

Homogeneous Liquids. The physical properties important in determining the suitability of a liquid for propellant application are the freezing point, vapor pressure, density, and viscosity. To a lesser extent, other physical properties are important such as the critical temperature and pressure, thermal conductivity, ability to dissolve nitrogen or helium (since gas pressurization is frequently used to expel propellants) and electrical conductivity. Also required are certain thermodynamic properties such as the heat of formation and the heat capacity of the material. The heat of formation is required for performing theoretical calculations on the candidate, and the heat capacity is desired for calculations related to regenerative cooling needs. 

Xenon is an odourless, colourless, non-explosive gas present in the atmospheres of both Earth and Mars in concentrations of approximately 0.08 ppm. Its density is approximately three times and its viscosity twice that of nitrous oxide. Like other noble gases, such as helium and argon, its outer electron shell contains the maximum number of electrons (8) making the molecule highly stable chemically. Despite this, its anaesthetic activity indicates that xenon binds to cell proteins and cell membrane constituents. 

Viscosity " Oxygen (02) b Carbon Dioxide (C02) Methane (CH4)c Helium (He)c Benzene (1 Decane d Acetone ... 

Figure 2.2—Optimum linear velocity and viscosity of carrier gas. The optimal mean linear velocities of the various carrier gases are dependent on the diameter of the column. The use of hydrogen as a carrier gas allows a faster separation than the use of helium while giving some flexibility in terms of the flow rate (which can be calculated or measured). This is why the temperature program mode is used. The significant increase in viscosity with temperature can be seen for gases. In addition, the sensitivity of detection depends on the type of carrier gas used.

---