Open Tube

The extractor consists of a glass cylinder A, terminating at the base in the open tube B. Fused within the top of A as shown is another tube C, having a small hole D blow n in the side a fine glass tube leads from the base of C, rises about two-thirds of the height of the cylinder to E, and then returns past F into the open tube B. 

Inlets for syringe sampling are divided kito two main categories one for packed-column and the other for capiHary-column devices. Eor packed columns, all material kijected is carried by the mobile phase onto the column. The inlet is usually an open tube, but sometimes, albeit rarely, the inlet itself may be packed, eg, to assure that the first centimeters of the column do not become contaminated with degradation products or nonvolatile materials that may affect the efficacy of the column. 

The capiUaiy rise in a smaU vertical open tube of circular cross section dipping into a pool of liquid is given by... 

Coil condenser. An open tube, into which is sealed a glass coil or spiral through which water circulates. The tube is sometimes also surrounded by an outer cooling Jacket. A double coil condenser has two inner coils with circulating water. 

Open Tube Sections (Water cooled) Tubes require no shell, only end headers, usually long, water sprays over surface, sheds scales on outside tubes by expansion and contraction. Can also be used in water box. Condensing, relatively low heat loads on sensible transfer. Transfer coefficient is low, takes up less space than pipe coil. 0.8-1.1... 

Open Tube Sections (Air Cooled) Plain or finned tubes No shell required, only end heaters similar to water units. Condensing, high level heat transfer. Transfer coefficient is low, if natural convection circulation, but is improved with forced air flow across tubes. 0.8-1.8... 

The column may be packed or it may be an open tube but in this example, a packed column will be specifically considered. The column is considered to have a length (L) and inlet and outlet pressures and inlet and outlet velocities of (Pi), (Po) (ui) and (uo), respectively. The pressure and velocity at a distance (x) from the front of the column is (Px) and (ux), respectively. According to D Arcy s equation for fluid flow through a packed bed, at any point in the column. 

It is seen that the value of (H) is completely dependent on the diffusivity of the solute in the mobile phase, the column radius and the linear velocity of the mobile phase. The simple uncoated open tube can clearly be used to determine the diffusivity of any solute in any given solvent (the mobile phase). This technique for measuring diffusivities will be discussed in a later chapter. 

The dispersion that takes place in an open tube, as discussed in chapter 8, results from the parabolic velocity profile that occurs under conditions of Newtonian flow (i.e., when the velocity is significantly below that which produces turbulence). Under condition of Newtonian flow, the distribution of fluid velocity across the tube... 

Figure 7. Graphs Relating the Variance and Standard Deviation of Peaks Passing Through an Open Tube against Tube Length...

Most sensor volumes, whether in LC (e.g., a UV absorption cell) or in GC (e.g., a katharometer cell), are cylindrical in shape, are relatively short in length and have a small length-to-diameter ratio. The small length-to-diameter ratio is in conflict with the premises adopted in the development of the Golay equation for dispersion in an open tube and, consequently, its conclusions are not pertinent to detector sensors. Atwood and Golay [12] extended the theory of dispersion in open tubes to tubes of small length-to-diameter ratio. The theory developed is not pertinent here as it will be seen that, with correctly designed cells, that dispersion from viscous sources can be... 

Katz and Scott [1] measured the diffusivity of 69 different solutes having molecular weights ranging from 78 to 446. The technique they employed was to measure the dispersion of a given solute band during passage through an open tube. 

The dispersion in an open tube has been previously discussed (chapter 9 page 287). Reiterating equation (8) from Chapter 8 page 266... 

Katz and Scott used equation (7) to calculate diffusivity data from measurements made on a specially arranged open tube. The equation that explicitly relates dispersion in an open tube to diffusivity (the Golay function) is only valid under condition of perfect Newtonian flow. That is, there must be no radial flow induced in the tube to enhance diffusion and, thus, the tube must be perfectly straight. This necessity, from a practical point of view, limits the length of tube that can be employed. 

A low volume (0.2 pi) Valeo sample valve was employed with one end of the open tube connected directly to the valve and the other connected directly to the sensor cell of the detector. The UV detector was the LC 85B manufactured by Perkin Elmer, and specially designed to provide low dispersion with a sensor volume of about 1.4 pi. The total variance due to extra-column dispersion was maintained at... 

To day peak widths are rarely used in chromatographic analysis except for the purpose of calculating peak areas. Peak widths, however, can provide a means of measuring the diffusivity of a solute which is a function of the molecular weight. Consequently, if a reliable relationship between diffusivity and molecular weight can be identified, then the molecular weight of the solute can be assessed. Peak widths of solutes eluted from an open tube can give very precise values of diffusivity. There are a number of equations that purport to relate diffusivity to... 

The length of the column is also defined by the Poiseuille equation that describes the flow of a fluid through an open tube in terms of the tube radius, the pressure applied across the tube (column), the viscosity of the fluid and the linear velocity of the fluid. Thus, for a compressible fluid. 

Substituting the function for the retention volume for an open tube,... 

BEOs consisting of open tube or duct ends can be connected directly to a source. In principle, these could be called closed systems, since their main function is to exhaust contaminants directly from the source, which is enclosed in the duct. However, they are usually regarded as basic exhausts since they function as such when not connected to the source. 

Rdstrohr, n. roasting tube, open tube (for qualitative teats). 

Open Tube 10-5A Tubes require no shell, only Condensing, relatively low heat Transfer coefficient is low. 0.8-1.1... 

Figure 10-6. Open tube sections. (Used by permission Griscom-Russell Co./Ecolaire Corp., Easton, PA.)...

Although a pressure gauge is more commonly used to measure the pressure inside a laboratory vessel, a manometer is sometimes used (Fig. 4.5). It consists of a U-shaped tube connected to the experimental system. The other end of the tube may be either open to the atmosphere or sealed. For an open-tube manometer (like that shown in Fig. 4.5a), the pressure in the system is equal to that of the atmosphere when the levels of the liquid in each arm of the U-tube are the same. If the level of mercury on the system side of an open manometer is above that of the atmosphere side, the pressure in the system is lower than the atmospheric pressure. In a closed-tube manometer (like that shown in Fig. 4.5b), one side is connected to a closed flask (the system) and the other side is vacuum. The difference in heights of the two columns is proportional to the pressure in the system. 

The height of the mercury in the system-side column of an open-tube mercury manometer was 10. mm above that of the open side when the atmospheric pressure corresponded to 756 mm of mercury and the temperature was 15°C. What is the pressure inside the apparatus in millimeters of mercury and in pascals ... 

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