Tubing Materials and Dimensions

Permeation Tubes A volatile liquid, when enclosed in an inert plastic tube, may escape by dissolving in and permeating through the walls of the tube at a constant and reproducible rate. The permeation rate depends on the properties of the tube material, its dimensions and on temperature. 

The value of the design factor Cph will depend on the type of head, the edge support (clamped or simply supported), the plate dimensions, and the elastic constants for the plate and tube material, and can be obtained from the design charts and equations given in BS 5500, clause 3.9. 

The selection of the tube material and tube dimension is based on the temperature and pressure profile calculation. Based on the temperature profile and the strength of the material (determined as the jdeld or strength (in the elastic temperature range of tube materials)) as the stress-to-rupture strength for a 100,000-h service time), the tube thickness is calculated. Frequently, this process is an economic optimization between process conditions, material choice, and cost of bulk materials. 

Effect of Uncertainties in Thermal Design Parameters. The parameters that are used ia the basic siting calculations of a heat exchanger iaclude heat-transfer coefficients tube dimensions, eg, tube diameter and wall thickness and physical properties, eg, thermal conductivity, density, viscosity, and specific heat. Nominal or mean values of these parameters are used ia the basic siting calculations. In reaUty, there are uncertainties ia these nominal values. For example, heat-transfer correlations from which one computes convective heat-transfer coefficients have data spreads around the mean values. Because heat-transfer tubes caimot be produced ia precise dimensions, tube wall thickness varies over a range of the mean value. In addition, the thermal conductivity of tube wall material cannot be measured exactiy, a dding to the uncertainty ia the design and performance calculations. 

Common to all air cooled heat exchangers is the tube, through which the process fluid flows. To compensate for the poor heat transfer properties of air, which flows across the outside of the tube, and to reduce the overall dimensions of the heat exchanger, external fins are added to the outside of the tube. A wide variety of finned tube types are available for use in air cooled exchangers. These vary in geometry, materials, and methods of construction, which affect both air side thermal performance and air side pressure drop. In addition, particular... 

Plain tubes (either as solid wall or duplex) are available in carbon steel, carbon alloy steels, stainless steels, copper, brass and alloys, cupro-nickel, nickel, monel, tantalum, carbon, glass, and other special materials. Usually there is no great problem in selecting an available tube material. However, when its assembly into the tubesheet along with the resulting fabrication problems are considered, the selection of the tube alone is only part of a coordinated design. Plain-tube mechanical data and dimensions are given in Tables 10-3 and 10-4. 

Numerous materials have been used to fabricate open tubular columns. Most early studies were conducted using stainless steel tubing and later nickel tubing of capillary dimensions [147-149]. These materials had rough inner surfaces (leading to non-uniform stationary phase films), metal and oxide impurities at their surface which were a cause of adsorption, tailing, and/or decomposition of polar solutes and because their walls were thick, thermal Inertia that prevented the use of fast temperature programming. None of these materials are widely used today. 

Stainless steel is the material of choice for process chemistry. Consequently, stainless steel microreactors have been developed that include complete reactor process plants and modular systems. Reactor configurations have been tailored from a set of micromixers, heat exchangers, and tube reactors. The dimensions of these reactor systems are generally larger than those of glass and silicon reactors. These meso-scale reactors are primarily of interest for pilot-plant and fine-chemical applications, but are rather large for synthetic laboratories interested in reaction screening. The commercially available CYTOS Lab system (CPC 2007), offers reactor sizes with an internal volume of 1.1 ml and 0.1 ml, and modular microreactor systems (internal reactor volumes 0.5 ml to... 

Hydrogen homogeneity was controlled by metallographic examination. Metallography of hydride structure on radial-axial and radial-transverse sections shows a uniform hydride distribution with hydrides elongated in the longitudinal direction (Fig. 1). From the hydrided pressure tube material curved compact toughness (CTT) specimens were machined. Except for the thickness and the curvature of the tube, the in-plane dimensions of specimens were in proportion described for compact specimen in ASTM standard test method (E-399). 

The barrel coupling, center coupling, and the end cap can all be bored and turned to the correct outside dia-meters as shown in the drawing after which they are cut apart, the ends faced square, and the center holes threaded as required The measurements given in the drawings are appropriate only if the same size outer tubes as the ones I used are available. These dimensions must be changed as required to accommodate whatever size tube material is... 

Tubular electrode detectors have been fabricated in many laboratories, most notably those of Blaedel (Blaedel et al, 1963), Johnson (Lown et al, 1980), and Armentrout et al (1979). A typical fl "vc U is shown in Fig. 22. Made from Kel-F plastic, the body of the cell is machined to accept an inlet tubing fitting, outlet tubing fitting, and a reference electrode. A tubular -electrode, in this case a carbon black/polyethylene material, is restrained between the inlet and outlet fittings by 1 1% spacers. The inner dimensions of the tubular electrode are 3/16 in. longX 1/16 in. diameter (approximately 10 /<1). The attractive feature of this detector is an easily replaced... 

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