Temperature gradient tube

Eichler, B., Domanov, V.P. Volatilization of radionuclides in air stream and their separation in temperature-gradient tube. J. Radioanal. Nucl. Chem. 28, 143-152 (1975)... 

Eichler, B., Zude, F., Fan, W., Trautmann, N., Herrmann, G. Volatilization and deposition of ruthenium oxides in a temperature gradient tube. Radiochim. Acta 56, 133-140 (1992)... 

The transport of Ru oxides in a temperature gradient tube appears to be more complicated. First indications that also Ru can be volatilized in the form of RUO4 were obtained in [94], but such a behavior was not observed in [95]. In contrast to... 

Vitreous silica is used for gas-heated or electrically heated devices ia various shapes, eg, as a tube or muffle because of its electrical resistivity, impermeabihty, and low expansion. In its simplest form, an electric-resistance furnace consists of a vitreous siUca tube or pipe on which the resistance element is wound (see Furnaces, ELECTRIC). Because of its iadifference to temperature gradients, a tubular furnace of vitreous siUca maybe made to operate at different temperatures at various portions of the tube, either by arrangement of the heating elements or by cooling sections of the tube with water. Vitreous siUca pipes may be employed ia vacuum-iaduction and gas-fired furnaces (see Vacuum technology) (221). 

An important effect in the design of a tubular flow reactor is the development of a radial temperature gradient in a highly exothermic reaction with wall cooling. The temperatures near the tube axis are... 

The conditions for heat flow through a thick-walled tube when the temperatures on the inside and outside are held constant are shown in Figure 9.8. Here the area for heat flow is proportional to the radius and hence the temperature gradient is inversely proportional to the radius. 

The calculation of the film coefficients on the fin side is complex because each unit of surface on the fin is less effective than a unit of surface on the tube wall. This arises because there will be a temperature gradient along the fin so that the temperature difference... 

Figure 2.6 shows a typical temperature profile.t l The temperature boundary layer is similar to the velocity layer. The flowing gases heat rapidly as they come in contact with the hot surface of the tube, resulting in a steep temperature gradient. The average temperature increases toward downstream. 

The wall boundary condition applies to a solid tube without transpiration. The centerline boundary condition assumes S5anmetry in the radial direction. It is consistent with the assumption of an axis5Tnmetric velocity profile without concentration or temperature gradients in the 0-direction. This boundary condition is by no means inevitable since gradients in the 0-direction can arise from natural convection. However, it is desirable to avoid 0-dependency since appropriate design methods are generally lacking. 

Temperature gradient at erystcd-growing junetion of tube. 

Figure 2.17 Traps for saaiple recovery from a gas chromatographic effluent. A, U-tube B, simple trap C, multiple temperature gradient trap D, Volmam trap.

---