Twisted tubes

Figure 10-4G. Twisted tubes with heat exchanger bundle arrangements. (Used by permission Brown Fintube Co., A Koch Engineering Co., Bui. B-100-2.)...

In addition to the use of antifouling chemical agents to mitigate the effect of fouling on the tube-side, twisted tubes can be used rather than plain tubes. These have surface irregularities. Plain tubes can also be fitted on the inside with tube inserts. Twisted tubes and tube inserts promote additional turbulence and pressure drop and reduce the surface temperature of the tube to mitigate fouling. Tube inserts will be dealt with in more detail later. 

You wave your hand. It doesn t matter. You pause and return to the discussion. As I ll show you later, the space we live in may also be curved, just like a twisted tube or a curved piece of paper. However, in terms of our degrees of freedom, we are living in a 3-D world. ... 

The hotter, fouled tubes must grow. But their horizontal expansion is constrained by the cleaner, colder tubes, since the colder tubes do not allow the hotter tubes to grow, the hot tubes bend. This, then, is the origin of the twisted tubes we see when an improperly designed tube bundle is pulled from its shell during a turnaround. 

The mechanical designs utilize bellows, diaphragm, d/p, and Bourdon tube designs. In 1852, Eugene Bourdon patented a curved or twisted tube,... 

Twisted Tube , internal spiral fins). All are designed to impart a natural swirl component to the flow inside the tubes. Each has been proved to solve the problem of tube-side vaporization at high vapor qualities up to and including complete tube-side vaporization. 

Fig. 4 Physical illustration of different types of curved tubes (A) horizontal helical coil, (B) bend tube, (C) serpentine tube (meander-shaped tube), (D) spiral, where r is the tube radius, R the eoiled tube eurvature, b the eoil piteh, and and Rmay. are minimum and maximum radii of eurvature of the beginning and end of the spiral, and (E) twisted tubes.

FIGURE 6.32 Diagram of two Twisted Tubes , showing how tubes are mutually self-supporting. (Courtesy of Koch Heat Transfer Company LP.)... 

Twisted Tube construction (Figure 6.32) eliminates the need for baffles altogether, since the tubes can be oriented ( tuned ) to contact surrounding tubes periodically along the exchanger. The shell-side flow is longitudinal, and special correlations have been developed for both heat transfer and pressure drop on both sides of the surface. Laminar flow inside the tube is enhanced by the secondary flow induced by the twisted flow path. 

Various investigators have studied in-tube condensation in noncircular passages. Fieg and Roetzel [121] and Chen and Yang [160] analyzed condensation inside elliptical tubes. Kaushik and Azer [161] established an experimental correlation for internally finned tubes. Lee et al. [162] experimentally studied condensation of R-113 within an internally finned tube and a spirally twisted tube and compared performance to that of a smooth tube. Using a modified form of the correlation of Cavallini and Zecchin [148] (Eq. 14.138) ... 

FIGURE 17.8 (a) Axial flow baffle, courtesy of Brown Fintube Company, Houston, Texas, (b) a twisted tube exchanger, courtesy of ABB Lummus Heat Transfer, Bloomfield, New Jersey. 

Under a microscope, a cotton fiber appears as a very fine, regular fiber, looking like a twisted ribbon or a collapsed and twisted tube. These twists are called convolutions there are about 60... 

Tube-side improvement use tube inserts, twisted tubes and tubes with internal fins Shell-side improvement use helical baffles, EM baffles, externally finned tubes, twisted tubes and shell-side seal strips (Fieberman, 2010)... 

Increase number of tubes and/or change square to triangular pitch, for shell and tube exchangers increase number plates for plate heat exchangers Increase number of passes Use shell and tube exchangers with twisted tubes, plate and/or spiral heat exchangers Use automatic/manual back flush system Use acoustic techniques for fouling reduction... 

FIGURE 10.18 Globular protein structures—twisted tube representation. Wider parts of tube contain a-helices and narrower parts correspond approx to random coiled chains. Location of Fe-containing haeme groups in these very similar oxygen storage proteins is denoted by H. 

Fig. 4 shows the objective computational cells and the helical replication of the structures of a (10,10) and the related (11,9) M0S2 nanotubes. Additionally, the lower part of Fig. 4 depicts the total energy as a function of the angular component 9 of the tube belonging to the (10,10) family. The energy minima in the curves correspond to the stress-free structures, whereas the arrows mark the angles that the non-twisted tubes of ideal symmetry obtain. The difference in these two values marks the intrinsic twist. 

Helix reactor Twisted tubes provide intense mixing of the flow Initially for replacing highly exothermic batch reactions 5... 

Figure 7.2. Stacking of double-twist tubes and frustration. The twist in each tube is taken to be right-handed, twisting to 45° at the tube boundary. (A) Right-handed corner the directors form an 5 defect that cannot escape and...

If such a program is carried out, the intersections between double-twist tubes can be shown to have incompatible directors, which leads in turn to frustration and the introduction of disclinations, as described earlier [9]. 

Figure 7.6. Cross-sectional view of a double-twist region. The director is parallel to the tube axis at the center, twisting along any radius. The energy of such a configuration is lower than for twist in a single direction, but only near the center. In a double-twist tube, the angle at the edge is 45°.

One can think of the blue phase as a lattice of double-twist tubes (which necessitates a lattice of disclinations) or a lattice of disclinations (which necessitates a lattice of double-twist tubes) [20]. Thus, a theory involving a lattice of double-twist tubes becomes implicitly a theory for a lattice of defects. 

The strategy is to assemble a lattice of defects having a particular space group symmetry and fill the interstices with nematic material. The director is then allowed to relax everywhere (except of course at the defects) and the free energy calculated. From this process one finds that there is also an interpenetrating lattice of double-twist tubes and that the whole structure is stable between the helical and isotropic phases. Figure 7.7 shows both the double-twist lattice and the defect lattices for the proposed structures scO and bcc(9 . Other structures—bccO and bccO +—have also been worked out [42]. 

Figure 7.7. Models of cubic blue phases, (a) Arrangement of double-twist tubes for the sc 0 structure, (b) Corresponding unit cell of defect Unes for the sc structure, (c) Arrangement of double-twist tubes for the bccO structure, (d) Unit cell of defect lines for the bcc structure. From Dubois-Violette and Pansu [10].

Since the cubic blue phases have three equivalent axes, an applied field breaks the cubic symmetry and creates a preferred axis. But, like the helical phase, blue phases are chiral, being composed of a lattice of double-twist tubes. It is therefore not surprising that applied fields lead to distortion of the lattice (electrostriction) and, for high enough fields, new lower-symmetry phases. These effects occur for both < 0 and a > 0. 

Smooth high alloy tubes Low-finned tubes Sintered metal tubes Spiral heat exchanger Tube inserts Twisted tubes Helical tube support baffles... 

The concept starts with the use of a tube that is itself twisted, the idea being to promote turbulence within the tube as a result of the tube wall shape. When you look at one of these tubes, the shape is like a large hollow drill bit (see Fig. 27.3). These twisted tubes are then... 

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