Tensioning systems

Ht s. In connection with the data on this figure, it should be noted that economical values of m Vp Vp will usually lie in the range between 1 and 2, so that overall heights of transfer units are not too unreasonable even for this high-interfacial-tension system. For lower interfacial tensions, Htoc will ordinarily be appreciably less. 

The hydraulieally tensioned, radial-fit bolt (Figure 6-32) replaees the traditional turbine shaft eoupling bolt and is reusable. The main body of the bolt is threaded at eaeh end and has a slight taper on the eenter seetion, whieh engages with the similarly internally tapered sleeve and the two nuts. The bolt is taper-bored at eaeh end to aeeept the puller that is part of the hydraulie tensioning system. 

A high-interfacial-tension system is more easily coalesced than one of low interfacial tension (J2). 

The above rules of thumb apply to organic and hydrocarbon systems, whose surface tensions are relatively low (a < 25 mN/m). For higher surface tensions, the liquid does not adhere well to the packing surfaces (underwetting), causing higher HETPs. In a water-rich system (a = 70 mN/m or so) HETPs obtained from Eqs. (14-156), (14-158), and (14-159) need to be doubled. For intermediate surface tension systems (some amines and glycols, whose surface tension at column conditions is 40 to 50 mN/m), HETPs obtained from Eqs. (14-156), (14-158), and (14-159) need to be multiplied by 1.5. 

Positive-surface-tension systems (ct + ) where surface tension increases as liquid flows down the column. 

Schmidt s correlation is sensitive to the contact angle estimats [both in Eqs. (8.85) and (8.38)]. Table 8.5 lists the range of applicability of Schmidt s correlation. The Schmidt correlation is based on data for Raschig and Pall rings (102), mainly for positive-surface-tension systems (58). 

Karr and Lo [63] have developed sin jle scaling rules for the Karr extractor. To scale HETS from one column size to another, requires that the plate spacing, amplitude, and total volumetric flow rate per unit area be kept the same for each extractor. They foimd for a high interfacial-tension system such as the o-xylene, acetic-acid, water system, that... 

For a low interfacial-tension system such as MIBK, acetic acid, water, the exponent is 0.36, only slightly different. 

The HETS for an extractor can be estimated by using the scaling rules developed by Karr and Lo [62] and experimental values of HETS summarized in Table 6.31. First, determine if the extraction system is a low interfacial-tension system or a high interfacial-tension system. Next, select a value of HETS from Table 6.31 from the following systems ... 

Then, scale this value of HETS for the extractor diameter using Equation 6.32.9. A simpler procedure for obtaining HETS, however, is to use the correlation given by Henley and Seader [31], shown in Figure 6.23. the correlation is acceptable for both a low and high interfacial-tension system. The problem, however, is that interfacial-tension data may not be available. 

An ultralow tension system was needed to study mechanisms of high Ca flow at relatively low velocities. A Witco petroleum sulfonate was used that had previously been studied by several researchers including Qutubuddin (15). The tension between the middle phase microemulsion and the excess oil phase was only 0.0015 dyne/cm. Surfactants were used as received, and all other chemicals were reagent grade. 

Baffle Tray Efficiency Baffle tray mass-transfer efficiency was observed to depend strongly on the tray spacing and system properties, as shown in Figs. 15-46 and 15-47. In these studies, a tray spacing of about 10 cm provided a minimum HETS. The data indicate that the performance of baffle trays relative to sieve trays depends upon the interfacial tension of the system. For the high-interfacial-tension system (Fig. 15-46), the baffle tray performance (in terms of capacity and mass transfer) is relatively low compared to that of a sieve tray. However, for the low-interfacial-tension system (Fig. 15-47), performance was somewhat better using 62 percent tray overlap. 

Witthayapanyanon, A., Acosta, E.J., Harwell, J.H. and Sabatini, D.A. (2006) Formulation of ultralow interfacial tension systems using extended surfactants. /. Surf. Deterg., 9(4), 331-339. 

Rotating disk contactor, RDC, ARD contactor Mixco, Scheibel, Treybal, Oldshue-Rushton, Kuehni product of the density difference with the interfacial tension (Mg/m, mN/m) between 1 and 4 and number of theoretical stages needed >2. Low HETS can handle dirty liquids, large throughputs. Needs flow ratios 1 1. Difficulty handhng low interfacial tension systems that tend to emulsify. 

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