Helical-tube evaporator

F . 2.J.1-7 Helical-tube evaporator with cylindrically wound tubes (cross section). 

The feedwater enters the feedwater nozzle with a temperature of 170°C. The water flows through the helical tubes from the bottom to the top. During this process it evaporates and is subsequently superheating. Via a compensating bundle above the heating tube bundle, the steam, which is 530°C hot enters the live-steam nozzle and passes through the live-steam line to the machine hall. 

Super-Phenix 1 (France) once-through evaporator and superheater with helical tubes... 

A vertically positioned Pyrex tube (1.2 x 40 cm) filled with glass helices was washed with sat. aq NaHCOj, HjO, acetone and hexane. The tube was heated to 450 C and a flow of Nj was established through it. A solution of 3-(l-methylcyclopropyl)cyclohex-2-enone (12.3 g, 82 mmol) in hexane (30 mL) was added dropwise to the column. The Nj flow was maintained throughout the pyrolysis and the thermolysate was trapped at — 78 C. GC analysis of the residue, obtained after evaporation of volatiles from the pyrolysate, indicated that it consisted of a mixture of Ic and its 8,y-unsaturated isomer 2c in a ratio of 3 7. This mixture was treated with MeOH (100 mL) containing a small amount of NaOMe and the resulting solution was stirred for 1 h at 0°C. After evaporation of MeOH, the residue was dissolved in EtjO, washed with brine, and dried (MgSO ). Removal of EtjO followed by vacuum distillation of the residual oil gave the title compound yield 10.7 g (87%) bp 55-58 C/0.3 Torr. 

The extension of these PECs to two-phase heat transfer is complicated by the dependence of the local heat transfer coefficient on the local temperature difference and/or quality. Heat transfer and pressure drop have been considered in the evaluation of internally finned tubes for refrigerant evaporators [14] and for internally finned tubes, helically ribbed tubes, and spirally fluted tubes for refrigerant condensers [15]. Pumping power has been incorporated into the evaluation of inserts used to elevate subcooled boiling critical heat flux (CHF) [16, 17]. A discussion of the application of enhancement to two-phase systems is given by Webb [373],... 

Cox et al. [101] used several kinds of enhanced tubes to improve the performance of horizontal-tube multiple-effect plants for saline water conversion. Overall heat transfer coefficients (forced convection condensation inside and spray-film evaporation outside) were reported for tubes internally enhanced with circumferential V grooves (35 percent maximum increase in U) and protuberances produced by spiral indenting from the outside (4 percent increase). No increases were obtained with a knurled surface. Prince [102] obtained a 200 percent increase in U with internal circumferential ribs however, the outside (spray-film evaporation) was also enhanced. Luu and Bergles [15] reported data for enhanced condensation of R-113 in tubes with helical repeated-rib internal roughness. Average coefficients were increased 80 percent above smooth-tube values. Coefficients with deep spirally fluted tubes (envelope diameter basis) were increased by 50 percent. 

FIGURE 15.134 Fraction of liquid evaporated before onset of critical heat flux as a function of mass velocity for a plain tube and for a tube with helical tape inserts q" is the flux corresponding to the evaporation of all the injected water (from Moeck et al. [326], with permission). 

SNR-300 (Germany) once-through evaporator and separate superfieater, tubes straight in 2 loops, helical in 3rd... 

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