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Rabas and Taborek correlation, for heat transfer in banks of low fin tubes, Rackett equation (modified) for liquid density Radiation: Radiation shields, in radiation heat transfer, Radiation source analysis, Radiative heat transfer: Radiators, automotive, construction, Radiometers, application in gas radiation property measurement, Radiosity, Stephan's law for, Radiosity-irradiation formulations in radiative heat transfer, Rankine cycle in refrigeration, Rao, B K Raoult's law for partial pressure, Rating of heat exchangers, Rayleigh instability, in free convection, Rayleigh number Reay, D Reboilers: Reciprocal mode integrating sphere, for reflection and transmission measurements in radiation, Rectangles: Rectangular ducts: Rectangular enclosures, free convective heat transfer in: Rectangular fins, for plate fin exchangers Reduced pressure, correlations for pool boiling using, Reference temperature: Refinery processes, fouling in, Reflection, of thermal radiation, from solid surfaces: Reflectivity, of solid surfaces, Reflectometer, heated cavity, Reflux condensers, Refractories, density of, Refractory surfaces, Refrigerants: Refrigerant 11 (Trichlorofluoromethane): Refrigerant 12 (Dichlorodifluoromethane): Refrigerant 13 (Chlorotrifluoromethane): Refrigerant 21 (Dichlorofluoromethane): Refrigerant 22 (Chlorodifluoromethane): Refrigerant 116: Refrigerant plant, entropy generation in, Refrigeration, heat transfer in, Regenerators and thermal energy storage, Regimes of heat transfer, in ducts, single phase flow, Reidel method, for predicting enthalpy of vaporisation, Reinforcing rings, for expansion bellows, Relaminarization, of turbulent flow, Reichenberg method, for effect of pressure on gas viscosity, Relief system design for shell-and-tube heat exchangers with tube side failure, Removal of fouling deposits: Renewable fuels, properties of, Renotherm, heat transfer medium, Repair, of expansion bellows, Residence times, in dryers: Resistance network analysis, Resistance (thermal) due to fouling: Reversible (minimum) work, in Reynolds number, Reynolds stress models, for turbulence, Rheologically complex materials, properties of: Rheological properties of drag reducing agents Rheology, shear flow experiments used in, Rhine, J M, Ribatski, G, Riblets for drag reduction, Richardson number, Richie, J M, Ring cells, in free convection, RODbaffles, in tube bundles with longitudinal flow, Rod bundles: Rohsenow correlation, for nucleate boiling, Roll cells, in free convection, Roller expansion, of tubes into tube sheets, Rose, J W, Rossby number, Rotary dryer, Rotating drums, heat transfer to particle bed in, Rotating surface, in an annular duct Rotation, as device for heat transfer augmentation, Roughness, surface: Rough walled passages, radiative heat transfer down, Rubber (sponge) balls, in fouling mitigation, Ryznar index for water quality,
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Surfactant Drag Reduction

DOI 10.1615/hedhme.a.000235

2.14.3 Surfactant drag reduction

A. Introduction

Drag reduction is observed with many surfactant solutions, but the results differ from those obtained with polymers in a number of ways which include:

  1. With surfactants, the mechanism of drag reduction is the formation of micelles (sub-microscopic structural units built up from the surfactant molecules). Though the micellular structures may be broken up in passage, say, through a centrifugal pump, they can reform downstream of the pump, reinstating the drag reduction effect. This contrasts with polymers where degradation is permanent (Hoyt, 1989).

  2. Drag reduction with surfactants increases with Reynolds number, but then decreases with high Reynolds number, presumably because the thread-like micelles break up in the higher shear fields. This effect is illustrated by the data of Zhang et al. (2005) shown in Figure 1.

  3. For surfactants, the drag reduction can be higher than the maximum obtained for polymers (namely the Virk maximum illustrated in Figure 234.7 and described by Equation 234.9). Results for drag reduction in a wide variety of surfactant systems are shown in Figure 2 (Zakin et al., 1996) and there is a corresponding increase in dimensionless velocity above the Virk maximum (Equation 234.14) as shown in Figure 3 (Chara et al., 1993). For surfactants, equations equivalent to Equation 234.9 and Equation 234.14 for maximum drag reduction are as follows:

\[\label{eq1}f=0.315\,\mbox{Re}^{-0.55}\tag{1}\]

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