Jacques L. Zakin

Surfactant Drag Reduction

3.1 FUNDAMENTAL CONCEPTS IN DRAG REDUCTION 13 3.2 DRAG REDUCTION OF ANIONIC SOAP SOLUTIONS 15 3.3 DRAG REDUCTION OF NONIONIC SURFACTANT SOLUTIONS 16 3.4 DRAG REDUCTION OF ZWTTTERIONIC SURFACTANT SOLUTIONS 18 3.5 DRAG REDUCTION OF CATIONIC SURFACTANT SOLUTIONS 19 3.5.1 Surfactant Structure Effects 19 3.5.2 Counterion Effects 21 3.5.3 Stability 23 3.6 DIAMETER EFFECTS 24 3.7HEATTRANSFERREDUCTIONIN DRAG REDUCING FLOWS 26 3.8 MAXIMUM DRAG REDUCTION ASYMPTOTE 28 3.9 INVESTIGATIONS ON MECHANISM OF SURFACTANT DRAG REDUCTION .. 29

The effect of surfactants on bubble growth, wall thermal patterns and heat transfer in pool boiling

Abstract During nucleate pool boiling of pure water and water with cationic surfactant, the motion of bubbles and the temperature of the heated surface were recorded by a high-speed video camera and an infrared radiometer. All experiments were performed at saturated boiling conditions. The boiling curves for various concentrations were obtained and compared. The results show that the bubble behavior and the heat transfer mechanism for the surfactant solution are quite different from those of pure water. The heat transfer dependence on the relative changes of both the surface tension and the kinematic viscosity was discussed.

A non-viscoelastic drag reducing cationic surfactant system

Abstract The drag reducing cationic surfactant system, Arquad S-50 (5 mM)/sodium salicylate (12.5 mM), was found to have unusual rheological properties. The system is highly drag reducing and birefringent. Cryo-TEM shows a network of thread-like micelles. However, the system shows no first normal stress difference, no recoil and no stress overshoot with shear start-up, and thus does not appear to be viscoelastic, contradicting the general belief that there is a correlation between viscoelastic properties and drag reduction. On the other hand, the system has high extensional viscosity, with high extensional viscosity-to-shear viscosity ratios. These results indicate surfactant solutions which do not appear to be viscoelastic can be drag reducing, and that extensional viscosity appears to be the key property controlling drag reducing ability.

Light-Responsive Threadlike Micelles as Drag Reducing Fluids with Enhanced Heat-Transfer Capabilities

Drag-reducing (DR) surfactant fluids based on threadlike micelles are known to suffer from poor heat-transfer capabilities. Accordingly, the use of these fluids is limited to recirculating systems in which heat exchange is not important. Here, we show for the first time that light-responsive threadlike micelles can offer a potential solution to the above problem. The fluids studied here are composed of the cationic surfactant Ethoquad O/12 PG (EO12) and the sodium salt of trans-ortho-methoxycinnamic acid (OMCA). Initially, these fluids contain numerous threadlike micelles and, in turn, are strongly viscoelastic and effective at reducing drag (up to 75% DR). Upon exposure to UV light, OMCA is photoisomerized from trans to cis. This causes the micelles to shorten considerably, as confirmed by cryo-transmission electron microscopy (cryo-TEM). Because of the absence of long micelles, the UV-irradiated fluid shows lower viscoelasticity and much lower DR properties; however, its heat-transfer properties are considerably superior to the initial fluid. Thus, our study highlights the potential of switching off the DR (and in turn enhancing heat-transfer) at the inlet of a heat exchanger in a recirculating system. While the fluids studied here are not photoreversible, an extension of the above concept would be to subsequently switch on the DR again at the exit of the heat exchanger, thus ensuring an ideal combination of DR and heat-transfer properties.

Compression of Flexible Chain Molecules in Solution

The compression of coiling molecules in good solvents at finite concentrations has been previously treated. However, the expressions were evaluated earlier by means of an expansion in the effective pressure acting on a coil. They are now presented in a form appropriate to include the range of reduced concentrations c/c0≥1. As an example volume ratios for polystyrene solutions in toluene are computed. They depend only slightly on molecular weight and amount to a reduction of about 30% in the most probable encompassed volume, at c/c0=1.

Enhanced heat transfer of drag reducing surfactant solutions with fluted tube-in-tube heat exchanger

Abstract Solutions containing drag reducing additives also show reduced heat transfer which limits their use in hydronic cooling and heating systems where heat exchange is critical. For Reynolds numbers 10,000–50,000 and test fluid inlet temperatures 50–70°C, a fluted inner tube heat exchanger showed increased heat transfer coefficients for both cationic and zwitterionic/anionic drag reducing surfactant solutions. The pressure drop penalty for heat transfer enhancement of the cationic surfactant solution flowing through the fluted tube is high while for the zwitterionic/anionic solution, significant heat transfer improvement was achieved with only a modest pressure drop penalty.

A molecular approach to predicting the onset of drag reduction in the turbulent flow of dilute polymer solutions

Abstract The significant variables in drag reduction have been separated into two classifications, flow variables and solution variables. A theory has been offered which permits prediction of the critical Reynolds number in the turbulent flow of polymer solutions. The theory states that the relaxation time of the polymer molecule in solution equals a characteristic flow time for the tube in question at the point of incipient turbulent suppression. This is equivalent to a Deborah number near unity. Reasonable agreement has been shown between the experimental results of this investigation and predictions of flow rates based on this theory for the presence or absence of drag reduction and for the onset of turbulence suppression. No adjustable parameters were used in the analysis. The theory seems to be applicable at values of C[η] greater than 0·10. The theory leads to the prediction that the wall shear rate at the point of incipient turbulence suppression decreases as the product of reduced viscosity, molecular weight and solvent viscosity increases. Thus for large effects this product should be made as large as possible. Friction factor measurements in both good and poor (Theta) solvents showed that the maximum drag reduction in the poor solvent was only about 40% of that in the good solvent at similar flow rates in the same tube. Thus the effect of an expanded configuration of the polymer molecule in solution is to increase drag reduction.

Low-speed streaks in drag-reduced turbulent flow

The effect of a surfactant drag-reducing additive (530 ppm Habon G solution) on the structure of wall turbulence, both in a flume and in pipe flow, was investigated experimentally. Real-time infrared thermography was used for flow visualization and measurements of the spanwise spacing between the thermal streaks. The experiments were carried out over a broad range of friction velocities, i.e., up*=0.51–3.27 cm/s. With wall shear velocities 1.54⩽up*⩽3.27 cm/s drag reduction of 82%–85% was achieved in a tube flow, well below the predictions of the Virk maximum drag reduction asymptote proposed for high polymers. The results of spanwise streak spacing indicate that wall shear velocity may be an appropriate parameter for describing nondimensional streak spacing behavior in drag reducing flows. A hypothesis, based on the average spanwise streak spacing λ+, can be applied to describe the mean velocity profiles of Habon G solutions. The ratio (λp+−100)/100 was applied to describe mean velocity profiles with 530 ...

Enhancing heat transfer ability of drag reducing surfactant solutions with static mixers and honeycombs

Abstract Solutions containing drag reducing additives also show reduced heat transfer which limits their use in district heating and cooling recirculation systems where heat exchange is critical. In this study, static mixers A and B and honeycombs were installed at the entrance to a heat exchanger to break the solution microstructure temporarily and thereby enhancing their heat transfer ability when passing through the heat exchanger. The effectiveness of the destructive devices in enhancing the heat transfer ability of drag reducing cationic and mixed zwitterionic/anionic surfactant solutions was investigated together with the microstructure recovery time and pressure drop penalty paid for the heat transfer enhancement.

Turbulence measurements of drag reducing surfactant systems

LDA measurements were made of mean velocity and of turbulence intensity in a 39.4mm diameter tube, the first measurements in three directions on drag reducing surfactant solutions (0.05% and 0.1% Habon G). Drag reduction exceeded the predictions of the Virk maximum drag reduction asymptote and elastic sublayer mean velocity profiles are steeper than the profile proposed by Virk for maximum drag reducing asymptote solutions. Axial turbulence intensities for Habon G solutions are higher than those for water near the wall, lower in most of the outer region and about the same at the center. Tangential and radial turbulence intensities are lower than those for water.