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experiments were conducted to study the drag-reduction and heat transfer performances of a newly synthesized zwitterionic surfactant solution (oleyl trimethylaminimide) in a two-dimensional channel. for testing the drag-reduction at subzero temperatures, a 20% ethylene glycol aqueous solution (eg/w) was used as solvent. the surfactant concentration ranged from 50 to 1000ppm and the temperature was 5 and 25℃, respectively. it was found that the novel zwitterionic surfactant solution showed both drag and heat transfer reduction characteristics, which were affected by concentration and temperature. the maximum drag-reduction was 83% at 25℃ for 200ppm surfactant solution. the effects of addition of nano2 to the surfactant solution were also investigated. for enhancing heat transfer of the surfactant drag-reducing flow, a destructive device, named block, was designed and used in the experiments. the block device has two contracting–expanding flow passages on both sides respectively with the central part blocked. it was found that the block device can enhance the heat transfer performance of the novel zwitterionic surfactant solution to some extent while having a very small pressure drop penalty compared with other researcher's destructive devices due to the dominant action of elongational stress.

for the purpose of cooling electronic components with high heat flux efficiently, some experiments were conducted to study the flow boiling heat transfer performance of fc-72 on silicon chips. micrpin-fins were fabricated on the chip surface using a dry etching technique to enhance boiling heat transfer. three different fluid velocities (0.5, 1 and 2m/s) and three different liquid subcoolings (15, 25 and 35k) were performed, respectively. a smooth chip (chip s) and four micro-pin-finned chips with the same fin thickness of 30 lm and different fin heights of 60 lm (chip pf30-60) and 120lm (chip pf30-120), respectively, were tested. all the micro-pin-finned surfaces show a considerable heat transfer enhancement compared to the smooth one, and the critical heat flux increases in the order of chip s, pf30-60 and pf30-120. for a lower ratio of fin height to fin pitch and/or higher fluid velocity, the fluid velocity has a positive effect on the nucleate boiling curves for the micro-pin-finned surfaces. at the velocities lower than 1m/s, the micro-pin-finned surfaces show a sharp increase in heat flux with increasing wall superheat, and the wall temperature at the critical heat flux (chf) is less than the upper limit, 85℃, for the reliable operation of lsi chips. the chf values for all surfaces increase with fluid velocity and subcooling. the maximum chf can reach nearly 150 w/cm2 for chip pf30-120 at the fluid velocity of 2m/s and the liquid subcooling of 35k.

the quantitative characteristics of vortex structures and turbulent events in turbulent channel flows with and without drag reduction were investigated experimentally. drag reducing aqueous solutions of ctac (ctac–cetyltrimethyl ammonium chloride) with concentration of 25ppm and 75ppm at 30 c were tested. particle image velocimetry (piv) was used to measure the instantaneous velocity field in the streamwise–wall-normal plane of the flow. through visualizing the instantaneous vector fields, contour maps of the swirling strength and instantaneous value of uv (uandvare the streamwise and wall-normal velocity fluctuations, respectively), the characteristic angle of vortex packets was quantified. it was shown that the drag-reducing ctac additive reduced both the strength and frequency of turbulent bursts near the wall, and the characteristics of vortex structures and bursts were not only dependent on drag-reduction level but also on concentration of additive. from the quantified parameters characterizing turbulent events in a wall-bounded turbulent flow, it was obtained that ft was linearly proportional to the product of frequency and strength of turbulent events.

turbulent friction drag and heat transfer reductions and rheological characteristics of a very dilute cationic surfactant solution, cetyltrimethyl ammonium chloride (ctac)/sodium salicylate (nasal) aqueous solution, were experimentally investigated at various temperatures. it was found that there existed a critical temperature above which drag and heat transfer reductions disappeared and shear viscosities rapidly dropped to that of water. it was surmised that drag and heat transfer reductions had a certain relationship with rheological characteristics and a rheological characterization of ctac/nasal surfactant solutions was performed to clarify this relationship. the effects of reynolds number and fluid temperature and concentration on drag and heat transfer reductions were qualitatively explained by analyzing the measured shear viscosity data at different shear rates and solution temperatures and concentrations. the giesekus model was found to fit the measured shear viscosities reasonably well for different temperatures and concentrations of the surfactant solution and the model parameter values obtained by fitting were correlated with temperature at certain solution concentrations. from the correlation results, the temperature effect on viscoelasticity of surfactant solutions was analyzed to relate the rheological characteristics with drag and heat transfer reduction phenomena.

he swirling flows of water and ctac (cetyltrimethyl ammonium chloride) surfactant solutions (50-1000ppm) in an open cylindrical container with a rotating disc at the bottom were experimentally investigated by use of a double-pulsed piv (particle image velocimetry) system. the flow pattern in the meridional plane for water at the present high reynolds number of 4.3 104 differed greatly from that at low reynolds numbers, and an inertia-driven vortex was pushed to the corner between the free surface and the cylindrical wall by a counter-rotating vortex caused by vortex breakdown. for the 1000ppm surfactant solution flow, the inertia-driven vortex located at the corner between the bottom and the cylindrical wall whereas an elasticity-driven reverse vortex governed the majority of the flow field. the rotation of the fluid caused a deformation of the free surface with a dip at the center. the dip was largest for the water case and decreased with increasing surfactant concentration. the value of the dip was related to determining the solution viscoelasticity for the onset of drag reduction.

in part i [wei et al., 2004, 2004 asme int. mech. eng. conference], we presented the experimental results for swirling flows of water and cetyltrimethyl ammonium chloride (ctac) surfactant solution in a cylindrical vessel with a rotating disk located at the bottom for a reynolds number of around 4.3 104 based on the viscosity of solvent. for the large reynolds number, violent irregular instantaneous secondary flows at the meridional plane were observed by use of a particle image velocimetry system. because of the limitations of our computer resources, we did not carry out direct numerical simulation for such a large reynolds number. the les and turbulence model are alternative methods, but a viscoelastic les/turbulence model has not yet been developed for the surfactant solution. in this study, therefore, we limited our simulations to a laminar flow. the marker-and-cell method proposed for newtonian flow was extended to the viscoelastic flow to track the free surface, and the effects of weissenberg number and froude number on the flow pattern and surface shape were studied. although the reynolds number is much smaller than that of the experiment, the major experimental observations, such as the inhibition of primary and secondary flows and the decrease of the dip of the free surface by the elasticity of the solution, were qualitatively reproduced in the numerical simulations.

a thermal energy storage system employing phase change material (pcm) fnp-0090 (product of nippon seiro co. ltd.) for rapid heat discharge was studied numerically and experimentally. in the numerical studies, the pcm was encapsulated in four different capsules (sphere, cylinder, plate and tube) for investigating the effects of geometrical configurations. the effects of the capsule diameter and shell thickness and the void fraction on the performance of the heat storage system were also investigated. the experiment was conducted by using a commercial plate heat exchanger as the heat storage tank. it was found that the spherical capsule showed the best heat release performance among the four types of investigated capsules, whereas the tubular capsule with low void fraction was not ideal for rapid heat release of the thermal energy stored in the pcm. the heat release performance decreased in the order of sphere, cylinder, plate and tube. the numerical results and the experimental data agreed within 10%.