Emulsion rheology and properties of polymerized high internal phase emulsions
High internal phase emulsions are highly concentrated emulsion systems consisting of a large volume of dispersed phase above 0.74. The rheological properties of high internal phase water-in-oil emulsions were measured conducting steady shear, oscillatory shear and creep/recovery experiments. It was found that the yield stress is inversely proportional to the drop size with the exponent of values between 1 and 2. Since the oil phase contains monomeric species, microcellular foams can easily be prepared from high internal phase emulsions. In this study, the microcellular foams combining a couple of thickeners into the conventional formulation of styrene and water system were investigated to understand the effect of viscosity ratio on cell size. Cell size variation on thickener concentration could be explained by a dimensional analysis between the capillary number and the viscosity ratio. Compression properties of foam are important end use properties in many practical applications. Crush strength and Young's modulus of microcellular foams polymerized from high internal phase emulsions were measured and compared from compression tests. Of the foams tested in this study, the foam prepared from the organoclay having reactive group as an oil phase thickener showed outstanding compression properties.
Rheology of foams and highly concentrated emulsions: IV. An experimental study of the shear viscosity and yield stress of concentrated emulsions
Abstract The yield stress and shear viscosity have been determined for a series of well-characterized, highly concentrated oil-in-water emulsions (φ > 0.74). The lower end effect in the concentric-cylinder viscometer was eliminated and wall slip was corrected for. The yield stress is given by r 0 = oφ 1 3 Y (φ) R 32 , where σ is the interfacial tension, φ is the volume fraction of the dispersed phase, R32 is the surface-volume mean drop radius, and Y(φ) is a function whose values are found to be significantly lower than those obtained in a previous study. The shear viscosity of all emulsions is accurately described by u e = r 0 Y + 32(φ−0.73)u Ca −1 2 , is the shear rate, μ is the viscosity of the Newtonian continuous phase, and Ca ≡ Ca (− 1 2 VS − 1 3 is the capillary number, whose upper value was about 10−4. The second, viscous term deviates from that predicted by our recent model in the value of the exponent of Ca ( −1 2 vs −1 3 ) and in the appearance of a simple geometric factor that is volume-fraction-dependent. The different exponent may be the result of disjoining-pressure effects in our experimental emulsion systems.
Turbine blade temperature calculation and life estimation - a sensitivity analysis
Abstract The overall operating cost of the modern gas turbines is greatly influenced by the durability of hot section components operating at high temperatures. In turbine operating conditions, some defects may occur which can decrease hot section life. In the present paper, methods used for calculating blade temperature and life are demonstrated and validated. Using these methods, a set of sensitivity analyses on the parameters affecting temperature and life of a high pressure, high temperature turbine first stage blade is carried out. Investigated uncertainties are: (1) blade coating thickness, (2) coolant inlet pressure and temperature (as a result of secondary air system), and (3) gas turbine load variation. Results show that increasing thermal barrier coating thickness by 3 times, leads to rise in the blade life by 9 times. In addition, considering inlet cooling temperature and pressure, deviation in temperature has greater effect on blade life. One of the interesting points that can be realized from the results is that 300 hours operation at 70% load can be equal to one hour operation at base load.