No description available.

No description available.

A study of the effect of shear rate on the inherent and intrinsic viscosities of polystyrene fractions, in dilute solution was carried out. Inherent viscosities were determined for five fractions (of molecular weights ranging from 2.9 x 10 to 4.8 x 106); in three solvents (Benzene, Toluene and Methyl Ethyl Ketone); at five temperatures (from 15°C to 85°C); and shear rates ranging from 1.0 x 103 to 2.8 x 104 sec.-1. Inherent viscosities thus determined were extrapolated to zero rate of shear and the extrapolated values plotted against concentration to determine intrinsic viscosities at zero rate of shear, [N] D=0 The inherent viscosity decreased with increasing shear rate. The slope of the curve of inherent viscosity vs shear rate was found to increase (ie become more negative) with increasing concentration, temperature and molecular weight and to be less in a poor solvent than in a good solvent. At very high molecular weights the value of inherent viscosity was found to decrease non-linearly with shear rate. The intrinsic viscosity was found to decrease with increasing shear rate. The slope of the [N] vs D curve was found to increase with increasing molecular weight and decreasing temperature; the slopes were smaller the poorer the solvent. For the three lower fractions the intrinsic viscosity was found to decrease with increasing temperature, very slightly in Methyl Ethyl Ketone and appreciably in Benzene and Toluene, the relative being greater at higher molecular weights. With the two highest fractions this trend was reversed. The slope of the [N] D=0 vs T curve becoming less negative (and actually positive for Benzene end Toluene). The [N] vs T curves ( [N] at free fall) for the three lower fractions were parallel to those at zero rate of shears but of lower intrinsic viscosity values. With the two highest fractions, the slope of the [N] vs T curve became less negative but not to as great a degree as was found with [N] D=0 vs curves. Intrinsic viscosities obtained at zero rate of shear were applied to the Flory-Fox theory. Calculated intrinsic viscosities for polystyrene fractions in Benzene and Toluene were found to agree to within+-4% of the experimental results. For Methyl Ethyl Ketone a wide variation in values was obtained. / Thesis / Master of Science (MS)

Great progress has been achieved over the past fifteen years in the computation of two-dimensional turbulent flows. The proceedings of the 1968 Stanford Conference (1) attest to the success of several methods in predicting skin friction and heat transfer coefficients, mean velocity and temperature fields, and to a lesser degree boundary layer separation. This success is due less to the fact that the physics of turbulence is well understood (it is not) than to the fact that the existent two-dimensional data obtained within pipes and on external surfaces have lent themselves to correlation. It is these correlations (particularly near-wall similarity or the law-of-the-wall) which serve as the empirical foundation of the mixing length and eddy viscosity "theories" of turbulence. The term mathematical model may more aptly describe the mixing length/eddy viscosity approach to turbulence than the word theory, for these concepts take into account little of the basic dynamics of turbulence (its production, intensity, frequency, and dissipation). Yet these methods are significant precisely because they do predict with uncanny accuracy the gross consequences of turbulence in a number of two-dimensional flows of practical interest. Mixing length/eddy viscosity models are attractive to the engineer because these models are agreeably simplistic. That is, their formulation is algebraic and does not involve differential equations or additional turbulent transport equations. The monograph (2) of Launder and Spalding presents an excellent review and evaluation of current mathematical models of turbulence. On account of their simplicity, the mixing length/eddy viscosity models are relatively straightforward to implement and economical to use. Thus they are ideally suited for industry. The present work is an investigation of the suitability of the eddy viscosity approach for the prediction of three-dimensional turbulent flows. The eddy viscosity formulation employed is essentially an extended two-dimensional model. Unfortunately, endeavors to correlate three-dimensional turbulent data have not been as successful as with the two-dimensional case. White (3) has neatly summarized the more significant postulations of a three-dimensional law-of-the-wall. All are patterned after the two-dimensional near-wall similarity hypothesis, and of course none can be confirmed without direct measurement of wall shear stress. No such measurements have been performed to date with the exception of the data of Pierce and Krornmenhoek (4), who did not specifically study the question of near-wall similarity in three-dimensional flows. Thus the present analysis is necessarily a simplistic one. It is based on the fact that every turbulent flow is actually three-dimensional and on the supposition that a correlation which succeeds with a two-dimensional mean velocity field may well succeed in the calculation of a three-dimensional field. / Ph. D.

The most important method of preserving perishable materials is by refrigeration. Refrigeration generally means the removal of heat from a body or substance to such an extent as to leave it, or maintain it, at a lower temperature than that of the surroundings. Mechanical refrigeration refers to the removal of heat by mechanical devices. In mechanical refrigeration cycles a large variety of refrigerants, such as ammonia, sulfur dioxide, methyl chloride, freon-12 (dichlorodifluoromethane), and propane are used. These refrigerants must have properties that render them suitable for use in refrigeration cycles. During the refrigeration cycle, the refrigerant is constantly changing state; that is, from a liquid to a gas and vice versa with a corresponding change in temperature. One of the fundamental properties affecting the mechanical behavior of a refrigerant is its viscosity. Not only is it the major factor in relation to the transfer of the material, but it also has marked effect on the heat transfer characteristics of the refrigerant. Inasmuch as the refrigeration cycle depends on both of these operations, a knowledge of the viscosity of the refrigerant is highly desirable. It was the purpose of this investigation to determine the liquid viscosities of an azeotropic of asymmetrical difluoromethane and dichlorodifluoromethane. / Master of Science

No / The rheological behavior of polymeric nanocomposites provides major determination for their processability. In this work, three carbon nanotubes (CNTs) with varied geometries were adopted as nanofiller and then were introduced into poly(methyl methacrylate) (PMMA) matrix with different loadings (0.07–1.0 wt %). The different preparation routine led to varied CNTs dispersion states, on which the shear viscosity and the compressibility of their melts were proved to be sensitive. The technology for the preparation of their nanocomposites played a crucial role in controlling their rheological behavior. With melting blended bare CNTs, the dynamic shear viscosity of PMMA/CNTs increased with the increase of CNTs content, accompanied by aggregated CNTs in which no polymer matrix was entrapped. With the help of surface modification and pre‐mixing, well dispersed CNTs were obtained and a rather low aggregation rate ca. 0.029% was revealed. The well dispersed CNTs with an organic layer which was constructed by small molecules and presented lower viscosity. Such CNTs led to no remarkable clusters within polymer host and played the role of lubricant with an increased‐mobility layer, which can be reflected from the weighted relaxation time spectra.

M.S.

by Tsang Kin Hung. / Title also in Chinese. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1992. / Includes bibliographical references. / Table of Contents / Acknowledgements / Abstract / Part I --- p.1 / Chapter Chapter 1 --- Introduction --- p.2 / Chapter Chapter 2 --- Viscosity of molten P40Ni40P20 --- p.6 / Chapter Chapter 3 --- Viscosity of molten Pd77Cu6.5Si16.5 and the principle of corresponding state --- p.26 / Chapter Chapter 4 --- Viscosity of molten Pd82Si18 and the scaling of viscosities of glass forming systems --- p.40 / Part II --- p.53 / Chapter Chapter 5 --- Installation of Dual Electron Gun Evaporator --- p.54 / Chapter Chapter 6 --- Calorimetric studies of the Heat Capacity and Relaxation of Amorphous Si prepared by electron beam evaporation --- p.67

No description available.

In general,the lubricants were composed by basestock and additive,and the basestock is usual use mineral oil. This paper examines the viscosity,viscosity index and antiwear properties of palm oil blended lubricants. To study the feasibility of using palm oil as the lubricant of automative engine . The V.I. of commercial sae 30 engine oil will increase from 101 to 147 via the blend of palm oil and SAE 30.The anti-wear charactisteristics test in a four-ball tribometer.Under conditions of 40kg,1200rpm,and a test duration of one hour at 120 ¢J. The test oil appear markedly superior to the reference SAE 30 engine oil .The palm oil blended lubricant showed is reduced to 10% scar than reference oil .