| dc.description.abstract | The present investigation has been undertaken using two oscillating?disc viscometers.
The first viscometer is a modified version of an earlier model to suit refrigerant vapours at pressures up to five atmospheres and ambient temperature. The experimental viscosity data obtained using this viscometer are presented in Part One of the thesis.
The second oscillating?disc viscometer is newly designed to suit refrigerant vapours at higher temperatures. The design and fabrication details, calibration, and experimental data obtained for pure refrigerant vapours and their mixtures are presented in Part Two of the thesis.
PART ONE
The viscosity of pure refrigerant vapours R12, R14, R22 and R114, and their binary, ternary, and quaternary mixtures, has been determined using the oscillating?disc viscometer, after suitable modifications, at 1 to 5 atmospheres and at an ambient temperature of 30癈. Viscosity in the case of pure refrigerant vapours increases with pressure at ambient temperature, confirming the trend reported by Makita.
The viscosity of binary mixtures calculated from Hirschfelder, Curtiss and Bird抯 equation, Wilke抯 equation, and Herning and Zipperer抯 equation is in good agreement with the present experimental viscosity data. However, the prediction by Dean and Stiel抯 equation for pure refrigerant vapours and their mixtures does not compare well with the present experimental results.
For ternary and quaternary mixtures also, at 1 atmosphere and 30癈, the viscosity predicted by Wilke抯 equation compares very well with the present experimental viscosity data.
An interesting observation was made in the case of ternary mixtures. For various combinations of ternary mixtures of R12, R14, R22 and R114 vapours, when the constituents of any two components of the ternary mixture are in the inverse ratio of their molecular weights, the viscosity of this ternary mixture at one atmospheric pressure is constant irrespective of the percentage of the remaining constituent in the mixture.
The force constants and second virial coefficients for pure refrigerant vapours R12, R14, R22 and R114 have been determined using the Lennard?Jones potential to enable prediction of the viscosity of these pure refrigerant vapours and their mixtures by theoretical equations developed from statistical mechanics. The agreement between theoretical and experimental viscosity is good.
Suitable correlations have been proposed to predict the force constants, aaa and ?\varepsilon?, which give an accuracy better than the correlations reported in the literature. It is found that aaa is related to the molecular weight according to the relation a/ln?M=1.06a / \ln M = 1.06a/lnM=1.06 for refrigerant vapours.
The viscosity dependence on the square root of absolute temperature (K) has been extended to binary, ternary, and quaternary mixtures of refrigerant vapours for a pressure of one atmosphere. The viscosity predicted by this method is in very good agreement with the present experimental viscosity data.
PART TWO
Based on the principles suggested by DiPippo, Kestin and Whitelaw, a high?temperature oscillating?disc viscometer has been designed, fabricated, and calibrated to determine experimentally the viscosity of pure nitrogen up to 400癈 and that of pure refrigerant vapours R12, R14, R22 and R114 with an accuracy better than �5% in the temperature range of 30癈 to 90癈. The viscosity of binary, ternary, and quaternary mixtures of R12, R14, R22 and R114 vapours at one atmosphere and in the temperature range 30癈 to 90癈 has also been experimentally determined.
The validity of the equation
?=?0(T/T0)n\mu = \mu_0 (T/T_0)^n?=?0?(T/T0?)n
has been established for refrigerant vapours. A temperature杤iscosity relationship for mixtures of pure refrigerant vapours using the zero?degree?centigrade viscosity, ?0\mu_0?0?, has also been obtained in the form:
?mix=?0mix(TT0)nmix\mu_{\text{mix}} = \mu_{0\text{mix}} \left(\frac{T}{T_0}\right)^{n_{\text{mix}}}?mix?=?0mix?(T0?T?)nmix?
The viscosity predicted by this method for binary, ternary, and quaternary mixtures is in good agreement with the present experimental viscosity data.
A complex relationship appears to exist between viscosity at one atmosphere and the corresponding entropy for refrigerant vapours. For the first time, a linear relationship of the form
ln??/ln?s=K(s)\ln \mu / \ln s = K(s)ln?/lns=K(s)
has been suggested. The coefficient K(s)K(s)K(s), designated as EBT - Entropy?Based Characteristic, is dependent on the nature of the refrigerant vapour.
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