The yield stress of frozen hydrocarbon fuels

Abstract

A more complete description of the flow properties of frozen hydrocarbon fuels is necessary to deal with practical problems such as tank drainage and line stoppage. A study has been made of the minimum stress necessary to effect a change in frozen fuels and hydrocarbon mixtures from solid-like to liquid-like behaviour, by measuring the torque required to rotate an immersed vaned rotor. Experimental variables that affect the interpretation of the results as a rheologically defined yield stress were explored. The yield stress was highly dependent on the temperature and the n-alkane composition of the sample. The total n-alkane concentration determined the rate of increase in yield stress with temperature decrease. For a given total n-alkane concentration, the temperature at which a given yield stress was reached increased with the average n-alkane carbon chain length. While yield stress of frozen hydrocarbons is primarily dependent on the total solids present, other mechanisms involving crystal interactions appear to be necessary for interpretation of the results. Information about yield stress of a frozen fuel as a function of temperature provides a precise, rheologically sound basis for formulating improved methods of forecasting field performance.