This invention relates to a method of and apparatus for determining the no-flow temperature of a liquid, such as domestic heating oil, plastic, paint, ice cream, margarine, oil, distillate fuel and aviation fuel. The determination of the no-flow temperature of such materials is important, because their production and handling is limited by their low temperature properties. It is evident that significant problems may arise, for example, if fuels such as aviation fuel or domestic fuel fail to flow through the handling system to a burner because of their limiting low temperature properties.
One of the critical specifications of liquids such as jet fuel, is the freeze point which is defined as the temperature at which wax crystals formed on cooling disappear when the temperature of an agitated fuel sample is allowed to rise. A major shortcoming of the freeze point specification is that it bears little relation to the fuel property that limits low temperature performance, viz., the ability of the fuel to flow from a fuel tank at low temperature. A prior art cold flow test consists of characterizing fuel by its hold-up factor, which is defined as the amount of fuel that is unable to flow from a first section of a tester to a second section and varies with the temperature of the fuel. The most important test parameter is the "zero percent hold-up temperature", which represents the lowest temperature to which the fuel can be subjected before total hold-up will occur, that is, the point at which none of the fuel can flow. It is this temperature that is likely to define the limit of a specification based on the low temperature flow properties of the fuel. The zero percent hold-up temperature cannot be determined directly by the prior art techniques. Rather, the usual procedure consists of constructing a graph of the temperature dependence of the hold-up factor over a range of readily determined values, which are typically between 10-90% hold-up, and extrapolating the plot to zero percent hold-up to obtain the zero percent hold-up temperature by this method, several points are necessary to construct the hold-up temperature profile, particularly in the region of low hold-up factors. Obviously, this is a time-consuming exercise.
Therefore, it is an object of the present invention to provide a method of and an apparatus for determining the no-flow temperature of liquids.