The present invention relates to measurement instruments and more particularly to a viscometer for measuring the viscosity at high shear rates, of a thick liquid.
The measurement of the viscosity of a thick liquid, using presently commercially available instruments, presents various problems. The measurement process may be time-consuming and difficult to integrate into an automatic control system. The present methods of viscosity measurement depend upon the training, skill and care of the person performing the measurement. In certain viscosity measurement systems pressure must be applied to one face of the liquid, in a supply vessel, so that a sample may be drawn off and weighed. However, the pressure may be uneven and the supply vessel may drip before or after the liquid sample is drawn.
These problems are particularly acute when the liquid is a coal slurry, such as a coal-in-oil or coal-in-water slurry, in which microscopic sized bits of coal are suspended in a thick oil or water. In a typical slurry the coal particles are less than 75 microns in diameter (85% of particles). The viscosity of the slurry should be frequently measured in order to burn the slurry at its best combustion efficiency and as a quality control measure in the manufacture, storage and purchase of the coal slurry.
The viscosity of a viscous liquid may be derived from the formula applicable to its flow in a uniform tube: EQU .eta.=D (.DELTA.P/Ql)
where .eta. is viscosity, P is pressure, Q is flow rate and l is length of tube.
The presently commercially available viscometer to measure slurries suffers from inaccuracies because the pressure (P) is not uniform from one measurement to another and because the flow rate is not uniform because of dripping of the sample.