Measurements of rheological properties have been continued. Measurements at relatively low temperature (450 K) showed that a coarser coal grind shows substantially lower viscosity. It was also shown that coal and solvent obtained from the Fort Lewis plant give slurries of much higher viscosity than slurries from our reference coal and solvent. At higher temperatures (540 K) substantially the same relationships were shown. The effect of solvent-to-coal ratio was also found to be very great. Differential scanning calorimetry gave some low reliability specific heat results and showed indication of a probable heat effect at about 500 K. No indication of exothermic reaction with hydrogen was found.

A Lysholm engine, or helical screw expander, is currently being evaluated at the University of California, Berkeley for staging with a conventional turbine in geothermal energy conversion. A pneumatic closed loop, proportional-integral control system was implemented to control the Lysholm engine's exhaust pressure for performance testing of the engine at constant inlet/outlet pressure ratios. The control system will also be used to control the exhaust pressure of the conventional turbine during future testing of the staged Lysholm-turbine system. Analytical modeling of the control system was performed and successful tuning was achieved by applying Ziegler-Nichol's tuning method. Stable control and quick response, of approximately 1 minute, was demonstrated for load and set point changes in desired exhaust pressures.