Harold Lown - MS

The important position that the gas turbine has gained among prime movers in recent years has been made possible by great improvements in its compressor efficiency and most important by the metallurgical development of high-temperature alloys.  Raising the compressor efficiency has increased the useful work of turbine by cutting down the work of compression and the high-temperature alloy have raised the base of operating temperature of the turbine to the point where favorable efficiencies can be attained.

The new role of the gas turbine has put a special emphasis on the development and testing of high-temperature materials used in its construction.  These materials may undergo a wide variation in conditions of temperature, pressure and stress in an actual machine.  Means must be developed to predict the behavior of such materials under actual service conditions (1).  It was, therefore, decided to deal with the most important condition; namely, the instantaneous temperature variation across the blades, and to develop proper instrumentation for measuring these temperature variations.

Knowledge of the temperature variation across the blades would help in the design of blades of greater endurance or greater temperature stress.  With the already existing heat-resisting alloys, this might enable a further elevation in the inlet temperature of the gases, which would in turn result in a higher turbine efficiency.  Furthermore, an improvement in the blades would also mean prolongation of the life of the gas turbine, as the blades are its most important limiting factor.

Previous methods used for measuring blade temperature, such as the thermocouple induction method, did not give sufficient information (2).  The induction method consisted of inserting thermocouples at definite points in the blade, and measuring the temperature at those points.  This only gave average point temperature, as the thermocouples could not follow rapidly enough a changing temperature.

Lacking suitable methods for measuring blade temperatures, it was decided to develop an electro-optical pyrometer, modeled after the one previously developed at the University of Wisconsin for measurement of instantaneous flame temperatures inside a Diesel-engine cylinder (3).

The eletro-optical pyrometer developed at the University of Wisconsin is base don the principle of radiation intensity from high-temperature source at two different wave-lengths.  Although the temperature of the blades is much lower than the flame temperature inside a Diesel-engine cylinder, it was thought possible to attain satisfactory results by developing more sensitive apparatus than that employed for the flame-temperature measurement.

This thesis explains the instrumentation developed and the problems encountered in trying to achieve suitable method for measurement of instantaneous gas-turbine blade temperature.