Patent GB-693642-A (GB)
Title: Temperature change signal devices
IPC: F01D21/02
Filed: 1950-11-29
Abstract: 693,642. Electric control systems; temperature alarms. METROPOLITAN-VICKERS ELECTRICAL CO., Ltd. Nov. 29, 1950 [Jan. 24, 1950], No. 29256/50. Classes 40 (i) and 118 (i) [Also in Groups XIII, XXVI and XXXV] In a device for producing a signal proportional to rate of change of temperature of the motive fluid in a gas turbine, two members having different heat capacities are disposed in and extend transversely across the fluid stream so that as the fluid temperature changes, the temperature of the member having the smaller heat capacity follows that of the fluid more rapidly than that of the other member, means responsive to the temperature differential between the members indicating the rate of change of fluid temperature. The two members may be portions of a single member and the signal output may continuously indicate the rate of change of fluid temperature, operate an alarm if this rate exceeds a predetermined value, or automatically control the fluid temperature. As shown, Fig. 1, the hot motive fluid' is fed from combustors through a nozzle ring 2 having stationary blades 2a for directing the fluid into the blades 3a carried by the rotor 3, after which the spent fluid is exhausted through an annular passage defined by concentric walls 4, 5 enclosed in an exhaust hood 6. Extending radially from a block 10 on the wall 4 are two rods 11, 12 having the same co-efficient of linear expansion but different sectional areas so that their heat capacities differ. The thinner rod 11 will then follow changes in the fluid temperature more quickly than the rod 12, and provided the rate of change is sufficiently great, the relative changes in length of the rods will rock abellcrank lever 13 pivotally mounted on the rod ends to close a signalling switch 14a or 14b to give warning of the change and its sense and, or. operate a device for controlling the fluid temperature e.g. by regulating the fuel supply. The device is independent of the absolute temperature and will not respond to transient changes owing to its time lag. The bellcrank may, alternatively, actuate an electrical or hydraulic modulating device giving a continuously variable signal proportional to rate of. change of temperature. As the rods 11, 12 extend radially across the whole exhaust passage the device responds to the averaged effect of fluid temperature changes radially across the exhaust. The rods 11, 12 preferably have the same cross-sectional area and shape as those of critical parts of the engine. For example, they may be similar to the rotor blades 3a or the fixed nozzle blades 2a, Fig. 2 (not shown). The two members in such a case may be the leading and trailing portions of a single streamlined member 16 Fig. 3, differentially connected thermocouples 18, 20 located in the two portions producing a net e.m.f. proportional to the rate of change of fluid temperature. The single member may be one of the blades 2a or 3a. In the latter case the signal output is a measure of the averaged effect of temperature changes around the circumference of the fluid flow path. To produce an output signal responsive to both radial and circumferential averaged effects'of fluid temperature changes, a plurality of thermocouple pairs may be disposed radially along one or more of the blades 3a. Alternatively, such an arrangement may be applied to one of the fixed nozzle blades 2a.