DAVIS. — A PQ PLANE FOR THERMODYNAMIC CYCLIC ANALYSIS. Co3 



In a cycle of type A, the temperature of the working substance after 

 compression (point c) is already comparatively high, but ia the second 

 cycle this temperature (point b) is still that of the atmosphere, and there- 

 fore, in general, much lower than that of the exhaust (point e) ; the 

 second cycle, therefore, but uot in general the first, may be modified by 

 introducing the idea of regeneration. If ef be an isothermal through e, 

 the working substance may be carried from the state b to the state /by 

 means of the heat which the exhaust gives up in passing from the state 

 e to the state a, and this too without any loss of available energy, by 

 simply passing the high pressure air and the exhaust in opposite direc- 

 tions through adjacent passages. A third type of cycle is thus obtained, 

 and may be culled 



Type 0. The Regenerative Cycle (a bfdea of Figure 2). 



Since these cycles themselves and not their applications to engineer- 

 ing are to be studied in this paper, there is no need of ruling out those 

 cases under types B and C in which the point e falls to the left of the 

 point a. Such cycles are figures-of-eight, and the work done by the 

 working substance may perfectly well be zero, or less than zero, but 

 the properties of such degenerate cycles fit on continuously with those of 

 cycles of the ordinary kind, and should be studied with them. In a figure- 

 of-eight case under type C the regenerative process consists in cooling 

 the high pressure air to the temperature of the exhaust, and cycles of 

 this kind are of some interest in connection with liquid air machines. 



In the study of gas turbine cycles a number of properties should be 

 considered. The most important of these is the temperature ( T^) of the 

 working substance after its expansion (point e), for if this be too high, 

 the blades of the turbine wheel will suffer. Another important property 

 is the velocity ( V) of the stream of gas as it leaves the nozzle, and here 

 also there is an upper limit, in that F should bear a definite ratio to the 

 peripheral velocity of the turbine wheel, and this is always limited by 

 structural or other considerations. There is also the efficiency {E) of 

 the cycle ; and finally the work (TF) which a unit mass of the working 

 substance dees in going once around a cycle is of interest because of its 

 bearing on the size of the machinery necessary for a given output. 

 Twelve sets of contour lines are therefore involved, four for each type 

 of cycle ; and the proposed problem is to determine by means of them 

 (1) which type of cycle is preferable, and (2) what the dimensions of a 

 cycle of that type should be, it being desirable to make E and W as 

 large as possible subject to the conditions T^ < T^ and V < V, where 

 T and Fare given constants. 



