Indicator diagrams

FIG. 10-91 Actual indicator diagram of a two-stage compressor showing the operation of clearance control at five load points. 

The thermal efficiency of the process (QE) should be compared with a thermodynamically ideal Carnot cycle, which can be done by comparing the respective indicator diagrams. These show the variation of temperamre, volume and pressure in the combustion chamber during the operating cycle. In the Carnot cycle one mole of gas is subjected to alternate isothermal and adiabatic compression or expansion at two temperatures. By die first law of thermodynamics the isothermal work done on (compression) or by the gas (expansion) is accompanied by the absorption or evolution of heat (Figure 2.2). 

Figure 2.2 The indicator diagrams for the Carnot and the Otto engines. The Carnot cycle operates between the two temperatures Tj and T2 only, whereas the Otto cycle undergoes a temperature increase as a result of combustion.

F or the following discussion, refer to Figure 3-5, which shows an ideal indicator diagram followed by a series of cylinder illustrations depicting piston movement and valve position. The figure shows in diagram form one... 

The working substance being initially at the temperature T2 of the refrigerator, we place the cylinder on the non-conducting stand, and compress the working substance reversibly until the temperature rises to Ti. By the conditions imposed, this is an adiabatic compression, and will be represented by a continuous curve on the indicator diagram, say AB (Fig. 8). 

Corollary 1.—The area enclosed by the circuit representing an isothermal reversible cycle on the indicator diagram is zero if, therefore, the curve is not a segment of a line transversed from A to B and then from B to A (Fig. 4), it must form two loops of equal areas but traversed in opposite senses, or else such a system of positive and negative loops that the total area is zero. 

The action of this series of engines may be represented on the indicator diagram (Fig. 

This is a change of configuration at constant temperature, and the line traced out on an indicator diagram if there were... 

If we draw the two isochores imiii, i 2< 2, on the indicator diagram (Fig. 14), all the paths of change must lie within these limits, which fix the range or amplitude of the process. Let the initial state ( i, T) be a, and let the gas expand isothermally and reversibly to a the maximum work AT is represented by the area aa vtf i, which is shown later to be ... 

There is a perfectly general theorem, which applies to all bodies, or systems of bodies, to the effect that an adiabatic, when it crosses an isotherm on the indicator diagram, is more inclined to the r-axis, or the adiabatic is steeper than the isotherm. 

Metastable states are represented on the indicator diagram by the prolongations of the isotherms of homogeneous states beyond the intersections with the line of heterogeneous states. Thus, the productions of the liquid and vapour portions of the isotherm, Fig. 38, meet the heterogeneous parts of the isotherms d2y 03 at Q, P, respectively. At each of these points there are two conditions of existence possible for the system, thus ... 

Ice type, 195 Ideal gas, 47, 135 Independent variables, 103 Indicator diagram, 45, 127 Inequality of Clausius, 79 Intensity factors, 111 Intrinsic energy, 32, 76, 484 Inversion point, 167 Irreversible processes, 67, 69, 75, 82, 84, 87... 

The first application of piezoelectricity to measure the pressure developed on expln was done by Sir J.J,Thomson in 1917 (Ref 36, pl6A) and this was followed by D.A.Keys in 1921 and by J.C.Karcher in 1922. The device constructed by Karcher at the US Bureau of Standards used quartz and proved to be successfulto obtain the indicator diagram of a gun discharge (Ref 3)... 

PV diagram. A plot of pressure vs. volume. Lines or curves on the indicator diagram represent j processes. The areas under curves on the indicator diagram are equal to the work released i by the process. 

---