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In fluid dynamics, an isentropic flow is a fluid flow that is both adiabatic and reversible. That is, no heat is added to the flow, and no energy transformations occur due to friction or dissipative effects. For an isentropic flow of a perfect gas, several relations can be derived to define the pressure, density and temperature along a streamline.
See relations between specific heats for the derivation of the thermodynamic relations between the heat capacities. The above definition is the approach used to develop rigorous expressions from equations of state (such as Peng–Robinson ), which match experimental values so closely that there is little need to develop a database of ratios or ...
Note that before and after the shock the isentropic relations are valid and connect static and total quantities. That means, p t o t a l ≠ p s t a t i c + p d y n a m i c {\displaystyle p_{total}\neq p_{static}+p_{dynamic}} (comes from Bernoulli, assumes incompressible flow) because the flow is for Mach numbers greater than unity always ...
Clausius–Clapeyron relation; Departure functions; Duhem–Margules equation; Ehrenfest equations; Gibbs–Helmholtz equation; Phase rule; Kopp's law; Noro–Frenkel law of corresponding states; Onsager reciprocal relations; Stefan number; Thermodynamics; Timeline of thermodynamics; Triple product rule; Exact differential
Since there is an increase in area, therefore we call this an isentropic expansion. If a supersonic flow is turned abruptly and the flow area decreases, the flow is irreversible due to the generation of shock waves. The isentropic relations are no longer valid and the flow is governed by the oblique or normal shock relations.
The difference relation allows one to obtain the heat capacity for solids at constant volume which is not readily measured in terms of quantities that are more easily measured. The ratio relation allows one to express the isentropic compressibility in terms of the heat capacity ratio.
Stagnation pressure is the static pressure a gas retains when brought to rest isentropically from Mach number M. [6]= (+) or, assuming an isentropic process, the stagnation pressure can be calculated from the ratio of stagnation temperature to static temperature:
Point 3 labels the transition from isentropic to Fanno flow. Points 4 and 5 give the pre- and post-shock wave conditions, and point E is the exit from the duct. Figure 4 The H-S diagram is depicted for the conditions of Figure 3. Entropy is constant for isentropic flow, so the conditions at point 1 move down vertically to point 3.