Question

The total enthalpy in a general flow at point 1 is H1 and at point 2, which is downstream, is H2. Then __________

(a) H1>H2 always

(b) H2>H1 always

(c) H1=H2 for general flow

(d) H1=H2 for adiabatic flow

The question was posed to me by my school teacher while I was bunking the class.

I want to ask this question from Definition of Total Stagnation Conditions in portion Compressible Flow – Preliminary Aspects of Aerodynamics

Answer 1

The correct choice is (d) H1=H2 for adiabatic flow

Easy explanation: The total enthalpy at two points along the flow may or may not be equal in general. The total enthalpies are equal in case of an adiabatic flow between the two points in consideration.