First law when expressed in terms of entropy takes the form_____

T ds = dh � p dv

T ds = de + p dv

T ds = de � p dv

T ds = dh + p dv

Correct Answer : T ds = de + p dv

Explanation : The first law of thermodynamics when expressed in terms of entropy gives us two alternate equations. These equations are T ds = de + p dv and T ds = dh – v dp. We have used the relation of heat and entropy in the first law equation to get these equations.

Recently Updated in Aerodynamics Questions

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

H1>H2 always

H2>H1 always

H1=H2 for general flow

H1=H2 for adiabatic flow

Correct Answer : Option (D) : H1=H2 for adiabatic flow

Explaination : 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.

For a steady, inviscid, adiabatic flow of a gas, the total temperate is constant along the flow.

True always

False always

False only for calorically perfect gas

True only for calorically perfect gas

Correct Answer : Option (D) : True only for calorically perfect gas

Explanation : The total enthalpy of a steady, inviscid, adiabatic gaseous flow is constant. For a calorically perfect gas the total enthalpy can be written in terms of total temperature times the specific heat at constant pressure (which is also a constant). Thus, the total temperature is also a constant.

Select the incorrect statement if all the streamlines of the steady, inviscid, adiabatic flow originate from a common uniform freestream.

h0 is not equal to the freestream value

h0 is constant along the entire flow

h + V² = h0 is energy equation per unit mass

Stagnation enthalpy is same for each streamline

Correct Answer : Option (A) : h0 is not equal to the freestream value

Explaination : h0 is the stagnation enthalpy for the steady, inviscid, adiabatic flow which is equal to the static enthalpy plus kinetic energy, all per unit mass. If all the streamlines originate from a common freestream, stagnation enthalpy is equal to the freestream value and is constant along the flow i.e. same for all streamlines.