# Computational Fluid Dynamics Questions and Answers – Equations of State

This set of Computational Fluid Dynamics Multiple Choice Questions & Answers (MCQs) focuses on “Equations of State”.

1. How many equations are related to solving a flow field?
a) 2
b) 3
c) 5
d) 4

Explanation: There are 5 equations related to solving a flow field.

1. Mass conservation equation
2. x-momentum equation
3. y-momentum equation
4. z-momentum equation
5. Energy equation

2. Among the unknowns of a flow field, some of the properties are given below. Which set contains only thermodynamic properties?
a) Density, pressure, specific internal energy, temperature
b) Density, velocity, specific internal energy, temperature
c) Velocity, pressure, specific internal energy, temperature
d) Density, pressure, specific internal energy, Velocity

Explanation: Velocity is a property completely related to fluid flow. The other properties – density, pressure, specific internal energy and temperature are thermodynamic.

3. Relationship between thermodynamic variables of a flow field can be obtained through ___________
a) Momentum conservation
b) Thermodynamic equilibrium
c) Energy equations
d) Zeroth law of thermodynamics

Explanation: Thermodynamic equilibrium is a state of a matter where there is no transfer of energy. This condition can be used to relate the thermodynamic properties with one another.

4. Fluid velocity is very high. Will thermodynamic equilibrium be applicable to fluid flows?
a) Yes, the external conditions help them stay in thermodynamic equilibrium
b) No, their flow properties change abruptly
c) No, they are influenced by external conditions
d) Yes, the fluid can thermodynamically adjust itself quickly to be in thermodynamic equilibrium

Explanation: The velocity of fluid flow is very high. This may affect their thermodynamic equilibrium. But, the particles are small enough to thermodynamically adjust themselves to equilibrium so quickly.

5. We can describe the state of a substance in thermodynamic equilibrium using two state variables. What are these two variables?
a) Density and temperature
b) Density and pressure
c) Pressure and Temperature
d) Velocity and Temperature

Explanation: There are four thermodynamic variables – density, temperature, pressure and specific internal energy. Among these, pressure and specific internal energy can be represented using density and temperature.

6. Let,
ρ → Density
p → Pressure
T → Temperature
How can we represent p of a perfect gas in terms of ρ and/or T?
a) p=ρ RT
b) p=RT
c) p=ρ T
d) p=ρ R

Explanation: For perfect gases, pV=mRT. This can be written in the form p=ρ RT.

7. Let,
ρ → Density
T → Temperature
i → Specific internal energy
How can we represent i of a perfect gas in terms of ρ and/or T?
a) i=T
b) i ∝ (1/T)
c) i=(1/T)
d) i ∝ T

Explanation: i=Cv T is the relation between temperature and specific internal energy (where Cv is the specific heat at constant velocity). This can be used to get the energy equation in terms of specific internal energy.

8. Which is/are the conservation laws that are enough to solve a complete fluid problem?
a) Energy and momentum conservation
b) Mass and energy conservation
c) Mass and momentum conservation
d) Mass equation

Explanation: A complete fluid flow problem can often be solved by only using the mass and momentum conservation equations. Energy conservation equation is not necessary.

9. Energy conservation equation is necessary to solve this property of fluid flow.
a) Pressure
b) Temperature
c) Density
d) Velocity

Explanation: Energy conservation should be solved for a fluid flow if we want the temperature distribution or if the system involves heat transfer.

10. Equations of state provide the linkage between ___________ and ____________
a) Conservative, non-conservative equation
b) Eulerian, Lagrangian equations
c) Energy equation, mass and momentum equations
d) Differential, Integral equations

Explanation: Equations of the state provide the linkage of Energy equation with mass and momentum equations. They give the thermodynamic properties in terms of the state variables.

Sanfoundry Global Education & Learning Series – Computational Fluid Dynamics.

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