Question

1) An isentropic flow: a) has no heat transfer, b) does not allow temperature to change, c) can occur in a real physical problem, d) can only occur when the fluid is at rest.

2) Based on the first law of thermodynamics (assuming no chemical reactions, i.e. just a simple gas like air or helium): a) changing the flow velocity can heat the flow, b) moving a solid body through a fluid can heat the fluid, c) compressing a perfectly insulated container that holds a non-moving gas can heat the gas, d) if a completely stationary gas is held within a rigid container that is perfectly insulated then the temperature of the gas will decrease with time.

3) The speed of sound: a) is computed assuming an isothermal process, b) decreases with increasing altitude in the troposphere of the US Standard Atmosphere, c) violates the 2nd law of thermodynamics, d) is about 900 m/s at sea level, e) is different at different times of the year at the same location (say, the Ames airport).

4) For a thermally perfect gas: a) specific heats are constants, b) internal energy and enthalpy are only functions of temperature, c) pressure obeys the ideal gas law, d) the temperature is high enough that the gas dissociates.

5) For a calorically perfect gas: a) specific heats are constants, b) internal energy and enthalpy are only functions of temperature, c) pressure obeys the ideal gas law, d) the temperature is high enough that the gas dissociates.

My guesses:

1) a) has no heat transfer

2) a) changing the flow velocity can heat the flow, b) moving a solid body through a fluid can heat the fluid, c) compressing a perfectly insulated container that holds a non-moving gas can heat the gas

3) b) decreases with increasing altitude in the troposphere of the US Standard Atmosphere

4) b) internal energy and enthalpy are only functions of temperature, c) pressure obeys the ideal gas law

5) a) specific heats are constants, c) pressure obeys the ideal gas law

Answer 1

1. An isentropic flow: Correct Answer is a) has no heat transfer, because Isentropic means no change in entropy.

2. Based on the first law of thermodynamics (assuming no chemical reactions, i.e. just a simple gas like air or helium): Corrcet option is c) compressing a perfectly insulated container that holds a non-moving gas can heat the gas, PV = nRT

3. The speed of sound: Correct option is e) is different at different times of the year at the same location as speed of sound depends on temperature so as temperature changes throughout the year speed of sound also changes.

4. For a thermally perfect gas: Correct option is b) internal energy and enthalpy are only functions of temperature, and  c) pressure obeys the ideal gas law

5) For a calorically perfect gas: Correct option is a) specific heats are constants, as per definition.