Mechanical Engineering - Thermodynamics - Discussion

In an isothermal process, change in internal energy is zero as there is no change in temperature. So according to the first law of thermodynamics dQ = dW. During an isothermal compression process, volume decreases as pressure increases after compression. So the work in compression dW =P2V2 on(V3/V2).

As explained able volume after compression is less than volume before compression. Hence the dW term decreases as V3<V2.

Now, dW becomes negative, hence dQ is also negative. As we know that negative dQ means loss or ejection of heat. Hence heat ejection is taking place in an isothermal compression process.

In the isothermal compression of a gas there is work done on the system to decrease the volume and increase the pressure. Doing work on the gas increases the internal energy and will tend to increase the temperature. To maintain the constant temperature, energy must leave the system as heat and enter the environment.

To maintain constant temperature during isothermal expansion, heat is absorbed by the system as the temperature tends to drop on increase in volume of gas. Also heat is rejected on isothermal compression as to maintain constant temperature because on compression the temperature tends to rise.

The answer is correct. Heat rejection takes place after isentropic expansion and during this heat rejection pressure increases but at a constant temperature so isothermal compression is the correct answer.

Heat rejection: Work done by surrounding on the system so heat will get rejected in compression.

Heat addition: Work done by a system on surrounding during expansion, so heat addition.

Answer is correct.

In isothermal expansion (1-2), the heat is added or absorb at a hot temp. While in isothermal compression (3-4) heat is rejected at cold temp.

Isentropic process : heat transfer not take place.

Isothermal expansion process: heat is injected.

Isothermal compr : heat is rejected.

There are 2 isothermal process (heat addition, heat rejection).

Heat rejection at isothermal expansion is correct.

Option (A) correct.

In isothermal compression, if heat is added then how heat rejection takes place in isothermal compression. It doesn't make sense.

Heat is added at isothermal expansion.

Heat is rejected at Isothermal compression.

The given Answer is absolutely correct.