The discussion revolves around the evaluation of compressor work in thermodynamics, particularly focusing on the use of the heat capacity at constant pressure (Cp) in scenarios where pressure varies between the inlet and outlet sides of a compressor. Participants explore the implications of using Cp in different thermodynamic contexts, including constant pressure processes and state functions.
Participants express differing views on the applicability of Cp in varying pressure scenarios, indicating that multiple competing perspectives remain without a clear consensus on the correct approach.
Limitations include the dependence on the definitions of Cp and the assumptions regarding the behavior of ideal gases, as well as the unresolved nature of how to handle varying heat capacities in calculations.
For a constant pressure process, the amount of heat Q is equal to ##C_p\Delta T##. Otherwise, Q is not equal to that. But, for an ideal gas, irrespective of the pressure variation, the enthalpy change ##\Delta H## is always equal to ##C_p\Delta T##. This is because, in thermodynamics, ##C_p## is defined in terms of the enthalpy change rather than in terms of the amount of heat transferred. The two definitions match only if the pressure is constant.rishi kush said:how can we use Cp.dT to evaluate compressor work even when one side (inlet side) is having different pressure than other side (outlet side). Cp should be used for constant pressure!
If you have a heat capacity which varies with temperature, you integrate ##dH=C_pdT## between the initial and final temperatures to get the enthalpy change.rishi kush said:since Cp is a state function , its value should be different for initial and final states of a process? and which value should we have to consider?