How to estimate enthalpy change across a compressor in simple vapor compression cycle

[bobkokke]

TL;DR

Calculate compressor side of a Vapour compression cycle without knowing output of the compressor.

Hi everyone,


I'm fairly new to HVACR systems and currently doing research on building an estimation model of a basic vapor compression cycle.


Right now, I'm trying to calculate the enthalpy change across the compressor — from point H1 (before the compressor) to point H2 (after the compressor). For my test setup, I’m assuming R134a as the refrigerant, with an inlet pressure of 2 bar. (if possible well asume 5K superheating)


As a reference, I’m using a Bitzer 2DC-3.2Y-40S compressor, but I don’t yet have outlet pressure or temperature data.


My questions are:

• How can I estimate the outlet enthalpy (H2) in this situation?
• Can I use the compressor's displacement and RPM to estimate the mass flow rate, and then use power input to find enthalpy increase?
• Are there any tools or databases you recommend for getting R134a property data?

Any help or guidance would be greatly appreciated!

 

[Chestermiller]

The mass flow rate is determined by the heat load of the overall system. Are you saying that you have no idea what the outlet conditions of the compressor are. If the compressor is operating adiabatically (and nearly reversibly), the inlet entropy- and outlet entropy per unit mass will be about the same. So you move on a constant entropy line for the compressor.

You can get thermodynamic data on 134a either from the manufacturer (e.g., DuPont) of probably from tables in Fundamentals of Engineering thermodynamics by Moran et al. There should be table online of 134a thermodynamic data also.