Methods based on a semi-empirical model for simulating scroll compressors with HFC and HFO refrigerants

Abstract

The aim of this work is to evaluate three methodologies regarding semi-empirical scroll compressor modeling for different refrigerants and conduct a comparative analysis of their results and accuracy. The first step is to improve a semi-empirical model for scroll compressors based on established techniques, and further enhance the physical background of some of its sub-processes leading to more accurate predictions. Focus is then given on the compressor operation when changing the refrigerant, proposing three methods in total. The first method refers to the standard model, requiring an optimization process for the calibration of all the model parameters. The second method relies on a reference refrigerant, and also uses optimization procedures, but for the fine-tuning of a small subset of the parameters. The third method is more generalized, without the need of any optimization process for the parameters identification, when fluid change occurs, leading to a very fast approach. Το evaluate the accuracy and verify the applicability of each method also related to the necessary computational time, two scroll compressors each with three different refrigerants are considered (HFCs and HFOs and their blends). The model is evaluated with the available manufacturer data, using R134a as reference refrigerant. The results show that the first method predicts the key indicators with a very high accuracy, with the maximum discrepancy of 2.06%, 4.17% and 3.18 K for the mass flow rate, electric power and discharge temperature respectively. The accuracy of the other two methods is dropping, but within acceptable levels in most of the cases. Therefore, in cases that reduced accuracy can be accepted, the third method is preferred for compressor performance prediction when changing the refrigerant, which provides results at a small fraction of time compared with the other two methods, once the parameters are calibrated for a reference case.

Identifying the performance and losses of a scroll compressor with vapour injection and R1234ze(E)

“…The semi-empirical model parameters are then fine-tuned 37 , when using the standard suction pressure drop model (with a constant friction factor) and the improved model (with the logarithmic correlation presented previously).…”

“…Where ρ su is the density at the compressor suction, cp is the volumetric flow rate calculated by the nominal swept volume and the rotational speed 37 , h r,int,is is the outlet enthalpy once the refrigerant is compressed isentropically from the suction up to the intermediate state, h r,ex,is refers to the specific enthalpy of the fluid following an isentropic compression from the intermediate state after mixing with injection line up to the discharge, and Ẇ cp is the total electrical power provided to the compressor that includes the electromechanical conversion and all related losses.…”