Abstract
Increasing number of refrigeration units has led to an increase of CO2 emissions and the destruction of the ozone layer. Using low global warming potential (GWP) refrigerants, improving the efficiency of vapour compression refrigeration (VCR) units, and minimising refrigerant leakages can reduce the global warming effect. Investigating the refrigerant distribution under varied operating conditions can provide a deeper understanding of refrigerant charge optimization. This study proposed a model of refrigerant mass distribution in a prototype oil-free VCR system using a linear compressor with variable strokes and R134a. The absence of the oil lubricant allows the adoption of compact heat exchangers, such as micro-channels, so that the total refrigerant charge can be reduced significantly. The predicted total refrigerant charge has a Mean Absolute Percentage Error (MAPE) of 3.7%. The simulation results indicate that refrigerant distributed in the condenser is most sensitive to operating conditions and total refrigerant charges. The refrigerant accumulated in the condenser is 6.8% higher at a total refrigerant charge of 0.33 kg than that of 0.22 kg. For a total refrigerant charge of 0.33 kg, 72.1% of the total refrigerant can accumulate in the condenser. At a fixed pressure ratio, the refrigerant as a two-phase form in the condenser decreases slightly with the increase of compressor strokes, resulting in a larger mass flow rate, thus cooling capacity. The present model can be adapted for optimization of a refrigeration unit and its components.
Highlights
The increasing number of refrigeration units has led to an increase of CO2 emissions and the destruction of the ozone layer
0.28 kg.ofThe the condenser condenser inlet,outlet, condenser outlet, and evaporator outlet based was calculated based on measured inlet, condenser and evaporator outlet was calculated on measured temperatures and temperatures and pressures according to the pressures according to the National Institute of Standards and Technology (NIST) thermal properties thermal properties database at enthalpyinlet at the evaporator assumed to be equaloutlet
The proposed model can effectively predict the refrigerant distribution in the prototype oil-free refrigeration unit
Summary
The increasing number of refrigeration units has led to an increase of CO2 emissions and the destruction of the ozone layer. Li et al [6] investigated the refrigerant distribution of a split air conditioner using R290 as the working fluid. 60% of the total charge of the refrigerant was accumulated in the heat exchanger at steady-state conditions. For steady-state conditions, the experimental results indicated that with the rise of the thermal load, the refrigerant mass increased in the condenser while a reverse trend was found in the evaporator. Han et al [10] experimentally investigated the transient refrigerant distribution inside the main components of an air conditioner in heating mode. The refrigerant is inevitably dissolved in oil lubricant, resulting in an increase of total refrigerant charge, higher refrigerant leakage. A novel oil-free VCR system has been prototyped for the purpose of refrigerant charge reduction, which can utilise compact heat exchangers (e.g., micro-channel). The oil-free system was tested with various refrigerant charges
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
