# A Bench Evaluation Test for Refrigeration Oils in a Refrigeration System Using a Screw Compressor
## 3 Experimental Setup  
Figure 1 shows a schematic diagram and a picture of the experimental test bench. It consists of three loops, being the refrigerating system loop, the regeneration loop, and the oil circulation loop. In the refrigerating loop, the refrigerant flows into the compressor, where it mixes with the oil. The refrigerant-oil mixture is discharged from the compressor into the separator, where the refrigerant and oil separates. The refrigerant vapor flows to the condenser, where it is condensed and then is throttled into the evaporator. In the evaporator, the refrigerant absorbs the thermal energy from the regeneration loop and vaporizes. Then the refrigerant vapor enters the compressor, and the next cycle starts. The lubricating oil is injected into the refrigerant in the compression chamber to cool the compressed refrigerant vapor. At the same time, the oil seals the compressor linkage path and lubricates the compressor. In the regeneration loop, water circulates between the condenser and evaporator to transfer the thermal energy from the condenser to the evaporator. In the oil circulation loop, the oil separated from the separator flows into the oil-water heat exchanger, where it is cooled by the cooling water from the cooling tower. The cold oil is then introduced to the compressor. Some of the oil is injected into the compression chamber to cool the compressed refrigerant vapor, in order to control the discharge refrigerant temperature, while the remaining oil is used to lubricate the bearings of the compressor.  
Figure 1: _Cont._  
In order to control the discharge temperature and ensure that the compressor operates under a reasonable load near the standard working conditions, two technical measures are adopted in the experiment. Firstly, a reversed flow bypass is set from the outlet of the separator to the suction pipe of the compressor to introduce high-temperature refrigerant back to the suction of the compressor to increase the discharge temperature. By adopting this method, the compressor discharge pressure can be controlled to the desired level. Secondly, a side pipe is set across the side of the oil cooler, to increase the temperature of the injected oil, to then control the discharge temperature of the compressor.  
All the pressures and temperatures are measured using pressure sensors and thermocouples, respectively. High precision K-type thermocouples are used to record the temperature with an accuracy of \(\pm\)1 \({}^{\circ}\)C and are calibrated from \(-\)50 to 200 \({}^{\circ}\)C. The pressure transducers are Kulite XTM-190 pressure transducers with an accuracy of \(\pm\)1% FSO (35 bar). Those pressure transducers are also verified using high precision pressure gauges. A mass flowmeter with an accuracy of \(\pm\)0.2% from 0 to 40 kg/h is used to measure the flow rate of the refrigerant in the refrigeration system.  
A screw compressor is applied in the experimental system and its parameters are listed in Table 4. The experimental operating conditions are listed in Table 3. Before testing, a helium mass spectrometer (leak detector) is used to check the seal performance. A vacuum-pumping system is then used to ensure the standard vacuum condition in the system before the refrigerant is charged.