Abstract
The oil-free compressor is a key component in fabricating polyethylene terephthalate (PET) bottles for beverages and water. At present, the main compressor type used for blowing PET bottles is the reciprocating compressor. However, compared to screw compressors, reciprocating compressors have shortcomings of high energy consumption and too many consumable parts. Many manufacturers of PET bottles in Asia are seeking to replace reciprocating compressors with screw compressors, as we know. Screw compressors can be classified as single-screw compressors (SSC) and twin-screw compressors. Since the load in a twin-screw compressor is far larger than that in an SSC, SSCs are more suitable for being developed for high-pressure applications such as PET bottle blowing. This paper presents a performance study on an oil-free single-screw compressor as the first stage of the PET compressor unit. A 5.4 m3·min−1 prototype and its test rig were developed. The thermophysical process of the moist air is theoretically analyzed. The pressure loss on the flow path and the influence of the important parameters are experimentally investigated. It is found that water vapor cannot be separated during the adiabatic compression process. The results also show that the pressure loss from the discharging duct to the check valve accounts for the largest percentage of the total pressure loss. The experimental results further show that the discharge capacity and shaft power increase almost linearly with the motor speed. The efficiency declines with increasing injected water temperature. The discharge capacity and shaft power all increase with the injected water flowrate, and an optimum flowrate is found to ensure a highest isentropic efficiency. With the increase in discharge pressure, the discharge capacity decreases, and the shaft power increases. The isentropic efficiency is found to have its maximum value at a certain discharge pressure.
Highlights
Polyethylene terephthalate (PET) is widely used in the stretch blow molding process for packaging applications [1], such as beverage bottles and mineral water bottles
The results showed that the multi column type (MCT) had the best wear resistance, and single straight line type (SSLT) had a poor performance
When the total pressure of the moist air increases from 1 atm to 8 atm, it can be observed that the partial pressure of water vapor raises from 1.89 kPa to15.13 kPa, and the water vapor specific volume v decreases from
Summary
Polyethylene terephthalate (PET) is widely used in the stretch blow molding process for packaging applications [1], such as beverage bottles and mineral water bottles. Liu presented a mathematical model of a two-stage oil-free screw compressor, analyzed how the interstage pressure was built, and developed a prototype with a total pressure of 9 bar [5]. Several studies have been published on the thermodynamic characteristics of the SSCs. In the refrigeration area, Wang et al investigated the heat transfer area influenced by the main geometric characteristics, proposed a model to calculate the heat transfer between the gas and the oil film adhering on the working chamber wall based on an assumption of poor oil atomization, studied the leakage properties and provided optimized design proposals for high volumetric efficiency, presented an injection model, and analyzed the relationship between the performance parameters of the compressor and the injection hole design parameters [33,34,35,36,37]. The obtained results may be valuable for developing two-stage SSC units for PET
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