Conference Agenda

In recent years, increasing research efforts have been made on modeling and testing positive displacement compressors with low global warming potential (GWP) working fluids and their systems. The ongoing HFC phase-down is forcing the HVAC&R industry to investigate low-GWP refrigerant alternatives as well as natural refrigerants (e.g., water, hydrocarbons, CO2). The transition to low-GWP and natural refrigerants requires research efforts on cycle configurations and components including compressors. More specifically, most of the existing positive displacement compressors employed in HVAC&R systems rely on lubricant oils to ensure correct operation and performance. To better understand the potential research directions in lubricant oils, a reciprocating compressor with CO2 as refrigerant was selected as the case study to investigate alternative lubricant oil formulations. In this study, a baseline POE-68 and two alternative lubricant oils were evaluated on a transcritical CO2 reciprocating compressor with respect to performance enhancement and potential issues and challenges. A hot gas bypass test stand was used to carry out the experimental studies. A total of 66 steady-state data points were collected, and control tests were performed after each alternative oil formulation to ensure correct operation of the compressor. The alternative lubricant oils showcased comparable performance data to the baseline lubricant oil under a wide range of operating conditions without sign of decomposition.

With the development of the hydrogen energy industry, it is crucial for hydrogen refueling stations that compressors can work efficiently and flexibly with a longer life span. Adopting ionic liquid as a liquid piston to compress hydrogen is a feasible method. The high stroke frequency of ionic compressor prevents the liquid piston from maintaining a stable shape, leading to the generation of the additional clearance volume and hydrogen sealing failure. In this article, a novel H-shaped piston was proposed and a 3d numerical model of an ionic compressor cylinder with it was established. The dynamic simulation of the two-phase fluid behavior in the cylinder during three cycles was performed using the volume of fluid method and the dynamic mesh technique. The effect of this piston on the variation of the two-phase interface and the clearance volume of the compressor has been discussed for optimizing the design of the ionic compressor. Results show that: the clearance volume of the cylinder with a H-shaped piston was smaller than that of the cylinder with a normal piston in all three compression cycles, which indicated that the higher volumetric efficiency could be obtained with the H-shaped piston. In addition, the application of the H-shaped piston allowed sufficient ionic fluid to be retained in critical sealing locations of the cylinder to keep hydrogen sealing and piston lubrication well.

One of the most crucial parts of a reciprocating compressor is the crankshaft, which conveys the motion of the rotor to the piston via the connecting rod. The effect of the gas, friction and inertial forces on the journal bearings not only creates the vibration but also initiates the mechanical losses. Since the design parameters of the crankshaft play a vital role in the losses, in this study, the bearing and lubrication model of a reciprocating compressor was developed in an analysis software to investigate the effect of design parameters. The forces and the torques emerging on the compressor were calculated and in-directly validated with mechanical loss experimental studies. Afterward, a sensitivity analysis is made by sweeping varying design parameters, and vital parameters are identified for the crankshaft to reduce the bearing loads and mechanical losses. Finally, a crankshaft design that demonstrates lower bearing forces than the investigated geometry is proposed with the genetic algorithm. Keywords: Crankshaft optimization, genetic algorithm, bearing forces