Latest research on R290 technology from Purdue Conferences

This summer the 21^st International Compressor Engineering Conference and the 14^th International Refrigeration and Air Conditioning Conference took place on the campus of Purdue University in West Lafayette, Indiana. Below hydrocarbons21.com summarises some of the latest research on R290 refrigeration technology presented at the conferences.

Minimum Viscosity for Bearing Reliability in R290 Rotary Compressors

Xingbiao Z. Bo, JIANGP Q. GAOP, B. GAOP

As the use of R290 compressors increases around the world, the importance of ensuring their high performance and reliability grows. This paper emphasises the fact that lubrication is essential to maintaining the proper functioning of an R290 rotary compressor and ensuring bearing reliability. The viscosity grade (VG) and the miscibility level with the refrigerant are important properties of the lubricating oil.

This paper describes a method for specifying the minimum safe viscosity of the high-side R290 rotary compressors based on lubricant film thickness calculations. The minimum lubricant/R290 mixture viscosity can be expressed as a function of discharge pressure and suction pressure. At any operating conditions, the compressor should be continuously operated with the mixture viscosity of the sump larger than the minimum mixture viscosity. From this minimum mixture viscosity, a minimum sump temperature will be specified.

Investigation of Low GWP Refrigerant Interaction with Various Lubricant Candidates, R. J. Beattie, J. A. Karnaz

Looking at current and future needs for lubricants for various refrigerants, this paper aims to help manufacturers in the air conditioning and refrigerant industry to evaluate the choices that need to be made in order to maintain the required system performance. For hydrocarbons most lubricants have good miscibility, which makes the choice of lubricants more dictated by other parameters. According to the paper the following lubricants are suitable to hydrocarbons:

Naphthenic mineral oils
Alkylbenzene oils (AB)
Polyol Ester oils
Polyakylene glycol oils

Principle of designing fin-and-tube heat exchanger with smaller diameter tubes for air conditioner, W. Wu, G. Ding, Y. Zheng, Y. Gao, J. Song

This study looks at the possibility of designing fin-and-tube heat exchanger with smaller tubes. Small diameter tubes in R290 systems would result in a lower refrigerant charge, and could hence increase the uptake of the natural refrigerant R290.

A fin configuration for 5 mm diameter tubes was designed using a Computational Fluid Dynamic-based method. The refrigerant circuit with 5 mm diameter tubes was designed using a simulation-based method. To verify the results of designs, experiments on air conditioner units were carried out, which confirmed the design principle, and indicated that the air conditioner with smaller diameter tubes had a better performance and lower refrigerant charge.

Condensation heat transfer and pressure drop with propane in a minichannel, D. Del Col, S. Bortolin, M. Bortolato, L. Rossetto

Due to its flammability charge minimisation is a major design objective for HVAC equipment using hydrocarbon refrigerants. Since the estimated charge of unitary air conditioners is expected to be mainly trapped in the heat exchangers, microchannel technology appears to be a good opportunity to minimise charge without performance loss. The research presented results on the condensation heat transfer coefficients and two-phase frictional pressure drop measures with R290 in a 0.96mm diameter circular minichannel. Results show that the condensation is sheer stress dominated for most of the data points.