In vapor compression cycles, lubricating oil is needed inside the compressors. A small portion of the oil circulates with the refrigerant throughout the system components and, in the heat exchangers, the lubricant in excess penalizes the heat transfer and increases the pressure losses: both effects are undesired but yet unavoidable. Nanolubricants – that is high conductive solid nanoparticles finely dispersed in the lubricant – are a potential cost-neutral technology to increase the heat transfer performance of heat exchangers in HVAC&R applications. This paper presents an experimental study that characterizes the basic thermophysical properties of nanolubricants and that shows the heat transfer enhancement potentials for in-tube flow boiling. Three types of Al2O3 nanolubricants were investigated and all had particles with nominal diameter of approximately 40 nm but used different surfactants to stabilize the nanoparticles. The nanolubricants appeared to have slightly lower solubility than that of R-410A but actually the nanoparticles did not really interfere with the POE oil solubility characteristics. High viscosity suspensions are expected to stabilize the nanoparticles and avoid clustering. This aspect was verified in the present work and the data in this paper showed optimum combinations of surfactants that achieved stable and uniform nanolubricants. The surfactants affected slightly the thermal conductivity, specific heat, viscosity, and solubility properties of the nanolubricants and several nanofluids models for these properties were verified with the new data of the present paper. Finally this paper presents preliminary laboratory experiments for in-tube two-phase flow boiling heat transfer of nanolubricants and refrigerant R- 410A mixture and the nanoparticles dispersed in the liquid phase increased the two-phase heat transfer coefficient with respect to the case of refrigerant and lubricant mixture without any nanoparticles.
Citation: ASHRAE Papers: 2015 ASHRAE Annual Conference, Chicago, IL
Product Details
- Published:
- 2015
- Number of Pages:
- 8
- File Size:
- 1 file , 810 KB
- Product Code(s):
- D-CH-15-C007
