Heat Transfer

Heat transfer research that supports the improvement of HVAC&R equipment performance is conducted on a fundamental basis. Currently, there are several focuses in phase change heat transfer of refrigerants and refrigerant/lubricant mixtures.

The Group measures and models two-phase refrigerant/lubricant mixture heat transfer including flow boiling and pool boiling. In support of this effort, a technique was developed to measure the lubricant excess surface density using the fluorescent properties of lubricant. The measurement technique has been instrumental in the development of a semi-theoretical pool-boiling model for refrigerant/lubricant mixtures. The model can be used to select lubricants that improve the evaporator performance of chillers.

The influence of lubricants containing dispersed nanoparticles (nanolubricants) on refrigerant boiling heat transfer is studied by varying the nanoparticle size and material. Boiling heat transfer enhancements as large as 275 % have been measured with CuO nanoparticles in R134a. Research is ongoing to determine the influence of nanoparticle concentration on boiling performance.

In addition to boiling and evaporation, condensation studies are also conducted along with the evaluation of the performance of brazed-plate heat exchangers.

The Group has also measured single-phase pressure drop in various micro-channels. This research was initiated in support of the design of a DNA chip and it is anticipated that the project will develop fundamental insight that will help in the development of microfluidic devices for HVAC&R equipment and building controls.

Mark Kedzierski
HVAC&R Equipment Performance Group
(301) 975-5282
mark.kedzierski@nist.gov