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A Sensitivity Study of the Refrigerant Property Uncertainties on the Vapor Compression Cycle

DOI: 10.1615/ICHMT.1986.IntSympHMTinRefCryo.270
pages 369-380

Piotr A. Domanski
National Bureau of Standards Gaithersburg, Maryland, USA

David A. Didion
Building and Fire Research Laboratory, National Institute of Standards and Technology, Gaithersburg, MD, 20899, USA


Over the past decade, there has been considerable attention devoted to the performance of refrigeration systems in both simulation model studies and laboratory measurement studies. The accuracy of these studies tacitly depends on knowledge of the various refrigerant thermodynamic and transport properties as well as other flow parameters. The uncertainty with which the property values are known is primarily a function of the state-of-the-art accuracy of the particular property measurement technique. In the case of refrigerant mixtures, there exists very little measured data, and it is therefore necessary to employ mixing rules along with component data. This can increase significantly the uncertainty. For example, vapor density can be evaluated quite well and usually is known within 2% uncertainty [1]; on the other hand, the specific volume of a liquid mixture may have an uncertainty of as much as 100% if it is evaluated by a mixing rule in the neighborhood of critical temperature of the lower boiling component [2]. In the case of evaporative heat transfer coefficients, the actual mixture value has been shown to be as much as 40% lower than that predicted by the ideal mixture weighting factor method [3].
The different refrigerant property and flow parameters affect the system performance with varying degrees of sensitivity. It is therefore necessary to establish the system sensitivity to each property value if the most effective information is to be obtained. Of course, accurate knowledge of refrigerant properties does not change the way the real system operates. However, the qualitative knowledge of the impact made by properties on performance on one by one basis, is desirable because it can establish the limits of uncertainty associated with simulation of refrigerant system. This in turn, will indicate the areas most in need of further research on prediction and measurement methods for refrigerants and refrigerant mixtures.

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