Christian J.L. Hermes

An improved correlation for two-phase pressure drop of R-22 and R-410A in 180° return bends

A correlation for two-phase flow pressure drop in 180° return bends is proposed based on a total of 241 experimental data points for R-22 and R-410A from two independent studies. The data span smooth tubes with inner diameters (D) from 3.3 mm to 11.6 mm, bend radiuses (R) from 6.4 mm to 37.3 mm, and curvature ratios (2R/D) from 2.3 to 8.2. The correlation consists of a two-phase pressure drop for straight-tubes and a multiplier that accounts for the bend curvature. The Buckinham-PI Theorem was used to formulate the curvature multiplier in terms of refrigerant properties, flow characteristics, and bend geometry. The correlation predicts all data with a RMS deviation of 25%, and 75% of the data fall within ±25% error bands.

Experimental mapping of the thermodynamic losses in vapor compression refrigeration systems

The present study introduces a methodology for mapping the thermodynamic losses of vapor compression refrigeration systems which consists of a theoretical model that splits the coefficient of performance into four terms: (i) the coefficient of performance of an ideal cycle (Carnot), (ii) the efficiency of a real cycle running with an ideal compressor, (iii) the compression efficiency of a real compressor, and (iv) the cycling efficiency. In addition, measurements of the relevant variables at several positions along the refrigeration loop are also required, generating performance data not only for the whole unit but also for each one of the system components. The proposed methodology points out the thermodynamic losses of the refrigeration system, identifying opportunities for energy performance improvement. In addition, the methodology is suitable for comparing different refrigeration systems with respect to the same thermodynamic baseline. Albeit the methodology was originally developed for household refrigerators, it can be easily extended to any kind of vapor-compression refrigeration systems.