Comparison of CHF measurements in R-134a cooled tubes and the water CHF look-up table

An exhaustive experimental study of the critical heat flux (CHF) in R-134a- cooled tubes has been recently completed. The objective of this study was t o provide a consistent set of CHF data to be used as a reference for future separate effect studies. The investigated range of flow parameters in R-13 4a was: outlet pressure 0.96-2.39 MPa (equivalent to 6-14 MPa in water), ma ss flux 500-3000 kg m(-2) s(-1) (equivalent to 700-4300 kg m(-2) s(-1) in w ater), and critical quality -0.1 to +0.9. To extend the range of critical q ualities, different heated lengths (0.45-2 m) and two-phase flow at inlet t o the test section were used. Scaling laws were applied to convert the stan dard CHF look-up table from water to R-134a equivalent conditions. The comp arison of the data with the water-based lookup table showed that for high m ass fluxes (G = 1400-4300 kg m(-2) s(-1) in water equivalent), the look-up table provides an excellent CHF prediction for R-134a-cooled tubes. The dif ferences were mainly noticeable for the limiting critical quality range and for low mass flux. A discussion of the observed limiting critical quality phenomenon is also included. (C) 2000 Elsevier Science Ltd. All rights rese rved.