Pressure Drop During Refrigerant Condensation Inside Horizontal Smooth, Helical Microfin, and Herringbone Microfin Tubes (original) (raw)
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A flow regime map for refrigerant condensation in herringbone micro-fin tubes (Part II).
Experiments were conducted with refrigerants R-22, R-134a and R-407C. Their thermodynamic properties were obtained from a reference database. 19 In these experiments, mass fluxes varied between 300 and 800 kg m -2 s -1 ; pressures between 1500 kPa and 1800 kPa; saturation temperatures between 39°C and 41°C; inlet vapour qualities between 0.85 and 0.98; and outlet vapour qualities between 0.02 and 0.15. Data were captured only once energy balance errors were below 1%. Uncertainties in the experimental work, which were calculated by Coetzee 20 and re-evaluated on the basis of present experimental results, 13 are presented in .
This work presents a detailed characterization study of two-phase condensing flows of two refrigerants, R134a and R-245fa, in a single water-cooled micro-channel with a 0.4 mm x 2.8 mm cross-section (0.7 mm hydraulic diameter and 7:1 aspect ratio) and length of 190 mm. A single micro-channel was chosen for the study to eliminate flow mal-distribution issues commonly encountered in micro-channel banks. The experiments included a parametric study of the effects on average heat transfer coefficient and overall pressure drop of variations across the micro-channel condenser with mass fluxes between 50 and 500 kg/m 2 s, saturation temperatures between 30ºC and 70ºC, and inlet super heats between 0ºC and 20ºC. The inlet state was kept either at 100% quality or superheat and the outlet condition at 0% quality; these calculations were based on water-side heat rejection. Careful design and instrumentation of the test setup resulted in energy balance uncertainty within +/-11% and uncertainty of average heat transfer coefficient within +/-12%. It was determined that inlet superheat has little effect on heat transfer coefficient and overall pressure drop, but that the corresponding effects of saturation temperature and mass flux are significant.
Horizontal Convective Condensation of Alternative Refrigerants Within a Micro-Fin Tube
Journal of Enhanced Heat Transfer, 1999
This paper presents local convective condensation measurements for four refrigerants: R134a, R410A(R32/R125, 50/50 % mass), R125, and R32 in a micro-fm tube^Both heat transfer and pressure drop measurements are provided. The heat transfer degradation associated with R410A was shown to be relatively small and believed to be mostly due to nonlinear property effects. The measured convective condensation Nusselt numbers for all of the test refrigerants were correlated to a single expression consisting of a product of dimensionless properties. The correlation was shown to predict some existing data from the literature within acceptable limits. The correlation poorly predicted the heat transfer performance of cross-grooved, micro-fm tubes. The pressure drop measurements for the micro-fm mbe were predicted satisfactorily by an existing correlation for flow boiling pressure drop in a smooth mbe. Correlation of the pressure drop measurements suggested that the heat transfer enhancement was due to the fins behaving as a surface roughness.
1999
This paper presents a pressure drop correlation for evaporation and condensation in smooth and micro-fin tubes for lubricant-free refrigerants and refi-igerantllubricant mixtures. The form of the generalized correlation was taken from the Pierre pressure drop model. NIST micro-fin tube pressure drop data for R134a, R22, R125, R32, R407C, R41OA, and R32R134a (25175 % mass) were regressed to a modified Pierre correlation. The NIST database was post-predicted with an average absolute residual of 10.8 %. Further validations performed with extensive data from the literature for lubricant-free refhgerants in smooth and micro-fin tubes showed an average absolute residual between measurements and predictions not to exceed 17.6 % for the various data sets. The condensation and evaporation pressure drops for different refrigerantllubricant mixtures were predicted with average absolute residuals not exceeding 19.6 % and 28.0 %, respectively.
2006
This paper deals with the condensation heat transfer and pressure drop of pure refrigerant in micro-fin tubes. The correlations for heat transfer and frictional pressure drop are proposed using experimental data for 11 micro-fin tubes with different fin dimensions, where test refrigerants were pure refrigerants R22, R123 and R134a. The proposed correlations are developed based on the correlation for void fraction micro-fin tube and the correlation for pressure drop of single phase flow in micro-fin tube. The predicted results show good agreement with experimental results within the deviation of about 30 % for both condensation heat transfer and pressure drop. Experimental results were also compared with previous correlations proposed for micro-fin tube.
This thesis presents a detailed study of parametric characterization of two-phase condensing flow of two selected refrigerants R134a and R-245fa in a single water-cooled micro-channel of 0.4 mm X 2.8 mm cross-section (0.7 mm hydraulic diameter and 7:1 aspect ratio) and 190 mm in length. To avoid flow mal-distribution associated with typical micro-channel tube banks, a single micro-channel was fabricated utilizing an innovative approach and used for the present study experiments. The study investigated the effects of variations in saturation temperature ranging from 30 o C to 70 o C, mass flux from 50 to 500 kg/m 2 s, and inlet super heat from 0 o C to 15 o C on the average heat transfer and overall pressure drop coefficient of the micro-channel condenser. In all cases the inlet vapor quality was kept at 100% quality (saturated vapor) and the outlet condition was always kept at 0% quality (saturated liquid). Accuracy of the fabricated channel geometry with careful design
In the present study the local condensation heat transfer characteristics in a horizontal microfin tube are found to be about 2 times higher than those of a smooth tube with the same inner diameter. This enhancement effect on heat transfer coefficient seems mainly caused by the enlargement ratio of heat transfer area. From this point of view, a correlation, which is modified from the correlation of Haraguchi et al. for smooth tubes, is developed for the condensation heat transfer in microfm tubes with pure refrigerants. With this correlation, the condensation heat transfer characteristics in some kinds of microfin tubes can be predicted very well.