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This paper quantifies the pool boiling performance of R134a, R1234yf, R513A, and R450A on a flattened, horizontal reentrant cavity surface. The study showed that the boiling performance of R134a on the Turbo-ESP exceeded that of the replacement refrigerants for heat fluxes greater than 20 kWm−2. On average, the heat flux for R1234yf and R513A was 16 % and 19 % less than that for R134a, respectively, for R134a heat fluxes between 20 kWm−2 and 110 kWm−2. The heat flux for R450A was on average 57 % less than that of R134a for heat fluxes between 30 kWm−2 and 110 kWm−2. A model was developed to predict both single-component and multi-component pool boiling of the test refrigerants on the Turbo-ESP surface. The model accounts for viscosity effects on bubble population and uses the Fritz (1935) equation to account for increased vapor production with increasing superheat. Both loss of available superheat and mass transfer resistance effects were modeled for the refrigerant mixtures. For most heat fluxes, the model predicted the measured superheat to within ± 0.31 K.

Although metal−phenolic species have emerged as one of the versatile material-independent-coating materials, providing attractive tools for interface engineering, mechanistic understanding of their film formation and growth still remains largely unexplored. Especially, the anions have been overlooked despite their high concentration in the coating solution. Considering that the anions are critical in the reactivity of metal−organic complex and the formation and/or property of functional materials, we investigated the anionic effects on the characteristics of film formation, such as film thickness and properties, in the Fe 3+ −tannic acid coating. We found that the film characteristics were strongly dictated by the counteranions (e.g., SO 4 2− , Cl − , and Br − ) of the Fe 3+ ion. Specifically, the film thickness and properties (i.e., mechanical modulus, permeability, and stability) followed the reversed anionic Hofmeister series (Br − > Cl − > SO 4 2− ). Mechanistic studies suggested that more chaotropic anions, such as Br − , might induce a more widely extended structure of the Fe 3+ −TA complexes in the coating solution, leading to thicker, harder, but more porous films. The reversed anionic Hofmeister effect was further confirmed by the additive effects of various sodium salts (NaF, NaCl, NaBr, and NaClO 4 ).

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In this study, condensation heat transfer coefficients (HTCs) of HCFC22, HCFC123, HFC134a and HFC245fa are measured on a horizontal plain tube 19.0 mm outside diameter. All data are taken at the vapor temperature of 39 with a wall subcooling temperature 3-8 . Test results show the HTCs of newly developed alternative low vapor pressure refrigerant, HFC245fa, on a smooth tube are 9.5% higher than those of HCFC123 while they are 3.3% and 5.6% lower than those of HFC134a and HCFC22 respectively. Nusselt's prediction equation for a smooth tube underpredicts the measured data by 13.7% for all refrigerants while a modified equation yielded 5.9% deviation against all measured data. From the view point of environmental safety and condensation heat transfer, HFC245fa is a long term good candidate to replace HCFC123 used in centrifugal chillers.

This paper presents local convective boiling heat transfer and Fanning friction factor measurements in a micro-fin tube for R134a and two possible low global warming potential (GWP) refrigerant replacements for R134a, namely R1234yf and R450A. Test section heating was achieved with water in either counterflow or in parallel flow with the test refrigerant to provide for a range of heat fluxes for each thermodynamic quality. An existing correlation from the literature for single and multi-component mixtures was shown to not satisfactorily predict the convective boiling measurements for flow qualities greater than 40%. Accordingly, a new correlation was developed specifically for the test fluids of this study so that a fair comparison of the heat transfer performance of the low GWP refrigerants to that of R134a could be made. The new correlation was used to compare the heat transfer coefficient of the three test fluids at the same heat flux, saturated refrigerant temperature, and refrigerant mass flux. The resulting example comparison, for the same operating conditions, showed that the heat transfer coefficient of the multi-component R450A and the single-component R1234yf were, on average, 15% less and 5% less, respectively, than that of the single-component R134a. Friction factor measurements were also compared to predictions from an existing correlation. A new correlation for the friction factor was developed to provide a more accurate prediction. The measurements and the new models are important for the evaluation of potential low-GWP refrigerants replacements for R134a.

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This article presents local convective boiling measurements in a micro-fin tube for three low global warming potential refrigerants: R448A, R449A, and R452B1. An existing correlation was modified to predict multi-component mixtures, which predicted 98% of the measurements to within ±20%. The new correlation was used to compare the heat transfer coefficient of the three test fluids at the same heat flux, saturated refrigerant temperature, and refrigerant mass flux. The resulting comparison showed that refrigerant R452B exhibited the highest heat transfer, in large part due to its approximately 28% larger liquid thermal conductivity and smaller temperature glide as compared to the tested low-global warming potential refrigerants. For the example case, the heat transfer coefficient for R449A was approximately 8% larger than that for R448A, while the heat transfer coefficient for R452B was more than 59% larger than either R448A or R449A. The heat transfer coefficients for R448A and R449A were roughly between 26 and 48% less than that of R404A for the example case. In contrast, the model predicts that the R452B heat transfer coefficient was approximately 13% larger than that of R404A for the same conditions.