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International Symposium on Heat and Mass Transfer in Refrigeration and Cryogenics
September, 1-5, 1986, Dubrovnik, Yugoslavia

DOI: 10.1615/ICHMT.1986.IntSympHMTinRefCryo


ISBN Print: 978-3-54017-957-3

Heat Transfer at Pool Boiling of Mixtures with R 22 and R 115

pages 243-257
DOI: 10.1615/ICHMT.1986.IntSympHMTinRefCryo.170
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SINOPSIS

The calculation of the heat transfer coefficient a with pool boiling of pure liquids has been improved substantially during the last decade, especially referring to the important parameters heat flux q and saturation pressure Ps. With binary mixtures, the situation is not so favourable, mainly because of the influence of the composition on the dependency of α from q and ps, and because of the lack of experimental data on combined measurements of heat transfer and phase equilibrium in literature. Above all, this holds for the range of higher saturation pressures and for systems forming azeotropic compositions.
Many investigations of pool boiling heat transfer with binary mixtures at pressures near atmospheric exist in literature, but much less are known at higher saturation pressures (cf.e.g./1/, /2/, /3/). Recently, Bier et al. reported on experimental investigations with three different nonazeotropic binary systems at pressures up to critical, the measurements extending over the entire concentration range and over a wide range of the heat flux /4/, /5/. In conjunction with these experiments, Schlunder developed a correlating method for the prediction of the combined influences of concentration, saturation pressure and heat flux /6/.
In this paper, measurements of the phase equilibrium and of the heat transfer coefficient a at pool boiling,corresponding to those in /4/, /5/, are discussed for the system R22 (CHF2Cl) - R115 (C2F5Cl), which forms azeotropic compositions. In addition to the pure components, seven mixtures with different compositions were investigated. The saturation pressure varied between approx. 3 and 50 bar, that means between the critical pressure of each mixture and approx. 7 per cent of this pressure; the corresponding saturation temperatures are −12°C and +96°C. Seven normalized saturation pressures between 93 per cent and 10 per cent of the critical pressure were chosen for the heat transfer measurements. The experimental results are compared with correlating techniques for the critical points of mixtures /7/ and for the heat transfer coefficient /6/, /8/.

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