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ISSN Online: 2377-424X

ISBN Print: 0-89116-559-2

International Heat Transfer Conference 8
August, 17-22, 1986, San Francisco, USA

POST-DRYOUT HEAT TRANSFER TO R12 IN A CIRCULAR 90-DEG-TUBE-BENDS

Get access (open in a dialog) DOI: 10.1615/IHTC8.4770
pages 2373-2378

Abstract

A study of post-dryout heat transfer to Freon 12 in an electrically heated circular 90-degree-tube-bend is reported. Experimental results at different mass flux densities (400 - 2000 kg/m2s), critical pressure ratios (0.225 - 0.675) and heat flux densities (2-8 W/cm2) are presented. When dispersed flow enters a bend separation of liquid from vapour phase occurs due to different inertial forces which leads to an increase in heat transfer at the outer and a decrease at the inner wall of the bend. The traverse motion of the droplets towards the outer wall mainly depends on drop size, velocity and density ratio of the two phases at the bend inlet. Rewetting of the outer wall is improved by decreasing pressure ratios and increasing mass flux densities. Due to a circumferential secondary flow induced by the centrifugal force and superimposed on the main flow, heat transfer at the inner side of the bend strongly depends on the conditions at the outer side. Therefore after an axial distance heat transfer at the inner side is improved, too and in some cases even rewetting can be observed.