2013 1(12)

HEAT TRANSFER AND AERODYNAMIC OF SINGLE TUBES OF FLAT-OVAL PROFILE

Kondratyuk V.A.¹, Semenyako A.V.¹, Terekh A.M.¹, Rudenko A.I.¹, Zhukova Yu.V.²

¹ National Technical University of Ukraine “Kyiv Polytechnic Institute”, Kiev, Ukraine
² A.V.Luikov Heat and Mass Transfer Institute of NAS of Belarus, Minsk, Belarus

Introduction

Cross-flow cylindrical heat transfer surfaces are widespread in modern different-purpose energy generation plants. Round, elliptical, and sometimes flat-oval tubes find use in recuperative heat exchange equipment. Up to now, flat-oval tubes are poorly understood. There are no reliable relations for calculation of heat transfer and drag both of single tubes and of tube bundles. Therefore, from practical and scientific terms, the investigation of heat transfer and drag of flat-oval tube is still actual at present.

Purpose

The purpose of that work is experimental investigation of heat transfer and aerodynamic drag of flat-oval tubes with different relative tube diameter ratio.

Method

The paper presents the experimental investigation on convective heat transfer and drag of single round and flat-oval tubes over the range of the relative tube diameter ratio d2/d1 from 1 (round tube) to 2.625. Experiments were made in the rectangular open-type wind tunnel over the range of the Reynolds number from 3000 to 25000. The turbulence degree, Tu, of the incoming flow was (3.5-4) % and the tube length-to-diameter ratio – h/d = 3.5. Use was made both of the method for electric heating of the test surface, according to which constant heat flux conditions were set on the inner tube surface, and of the method for regular cooling of simple-configuration tubes (for a round tube with d = 16 mm), according to which the conditions tw = const  were provided.

Results

The analysis of the data obtained is indicative of the fact that heat transfer of round tubes is, on the average, by (16-35) % higher than that of flat-oval ones depending on d2/d1. Drag of single flat-oval tube is by a factor of 1.8-2 less as against that of single round one. For the first time in the Ukraine, the generalized empirical relations are obtained for determination of heat transfer coefficient and drag of single flat-oval tubes that take into account the influence of the relative profile extension on heat transfer and drag

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