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DOI: 10.1615/ICHMT.2000.TherSieProcVol2.610
143 pages

Rade Milenkovic
Department of Thermomechanics, University of Belgrade, Faculty of Mechanical Engineering, 27 Marta, 80, 11000 Belgrade, Yugoslavia

Bogosav Vasijevic
Department of Thermomechanics, University of Belgrade, Faculty of Mechanical Engineering, 27 Marta, 80, 11000 Belgrade, Yugoslavia


This paper presents the results of an experimental investigation of convective heat transfer, friction factor and also overall heat transfer coefficient of double pipe heat exchanger with wire-coil insert for following geometricaI characteristics: helical pitch 14 mm, wire diameter 1 mm and helical angle 60 °C.
The test were conducted on a two concentric double- pipe heat - exchangers of counter-flow type, constructed with copper tubes 26 mm and 16 mm inner diameter. The heat exchangers were instrumented for measurement of a bulk fluid temperatures and wall temperatures for computerized data- acquisition and data-processing. All temperatures were measured using iron-constantan ("Omega Engineering, INC.", J-type, 1SO 9001) thermocouples. Voltage (dc) output from thermocouples was directly fed into the data-acquisition system HP3421A and computer HP35731B. The fluid flow rates were estimated by measuring fluid pressure drop along short copper tube 10 mm inner diameter, with U-tube manometer. Fluid pressure drop along test sections were measured by U-tube manometer.
Measurements were obtained to determine the convective heat transfer coefficient at the inside surface of the inner pipe and also in an annular sections, overall heat transfer coefficient and fluid friction factor.
Results of convective heat transfer coefficient along with the friction factor are presented for forced convection transient and turbulent flow over a range of Reynolds number Re=2300÷20000. The results indicate, that wire-coil inserts can increase overall heat transfer coefficient significantly in the case when Reynolds number is lower than 10000.
The improvement of the heat transfer coefficient is about 80 % in the case of Re<10000. The improvement of the overall heat transfer coefficient is about 40 % in the case Re< 10000 and about 20% when Re=10000-20000.
The friction factor is about seven-fold increase over that for empty heat exchanger. These inserts can be used in the cases when the size of heat exchanger can not be changed and when high fluid pressure drop is tolerable.

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