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International Heat Transfer Conference 15

ISSN: 2377-424X (online)
ISSN: 2377-4371 (flashdrive)

Heat Transfer Characteristics in Forced Convection Through a Rectangular Channel with V-Shaped Rib Roughened Surfaces

Damiano Fustinoni
Politecnico di Milano, Department of Energy, Campus Bovisa, Via Lambruschini 4, 20156 Milano, Italy

Pasqualino Gramazio
Politecnico di Milano, Department of Energy, Campus Bovisa, Via Lambruschini 4, 20156 Milano, Italy

Luigi Pietro Maria Colombo
Politecnico di Milano, Department of Energy, Campus Bovisa

Alfonso Niro
Department of Energy, Politecnico di Milano, Via Lambruschini 4, Milano IT−20156, Italy

DOI: 10.1615/IHTC15.hte.009262
pages 4065-4072


KEY WORDS: Heat transfer enhancement, Heat exchanger, V-shaped rib, k-rougheness

Abstract

In this paper we present experimental results for a channel with the lower and upper surfaces with V-shaped ribs pointing upward. The duct cross-section is 120-mm wide and 12-mm height, and the channel is operated with the lower and upper walls at fixed temperature whereas sides are adiabatic. The ribs have square cross section of 2 mm in side, a V-apex angle of 60°, and three pitch-to-side ratios (10, 20, 40); finally, they are in-line arranged on the two walls. Air flow-rates have been varied in order to investigate Reynolds numbers, based on the duct hydraulic diameter, between 700 and 7500. Data in a similar channel but with flat surfaces have been collected for comparison as well. The data show that the flow regime seems to be turbulent even at the lowest tested value of Re; the friction factor displays the typical trend for k-roughened surfaces, i.e., it becomes of Re for sufficiently high values of Re. The dependence of the Nusselt number on the Reynolds number and the pitch-to-side ratio is presented in the form of a power law correlation. Various figures of performance have been evaluated, showing that for Re>1300 the adoption of the ribbed surface is always advantageous and allows a maximum heat transfer enhancement factor between 2.5 and 4, decreasing with the pitch-to-side ratio.

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