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International Heat Transfer Conference 13

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

TURBULENT THERMAL MIXING OF HOT AND COLD AIRFLOWS IN T-JUNCTION

DOI: 10.1615/IHTC13.p1.110
12 pages

Masafumi Hirota
Department of Micro-Nano Systems Engineering, Nagoya University, Chikusa-ku, Nagoya 464-8603; Department of Mechanical Engineering, Mie University, Kurimamachiya-cho 1577, Tsu-city 514-850

H. Asano
Nagoya University, Nagoya; and Air-Conditioning Testing and Evaluation Department, DENSO CORPORATION, Showa-cho, Kariya 448-8661

H. Nakayama
Fuel Cell Laboratory, Daido Institute of Technology, Minami-ku, Nagoya 457-8530, Japan

T. Asano
Denso Corporation, Kariya, Japan

H. Goto
Nagoya University; Nagoya Aerospace Systems Works, Mitsubishi Heavy Industry

S. Hirayama
Air-Conditioning Testing and Evaluation Department, DENSO CORPORATION, Showa-cho, Kariya 448-8661, Japan

Abstract

In this paper, experimental results are reported on turbulent thermal mixing of hot and cold airflows in a T-junction with rectangular cross sections, which simulates the mixing region in the HVAC (Heating, Ventilating, Air-Conditioning) unit for automobile air-conditioning system. The cross-sectional aspect ratio of the main channel was 2, and the width of the branch was the same as that of the main channel. The Reynolds number and temperature of the main-channel flow were kept at 2.5×104 and 12 °C, respectively, and the velocity of the branching-channel flow (60 °C) was changed so as to make two velocity ratios of 0.5 and 1. The flow characteristics and the mean temperature distributions were measured by PIV and a thermocouple rake, respectively. Moreover, simultaneous measurements of fluctuating velocity and fluctuating temperature were conducted using LDV and cold-wire thermometer to elucidate the distributions of the turbulent heat fluxes. The flow entering the main channel from the branch is separated at the edge of the T-junction and forms a large separation bubble. Longitudinal vortices are formed around this separation bubble, thus the flow field shows a complex three-dimensional feature. In spite of such a 3-D flow structure, the local temperature of the mixed flow shows quite uniform distributions in the spanwise direction of the channel. The turbulent heat flux attains the maximum in the center of the thermal mixing layer, while the turbulent shear stress shows large values around the separation bubble that is located below the mixing layer. This dissimilarity causes the failure of the turbulent Prandtl number model for turbulent heat fluxes, and it also suggests that the high turbulence produced around the separation bubble does not contribute effectively to the turbulent heat transport between the hot and cold airflows.

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Measurement of fluid temperature with an arrangement of three thermocouples