A calibrated thermochromic liquid crystal technique was used to acquire wall temperature data for laminar and turbulent forced convection in an asymmetrically heated channel. The experiments were carried out in upward flow in rectangular channels with channels spacings of 2.0, 1.0, and 0.5 mm and aspect ratios of 1:10, 1:20, and 1:40. One side was uniformly heated, and the remaining sides were approximately adiabatic. The entire surface temperature field of the heated wall was acquired in one color image, and the temperature was determined by hue-based image processing. In the laminar regime, buoyancy effects elevated the local Nusselt number to values significantly above those expected for purely forced convection in both the developing region and in the fully developed region. In the turbulent regime, the fully developed Nusselt number agreed well with previous observations, but the facility produced an unexplained linear trend in a portion of the developing region of the channel. While the channel aspect ratio affected the fully developed Nusselt number, no evidence was found that small channel spacing in itself produces Nusselt numbers that are at variance with accepted values.

Issue Section:
Forced Convection
Keywords:
Channel Flow, Heat Transfer, Laminar, Mixed Convection, Turbulent, forced convection, laminar flow, turbulence, channel flow, entropy, liquid crystal devices, temperature measurement, image processing
Topics:
Flow (Dynamics), Temperature, Turbulence, Liquid crystals, Laminar flow, Forced convection, Convection, Fluids, Heat transfer, Temperature measurement, Buoyancy
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