Experimental investigation of heat transfer from a horizontal flat surface to aqueous foam flow

Due to the dimple’s unique characteristics of comparatively low pressure loss penalty and good heat transfer enhancement performance, dimple provides a very desirable alternative internal cooling technique for gas turbine blades. In the present study, an experimental investigation was conducted to quantify the flow characteristics over staggered dimple arrays and to examine the vortex structures inside the dimples. In addition to the surface pressure measurements, a high-resolution digital Particle Image Velocimetry (PIV) system was also utilized to achieve detailed flow field measurements to quantify the characteristics of the turbulent channel flow over the dimple arrays in terms of the ensemble-averaged velocity, Reynolds shear stress and turbulence kinetic energy (TKE) distributions. The experimental measurement results show that the friction factor of the dimpled surface is much higher than that of a flat surface. The measured pressure distribution within a dimple reveals clearly that flow separation and attachment would occur inside each dimple. In comparison with those of a conventional channel flow with flat surface, the channel flow over the dimpled arrays was found to have much stronger Reynolds stress and higher TKE level. Such unique flow characteristics are believed to be the reasons why a dimpled surface would have a better heat transfer enhancement performance for internal cooling of turbine blades as reported in those previous studies.

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Different Type Tube Bundle Heat Transfer to Vertical Foam Flow

ASME 5th International Conference on Nanochannels, Microchannels, and Minichannels ◽

10.1115/icnmm2007-30070 ◽

2007 ◽

Author(s):

Jonas Gylys ◽

Stasys Sinkunas ◽

Tadas Zdankus ◽

Vidmantas Giedraitis

Keyword(s):

Heat Transfer ◽

Experimental Investigation ◽

Flow Velocity ◽

Void Fraction ◽

Tube Bundle ◽

Auxiliary Equipment ◽

Foam Flow ◽

Flow Parameters ◽

Tube Bundles ◽

Foam Generator

Gas-liquid foam due to especially large inter-phase contact surface can be used as a coolant. An experimental investigation of the staggered and in-line tube bundles’ heat transfer to the vertically upward and downward laminar foam flow was performed. The experimental setup consisted of the foam generator, vertical experimental channel, tube bundles, measurement instrumentation and auxiliary equipment. It was determined dependency of heat transfer intensity on flow parameters: flow velocity, direction of flow, volumetric void fraction of foam and liquid drainage from foam. Apart of this, influence of tube position in the bundle to heat transfer was investigated. Foam flow structure, distribution of the foam’s local void fraction and flow velocity in cross-section of the channel were the main factors which influenced on heat transfer intensity of the different tubes. Experimental investigation showed that the heat transfer intensity of the frontal and further tubes of the bundles to vertical foam flow is different in comparison with one-phase fluid flow. The results of the experimental investigation are presented in this paper.

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