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Force analysisi for isolated bubbles growing from smooth and evaporator tubes

Chen Y., Groll M., Mertz R., Kulenovic R.

Transactions of the Institute of Fluid-Flow Machinery

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2003

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nr 112

57--74

EN

Various forces acting on a bubble growing on a horizontal smooth and enhanced tube have been evaluated by using the measured geometric bubble data. Great effort has been made to accurately evaluate the dynamic forces. It has been shown that the dynamic forces play a more important role in the bubble growth on an enhanced surface than on a smooth surface. A correlation for predicting the bubble departure diameter from an enhanced tube has been derived from the force balance. This correlation has a form similar to that commonly used for smooth tubes while baring a different physical meaning.

2

Experimental investigation of flow boiling in vertical microchannels

Shuai J., Kulenovic R., Mertz R., Groll M.

Archives of Thermodynamics

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2002

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Vol. 23, no 4

39-48

EN

Flow boiling heat transfer in micro-scale vertical channels is attracting increasing attention with the progressing miniaturization in many industrial fields, e.g. electronics, chemical engineering, etc. Experiments have been conducted to investigate the heat transfer and flow boiling phenomena in microchannels (rectangular channels with 2 mm x 4 mm and 0.5 mm x 2.0 mm (width x height). The working fluid is deionized water. The flow rate is 200--700 kg/(m'2s) at atmospheric pressure. With the aid of video camera, flow boiling phenomena are observed as well. Three flow patterns, i.e. bubbly flow, slug flow and annular flow, could be distinguished. Features of pressure drop fluctuations between the inlet and outlet of the test section are also presented.

3

Experimental investigation of boiling phenomena in a debris bed

Schafer P., Steiner D., Kulenovic R., Groll M.

Archives of Thermodynamics

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2002

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Vol. 23, no 4

29-38

EN

An experimental investigation of boiling phenomena in an inductively heated cylindrical debris bed (height 640 mm, diameter 125 mm, 6 mm resp. 3 mm stainless stel balls) has been performed. Boiling experiments (bottom- and top-fed) as well as dryout experiments have been carried out under atmospheric pressure. The pressure gradients inside the bed and the dryout heat flux have been determined. The experimental data of the pressure gradient show reasonable agreement with simulation data of IKE's WABE code, in which various interfacial drag models have been considered and compared.