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CFD simulation of DEBORA boiling experiments

Rzehak R., Krepper E.

Archives of Thermodynamics

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2012

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Vol. 33, no. 1

107-122

EN

In this work we investigate the present capabilities of computational fluid dynamics for wall boiling. The computational model used combines the Euler/Euler two-phase flow description with heat flux partitioning. This kind of modeling was previously applied to boiling water under high pressure conditions relevant to nuclear power systems. Similar conditions in terms of the relevant non-dimensional numbers have been realized in the DEBORA tests using dichlorodifluoromethane (R12) as the working fluid. This facilitated measurements of radial profiles for gas volume fraction, gas velocity, bubble size and liquid temperature as well as axial profiles of wall temperature. After reviewing the theoretical and experimental basis of correlations used in the ANSYS CFX model used for the calculations, we give a careful assessment of the necessary recalibrations to describe the DEBORA tests. The basic CFX model is validated by a detailed comparison to the experimental data for two selected test ca cases. Simulations with a single set of calibrated parameters are found to give reasonable quantitative agreement with the data for several tests within a certain range of conditions and reproduce the observed tendencies correctly. Several model refinements are then presented each of which is designed to improve one of the remaining deviations between simulation and measurements. Specifically we consider a homogeneous MUSIG model for the bubble size, modified bubble forces, a wall function for turbulent boiling flow and a partial slip boundary condition for the liquid phase. Finally, needs for further model developments are identified and promising directions discussed.

2

Experimental and numerical investigation of one and two-phase natural convection

Krepper E., Prasser H.M.

Zeszyty Naukowe Politechniki Świętokrzyskiej. Mechanika

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2003

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Z. 77

33-39

EN

Experiments were performed to investigate heating up processes of fluids in storage tanks under the influence of an external heat sourec. Several teste were carried out both with heating from the bottom an with heating from the side walls. The test tank was equipped with thermocouples for measuring the temperature distriburion and with needle probes for measuring of the local void fraction.

3

Evolution of flow patterns, gas fraction profiles and bubble size distributions in gas-liquid flows in vertical tubes

Lucas D., Krepper E., Prasser H. M.

Transactions of the Institute of Fluid-Flow Machinery

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2003

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nr 112

37-46

EN

Air-water flow at ambient conditions in a vertical pipe an inner diameter of 51.2 mm is investigated. An electrode wire-mesh sensor enables the measurement of the phase distribution with a very high resolution in space and in time. Local bubble size distributions are calculated from the data. The measurements were done in distances from the gas injection device. As a result, the development of bubble size distributions as well as the development of the radial gas fraction profiles can be studiet. It was found, that the bubble size distribution as well as local effects determine the transistion from bubble flow. The data are used for the development of a model, which predicts the development of the bubble size distribution and the transition from bubble flow in the case of stationary flow in a vertical pipe.