[en] Application of the macrolayer dryout model has been performed to predict CHF at inclined plates. For the identification of the detachment frequency of coalesced bubble, experiments have been performed with high-speed motion analyzer and bubble behaviors at inclined plates have been investigated. Based on the observed bubble behaviors, the detachment frequency of the coalesced bubble is measured and linear relations between detachment frequency and heat flux have been developed. In the case of 60 .deg. and 90 .deg. inclined plate, the detachment frequency decreases with the increase of heat flux. However, opposite trend has been identified in 30 .deg. inclined plate: the detachment frequency increases with the increase of heat flux. Using the correlation of macrolayer thickness suggested by Haramura and Katto and the extrapolation of the identified linear relations, CHFs at different conditions have been predicted. According to the prediction results, CHF values are well predictable

[en] The results from several experiments on the heat transport behavior of He II above the critical heat flux are reported. Very different behavior are observed to occur dependent on whether the experiment is performed in saturated or subcooled helium and whether the helium is static or forced flow. In vertically oriented channel experiments, the heat transport in saturated He II is enhanced by exceeding the critical heat flux an effect brought on by the bulk boiling. In subcooled helium above the critical heat flux, a large increase in the liquid helium temperature occurs with associated formation of liquid He I. These results are discussed in terms of the effective cooling of superconducting magnets subjected to large thermal disturbances

[en] An experimental study on the critical heat flux (CHF) has been performed for water flow in non-uniformly heated vertical annulus under low flow and a wide range of pressure conditions. The objectives of this study are to investigate systematically the parametric trends of the CHF under low flow and a wide range of pressure conditions, and to identify the effect of the axial heat flux distribution on the CHF. The experiment has been performed in the following conditions: pressure of 0.57∼ 15 MPa, mass flux of 200 ∼ 650 kg/m²s, inlet subcooling of 85 ∼ 353 kJ/kg. Most of the CHFs are occurred in the annular flow pattern, thus the possible CHF mechanism is thought to be the liquid film dryout in annular flow regime. The parametric trends of the critical power at CHF condition are generally consistent with previous understandings for uniform heat flux distributions. The effect of the heat flux distribution is large at low pressure conditions, but the effect becomes small as the system pressure increases

[en] A phenomenologically based correction factor has been proposed for the prediction of CHF in a channel with nonuniform axial heat flux profiles. The basic formulation of the correction factor was devised on the basis of the vapor removal limit and bubble crowding model proposed by Weisman and Pei. It reveals that the thickness, mass velocity, and the enthalpy gradient in the bubbly layer are the key parameters representing influence of flux-non-uniformity on CHF. The proposed correction factor contains only one empirical constant. In the aspects of prediction accuracy and parametric trend, the proposed model revealed a performance as good as existing correction method such as Tong's F-factor. For further validation of the proposed model, it is needed to examine various axial heat flux profiles including multiple-peaked conditions

[en] In order to attain a better understanding of the CHF phenomena, parameteric trends of CHF are investigated using existing experimental data in pool boiling. The CHF is very sensitive to the change of several parameters and can be affected by the influences of fluid sides as well as by the influences of heater side and fluid-heater interface. Also the CHF can be affected by interactions among various parameters. In relation with the mechanism of CHF in different boiling conditions, all of the CHF data show smooth trends and approach an asymptotic value. It seems to support that the basic mechanism of the CHF is same even though the boiling conditions are different

[en] The experiments were carried out for a horizontal pool boiling of saturated water using a transparent ITO heating surface. Details of boiling structure near the heated surface have been clearly observed by applying the total reflection and diagonal view techniques in a synchronized manner. Mechanisms for the bubble coalescence and dry area expansion processes were clearly identified. The base of the large massive bubble was mostly dry with some trapped liquid. The appearance of this large dry area at high heat flux close to CHF was basically resulted from the multiple steps of bubble coalescences which occur while the bubbles are growing, attached to the boiling surface not before they depart from the boiling surface. The thin liquid layer with distributed vapor stems was not observed under the large massive bubble. (author)

[en] The prediction of critical heat flux (CHF) in rod bundles of light water reactors is basically performed with the aid of empirical correlations derived from experimental data.Many CHF correlations have been proposed and are widely used in the analysis of the thermal margin during normal operation, transient, and accident conditions.Correlations found in the open literature are not sufficiently verified for the thermal hydraulic conditions that appear in the CAREM core under normal operation: high pressure, low flow, and low qualities.To compensate this deficiency, an experimental investigation on CHF in such thermal-hydraulic conditions was carried out.The experiments have been performed in the Institute of Physics and Power Engineering of Russian Federation.A short description of facilities, details of the experimental program and some preliminary results obtained are presented in this work

[en] The experimental data on critical flow, heat transfer and critical heat flux have been obtained at the test loop of supercritical water in China Institute of Atomic Energy. The major characteristics and parametric trends of these phenomena are presented, and the experimental results are compared with the calculations of existing correlations and models. (author)

[en] This paper discusses the design of a critical heat flux (CHF) experimental water flow loop being constructed at McMaster University. A brief review of existing water-based CHF data in open literature is presented. The loop's physical specifications, mass flux, heat flux, sub-cooling, and pressure, are determined so that some identified gaps in current CHF data can be eliminated by performing experiments. The design of the loop structure, data acquisition system, calibration requirements, instrumentation and uncertainties, standard operating procedures and some measurement uncertainties are also presented. (author)

[en] This study has been carried out to investigate the hydrodynamic stabilities and Critical Heat Flux (CHF) characteristics for the natural and forced circulation. A low pressure experimental loop was constructed, and experiments under various conditions have been performed. In the experiments of the natural circulation, flow oscillations has been observed and the average mass flux under flow oscillation have been measured. Several parameters such as heat flux, the inlet temperature of test section, friction valve opening and riser length have been varied in order to investigate their effects on the flow stability of the natural circulation system. And the CHF data from low flow experiments, namely the natural and forced circulation, have been compared with each other to identify the effects of the flow instabilities on the CHF for the natural circulation mode. The test conditions for the CHF experiments were a low flow of less than 70 kg/m²s of water in a vertical round tube with diameter of 0.008 m at near atmospheric pressure. (author)