M.W. Wambsganss

Two-phase pressure drop, boiling heat transfer, and critical heat flux to water in a small-diameter horizontal tube

Abstract Two-phase pressure drop, boiling heat transfer, and critical heat flux to water were studied in a small horizontal tube of 2.98-mm inside diameter and 0.91-m heated length. Experiments were performed at a system pressure of 200 kPa, mass fluxes of 50–200 kg/m2s, and inlet temperatures from ambient to 80 °C. Experimental results and comparisons with state-of-the-art predictive correlations are presented. Modifications were made to the Chisholm two-phase multiplier correlation and to the Argonne National Laboratory small-channel boiling heat transfer correlation to better predict the experimental data of the present study.

Parallel-flow-induced vibration of fuel rods

A mathematical model is proposed to describe the phenomena of parallel-flow-induced vibrations of a flexible rod, and a solution is obtained for a rod with arbitrary end conditions; the solution can be used for fixed, hinged, cantilevered, and other elastically supported end conditions. Comparisons between model predictions and flow-test data for rods with fixed and cantilevered end conditions show that the model successfully predicts the essential features of the system behavior: (1) the adjacent rods and duct wall may considerably increase the added mass; (2) the fundamental frequency may increase or decrease with flow velocity, depending on the end conditions; (3) the system damping increases with increasing flow velocity, and is attributed to the normal drag force and the Coriolis acceleration; (4) the rms rod response increases with flow velocity and follows an approximate power function relationship; and (5) the increase in rigidity at the ends tends to reduce the rms response.

Thermal Management Concepts for Higher-Efficiency Heavy Vehicles

Thermal management is a cross-cutting technology that directly or indirectly affects engine performance, fuel economy, safety and reliability, aerodynamics, driver/passenger comfort, materials selection, emissions, maintenance, and component life. This review paper provides an assessment of thermal management for large trucks, particularly as it impacts these features. Observations arrived at from a review of the state of the art for thermal management for over-the-road trucks are highlighted and commented on. Trends in the large truck industry, pertinent engine truck design and performance objectives, and the implications of these relative to thermal management, are presented. Finally, new thermal management concepts for high efficiency vehicles are described.

Two-phase flow and pressure drop in flow passages of compact heat exchangers

Two-phase flow experiments were performed with air/water mixtures in a small rectangular channel measuring 9.52 {times} 1.59 mm (aspects ratio equal to 6), for applications to compact heat exchangers. Pressure drop and flow pattern definition data were obtained over a large range of mass qualities (0.0002 to 1), and in the case of flow pattern data, a large range of mass fluxes (50 to 2,000 kg/m{sup 2}s). A flow pattern map, based on visual observations and photographs of the flow patterns, is presented and compared with a map developed for a rectangular channel of the same aspect ratio but with dimensions twice those of the test channel, and with a map developed for a circular tube with the same hydraulic diameter of 3 mm. Pressure drop data are presented as a function of both mass quality and Martinelli parameter and are compared with state-of-the-art correlations and a modified Chisholm correlation. 13 refs.

Dynamic responses of a pair of circular tubes subjected to liquid cross flow

Abstract This paper presents the results of two experimental investigations of a pair of circular tubes subjected to liquid cross flow: (1) two tubes in a plane normal to the flow stream; and (2) two tubes in tandem. Tube response characteristics, including natural frequencies, damping, displacements and vibration orbits, are measured and reported. Results of this study provide additional insight into the interaction of pairs of tubes in liquid flow, including such phenomena as flow velocity-dependent damping and the frequency “lock-in” region of tube motion in the drag direction.

Flow-induced vibration in LMFBR steam generators: A state-of-the-art review

Abstract This state of the art review identifies and discusses existing methods of flow-induced vibration analysis applicable to steam generators, their limitations and base-technology needs. Also included are discussions of five different LMFBR steam generator configurations and important design considerations, failure experiences, possible flow-induced excitation mechanisms, vibration testing and available methods of vibration analysis. The objectives are to aid LMFBR steam generator designers in making the best possible evaluation of potential vibration in steam generator internals, and to provide the basis for development of design guidelines to avoid detrimental flow-induced vibration.

Second-order effects as related to critical coolant flow velocities and reactor parallel plate fuel assemblies

Abstract Second-order effects, removed by the linearization process in the analyses of Miller, Rosenberg and Youngdahl, and others, are retained in a stability analysis of the equation of motion of a flat fuel plate in a reactor parallel plate fuel assembly. The second-order terms generate an additional stability criterion is the form of an upper bound (critical deflection on the amplitude of quasi-static deflections for stable oscillations, or neutral stability, about the undeflected fuel plate position. The critical flow velocities derived in the earlier studies, and again as a consequence of this analysis, are upper bounds to insure local stability about the undeflected plate position. A constant of proportionality, relating the critical deflection to the initial channel depth, is designated as a design constant . When assigned a value, the design constant defines new critical coolant flow velocities which are lower than those first arrived at by Miller.

Dynamics of component-support impact: An elastic analysis

Abstract Flow-induced vibrations of certain reactor components can induce fretting and wear due to continuous component-support impacting, and possibly result in component failure. As a part of the effort to correlate the flow excitation to the rate of component wear, the present paper studies a simple analytical model for the further understanding of the fundamental mechanism of component-support interaction. The usual modal expansion approach was adopted. Static Hertz type of contact was assumed for the component-support impact. For the convenience of comparing the model with experimental results, the analysis was restricted to a fixed-fixed beam with a central baffle support subjected to free vibrations. For simplicity, damping effects were suppressed. Thus both the beam property and the contact action were assumed to be elastic. Numerical results of the study demonstrate a favorable correlation with the results of the experiments.

Tube vibration in a half-scale sector model of a helical tube steam generator

Abstract This paper presents the experimental technique and results of tests on a half-scale sector model of a steam generator helical coil tube bank. A series of tests was performed: (1) bench tests of a single helical tube in air; (2) tests of the sector model in air; (3) tests of the sector model in stationary water to determine natural frequencies and damping; (4) tests in flow. The experimental results reveal the general characteristics of the sector model and provide the information for the design evaluation of a helical tube array to avoid detrimental fluidelastic instability.

Critical Heat Flux and Boiling Heat Transfer to Water in a 3-mm-Diameter Horizontal Tube

Boiling of the coolant in an engine, by design or by circumstance, is limited by the critical heat flux phenomenon. As a first step in providing relevant engine design information, this study experimentally addressed both rate of boiling heat transfer and conditions at the critical point of water in a horizontal tube of 2.98 mm inside diameter and 0.9144 m heated length. Experiments were performed at system pressure of 203 kPa, mass fluxes in range of 50 to 200 kg/m{sup z}s, and inlet temperatures in range of ambient to 80 C. Experimental results and comparisons with predictive correlations are presented.