Two-Phase Flow Instabilities

Date of Award




Degree Name

Doctor of Philosophy (Ph.D.)


Mechanical Engineering


Pressure-drop and density-wave oscillations which are the most common kinds of two-phase flow oscillations have been investigated experimentally and theoretically. Experiments with Freon 11 as the test fluid have been carried out to investigate the effect of the heater surface configurations on two-phase flow instabilities in a single-channel upflow boiling system operating between constant pressures, with upstream compressibility introduced through a surge tank. The experiments have been conducted at a constant inlet temperature of 73(DEGREES)F and at five different heat input values for each of the six heater tubes. Stability maps have been generated with respect to the pressure-drop oscillations for different heater surface configurations. Oscillations have been observed whenever there is boiling in the heater; no stable interval has been detected between the pressure-drop and the density-wave instability regions.Two different two-phase flow models, namely a constant-property homogeneous flow model and a variable-property drift-flux model, have been developed. Conditions of thermodynamic equilibrium between the phases are assumed in each model. The effect of the wall heat storage and the variation of the fluid properties with pressure are neglected in the homogeneous-flow model. In the drift-flux model, the effect of the wall heat storage is taken into consideration, the heat flux may change in time and along the channel, and all the fluid properties are evaluated at local pressures.The system stability is studied both in the frequency domain and in the time domain. In the frequency-domain analysis, the governing equations for both models are first linearized for small perturbations and that stability of the linearized equations is investigated. Using the homogeneous-flow model, simple algebraic expressions have been developed for the steady-state system pressure drop and the pressure-drop instability boundaries. Computer solutions have been generated for the drift-flux model to the same purposes. Good agreement with experimental results is indicated in both cases. . . . (Author's abstract exceeds stipulated maximum length. Discontinued here with permission of author.) UMI


Engineering, Mechanical

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