Prediction and Control of Internal Condensing Flows in the Experimental Context of their Inlet Condition Sensitivities

Abstract

The reported experimental results involve fully condensing flows of pure FC-72 vapor on a horizontal condensing surface (316 stainless steel) which is the bottom surface (wall) of a rectangular cross-section duct of 2 mm height, 15 mm width, and 1 m length. The sides and top of the duct are made of clear plastic. The experimental system in which this condenser is used is able to control steady-in-the-mean (termed quasi-steady) mass flow rate, exit pressure, and wall cooling conditions. It has been found that, with the condenser mean (time averaged) inlet mass flow rate, exit pressure, and wall cooling condition held fixed at steady values, there is a very strong sensitivity to high amplitude pressure fluctuations and flow rate pulsations at the condenser inlet. This sensitivity often significantly alters the condenser mean inlet pressure, pressure drop, local heat transfer rates (>200% increase at certain locations), and the condensing flow morphology. These effects are representative of fluctuations/pulsations that are typically encountered in applications but are either not accounted for or are not detected. The effects of imposed fluctuations/pulsations, as opposed to cases involving negligible imposed fluctuations/pulsations, are dependent on the amplitude and the frequency content of the imposed fluctuations and this is discussed in a separate paper. A significant upstream annular regime portion of the reported shear/pressure driven fully condensing flows operate under conditions where the laboratory’s transverse gravity effects are negligible and, therefore, the identified sensitivity phenomenon is highly relevant to zero- or micro-gravity conditions. The micro-gravity relevance of this sensitivity for the annular regime phenomenon is currently also being demonstrated with the help of computations and simulations.