Reported experimental and computational results confirm that both the flow features and heat transfer rates inside a condenser depend on the specification of inlet, wall, and exit conditions. The results show that the commonly occuring condensing flows’ special sensitivity to changes in exit conditions (i.e. changes in exit pressure) arise from the ease with which these changes alter the vapor flow field in the interior. When exit pressure is changed from one steady value to another, the changes required of the interior vapor flow towards achieving a new steady duct flow are such that they do not demand removal of the new exit pressure imposition back to the original steady value — as is the case for incompressible single phase duct flows with an original and “required” exit pressure. Instead, new steady flows may be achieved through appropriate changes in the vapor/liquid interfacial configurations and associated changes in interfacial mass, heat transfer rates (both local and overall), and other flow variables. This special feature of these flows is for the commonly occurring large heat sink situations for which the condensing surface temperature (not heat flux) remains approximately the same for any given set of inlet conditions while exit condition changes. In this paper’s context of flows of a pure vapor that experience film condensation on the inside walls of a vertical tube, the reported results provide important quantitative and qualitative understanding as well as allow us to propose important exit-condition based categorization (viz. Categories I – III) of these flows.

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