Experimental results on gravity driven fully condensing flows in vertical tubes, their agreement with theory, and their differences with shear driven flows’ boundary-condition sensitivities

This paper synthesizes experimental results with computational results towards development of a reliable heat transfer correlation for gravity driven annular wavy condensing flows inside a vertical tube. For fully condensing flows of pure vapor (FC-72) inside a vertical cylindrical tube of 6.6 mm diameter and 0.7 m length, the experimental conditions are typically annular wavy and they cover: mass flux G over a range of 2.9 kg/m2 s ⩽ G ⩽ 87.7 kg/m2 s, temperature difference ΔT of 5–45 °C, and length of full condensation xFC in the range of 0 < xFC < 0.7 m. The range of flow conditions over which there is good (within 15%) and poor (15–30% or >30%) agreement with the theory and modeling assumptions are discussed and these conditions have been identified. The paper also refers to key experimental results with regard to sensitivity of the flow to time-varying or quasi-steady (i.e. steady-in-the-mean) impositions of pressure at both the inlet and the outlet.