Single and two-phase frictional pressure drop in helically coiled tubes

[摘要] Correlations for pressure drop, in terms of mass flux and tube diameter, have been obtained for two-phase flow in tubes, both straight and coiled. The two-phase correlation for straight test sections is presented in Equations 5.1 and 5.2: &phis;1 2new = &phis;1 2 C3. The parameter &phis;1, used above, is a two-phase multiplier of a type used by Chisholm (34) and a standard correlation for this has been developed by HTFS In the present work a revised parameter "1 new" is introduced, related to 01 by coefficient C3 The earlier correlations of Baroczy and Chisholm Sutherland have been restricted to mass fluxes less than 4000 kg/m2 s A correlation for single-phase friction factor in the coils tested, is presented (Equation 6 3) and is shown to agree well with other well established correlations fc(D/d)0 5=0.081 (Re(d/D)2)-0.225 (6.3) where D and d are the coil diameter and tube bore respectively, in metres. An improved correlation for two-phase frictional pressure loss in helically coiled tubes is also presented (Equations 5.1 and 5.3). Another aspect of this research was the discovery of flow pattern induced vibration in the test coils It was noted that when the mass flux of the two-phase mixture was greater than approximately 1000 kg/m2 s and the quality greater than 0.005 (mass flow of air/total mass flow), then vibration started in the coils The frequency appeared to increase with air mass flowrate The vibrations became severe, shaking the whole test bench and apparatus The test coils were replaced with clear plastic tubes of similar dimensions to enable flow visualisation tests to take place These tests showed that the flow regime known in straight tube, two-phase flow, terminology as churn flow was seen to rotate within the tube While the test apparatus did not allow conclusive tests to be carried out, some high speed photographs were taken which showed that the rotation could switch in either direction and that there was no evidence of a time related pattern Suggestions are presented for possible flow patterns that might be occurring under these vibrating conditions.

[发布机构] University:University of Glasgow

[关键词] Mechanical engineering, Hydraulic engineering