Study On The Local Pressure Drop Characteristics Of Gas-liquid Two-phase Flow In A Combined Bend Under The Effect Of Gravity

In the context of implementing energy conservation and emission reduction in the engineering practice,it is of apparent engineering guidance and academic value to research the local pressure drop characteristics of gas-liquid two-phase flows in combined bends under the effect of gravity.Because there is relatively less research on the local pressure drop characteristics of gas-liquid two-phase flows in the bends(especially the combined bends more suitable for the actual engineering practice)under the effect of gravity.In the current thesis,we use the Realizable k-εturbulence model combined with the Mixture two-phase flow model of the Fluent to systematically investigate the local pressure drop characteristics(mainly including the local pressure drop ratioλand the local pressure drop coefficientξ)of the gas-liquid two-phase flow in a single bend(namely,L-shaped bend)and a combined bend(namely,Z-shaped,90°,and 180°combined bend)under the effect of gravity.Specifically,the influence law of the local pressure drop ratioλand the local pressure drop coefficientξbetween the dimensional parameters,e.g.,the three different flow directions,the bend-diameter ratio R/D,the high-diameter ratio H/D,the gas-phase volume ratioα,and the liquid-phase Reynolds number Re_l(which is dimensionless by the gas-liquid two-phase flow velocity)are systematically investigated.First,the local pressure drop characteristics of the gas-liquid two-phase flow in the L-shaped bend under the effect of gravity are systematically studied in the parameters of R/D=1～7、α=0～0.3,and Re_l=2.9×10~4～2.1×10~5.The results show thatλincreases and then decreases with increasingαwhen R/D<2,andλshows the opposite trend when R/D>2;λincreases with increasing Re_l when 0.05≤α≤0.3,and the growth trend ofλ-Re_lrelationship curve remains almost constant when R/D>4;when 0.05≤α≤0.3,ξincreases continuously with the increase ofα,and the increasing trend gradually decreases;ξchanges more significantly whenαincreases from 0to 0.2,and after that it can be approximated that the change ofξis independent ofα;ξdecreases first with the increase of R/D and then tends to be stable.Secondly,the local pressure drop characteristics of the gas-liquid two-phase flow in the Z-bend under the effect of gravity are systematically studied in the parameters of R/D=1～8,H/D=1～16,α=0～0.3,and Re_l=2.9×10~4～2.1×10~5 in combination with three flow directions.The results show that keeping R/D=2 constant,λdecreases whenαincreases;λincreases with Re_l under different flow direction conditions,and the increase inλremains basically constant with the increase in H/D;when Re_l is relatively small,ξdecreases with the increase in Re_l,and as Re_l continues to increase,ξwill not change significantly with the change in Re_l;for upward flow,ξincreases with the increase of H/D,and for horizontal flow and downward flow,ξdecreases with the increase of H/D;ξdecreases first with the increase of R/D and then remains basically the same.Finally,three combination bends of 0°(Z-shaped),90°,and 180°are selected to investigate the intrinsic correlation between the adjacent influence effects(including the adjacent influence coefficient C and the adjacent influence length H_m)and H/D.Subsequently,the prediction equations for theξof the L-shaped and the three combinations bends with R/D,H/D,α,and Re_l are established based on many numerical results in both upward and downward flow directions.The results show that C shows the same trend with the change of H/D;C is 0°bend>90°bend>180°bend for upward flow,and 90°bend>0°bend>180°bend for downward flow;Hm shows the opposite variation law with C under the two flow conditions;the fitting error between the prediction equations and the numerical results is basically within 20%.