Numerical Simulation On Heat Performance Outside Of Elliptical Tube Heat Exchanger With Steam Condensation

The process of condensation heat transfer in the presence of noncondensable(NC) gases widely exists in these industrial equipments such as heating, ventilation and air conditioning(HVAC), passive containment cooling systems(PCCS), and the condensing heat exchanger of gas fired condensing boiler. NC gases have great influence on vapor film condensation,which make it different from pure vapor condensation and more complicated.But few studies and reports pay attention to this phenomenon outside of pipe and pipe bundle. This paper focuses on the matter using software ANSYS Fluent 15.0.First, theoretical analysis was conducted briefly, and corresponding UDF program relating condensation was compiled. After the program and numerical simulation method being verificated, a series of studies with computerized simulation was completed.In the first section, the heat and mass transfer process of vapor condensation with non-condensable gas outside of single elliptical pipe was studied.In the second section, the condensation heat and mass transfer process of airvapor mixture crossing tube-bundle was emphatically studied. This part specifically dealt the impacts of axial ratio(a/b)、water vapor concentration and approaching velocity on condensation heat transfer, pressure loss and the comprehensive performance. The variation of local condensation heat transfer coefficient(HTC) was yet presented.The study reveals that the condensation HTC of elliptical pipe is decreased, compared with round pipe with same parameter; For the case of a/b equal to 4.0, it decreases by 20%. The results also show that high value of ν or Yv will raise total heat transfer rate when a/b remains constant.For in-line bundle, maximum of condensation heat transfer coefficient appears in the first row; whereas for staggered bank of tubes, it appears in the second row.Local condensation heat transfer coefficient show an decreasing trend, despite of what arrangement, but for in-line bundle, it drops rapidly when row n≤3, then it declines slow when row n≥3; For staggered bank of tubes, when row is not more than 4, it decline as wave-shaped, when row lager than 4, it present a the step-down curve.In addition, different bundle arrangement lead to different variety of the last row tube condensation heat transfer coefficient. For in-line bundle, last row condensation heat transfer coefficient is higher than the front row’s, but the contrary is the case for the staggered bank of tubes.With the axial ratio increasing, both condensation rate and total heat transfer tend to decrease. Compared with in-line bundle, the staggered bank of tubes reduced with more extent. Furthermore, pressure loss shows a similar tendency.This part also demonstrates that high value of ν or Yv will raise heat transfer rate in general. the staggered bank of tubes possesses a high condensation heat transfer over in-line bundle in the range of consideration, the condensation rate increases by 7.80%, and total heat transfer coefficient 24.06%, but pressure loss increases strikingly by 83.52%.The synthesized heat exchanging performance analysis and field synergy principle share a basic coherence that the condensation HTC of elliptical pipe bundle is lower than round pipe bundle with same perimeter.Hence, we conclude that, from the perspective latent heat recovery and heat transfer augmentation, staggered bank of tubes are the appropriate choice; but for low pressure loss, in-line bundle is recommended.