Modelling of conventional and microchannel delugeable tube bundle for a direct air-cooled steam condenser

This study presents the thermal performance modelling of conventional and microchannel delugeable tube bundle which incorporated into a second stage of the induced Hybrid (Dry/Wet)) Dephlegmator (HDWD). Hybrid dry/wet dephlegmator was proposed to replace a Conventional Dephlegmator (CD) of a direct Air-Cooled Condenser (ACC) system, coupled to 30 MW steam turbine of a generating unit. The Conventional Delugeable Tube Bundle (CDTB) thermal performance was modelled and configured using one- and two - dimensional models by employing heat and mass transfer approach. The geometric parameters for both first and second stages tube bundles of HDWD were derived from that of CD of ACC system of the considered generation unit. Therefore, the thermal performance of CDTB was optimised to ensure highest performance, and appropriate geometric parameters that are corresponding to that of CD and available space for installation. The best CDTB configuration’s performance was compared to similar existing Delugeable Round Tube Bundle (DRTB) in literatures. When the tube pitch varied from 25 mm to 38 mm, the DRTB’s heat transfer rate and air-side pressure drop were found to be in the range of 1.4 to 2 times and 1.3 to 2.2 times that of CDTB, respectively. The Microchannel Delugeable Tube Bundle (MDTB) thermal performance was analysed using semi-empirical model, which comprises of microchannel heat transfer and flow correlations. The size and geometric parameters of MDTB was equivalent to that of CDTB, and the only difference was that, the MDTB has microchannel/ ports on the steam-side. The MDTB thermal performance was found to increase as the hydraulic diameter of the channels decreased. The thermal performance comparison of the CDTB and MDTB at bundle, component and system levels was carried out. At all the levels, the MDTB performance was higher than that of CDTB. However, this higher performance came at expense of higher steam-side pressure drop. As the ambient air temperature increa