Modelling of conventional and microchannel delugeable tube bundle for a direct air-cooled steam condenser
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Date
2023
Authors
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Journal ISSN
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Publisher
University of Namibia
Abstract
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
increased from 32 ℃ to 44 ℃, the MDTB’s heat transfer rate for 140 𝜇𝑚 hydraulic
diameter was found to be 9 to 6 % higher than that of CDTB. The air-side pressure drop
variations between the two bundles were insignificant. Furthermore, the thermal
performance of HDWD incorporated with either CDTB or MDTB was compared to that
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of CD at component and system levels. At system level, and as the ambient air temperature
increased from 32 ℃ to 44 ℃, the heat transfer rate of the CD was found to be 27 % to 31
% less than that of HDWD incorporated with either CDTB or MDTB. The Air-side
pressure drop for HDWD was found to be about 41 % higher than that of CD.
Additionally, the steam turbine output and net powers were found to be higher when the
ACC was incorporated with HDWD than when CD was incorporated into ACC
Description
A dissertation report submitted in fulfilment of the requirements for the degree of doctor of philosophy in mechanical engineering
Keywords
Air-Cooled Condenser, Delugeable Tube Bundle, Thermal performance, Modelling of conventional and microchannel