Thermal Performance Modelling of a Flat Bare Tube Bundle Under Deluging Cooling Conditions

Abstract

This work focuses on developing and improving a one-dimensional analytical, thermal model to be employed in predicting and optimizing of the performance of a flat bare tube bundle, under deluging cooling condition, commonly found the literatures. The flat bare tube bundle to be incorporated into the second stage of an induced draft Hybrid (Dry/Wet) Dephlegmator (HDWD) for a Direct Air-Cooled Steam Condenser (ACSC). The developed model is validated theoretically and evaluated analytically by using three approaches, which are: Poppe, Merkel, and heat and mass transfer analogy. The present model was also validated against the models for flat bare tube bundles from the literatures. The geometric orientation of the tubes (flat and round ends sections) was taken into account when modelling was performed. For the flat section of the tube, the governing differential equations were conducted in Cartesian coordinates. The cylindrical coordinates were employed, to derive the governing differential equations, for round ends tube. Heat transfer rate obtained by Poppe method is found to be 2.8% and 9.2% higher than that of Merkel, and heat and mass transfer analogy methods, respectively. By comparing the present model to that of flat bare tube bundle in the literatures, the heat transfer rate and air-side pressure drop were found to be 11% and 88% higher, respectively for both methods. Furthermore, the heat transfer rate for the model of delugeable round bare tube bundle (DRBTB) was found to be higher than that of the present model at both smaller and larger tube pitch, while the air-side pressure drop for the model of DRBTB was found to be lower and higher than that of the present model at smaller and larger tube pitch, respectively.