폴리머 공기예열기의 열유동 해석

Abstract

The corrosive characteristic of flue gas to metal rotary regenerator (RR) working in thermal power plant gained its gravity many years ago. In this study, the RR made of polymer, as known as a highly corrosive resistant material, is applied and experiences a comparison of heat exchanger efficiency to metal. Those materials are polytetrafluoroethylene (PTFE), polyether ether ketone (PEEK), perfluoroalkoxy alkanes (PFA), aluminum (Al) and corrosive resistant low alloy steel (CRLS). The 2D computational fluid dynamic (CFD) model are established and their numerical results are validated with available literatures. There are also two mathematical configurations which are applied in this study. The first one is a simple model with equations of one – dimensional (1D) fluid flow and two – dimensional (2D) wall. The flow characteristic for both fluid flows is considered as laminar by uniform and constant inlet velocity. Heat transfer coefficients along with length of the plate are figured out from a Nusselt empirical correlation and put in the fluid flow equations. After checking the condition of energy conversation, the heat exchanger effectiveness depending on either variable wall or flow channel thicknesses of those materials has compared each other. For the second one, although the fluid flow is laminar, mathematical model is chosen as transient weakly compressible turbulent forced convection in channel. A range of different mass flow rate is also put at inlet condition for both fluid flow. The energy equations of fluid flow and matrix wall (solid region) are also transient heat convection and conduction. The results of Nu number and effectiveness of present study are validated with empirical correlations and analytical solution ε_NTU method, respectively. For both mathematical models, they are coupled and solved by finite element method from COMSOL Multiphysics. The influence of different Reynold numbers and thickness of matrix wall and flow channel on the rotary regenerator’s behavior has also been examined. As a consequence, the comparable quantity of effectiveness, under 10% of difference, is witnessed between two kinds of material. The narrower the flow channel is, the higher the effectiveness is. Otherwise, wall thickness influences weakly to heat exchanger effectiveness. Eventually, a sensitivity analysis of those materials is performed based on the light change of thermal conductivity and volumetric heat capacity to test its influence on the total effectiveness. Conclusively, materials with larger thermal mass are more desirable than those with higher thermal conductivity.