Numerical Simulation Of Flow And Heat Transfer In Plate-fin Heat Exchangers With Several Common Fins

Plate-fin heat exchangers have been widely used in automobile, aviation, air conditioning industries for its compactness and high efficiency. Using the CFD method which has been verified by experimental results to reveal the heat transfer flow and heat transfer characteristics in the narrow fin passages are important to optimize the fin structure and develop new kind of fins.According to the flow characteristics of plain, offset, corrugated fins, three dimensional numerical models for accurate calculation of fin performance are established by selecting the appropriate low Reynolds number turbulence model and combining with the turbulent Prandtl number model. The above two measures improve the calculation precision, and the average absolute error for j factor reduces from 17.94% to 6.93%. Computational results show that: temperature at center of fin is lowest and is called Tc for convenience, temperature difference between Tc and Tin(temperature of fluid before entering fin passage) is about 5-18% lower than difference between up(down) plate and Tin and the longitudinal heat conduction of the fin could not be neglected. In order to develop correlations for j and f factors, 18 plain fins with different parameters are simulated, and the proposed correlations can match better with experimental work than the widely used ALEX performance curve.After validating the numerical model for the offset fin, the effects of Reynolds number, fin thickness, fin pitch, fin height and other parameters on the flow and heat transfer are explored. The fin thickness and fin pitch have great influence on the performance. With the increasing fin thickness, vortex form symmetrically in windward side, so the pressure drop, but the effect of heat transfer enhancement is not obvious. By reducing fin length, temperature and velocity boundary layers are destroyed more frequently, consequently, the heat transfer coefficient and pressure drop both increase.After validating the numerical model for the wavy channel, the effects of Reynolds number on the flow and heat transfer are studied. At low Reynolds number, the flow is similar as plain fin. With the increase of Reynolds number, vortex is formed in peak and trough regions, mixing the fluid near wall region and body fluid and enhancing heat transfer process. In the longitudinal direction, close to the upper and lower plate, Taylor-Gortler vortex is formed symmetrically. In transitional flow vortex is large, but in the turbulent region, the turbulence will inhibit the formation of Taylor-Gortler vortex and vortex becomes small.