Evaluate the use of elliptical finned tubes in heat exchanger design and performance : 'the structural characteristics of finned tubes'

[摘要] ENGLISH ABSTRACT:This report describes the Experimental and Numerical Investigations conducted, duringthe determination of the structural mechanics of elliptical tubes, viz. the F- and the Atubes.This report is requested in an endeavour to assist Sasol, who is currently busydeveloping and updating specifications on Air Cooled Heat Exchangers.The objectives of this report therefore are to : (1) determine the strength and theeffectiveness of the tube-to-tube-sheet joints. (2) determine the allowable pressurelimits on the tubes and (3) investigate the effects of thermal load and vibration on thetube bundle. A series of experiments were conducted to meet these objectives. From aShear Load experiment it was found that the maximum allowable axial load on the Fandthe A-tube is 14.55 kN and 20. 86 kN respectively. Fin Plates were found to havelittle effect on the bending strength of the tube, w~ilst they have significant effect on theresistance to volumetric expansion of the tube. In fact the more fins per unit length thegreater the resistance to volumetric expansion of the tube. These conclusions weredrawn from Bending and Pressure Load experiments respectively and supported byFEM analysis of the tube using NASTRAN.When the design pressure limit given by the manufacturer (GEA Air Cooled Systems),were tested using FEM analysis, it was found that they cause no significant deformationand failure of the tubes. Thermal stresses on the tube bundle greatly affect the first tubein the first row (row closest to the flanges) of the tube bundle and it is recommendedthat provision for thermal expansion be made to reduce these stresses. To reducevibrations induced by the fan, it is recommended that the natural frequency of the tubebundle must not equal the number of blades (N) times the angular frequency (co) of thefan, or multiples thereof, of each mode of vibration.

[发布机构] Stellenbosch University