Performance evaluation of tube-in-tube heat exchangers with heat transfer enhancement in the annulus

Different techniques as angled spiraling tape inserts, a round tube in side a twisted square tube and spiraled tube in side the annulus have been used to enhance heat transfer in the annulus of tube-in-tube heat exchangers. The heat transfer enhancement in the shell can be supplemented by heat transfer augmentation in tubes using twisted tape inserts or micro-finned tubes. The effect of the thermal resistance of the condensing refrigerant could also be taken into consideration. To assess the benefit of using these techniques extended performance evaluation criteria have been implemented at different constraints. The decrease of the entropy generation can be combined with the relative in crease of the heat transfer rate or the relative reduction of the heat transfer area to find out the geometrical parameters of the tubes for optimal thermodynamics performance. The results show that in most of the cases considered, the angled spiraling tube insert technique is the most efficient

PERFORMANCE EVALUATION OF TUBE-IN-TUBE HEAT EXCHANGERS WITH HEAT TRANSFER ENHANCEMENT IN THE ANNULUS by

Dif fer ent tech niques as an gled spi ral ing tape in serts, a round tube in side a twisted square tube and spi raled tube in side the an nu lus have been used to en hance heat trans fer in the an nu lus of tube-in-tube heat exchangers. The heat trans fer en hance ment in the shell can be sup ple mented by heat trans fer aug men ta tion in tubes us ing twisted tape in serts or mi cro-finned tubes. The ef fect of the ther mal re sis tance of the con dens ing re frig er ant could also be taken into con sid er ation. To as sess the ben e fit of us ing these tech niques ex-tended per for mance eval u a tion cri te ria have been im ple mented at dif fer ent con straints. The de crease of the en tropy gen er a tion can be com bined with the rel a tive in crease of the heat trans fer rate or the rel a tive re duc tion of the heat trans fer area to find out the geo met ri cal pa ram e ters of the tubes for op-ti mal ther mo dy nam ics per for mance. The re sults show that in most of the cases con sid ered, the an gled spi ral ing tube in sert tech nique is the most ef fi-cient. Key words: enhanced heat transfer in annulus, spiraling tape insert, spiraled tube, performance evaluation criteri