Influence of triangle tube structure with twisted tape on the thermo-hydraulic performance of nanofluids in heat-exchange system based on thermal and exergy efficiency

An experiment is carried out to research the thermo-hydraulic performance of TiO2-H2O nanofluids in triangle tubes while taking the effect of twisted tapes into consideration. The theories of thermal and exergy efficiency are applied to estimate this system. The influence of mass fractions of nanoparticles (0.1 wt%, 0.3 wt% and 0.5 wt%), Reynolds numbers (Re = 800-9000), different structures of triangle tubes (isosceles right triangle tube (tube 1), isosceles 45 degrees triangle tube (tube 2)) and twisted tape on the Nusselt number, Nusselt number ratio, resistance coefficient, resistance coefficient ratio and pressure drop are experimentally studied respectively. Results show that there are three positive factors for heat transfer performance including large nanoparticles concentration, large Reynolds number and existence of the twisted tape. Compared with the smooth tube, tubes (tubes 1 and 2) with twisted tape can enhance heat transfer, but that without twisted tape can deteriorate heat transfer, for heat transfer performance, tube 2 is better than tube 1. Tube 2 with twisted tape has the biggest value of comprehensive performance index R3. A better exergy efficiency performance can be obtained when Reynolds number is greater than 5000 and the exergy efficiency reaches the best when Re = 8000.