The effect of linearly increasing/decreasing pitch ratio twisted tape with various progression rate and nanofluid towards the system performance

Abstract

The overall enhancement ratio decreases with increasing Reynolds number for most of the existing modification of twisted tape. Hence, in this study, a new innovative twisted tape with linearly increasing/decreasing pitch ratio at various progression rate of 0.2, 0.25 and 0.3 (LIPR/LDPR) combined with three different nanofluid (Al2O3/water, SiC/water and CuO/water) are designed and analyzed. The analysis is conducted at Reynolds number ranges from 4000 to 16,000 and volume fraction ranges from 1% to 3% by using numerical and experimental approaches. ANSYS FLUENT software is selected for simulation analysis by adopting RNG K-ε turbulent model using enhanced wall treatment method. Five different geometries of twisted tape including standard twisted tape with constant PR of 2 (TT PR 2), linearly-increasing-progression-rate of 0.2 twisted tape (TT LIPR 0,2), linearly-increasing-progression-rate of 0.25 twisted tape (TT LIPR 0.25), linearly-increasing-progression-rate of 0.3 twisted tape (TT LIPR 0.3) and linearly-decreasing-progression-rate of 0.25 twisted tape (TT LDPR 0.25) are used for analysis. Among all geometries of twisted tapes, TT LIPR 0.25 creates the highest turbulent kinetic energy value at the cross-sectional area. TT LIPR is the best choice to be utilized under turbulent flow regime where Reynolds number >10,000 as it creates higher overall enhancement ratio compared to TT PR 2 and TT DPR. The simultaneous use of 1% SiC/water nanofluid and TT LIPR 0.25 at 10,000 Reynolds number has increased overall enhancement ratio up to 2.985. The empirical correlation is generated for future prediction of Nusselt number, friction factor and overall enhancement ratio with wide range of nanofluid type, fluid flow range and Reynolds number of twisted tapes.