Influence of twist length variations on thermal-hydraulic specifications of twisted-tape inserts in presence of Cu-water nanofluid

摘要

Heat transfer, pressure drop, and overall performance specifications of the twisted-tape inserts with variable twist lengths are experimentally investigated in the presence of Cu-water nanofluid at 0, 0.1, and 0.3 wt.% The Cu-water nanofluids are produced by a one-step method, namely electro-exploded wire technique, and thermo-physical properties of the nanofluids are measured systematically. To evaluate the overall enhancement ratio (OER), the base fluid flow inside the plain tube is employed as base line. The experiments are performed in turbulent regime (7500 <= Re <= 15,000). A good agreement is obtained, when the results are validated with the previous correlations proposed for the plain tube and tube fitted with the uniform twisted-tape insert. The results reveal that all the twisted-tape inserts with the nonuniform twist lengths, i.e. Low-High, High-Low, Low-High-Low, and High-Low-High, yield higher heat transfer coefficient and Nusselt number values than the uniform one. It is also found, creating short twist lengths at the beginning of twisted-tape inserts enhances both the heat transfer coefficient and the pressure drop values. However, this technique improves the OER about 45%. The simultaneous utilization of Cu-water nanofluid with 0.3 wt.% concentration and twisted-tape insert with Low to High twist lengths improves the OER about 87%. (C) 2014 Elsevier Inc. All rights reserved.