Laminar heat transfer and pressure drop in tube fitted with helical louvered rod inserts using CNT/water nanofluids

Experimental investigation has been focused on the convective heat transfer and pressure drop in a tube fitted with helical louvered rod and carbon nanotubes (CNT)/water nanofluid with constant heat flux under laminar flow condition. Nanofluids of 0.5% volume fraction have been prepared by a two step method. Thermo-physical properties like thermal conductivity and viscosity are measured by using KD2 thermal property analyzer and Brooke field cone and plate viscometer respectively. From the measurements, it is understood that increase in viscosity is substantially higher than the increase in the thermal conductivity. The helical louvered rod inserts with twist ratios Y = 3, 2.44 and 1.78 are used to study the convective heat transfer and pressure drop characteristics under laminar flow in the Reynolds number range of 500-2,200. All these data show that the helical louvered rod is a promising tube insert which can be used in heat transfer and friction factor which causes enhancements in laminar flow. Two different louvered rod insert arrangements (forward and backward) have been used and the effects of various louvered rod pitches have also been investigated. The maximum enhancements in Nusselt number for nanofluids forward arrangements with twist ratios of 1.78, 2.44 and 3 are 47.5%, 42.8% and 39.6% and backward arrangements with same twist ratio are 43.3%, 38.6% and 34.23% respectively when compared to water in plain tube. The helical louvered rod inserts with different twist ratios have been experimented using 0.5% volume concentration of CNT/water nanofluid. Thermal performance analysis based on the constant pumping power criteria shows that helical louvered rod tape inserts with forward arrangement lead to better thermal performance than that with backward arrangement. Copyright © 2014 American Scientific Publishers