Numerical and Experimental Analysis of the Thermal Performances of SiC/Water and Al2O3/Water Nanofluid Inside a Circular Tube with Constant-Increased-PR Twisted Tape

Abstract

The simultaneous use of two passive methods (twisted tape and a nanofluid) in a heat transfer system will increase the average Nusselt number (Nu) of the system. However, the presence of inserts and nanoparticles inside the tube will create higher pressure drop (ΔP) in the system, which can eventually affect the overall enhancement ratio (η), especially at higher Reynolds numbers (Re). Several modifications of twisted tapes have been made to reduce ΔP, but most showed a decreasing trend of η as Re increased. The objective of this study is to design a new geometry of twisted tape that yields a larger value of Nu and a smaller value of ΔP, which can result in a larger value of η especially at higher Re. A simulation and experimental analysis are conducted in which Re ranges from 4000–16,000 with two types of nanofluids (SiC/Water and Al2O3/Water) at various values of the volume fraction, (φ) (1–3%). ANSYS FLUENT software with the RNG k-ɛ turbulent model is adopted for the simulation analysis. Three types of twisted tape are used in the analysis: classic twisted tape with a pitch ratio of 2 (TT PR2), constant-increasing-pitch-ratio twisted tape (TT IPR) and constant-decreasing-pitch-ratio twisted tape (TT DPR). The use of TT IPR generates a stronger swirling flow at the inlet of the tube and smaller ∆P, especially near the outlet region. The highest value of η is obtained for 3% SiC/Water nanofluid that is flowing through a smooth circular tube with TT IPR inserts at Re of 10,000.

Effect of Conical Strip Inserts and ZrO2/DI-Water Nanofluid on Heat Transfer Augmentation: An Experimental Study

“…The increase in the volume concentration increases the thermal conductivity [53] of the nanofluid, which in turn promotes more convective heat transfer due to nano clustering and Brownian motion. The mechanisms [54,55] responsible for heat transfer enhancement by inserts were one and the same for both patterns; however, the backward pattern inserted into the test section had more contact surface area, leading to additional blockage of the working fluid and offering increased turbulence in succession with more heat transfer augmentation being achieved than that forward pattern. The heat transfer enhancement summarized for the both patterns of conical strip inserts, different twist ratios, and vol.% concentrations is presented in Table 4.…”

Advances in the Development of New Heat Transfer Fluids Based on Nanofluids

“…In the work of Ahmad et al [6], both a numerical investigation (using Ansys Fluent) and experimental analysis were carried out to evaluate the thermal performance of SiCwater and Al 2 O 3 -water nanofluids inside a circular tube with constantly increased PR twisted tape. The main results of their study were an increase in heat transfer performance.…”

Heat Transfer Intensification in a Heat Exchanger by Means of Twisted Tapes in Rib and Sawtooth Forms

“…Several twisted tape designs have been proposed to enhance heat transfer with a reasonable pressure drop increase to improve thermal performance [21][22][23][24][25][26][27]. Wijayanta et al [21] numerically studied single-phase flow inside an enhanced tube equipped with square-cut twisted tapes at various twist ratios (y/W) of 2.7, 4.5, and 6.5 for the Reynolds number range of 8000 to 18,000, with water as the working fluid.…”

“…The maximum thermal performance factor offered by the modified twisted tapes was as high as 1.23, which was greater than that of a typical twisted tape (1.18). Ahmad et al [22] utilized twisted tapes with increasing and decreasing pitch ratios in SiC/water and Al 2 O 3 /water nanofluid flows. They observed that using twisted tapes with increasing pitch ratios better enhanced swirling flow with smaller pressure losses than ones with decreasing pitch ratios, especially near the outlet region.…”