# Numerical Study of Heat Transfer Enhancement for Laminar Nanofluids Flow
## 1 Introduction
[26] investigated the effect of nanofluids on convective heat transfer through a circular straight tube with constant heat flux condition under both the laminar and turbulent flow regimes. For Al\({}_{2}\)O\({}_{3}\) nanofluids with \(\phi_{b}\) = 3%, the thermal conductivity and HTC increases by 8% and 20%, respectively. The enhancement of the convective HTC at the entrance region was due to the Brownian motion of the nanoparticles. [PERSON] et al. [27] investigated the laminar convective heat transfer and viscous pressure loss for Al\({}_{2}\)O\({}_{3}\)-water and ZrO\({}_{2}\)-water nanofluids flow in a vertical heated tube. The HTC's in the entrance and fully developed regions were found to be enhanced by 17% and 27%, respectively, for water-based Al\({}_{2}\)O\({}_{3}\) nanofluid at \(\phi_{b}\) = 6%, as compared to the water. [PERSON] et al. [28] studied the laminar forced convective heat transfer in a circular tube for three different nanofluids (Al\({}_{2}\)O\({}_{3}\)-water, ZrO\({}_{2}\)-water and TiO\({}_{2}\)-water). They reported that for the same Re comparison criteria, the HTC for nanofluids is found to be significantly higher (18%) as compared to the base fluid. [PERSON] et al. [29] investigated the heat transfer characteristics of a straight microtube for three different nanofluids (Al\({}_{2}\)O\({}_{3}\)-water, ZrO\({}_{2}\)-water and TiO\({}_{2}\)-water) under laminar condition (Re = 200-2200). For the nanofluids considered, the HTC was reported enhanced by 23% as compared to water. [PERSON] et al. [30] utilized a numerical method to investigate the convective heat transfer of nanofluids in microtube under constant heat flux with different types of nanoparticles (Al\({}_{2}\)O\({}_{3}\), CuO, SiO\({}_{2}\) and ZnO) with different volume fractions ranged from 1% to 4% using ethylene glycol and water as a base fluid. The maximum heat transfer enhancement was 22%. Table 1 shows a summary of the different nanofluids and their process parameters (Re, Pr and \(\phi_{b}\)) for convection heat transfer under laminar flow condition. The parameters were selected based on the potential of the nanofluids for their practical applications as studied by previous authors and presented in Table 1. The highest Prandtl number and volume fraction of nanoparticles were 753 and \(\phi_{b}\) = 10%, respectively. The extensive studies, both experimental and theoretical have been conducted to calculate the convective HTC of the nanofluids flow in straight tube. It is conclusive from the literature review that the HTC not only enhanced by the thermal conductivity but also due to the disturbances of thermal boundary layer caused by the Brownian motion of the nanoparticles. It may also be noted that there are only few studies with a wider range of nanoparticles and particle concentrations. This is mainly because the experimental analysis can be complicated for the wider range of the design parameters. A considerable amount of research has been done on nanofluids over the past decade, the conclusions on their behavior, characteristics, and performances remain somewhat controversial. There is still lack of consistency in experimental values found in the literature [18; 19] and challenges that need to be addressed and overcome before this new field of study can be fully established. It is imperative to conduct more investigations to properly quantify the effects of nanoparticles in heat transfer enhancement. Therefore, in this study, the single-phase model was used for a wide range of nanofluid properties including three different base fluids with Prandtl numbers ranging from 6-500 and five different nanoparticles viz. Al\({}_{2}\)O\({}_{3}\), TiO\({}_{2}\), CuO, SiO\({}_{2}\), and ZnO. The wide range of fluid properties enables the evaluation of the performance of convective heat transfer in a larger number of engineering applications that can benefit from a better understanding of the thermal enhancement of nanofluids.