## 1 Introduction  
Convective heat transfer is one of the main mechanisms in heat transfer for flow in pipes, such as heat exchangers. It could be improved by changing thermophysical properties of working fluids and/or geometrical change in flow or boundary conditions. One of the methods to accomplish this is adding nanoparticles to the base fluid [1]. This innovative idea was put forth by [PERSON] in 1873 [2], which has generated a great interest for researchers to develop high-performance heat transfer fluids [3]. The effects of nanoparticles on heat transfer enhancement, however, have produced challenges, regardless of their positive effects [4]. These challenges could result from parameters that affect heat transfer enhancement, such as volume fractions, aspect ratio, base fluids, and entrance effects, among others, which are still unclear and require more research. Advanced technology applications that have adopted nanofluids have attracted a wide spectrum of research. Nanofluids could become very significant when acting as smart fluids and applied to biomedical, heating, and automotive, among other, applications [5]. The development of artificial organs has highlighted the importance of biofluid mechanics, which is a promising field of research for nanofluids, for example, in the blood vessels/respiratory tract/lymphatic and gastrointestinal systems/urinary tract zones [6; 7]. The design of electronic thermal management systems critically depends on the nanofluid type used [8] and is considered very important to the electronic cooling industry [9]. Also, nanofluids were applied to solar thermal collectors with attention to environmental concerns and production costs [10; 11] and applied to solar energy desalination to overcome the relatively lower efficiency and lower yield of solar stills [12]. Nanofluids in automobiles have significant opportunities in areas such as radiator coolants, lubricants, brake fluid, and shock absorbers [13]. The list of applications is long and forces the current work to focus on nanofluid applications to gaseous laminar flow through pipes. [PERSON] and [PERSON] [14] reported, experimentally, that the use of nanoparticles caused an increase in the heat transfer performance in pipe flows, and they developed a correlation in terms of the Reynolds number (Re), Prandtl number (Pr), and Nusselt number (Nu). Likewise, [PERSON] and [PERSON] [15] demonstrated that including a small-volume fraction of aluminum oxide (Al\({}_{2}\)O\({}_{3}\)) with fluids has enhanced the particle-fluid mixture's thermal conductivity when compared with those of base fluids like air or water. Furthermore, a study on the convective heat transfer of \(\gamma\)-Al\({}_{2}\)O\({}_{3}\) nanoparticles and deionized water flowing through a tube in the laminar flow regime was published by [PERSON] and [PERSON] [16]. Their results presented that the use of \(\gamma\)-Al\({}_{2}\)O\({}_{3}\) nanoparticles significantly enhanced the entrance region convective heat transfer. The reported enhancement was a function of nanoparticle volume fraction and axial distances. These results were confirmed by the study by [PERSON] and [PERSON] [17], which was supported by a detailed literature review. [PERSON] and [PERSON] [18] worked on forced convective heat transfer in Al\({}_{2}\)O\({}_{3}\)-air nano-aerosol. They reported that a small particle mass loading is required to increase the value of Nu. [PERSON] et al. [19] investigated how a horizontal circular tube's laminar forced convective heat transfer would be affected by nanoparticles by utilizing the computational fluid dynamics (CFD) approach. They showed that the addition of nanoparticles caused an increase in the pressure drop, the friction factor coefficient, and the coefficient of convective heat transfer. Moreover, [PERSON] et al. [20] studied, using an experimentally validated CFD model, the convective heat transfer and flow characteristics of nanofluids and indicated that the heat transfer coefficient and Nu increased with an increase in the Re value.