## 1 Introduction  
The accelerated increase in the cost of electricity is associated with a deterioration in the level of fossil fuels, which coincides with a rise in demand, in addition to the various environmental problems. These problems represent the primary motive to the search for clean and sustainable energy sources to replace fossil fuels [1]. Different alternative energy sources have been used in recent years (e.g., solar, wind, geothermal, and biomass energies) have had remarkable effects on minimizing pollution and in achieving sustainable development [2]. Many reasons support the use of solar energy as a source of energy more than other renewable sources because of its availability, ease of transportation for energy production, and its ability to be integrated with other applications [3]. Therefore, several kinds of research have been carried out on solar energy aiming to investigate its ability to produce adequate energy from the solar radiation intensity as well as its economic effects. In addition, researchers have investigated the effects of solar energy resulting from association with other applications, such as heating [4], cooling and air conditioning [5], and industrial processes [6]. Concentrated solar power (CSP) improves the utilization of solar energy and reaches a high energy output. Such applications include linear Fresnel lenses [7], parabolic trough collectors (PTCs) [8], and solar towers [9]. However, PTCs offer the ability to produce temperatures that have a superior efficiency as well as a limited cost when compared with other CSP applications. On this basis, several studies related to PTCs have aimed to investigate the geometry of the designs, optical efficiency, and methods to improve heat transfer. These studies have been summarized in several review papers [10,11]. In their prestigious reviews, [PERSON] and [PERSON] [12,13] summarized several techniques that have been utilized in the literature to improve the thermal efficiency of PTCs that, in turn, increase energy productivity at an acceptable cost. [PERSON] et al. [14] presented comprehensive details, on the present situation of using nanofluids in low- to medium-temperature PTC applications. Different methods (passive and active) were investigated experimentally and numerically for the improvement of thermal transfer in the PTC recipient section and their effect under the various conditions have been expounded in various studies [15,16]. [PERSON] and [PERSON] [17] numerically demonstrated how to test the improvements in thermal efficiency by using porous disks in PTC tubes using computational fluid dynamics (CFD). [PERSON] [18] experimentally tested the use of copper metal foam on the thermal efficiency of the recipient tube of a manufactured PTC. Recently, enhancements in PTCs have been reached using new modified thermal fluids called nanofluids. Those nanofluids have been obtained by adding nanoparticles, which have small diameters (10 nm-100 nm) to base fluids types to enhance their thermal properties. In fact, this is done to improve the PTC's thermal efficiency [19]. Interest in using nanofluids as an enhancement category has been indicated by the gradual increase of their use through in researches (either experimentally or numerically) [20]. Thermal enhancement using alternative fluids aims to raise the rate of fluid mixing or heat removal on the absorber tube's inner surface. Based on this, various evacuated or unevacuated tubes with different shapes have been examined under the impact of utilizing various types of nanofluid. [PERSON] et al. [21] evaluated the performance of an evacuated tube solar collector, using a carbon acetone nanofluid in the heat pipe. The results demonstrated that a thermal efficiency of 91% was achieved, above that of the average thermal efficiency (72.6%) when using acetone alone. [PERSON] et al. [22] numerically compared the thermal performance of a U-shaped evacuated tube resulting from the adding several nanoparticle oxides (CuO, Al\({}_{2}\)O\({}_{3}\), and TiO\({}_{2}\)) to water.