Entropy Generation Analysis of Laminar Flows of Water-Based Nanofluids in Horizontal Minitubes under Constant Heat Flux Conditions

Abstract

During the last decade, second law analysis via entropy generation has become important in terms of entropy generation minimization (EGM), thermal engineering system design, irreversibility, and energy saving. In this study, heat transfer and entropy generation characteristics of flows of multi-walled carbon nanotube-based nanofluids were investigated in horizontal minitubes with outer and inner diameters of~1067 and~889 µm, respectively. Carbon nanotubes (CNTs) with outer diameter of 10-20 nm and length of 1-2 µm were used for nanofluid preparation, and water was considered as the base fluid. The entropy generation based on the experimental data, a significant parameter in thermal design system, was examined for CNTs/water nanofluids. The change in the entropy generation was only seen at low mass fractions (0.25 wt.% and 0.5 wt.%). Moreover, to have more insight on the entropy generation of nanofluids based on the experimental data, a further analysis was performed on Al 2 O 3 and TiO 2 nanoparticles/water nanofluids from the experimental database of the previous study of the authors. The corresponding results disclosed a remarkable increase in the entropy generation rate when Al 2 O 3 and TiO 2 nanoparticles were added to the base fluid.

Fluid Flow and Entropy Generation Analysis of Al2O3–Water Nanofluid in Microchannel Plate Fin Heat Sinks

“…Figure 9 demonstrates the comparison of the Fanning friction factor between the current results and the available experimental results from Karimzadehkhouei et al [ 66 ], Hussien et al [ 68 ], Jung et al [ 80 ], Lee and Mudawar [ 81 ], Ho et al [ 82 ], Hussien et al [ 83 ], and Peyghambarzadeh et al [ 84 ]. It is observed that our results agree favorably with the experimental data reported by Karimzadehkhouei et al [ 66 ], Lee and Mudawar [ 81 ], Ho et al [ 82 ], and Hussien et al [ 83 ], and our results are close to the available analytical data from Duan and Muzychka [ 76 ]. Most of the experimental data from Peyghambarzadeh et al [ 84 ] are close to the theoretical solution.…”

“…Entropy generation minimization [ 52 , 53 ] and the principle of least action [ 54 , 55 , 56 ] are two important methods to study the performance optimization of a thermal system. Some efforts have been made to research into the entropy generation of different thermal systems [ 23 , 37 , 57 , 58 , 59 , 60 , 61 , 62 , 63 , 64 , 65 , 66 , 67 , 68 ]. Khan et al [ 59 ] studied the performance of MCHS using an entropy generation minimization procedure, and proposed a general expression evaluating irreversibilities.…”

Bio-coated surfaces with micro-roughness and micro-porosity: Next generation coatings for enhanced energy efficiency

“…The larger exergy losses between evaporator inlet and outlet in the non-coated evaporator are due to i) higher wall superheats required for the onset of nucleate boiling, ii) non-uniform surface temperature due to lower number of active nucleation sites, iii) larger frictional pressure drop due to the presence of larger vapor bubbles [47], [48], [49]. Generated larger bubbles (Figure 5) on the non-coated evaporator results in larger bubble slip velocity and higher deformability, which all eventually increase the frictional pressure drop of the boiling flow inside the 2-m long evaporator [50].…”

Heat transfer and entropy generation analysis of internal flow of nanorefrigerant with slip condition at wall

“…Moreover, entropy generation analysis results by Karimzadehkhouei, et al [21] show a significant increase in entropy generation while adding Al2O3 and TiO2 to the base fluid. The effect of slip boundary condition is not considered in their study as well.…”