Iranian Journal of Chemical Engineering (IJChE)

Abstract In this novel study, various heat exchangers are compared to identify the most efficient one for heat transfer. This investigation involves shell and tube, double pipe, and plate heat exchangers, of which each is filled with different nanofluids. Following several hours of operation, output temperatures are recorded. The effects of nanofluids, containing aluminium oxide, magnesium oxide, and silicon oxide, at concentrations of 0.2%, 0.4%, and 0.6% are simulated. These simulated results are then compared with laboratory findings. Among the tested nanofluids, the most significant enhancement in the heat transfer coefficient is demonstrated by magnesium oxide, achieving a 40% improvement. Additionally, graphs illustrating the increase in the heat transfer coefficient and Nusselt number for Reynolds numbers of 900, 600, 300, and 1800 are obtained and compared. Finally, tables summarizing the tests performed on different heat exchangers using various nanofluids are presented. Using laboratory-obtained temperatures, several parameters are calculated, including the logarithmic mean temperature difference, heat loss from hot water, heat gain by cold water, overall heat transfer coefficient, and total heat transfer. Based on these analyses, the shell and tube heat exchanger was purposed as the most efficient heat exchanger with the overall heat transfer coefficient of 5.06 W/m²K.

Abstract The effect of temperature (25, 40, 55 and 70°C) and weight fraction of MWCNTs (0.125, 0.25 and 0.5 %wt) on the viscosity of nanofluids containing pristine and functionalized MWCNTs have been investigated. For this purpose, all of the measurements were carried out in triplicate and were analyzed using two factors completely randomized design and comparison of data means is carried out with Duncan’s multiple range test. The level of statistical significance was determined at 95%. The experimental and statistical results show that the viscosity of the both nanofluids increases with respect to the weight fraction and by decreasing the temperature. Statistical analysis of viscosity shows that temperature, weight fraction and interaction effect of them have a significant influence on the viscosity of nanofluids containing pristine and functionalized MWCNTs (α=0.05). Meanwhile, the results show that there was a significant difference at different levels of temperature on the viscosity of the both nanofluid.

Abstract In this paper, three-dimensional incompressible laminar fluid flow in a rectangular microchannel heat sink (MCHS) using Al2O3/water nanofluid as a cooling fluid is numerically studied. CFD prediction of fluid flow and forced convection heat transfer properties of nanofluid using single-phase and two-phase model (Eulerian-Eulerian approach) are compared. Hydraulic and thermal performance of microchannels are investigated according to the results of the friction factor, pumping power, average heat transfer coefficient, thermal resistance, average temperature of the walls and entropy generation. In addition, due to the CFD results, two correlations for predication of Nusselt number and friction factor are presented. Comparing the predicted Nusselt number using single-phase and two-phase models with experimental data shows that the two-phase model is more accurate than single-phase model. The results show that increasing the volume fraction of nanoparticles leads to increases the heat transfer coefficient and reduces the heat sink wall temperature, but it leads to the undesirable effect of increase in pumping power and total entropy generation.

Abstract Using Co-Mo/MgO catalyst, single walled carbon nanotubes with a diameter of 2nm and a length of 10 μm were produced by chemical vapor deposition process and characterized by XRD, FTIR and SEM. Synthesized single-walled carbon nanotubes were dissolved in water to make a 1w% solution and stabilized by adding sodium dodecyl sulfate surfactant. The synthesized stabilized nanofluid was used in the gaseous hydrate formation at a temperature of 4˚C and pressure of 1000 psig. The results were compared with a water/surfactant control solution and it was found that carbon
nanotubes have reduced the duration of dissolution process by 58.9% and duration of the induction process by 75.5%. In addition, the amount of gas entrapment and stability of the gas in the hydrate were increased by 13.6% and 18.2%,  respectively.

Abstract The turbulent convective heat transfer and pressure drop characteristics of CNT-water nanofluid in a horizontal tube fitted with wire coil inserts are studied experimentally. CNTs were synthesized by chemical vapor deposition (CVD) method with purity of more than 99%, functionalized by acid treatment and dispersed in distilled water in different concentrations. Also, the thermal conductivity and viscosity of synthesized nanofluids were measured experimentally. Convective heat transfer experiments are conducted with water and nanofluids in the range of 5000 < Re < 22000, CNT volume concentration 0 < ϕ < 0.1 % and wire coil with wire pitch of 2. The experimental results indicate that the convective heat transfer increases up to 23% in 0.05 vol% CNT-nanofluid and the heat transfer coefficient increases with CNT vol% and Reynolds number. Wire coil inserts increase the heat transfer coefficient of water and nanofluids up to 102% in Re=5700 but its performance decreases with Reynolds number. Experiments have shown that only use of wire coil inserts increases pressure drop of working fluid. Moreover, empirical correlations for Nusselt number and friction factor are proposed from nonlinear regression of the experimental data. Further, performance evaluation of enhanced tube is determined with considering opposing thermal resistance.

Abstract In this study, forced convection heat transfer of non-Newtonian nanofluids in a horizontal tube with constant wall temperature under turbulent flow conditions was investigated using computational fluid dynamics tools. For this purpose, non-Newtonian nanofluids containing three types of nanoparticles (Al2O 3, TiO 2 and CuO) with carboxymethylcellulose aqueous solution as a liquid single phase with three average particle sizes of 10, 25 and 40 nm nanofluids were investigated. Effects of nanoparticle type and Peclet number on the convective heat transfer coefficient were investigated in fully turbulent region of a horizontal tube. A correlated equation was obtained for Nusselt number using the dimensionless numbers by applying the simulation results. Results showed that the correlated data were in very good agreement with the experimental ones obtained from the literature. The maximum error was 12%.

Abstract In the current study, numerical simulation of laminar flow and heat transfer of water mixture with carbon nanotubes (CNT) as nanofluids in a 90 degree curved pipe are considered. The incompressible Navier-Stokes and energy equations are solved numerically in a body fitted coordinates system using a control volume technique. An interfacial layer-based model is applied to predict the thermal conductivity of nanofluid. The axial velocity contours, secondary flow patterns and temperature fields for different values of the particles concentrations are examined in detail. Furthermore, the effects of nanoparticles concentration on the heat transfer are studied. The results indicate that due to the secondary flows induced by curvature effects, the heat transfer rate is improved, and enhanced remarkably further using nanofluids. Furthermore, the nanoparticles, especially at higher concentration levels, generate more uniform cross sectional temperature distributions.