An experimental investigation was carried out to study convective heat transfer of nanofluid flow inside an inclined copper tube under uniform heat flux condition. Required data are acquired for laminar and hydrodynamically fully developed flow inside a round tube. The stable CuO-base oil nanofluid with different nanoparticle weight fractions of 0.5%, 1% and 2% was produced by means of ultrasonic device in two steps method. In this study, the effect of different parameters such as tube inclination, nanofluid weight fraction and Reynolds number on heat transfer coefficient was considered. Results show that the heat transfer coefficient of nanofluid with different weight fractions increases with the increasing Reynolds number inside horizontal and inclined round tubes. Also, nanofluid flow inside the inclined tube at 30 degrees exhibit the most heat transfer enhancement amongst other tube inclinations at same Reynolds number.

In this study, the thermal characteristics of turbulent nanofluid flow in a helical tube in the tube heat exchanger (HTTHE) were assessed numerically through computational fluid dynamics (CFD) simulation. The findings of both the turbulent models: realizable k-epsion (k-ε ) and re-normalisation group (RNG) k-epsilon were compared. The temperature distribution contours show that realizable and RNG k-ε models, together with the swirl dominated flow are of more uniform temperature distributions. The proper prediction of two layer theory leads to having a uniform temperature distribution and proper dimensionless wall distance (Y+). The turbulent flow and heat transfer of two nanofluids (SiO2, Al2O3) and base fluid with respect to swirl dominated flow was simulated through the RNG model. The effects of the concentration of nanoparticles on heat transfer characteristics in HTTHE and two turbulent models were analyzed in a comprehensive manner. It is concluded that up to 1% concentration of SiO2 and 1% concentration of Al2O3, similar heat transfer characteristics are observed. Comparison between the CFD results with the predicted values for friction factor coefficient (f) and Nusselt number (Nu) calculated through experimental correlations indicate the maximum errors of 6. 56% and 0. 27%, respectively.

Improving the insulating and thermal properties of transformer oil is one of the factors in the use of nanoparticles (NPs) in oil. However, the use of NPs may only have a positive effect on some properties of the oil or even have a negative effect on the other properties of the oil. For this reason, hybrids nanofluid (HNF) were used to improve the properties of the transformer oil. By performing the Breakdown Voltage (BDV) test on different weight percentages (wt%) of TiO2 and CNT, it was proved that the best wt% for TiO2 is 0. 0075 and for CNT is 0. 001 to maximize the BDV. In this case, the HNF was able to improve the BDV and heat transfer by 9% and 8%, respectively. Another surprise that the HNF has been able to reduce the amount of C2H4 and C2H6 dissolved in oil by more than 70%. This reduction in the number of gases has another very desirable result and has reduced the PD by 63%. HNF proved that by using the right combination of different nanomaterials in transformer oil, more properties of the transformer oil can be improved.

Heat transfer is one of the most critical processes in the industry, and by increasing the efficiency of the heat exchanger, energy consumption of systems will be reduced. Very tiny particles in nanoscale dimensions, when uniformly dispersed and stably suspended in the base fluid, efficiently improve the thermal properties of the base fluid. With the help of nanofluids, the heat transfer rate increase. The purpose of this research is to investigate the thermal and hydraulic characteristics of nanofluid in turbulent flow regime in a plate heat exchanger with a sine pattern in which cold and hot flows alternately pass through the plates. First, problem geometry is modeled and simulated in ANSYS-FLUENT software. All properties of nanoparticles are dependent on temperature, velocity, and particles diameter, and are added to software in the form of a separate code. Simulations are for different parameters such as wavelength to amplitude ratio (L/A), Reynolds number, volume fractions of nanoparticles and nanoparticle diameter. The results indicate that the best shape of the wave for the highest heat transfer rate in the heat exchanger is gained for equal wave amplitude and wave length.

In this investigation, Control Volume based Finite Element Method is applied to simulate the effects of different governing parameters on natural convection heat transfer in an inclined L-shape enclosure filled with Cu-water nanofluid. The numerical investigation is performed at a fixed Prandtl number (Pr) equal to 6.2 and various values of non-dimensional governing parameters namely, volume fraction of nanoparticles, Rayleigh number and different inclination angles. The results show that for Ra=104 the maximum and minimum average Nusselt number correspond to z=-45o and 45o respectively, whereas an opposite trend is observed for Ra=105.

This study has primarily aimed at the examination of the effect of flow rate, solid volume fraction and their interactions on the Nusselt number of Al2O3/water nanofluids. To investigate the main and interaction effects on the response, Response Surface Methodology (RSM) has been used based on the miscellaneous design. By using the analysis of variance (ANOVA) the significance of the model is tested. The responses to the Nusselt number of nanofluids are also estimated using second-order polynomial equations. The results show that the Nusselt number increases with a higher amount of flow rate and solid volume fraction. According to the analysis of variance, the Reynolds number (A), first and second order of effects of volume fraction (B, B2), the interaction of Reynolds number and volume fraction (AB) are the most effective factors on the Nusselt number. Finally, the optimum condition of the process is predicted based on the RSM method. Having considered the optimum condition, the Nusselt numbers are compared with experimental data. The results show that there is a good agreement between the results of the proposed model and experimental data. Therefore, according to the results, the Nusselt number is precisely predictable in the model proposed by the Design Expert software.

The onset of convection in a porous medium saturated by a dielectric nanofluid with vertical AC electric field is investigated. The flux of volume fraction of a nanoparticle with the effect of thermophoresis is taken to be zero on the boundaries and the eigenvalue problem is solved using the Galerkin method. The model used for nanofluid incorporates the combined effect of Brownian diffusion, thermophoresis and electrophoresis, while for porous medium Darcy model is employed. The results show that increase in the AC electric Rayleigh-Darcy number, the Lewis number, the modified diffusivity ratio and the concentration Rayleigh-Darcy number are to hasten the onset of convection. The size of convection cells does not depend on nanofluid parameters, but decreases with increasing the AC electric Rayleigh-Darcy number. The non-existence of oscillatory convection is also obtained.