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.

Drilling muds are the most applicable fluids in drilling. Two basic types of drilling fluids are used, water based muds (WBM) and oil based muds (OBM). Water based muds are more applicable than oil based muds. One of the most important applications of this fluid is cooling a bit. Chemical engineers try to change drilling mud‘s rheological property in order to increase heat transfer to the bit. Rheological properties of drilling muds are well described by the Herschel Bulkley model. Adding polyacrylic acid to water changes its rheological property to Herschel Bulkley fluid. Standard equations like Shah and London and Hausen correlations were not able to predict local NUSSELT NUMBER of non-Newtonian fluids. This study concerns estimating parameters of a local NUSSELT NUMBER of Herschel Bulkley fluids with CuO nanoparticles in four concentrations of 0.1, 0.3, 0.6 and 0.05% in constant heat flux and laminar region. A nonlinear optimization algorithm (CMA-ES) was used to estimate local NUSSELT NUMBER. There is good agreement between experimental data and those predicted by proposed correlations with R2 greater than 0.99.

The present study aimed to experimentally investigate the heat transfer in Fe3O4 / water ferrofluid in a channel with a square cross-section, ​​0.8 m × 0.01 m × 0.01 m in dimension under the influence of uniform heat flux in a laminar flow regime in the presence of a local external magnetic field. Local NUSSELT NUMBER investigated with different volume fractions (0.5 and 1 vol.%) in the presence of magnetic field and under the influence of some heat fluxes (30, 86.7, 229.95, 433.65, 573.51 Watts). The heat flux is applied evenly to all surfaces of the duct. The effect of heat flux, local magnetic field, and volume fraction of Ferro-particles on NUSSELT NUMBER are investigated simultaneously and separately. Under the external local magnetic field, the NUSSELT NUMBER increased 1.33 times. Under the influence of an external local magnetic field compared to pure water, the NUSSELT NUMBER increased 1.36 times. These maximum values ​​occurred in 1 vol.% and the lowest applied heat flux of 30 Watts. These results show that usage of Fe3O4 particles and externally applied magnetic fields have a synergistic effect on increasing the NUSSELT NUMBER.

In this article, turbulent flow heat transfer in the air gap between rotor and stator of a generator under nonhomogenous heat flux is studied experimentally. The rotor consists of four symmetrical triangular grooves. The stator surface is smooth and does not include any grooves. The relative heat flux between the rotor and the stator is 1 to 3. Temperature and heat flux are measured locally at three axial and two angular positions of inner and outer surface. The pressure drop of air flow through the air gap is also measured. In this work, the axial Reynolds NUMBER and rotational velocity of the rotor ranges are 4000<Rez<30000 and 300rpm<w<1500rpm, respectively. The results indicate that increasing the rotational velocity causes the rotor and stator heat transfer coefficient to increase considerablly and the respective value to the rotor is higher than that to the stator. In addition, the rotational velocity causes the air flow to be developed sooner.

The heat transfer coefficient of fluid is one of the most important effective factors on the performance of fluid in the heat transfer process. Due to the higher conductive heat transfer coefficient of metals than liquids, metal particles can be used to increase the heat transfer rate of liquids. Nanofluid is one of the novels and developing methods to improve the heat transfer rate in heat exchangers. In this paper, the main effective parameters (flow rate and concentration) on increasing the convective heat transfer coefficient of water carbon nanofluid compared with water as a base fluid, are investigated in the Reynolds range of 7,100 to 16,700. The results illustrate that increasing the Re leads to increase in the NUSSELT NUMBER and convective heat transfer coefficient, and also to decrease the friction factor. It is also shown that at a constant Re, carbon nanofluid is able to enhance the convective heat transfer coefficient up to 10.17%, compared with pure water. It is found that adding carbon nanoparticles to water, initially leads to increasing the convective heat transfer coefficient, while this trend continues until the concentration of about 0.2 wt%, and then has a descending trend. In addition, the pressure drop was investigated due to changes in Re and was shown that the behavior of this curve is in agreement with Moody’s diagram.

The usages of Stirling engine in many industries such as aerospace, submarines and combined heat and power systems, requires more and detailed analysis in such engines. This type of engine is an external combustion which may use almost any type of fuel. In this article the NUSSELT NUMBER and friction coefficient of a Stirling engine heat exchanger is investigated numerically. The geometry of this heat exchanger is an arc shape pipe with reciprocating flow. Various parameters such as angular frequencies, type of fluids, working gas pressures, flow regime and heater geometry impact on the NUSSELT NUMBER and friction coefficient of the heater were investigated. By increasing the angular frequency and the working gas pressure the NUSSELT NUMBER increases but the friction coefficient decreases. The influences of different working fluids indicated that carbon dioxide has the highest NUSSELT NUMBER. The results also show that the friction coefficient is highly dependent on the flow regime. Comparison between the two different geometry type heaters shows that the arc-type geometry led to higher NUSSELT NUMBER. The friction coefficients of both geometries are almost similar to each other at high frequencies.

The aim of this paper is to study the local NUSSELT NUMBER of the symmetrical liquid-liquid jets emitting from a nozzle. Equations obtained from theoretical works are arranged in the form of a computerized model. The validity of this model was tested by the data from an experimental paper [1]. After few adjustments the model predicted the experimental data with a reasonable accuracy. Making sure of the model acceptable operation the effects of changes of hydrodynamic and thermal parameters on local NUSSELT NUMBER were investigated which eventually lead to an equation for predicting numerical values of local NUSSELT NUMBER as a function of liquid jet length.

Solving many important industrial problems requires knowing the values of the heat transfer coefficient of passing of one or more fluid streams in different equipment, systems or pipes. In the present study, a numerical model has been developed to simulate compressible fluid flow at the inlet of a hot pipe with different angles to the horizon. In this zone, the hydrodynamic and thermal boundary layers of the fluid flow are developing. Due to the turbulence of the fluid flow due to the interaction of heat and fluid flow inside this tube, a three-dimensional turbulent model was used for this simulation. For this purpose, continuity and compressible Navier-Stokes equations, Reynolds stress model, and turbulent and compressible energy equation have been solved simultaneously. Then, using a set of numerical runs by the concepts of experimental design and optimization methods, a predictive formula for the NUSSELT NUMBER for these flows has been obtained. Finally, the ability of this formula has been investigated using a set of laboratory data.

Because of anomalous heat transport behavior in nanofluids, several possible mechanisms suggested by various authors to explain the thermal conductivity and heat transfer coefficient enhancement lack unanimity. Hence, this research article aims to explore convective heat transfer enhancement mechanisms by correlating them with observed experimental data of nanofluids. The analysis is carried out by comparing the order of magnitude of different diffusion mechanisms for different types of nanofluid systems. Four different types of nanofluids, Al2O3/EG-W (0. 6, 0. 9, 1. 2, and 1. 5 vol. %. ), Al2O3/PG-W (1, 1. 5, 2, and 2. 5 vol. %. ), CuO/PG-W (0. 25, 0. 5, 0. 75 and 1 vol. %) and MgO/PG-W (0. 3 and 0. 66 vol. %) have been studied in this research. A generalized mechanism-based correlation has been proposed to predict the NUSSELT NUMBER for these nanofluids, for flow through a straight tube under laminar conditions. Results showed that the Brownian motion is very slow in comparison to nano convection-diffusion and heat diffusion. The proposed model predicted the combined data for all the nanofluids studied well within a range of ± 5%. Statistical errors of the proposed model were also calculated. Data from other authors were also validated using the proposed correlation, and the parity plot showed that the relationship predicted the data well within a range of ± 15%.

Examining the cooling rate using impingement of air jet finds a wide application in electronic packaging and micro-scale fluid heat interaction systems, While the prediction of NUSSELT profile at low nozzle-target spacing is a big issue. The plot of area average NUSSELT NUMBER magnitude against the nozzle-target spacing (Z/d) shows a gradual decrement in the profile upto Z/d = 1 and beyond that is steady. The present work aims in anticipating the profile of NUSSELT NUMBER using semi-empirical relations. These semi-empirical relations are derived using using regression analysis which is carried out between Re, Z/d and local NUSSELT NUMBER. The data required for regression are obtained through computation. Numerical simulations are accomplished for different impinging and geometric parameters. The semi-empirical power law relations are correlated between Z/d and Re. These are predicted differently for four distinct region of heat sink (stagnant point, near jet region, far jet region, near wall region). The developed correlations are found to bear negative exponent with Z/d and positive exponent with Re. The negative power of r/d and Z/d varies from 0. 23 – 0. 64 and 0. 0025 – 0. 38, respectively, While the exponents of Re varies in the positive range of 0. 4-0. 76.