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.

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 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.

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.

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.

In this Study, radiator performance for passenger car has been studied experimentally in a wide range of operating conditions. Experimental prediction of NUSSELT NUMBER and heat transfer coefficient for coolants in radiator tubes are also performed with e-NTU method. The total effectiveness coefficient of radiator and heat transfer coefficient in air side is calculated via trial and error method considering experimental data. The Colburn factor and pressure drop are also estimated for this heat exchanger. Examples of application demonstrate the practical usefulness of this method to provide empirical data which can be used during the design stage.

Vapor compression is an effective method of desalination in a small scale system. Such system has two hot outlet flows. These flows are used to preheat the feed water. In this research, tube-in-tube heat exchanger with different NUMBER of inner tubes was designed and constructed as preheater. This heat exchanger contains many inner tubes where each tube is a separate inner flow line for hot flow. Heat exchanger was tested with one, two and three inner tubes. Volumetric flow rates varied from 30 to 120 lit/h in annulus and 20 to 90 lit/h for inner tubes respectively. The results showed that by changing the NUMBER of inner tubes from 1 to 3, heat transfer increased 29%. However, 38.4% decrease in equivalent hydraulic diameter led to 22% drop in average NUSSELT NUMBER. Afterward, a dimensionless coefficient of performance enhancement, defined as the ratio of heat transfer rate variation and the required pumping power, was used to determine NUMBER of inner tubes. The results implied that heat exchanger performance improved by increasing the NUMBER of inner tubes from 1 to 2. But there is no significant improvement when NUMBER of inner tubes changes from 2 to 3. Finally, a semi-empirical equation is presented for determination of NUSSELT NUMBER in a heat exchanger with two inner tubes. This study indicated that this type of heat exchanger has the best performance for the system within the tested range.

The present study aims to investigate numerically the natural convection of various nanofluids inside a square enclosure with a central heat source at different aspect ratio. Also, some correlations are presented in order to calculate the NUSSELT NUMBER in terms of Rayleigh NUMBER and volume fraction of nanoparticles. The heat source and cavity walls are kept at constant temperatures of Th and Tc, respectively. The nanofluids are considered to be water as the base fluid and different nanoparticles such as Cu, CuO, Ag, Al2O3, or Tio2. To discretize the governing equations, the control volume method and SIMPELER algorithm have been employed. The study has been carried out for aspect ratios from 0.2 to 0.8, Rayleigh NUMBERs from 1e3 to 1e6 and the volume fractions of nanoparticles ranging in 0-0.05. The results indicated that the NUSSELT NUMBER increases with increasing the volume fraction of nanoparticles as well as the aspect ratio. Furthermore, by increasing the Rayleigh NUMBER, some eddies, of kind of Rayleigh-Benard, are developed in the space between the heat source and the upper wall of the enclosure. Based on the obtained results, several correlations with high accuracy have been present in order to evaluate the NUSSELT NUMBER.