Convective Heat Transfer of MgO-water nanofluid in a microchannel Heat sink is experimentally investigated in various concentrations of 0. 01, 0. 05, 0. 1, and 0. 6 wt%. The microchannel consisted of 48 parallel rectangular cross section channels with the height of 800 μ m, width of 524 μ m and length of 52 mm. A well stability duration (ca. 1 month) was resulted by a 180 min ultra-sonication of the MgO suspension. The experiments in the microchannel were then performed in a flow rate range of 0. 5 to 2. 2 l/min while the inlet temperature and Heat flux were constant. The results indicated that using the MgO nanofluid in low flow rates and concentration has less effect in improving the Heat Transfer Coefficient, while it becomes highly efficient by the simultaneous increase of flow rate and concentration. An enhancement of 162. 3% in Convective Heat Transfer Coefficient at the channel inlet was achieved at the concentration of 0. 6 wt% and the flow rate of 2. 2 l/min, and at the same condition, the average Nusselt number also increased up to 52. 8%. However, the nanofluid at 0. 1 wt% was more efficient compared to the other concentrations in increasing Nu at higher Re.

This study investigates the simultaneous estimation of Heat flux input into a work piece and Convective Heat Transfer Coefficient in milling operations. The material of the work piece is AISIH13. Temperatures in 5 points inside the work piece were measured using thermocouples(K-type). Two thermal models for the work piece were considered to solve the direct problem. Work piece material is an isotropic and the thermal property of work piece is constant. In the first thermal model, it is assumed that temperature changes only with time. This model uses the mean temperature of all thermocouples. For direct problem solving, the code of this model is written in MATLAB software. The second thermal model is a transient 3D problem and temperature inside work piece changes with time and location. This model uses the temperature of each thermocouple. For direct problem solving, the code of this model is written in ANSYS software. Heat flux and Convective Heat Transfer in two thermal models are unknown. Thus, the inverse Heat Transfer method is used to estimate the unknowns. This problem will not be solved by standard inverse algorithms. Thus, pattern search algorithm and Nealder-Mead method are used. For both of algorithms, MATLAB toolbox was used. In this study, two cutting speeds of: 50mm min and 100mm min were considered. The estimated values for of the unknowns by using two thermal models were different due to the assumptions are considered for models. The results obtained by two thermal models are independent of the inverse algorithms. The results show the Heat flux input into the work piece as the cutting speed increases. Convective Heat Transfer Coefficient increases with increasing the cutting speed in the first thermal model; however, this parameter decreases with increasing the cutting speed in the second thermal model. The main reason for this behavior is that, in the second thermal model, the temperature gradient in all directions (XYZ) inside the work-piece was considered. Estimated temperatures are in good agreement with measured temperatures.

Nanofluids are stable suspensions of nanoparticles in a conventional fluid. They have shown superior potential in Heat Transfer enhancement. In this research, ZnO/water nanofluids were prepared at various concentrations from 0. 2 to 1. 5vol%, and their thermal conductivity was measured. The results showed that the thermal conductivity of ZnO/water nanofluids depends on particle concentration and increases non-linearly with the volume fraction of nanoparticles. The effects of particle size and temperature on the thermal conductivity were also investigated at 1. 5vol%. The results indicated that thermal conductivity enhanced with decreasing particle size and increasing with temperature. For nanofluids containing 10-15 nm and 45-50 nm particle sizes, the enhancements were 26. 3 and 22. 8% at 40oC, respectively. In this research, the Convective Heat Transfer Coefficient of ZnO/water nanofluids with the above particle sizes was also measured under laminar flow in a horizontal tube Heat exchanger. It was observed that both nanofluids showed higher Heat Transfer Coefficients compared to the base fluid at a constant concentration (1. 5 vol%). For nanofluids with 10-15 nm and 45-50 nm particle sizes, the average Heat Transfer Coefficient enhancement was 18. 1 and 14. 9% at Re=1115, respectively.

Heat Transfer Coefficient and thermal efficiency of γ-Al2O3/water nanofluids flowing through a double tube Heat exchanger were experimentally investigated. The nanoparticles were well dispersed in distilled water at 0. 05– 0. 15 %vol. A large number of experiments were performed at different fluid flow rates under turbulent flow regime (18, 000

Nanofluids are suspensions of nanoparticles in base liquid and can be employed to increase Heat Transfer rate in various applications. In this work forced Convective Heat Transfer Coefficient of Al2O3/Ethylene Glycol nanofluid have been investigated experimentally in the double-pipe and plate Heat exchangers. Experimental results indicate that Heat Transfer Coefficient increases with nanoparticles concentration as well as operating temperature. Considerable deviations for high operating temperatures and nanoparticles concentration were observed from comparison of experimental and semi-empirical correlations’ results. The nanofluid Nusselt number for different nanoparticles concentrations as well as various operating temperatures was obtained and shown the enhancement up to maximum 50% using nanoparticles.

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.

Augmentation of Heat Transfer and pressure drop during laminar flow of oil inside one smooth tube and seven wire-coil inserted tubes of varying wire diameter and pitch have been investigated experimentally. The experimental set-up which was used in this investigation was an oil system equipped with all necessary instruments. The Heater of this system was a double pipe counter flow Heat exchanger in which oil is Heated inside inner tube by the steam flowing in the annulus. All together 120test runs with various flow rates were performed for plain and roughed tubes (tubes with coiled wire inserts). Results show that increase in the friction factor is comparatively low at lower Reynolds number and at higher values it is very large due to some induced turbulence. Also Heat Transfer Coefficients of tubes with coiled wire insert are significantly higher than plain tube and it is a function of Reynolds number, helix angle and Prandt1 number. The maximum obtained enhancement in Heat Transfer Coefficient was as high as 230 percent.On the basis of the experimental data of this investigation, a correlation was developed for predicting of Heat Transfer Coefficient during Heating of oil flowing inside tubes with coiled wire inserts. The Heat Transfer Coefficients calculated by this correlation were within ±20% of the experimental values for most of the data. So there is a good compliance between this correlation and experimental values.

The paper deals with the application of the infrared thermography to the determination of the Convective Heat Transfer Coefficient in complex flow configurations. The fundamental principles upon which the IRTh relies are reviewed. The different methods developed to evaluate the Heat exchange are described and illustrated through applications to the aerospace and aeronautical field as well as to the industrial processes.

This paper reports a review and comparison of the methods used for calculating Convective Heat Transfer Coefficient in combustion chambers and in diverging-converging nozzles. Therefore, a history of applying different methods for calculating the Convective Heat Transfer Coefficient is explained first. Then, the nozzle flow is numerically solved, using the explicit McCormack method. In a Bates nozzle, The methods of Bartz, Stanton, Preiskorn, and Adami were selected among the proposed methods and were compared with CFD. Convective Heat Transfer Coefficient of a solid fuel engine was calculated by taking into account the flow parameters in the engine chamber. Consequently, it was found that as wet move to the nozzle, Heat Transfer Coefficient increases with velocity of the flow. This results revealed that in analytical methods, the maximum Convective Heat Transfer Coefficient occurs in the nozzle throat, while CFD results show that the maximum occurs upstream of the nozzle throat. These methods require less computational time than CFD, however CFD has to be considered more accurately. As a result, during a preliminary design procedure, the much faster and slightly less precise method can be used, in particular at the throat where the relative difference between the methods is quite low. Finally, it was shown that the innovative approach of combining Adami and Bartz methods has the lowest possible error, compared to the CFD.