Effect of Flow and Heat Transfer of Vertical Magnetic Field to Fe3O4-H2O Nanofluids

NANO ◽  
2021 ◽  
pp. 2150053
Author(s):  
Jiajie Lei ◽  
Sixian Wang ◽  
Xiaoyan Huang ◽  
Shan Qing ◽  
Fuyu Li ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Field Strength ◽  
Transfer Coefficient ◽  
Heat Exchangers ◽  
Convective Heat Transfer Coefficient ◽  
Vertical Magnetic Field ◽  
Flow And Heat Transfer ◽  
Magnetic Nanofluids

Heat transfer coefficient is a key parameter for efficiency evaluation of heat exchangers. Good stability and high heat transfer coefficient are essential for the application of nanofluids in heat exchangers and solar systems. In this work, nanofluids with good stability were prepared, and the influence of vertical magnetic field on flow and heat exchange of magnetic nanofluids under laminar and turbulent conditions was mainly studied. The flow and heat transfer rules of Fe3O4 nanofluids with or without magnetic field conditions, magnetic field strength, magnetic field distribution, the nanoparticle concentration and nanofluids temperature were systematically studied by setting up an experimental platform. The results show that the intensity and distribution of magnetic field had a significant influence on the heat transfer of magnetic nanofluids, whether in laminar or turbulent flow. When the magnetic field strength is 800G and 1000G, the convective heat transfer coefficient increases by an average of 23.89% and 26.12%. However, the influence of magnetic field on its flow characteristics is not obvious, and the effect on resistance coefficient increases by only 2.01%. In addition, the characteristics of magnetic nanofluids also have a certain influence on its flow and heat transfer. When the temperature of magnetic nanofluids is increased, the convective heat transfer coefficient will increase. When the concentration of magnetic nanofluids is increased, the pressure drop will also increase, but it has little effect on the drag coefficient.

A Critical Review on the Determination of Convective Heat Transfer Coefficient During Condensation in Smooth and Enhanced Tubes

2013 ◽  
Author(s):  
Ahmet Selim Dalkiliç ◽  
Ali Celen ◽  
Mohamed M. Awad ◽  
Somchai Wongwises
Keyword(s):  
Neural Network ◽  
Heat Transfer ◽  
Experimental Data ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Critical Review ◽  
Heat Exchangers ◽  
Convective Heat Transfer Coefficient ◽  
Enhanced Tubes

Heat exchangers using in-tube condensation have great significance in the refrigeration, automotive and process industries. Effective heat exchangers have been rapidly developed due to the demand for more compact systems, higher energy efficiency, lower material costs and other economic incentives. Enhanced surfaces, displaced enhancement devices, swirl-flow devices and surface tension devices improve the heat transfer coefficients in these heat exchangers. This study is a critical review on the determination of the condensation heat transfer coefficient of pure refrigerants flowing in vertical and horizontal tubes. The authors’ previous publications on this issue, including the experimental, theoretical and numerical analyses are summarized here. The lengths of the vertical and horizontal test sections varied between 0.5 m and 4 m countercurrent flow double-tube heat exchangers with refrigerant flowing in the inner tube and cooling water flowing in the annulus. The measured data are compared to theoretical and numerical predictions based on the solution of the artificial intelligence methods and CFD analyses for the condensation process in the smooth and enhanced tubes. The theoretical solutions are related to the design of double tube heat exchangers in refrigeration, air conditioning and heat pump applications. Detailed information on the in-tube condensation studies of heat transfer coefficient in the literature is given. A genetic algorithm (GA), various artificial neural network models (ANN) such as multilayer perceptron (MLP), radial basis networks (RBFN), generalized regression neural network (GRNN), and adaptive neuro-fuzzy inference system (ANFIS), and various optimization techniques such as unconstrained nonlinear minimization algorithm-Nelder-Mead method (NM), non-linear least squares error method (NLS), and Ansys CFD program are used in the numerical solutions. It is shown that the convective heat transfer coefficient of laminar and turbulent condensing film flows can be predicted by means of theoretical and numerical analyses reasonably well if there is a sufficient amount of reliable experimental data. Regression analysis gave convincing correlations, and the most suitable coefficients of the proposed correlations are depicted as compatible with the large number of experimental data by means of the computational numerical methods.

3D Numerical Simulation of Fluid Flow and Heat Transfer in Tube with Spiral-Flange Insert

2011 ◽  
Vol 236-238 ◽  
pp. 1508-1515
Author(s):  
Qun Song Li ◽  
Qian Yang ◽  
Zhi Song Li ◽  
Tian Lan Yu
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Heat Transfer Coefficient ◽  
Fluid Flow ◽  
Transfer Coefficient ◽  
Turbulence Intensity ◽  
Convective Heat Transfer Coefficient ◽  
3D Numerical Simulation ◽  
Flow And Heat Transfer ◽  
Smooth Tubes

With the help of Fluent 6.2 and supporting software, 3D numerical simulation of fluid flow and heat transfer enhancement of plastic spiral tubes were performed on computer, and the velocity, turbulence intensity and improvement of convective heat transfer coefficient distribution in plastic spiral tubes were analyzed and compared with those in smooth tubes, and characteristics of fluid flow and heat transfer were obtained. The results showed that there were obvious axial, tangential and radial velocities in spiral space, and they were bigger than those in smooth tubes. The turbulence intensity was also increased greatly because of the existence of spiral channels. The dirt production was prevented and the tube's convection heat transfer was effectively strengthened. Its surface average heat transfer coefficient had been enhanced by about 20% compared with the smooth tubes; The pressure drop caused by plastic spiral flange was in the permissible range of engineering application. It was suitable for the heat exchanger at a flow velocity lower than 0.8m/s.

Shell Side Flow and Heat Transfer Performances of Trisection Helical Baffle Heat Exchangers

2013 ◽  
Author(s):  
Yaping Chen ◽  
Cong Dong ◽  
Jiafeng Wu
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Exchangers ◽  
Incline Angle ◽  
Shell Side ◽  
Single Vortex ◽  
Flow And Heat Transfer ◽  
Helical Baffle ◽  
Side Flow

The flow and heat transfer performances of three trisection helical baffle heat exchangers with different baffle shapes and assembly configurations, and a continuous helical baffle scheme with approximate spiral pitch were numerically simulated. The four schemes are two trisection helical baffle schemes of baffle incline angle of 20° with a circumferential overlap baffle scheme (20°TCO) and a end-to-end helical baffle scheme (20°TEE), a trisection mid-overlap helical baffle scheme with baffle incline angle of 36.2° (36.2°TMO), and a continuous helical baffle scheme with baffle helix angle of 16.8° (18.4°CH). The pressure or velocity nephograms with superimposed velocity vectors for meridian slice M1, transverse slices f and f1, and unfolded concentric hexagonal slices H2 and H3 are presented. The Dean vortex secondary flow field, which is one of the key mechanisms of enhancing heat transfer in heat exchangers, is clearly depicted showing a single vortex is formed in each baffle pitch cycle. The leakage patterns are demonstrated clearly on the unfolded concentric hexagonal slices. The results show that the 20°TCO and 18.4°CH schemes rank the first and second in shell-side heat transfer coefficient and comprehensive indexes ho/Δpo and ho/Δpo1/3. The 20°TEE scheme without circumferential overlap is considerably inferior to the 20°TCO scheme. The 36.2°TMO scheme is the worst in both shell-side heat transfer coefficient and comprehensive index ho/Δpo1/3.

Heat Transfer Coefficient in Helical Heat Exchangers under Turbulent Flow Conditions

2008 ◽  
Vol 4 (1) ◽  
Author(s):  
Pablo Coronel ◽  
K.P. Sandeep
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Heat Exchangers ◽  
Convective Heat Transfer Coefficient ◽  
Flow Conditions ◽  
Overall Heat Transfer Coefficient ◽  
Turbulent Flow Conditions

This study involved the determination of convective heat transfer coefficient in both helical and straight tubular heat exchangers under turbulent flow conditions. The experiments were conducted in helical heat exchangers, with coils of two different curvature ratios (d/D = 0.114 and 0.078), and in straight tubular heat exchangers at various flow rates (1.89 x 10-4 - 6.31 x 10-4 m3/s) and for different end-point temperatures (92 - 149 °C). The results show that the overall heat transfer coefficient (U) in the helical heat exchanger is much higher than that in straight tubular heat exchangers. In addition, U was found to be larger in the coil of larger curvature ratio (d/D = 0.114) than in the coil of smaller curvature ratio (d/D = 0.078). The inside (hi) and outside (ho) convective heat transfer coefficients were determined based on the overall heat transfer coefficient and a correlation to compute the inside convective heat transfer coefficient (hi) as a function of NRe, NPr, and d/D was developed.

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