Field Controlled Charge and Heat Transfer Involving Macroscopic Charged Particles in Liquids

1975 ◽  
Vol 97 (3) ◽  
pp. 429-434 ◽  
Author(s):  
P. W. Dietz ◽  
J. R. Melcher
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Charged Particles ◽  
Particle Diameter ◽  
Particle Migration ◽  
Electrically Conducting ◽  
Fluid Convection ◽  
Experimental Values ◽  
Insulating Liquid ◽  
Parallel Electrode

When an electric field is applied to a system of electrically conducting particles in an insulating liquid, the rates of charge and heat transfer are augmented. Charged during collisions in the field, the particles execute field-induced excursions between the electrodes interrupted by collisions with other particles. Thus a combination of particle migration and particle-induced fluid convection results in the increase in heat transfer. Experimental values for the Nusselt number are obtained for heat transfer across the parallel electrode configuration. The model developed using these results consists of a well-mixed central region with thermal boundary layers about one particle diameter thick near each electrode.

A COMPARATIVE STUDY OF MULTIPLE REGRESSION AND MACHINE LEARNING TECHNIQUES FOR PREDICTION OF NANOFLUID HEAT TRANSFER

2021 ◽  
pp. 1-22
Author(s):  
Eyup Kocak ◽  
Ulku Ece Ayli ◽  
Hasmet Turkoglu
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Multiple Regression ◽  
Volume Fraction ◽  
Particle Diameter ◽  
Machine Learning Techniques ◽  
Exponential Factor ◽  
Nano Fluid ◽  
Neuro Fuzzy ◽  
Interface System

Abstract The aim of this paper is to introduce and discuss prediction power of the multiple regression technique, Artificial Neural Network (ANN) and Adaptive Neuro-Fuzzy Interface System (ANFIS) methods for predicting the forced convection heat transfer characteristics of a turbulent nano fluid flow a pipe. Water and Al2O3 mixture is used as the nano fluid. Utilizing FLUENT software, numerical computations were performed with volume fraction ranging between 0.3% and 5%, particle diameter ranging between 20 and 140 nm and Reynolds number ranging between 7000 and 21000. Based on the computationally obtained results, a correlation is developed for Nusselt number using the multiple regression method. Also, based on the CFD results different ANN architectures with different number of neurons in the hidden layers and several training algorithms (Levenberg-Marquardt, Bayesian Regularization, Scaled Conjugate Gradient) are tested to find the best ANN architecture. In addition, Adaptive Neuro-fuzzy Interface System (ANFIS) is also used to predict the Nusselt number. In the ANFIS, number of clusters, exponential factor and Membership Function (MF) type are optimized. The results obtained from multiple regression correlation, ANN and ANFIS were compared. According to the obtained results, ANFIS is a powerful tool with a R2 of 0.9987 for predictions.

scholarly journals Heat transfer studies in compact heat exchanger using ZnO and TiO2 nanofluids in ethylene glycol/water

2018 ◽  
Vol 24 (4) ◽  
pp. 309-318
Author(s):  
Srinivasan Manikandan ◽  
Rajoo Baskar
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Ethylene Glycol ◽  
Volume Fraction ◽  
Inlet Temperature ◽  
Percentage Increase ◽  
Cold Side ◽  
Volume Fractions ◽  
Experimental Values ◽  
Tio2 Nanofluids

This paper reports an experimental study on the heat transfer characteristics of a nanofluid consisting of ZnO/water/ethylene glycol (EG) and TiO2/water/ /ethylene glycol. In this study, the base fluids of ethylene glycol (EG):water (W) with volume fractions of 30:70, 40:60, and 50:50 were prepared, and 0.2 to 1.0 volume fractions of ZnO and TiO2 nanofluids were used as a cold side fluid. The prime objective of this study is to identify the effects of nanofluid concentration and three different hot fluid inlet temperatures viz., 55, 65 and 75?C C on the heat transfer enhancement of cold side fluid. The results are compared with base fluids and the percentage increase of the Nusselt number because of nanoparticle addition is noted both experimentally and theoretically. The results showed that at the hot fluid inlet temperature of 75?C, the increase in the Nusselt number is maximum with volume concentrations of 0.6 and 0.8% for ZnO and TiO2 nanofluids, respectively. The corresponding maximum Nusselt number enhancements are about 11.5 and 21.4%, respectively, for the base fluid volume fraction of 30:70 (EG:W). There is good agreement between the results calculated from experimental values and the correlation.

Parametric Study of Mixed Convection in a Porous Medium Between Vertical Concentric Cylinders

1991 ◽  
Vol 113 (1) ◽  
pp. 128-134 ◽  
Author(s):  
N. J. Kwendakwema ◽  
R. F. Boehm
Keyword(s):  
Heat Transfer ◽  
Porous Medium ◽  
Nusselt Number ◽  
Mixed Convection ◽  
Numerical Study ◽  
Convection Heat Transfer ◽  
Particle Diameter ◽  
Darcy Law ◽  
Axial Distance ◽  
Concentric Cylinders

A numerical study has been performed to evaluate mixed convection heat transfer in a porous medium between two vertical concentric cylinders for a constant-temperature outer and an insulated inner boundary conditions. In modeling the flow in the bed a finite difference technique was utilized to represent the governing equations with appropriate boundary layer assumptions. The effects of flow inertia, variable porosity and properties, and the Brinkman friction were all taken into account. The model simulated the condition where water was the fluid flowing through the porous material. In all flow simulations the Darcy law condition was obeyed, i.e., the Reynolds number based on the particle diameter was less than unity. Results obtained include radial and axial velocity and temperature profiles in the bed. The dependence of local Nusselt number on the axial distance for several Reynolds numbers was also obtained. Correlations of the average Nusselt number against the Grashof, Peclet, and Darcy numbers were obtained for various radius ratios. Comparisons of the heat transfer predictions to data and calculations of others for special situations showed excellent agreement.

scholarly journals Numerical Simulation of Flow and Heat Transfer in Structured Packed Beds with Smooth or Dimpled Spheres at Low Channel to Particle Diameter Ratio

Energies ◽  
2018 ◽  
Vol 11 (4) ◽  
pp. 937 ◽  
Author(s):  
Shiyang Li ◽  
Lang Zhou ◽  
Jian Yang ◽  
Qiuwang Wang
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Pressure Drop ◽  
Heat Transfer Performance ◽  
Particle Diameter ◽  
Packed Bed ◽  
Packed Beds ◽  
Transfer Performance ◽  
Heat Transfer Characteristics ◽  
Flow And Heat Transfer

Packed beds are widely used in catalytic reactors or nuclear reactors. Reducing the pressure drop and improving the heat transfer performance of a packed bed is a common research aim. The dimpled structure has a complex influence on the flow and heat transfer characteristics. In the present study, the flow and heat transfer characteristics in structured packed beds with smooth or dimpled spheres are numerically investigated, where two different low channel to particle diameter ratios (N = 1.00 and N = 1.15) are considered. The pressure drop and the Nusselt number are obtained. The results show that, for N = 1.00, compared with the structured packed bed with smooth spheres, the structured packed bed with dimpled spheres has a lower pressure drop and little higher Nusselt number at 1500 < ReH < 14,000, exhibiting an improved overall heat transfer performance. However, for N = 1.15, the structured packed bed with dimpled spheres shows a much higher pressure drop, which dominantly affects the overall heat transfer performance, causing it to be weaker. Comparing the different channel to particle diameter ratios, we find that different configurations can result in: (i) completely different drag reduction effect; and (ii) relatively less influence on heat transfer enhancement.

Pressure Drop and Heat Transfer of Nanofluid in Turbulent Pipe Flow Considering Particle Coagulation and Breakage

2014 ◽  
Vol 136 (11) ◽  
Author(s):  
Jian-Zhong Lin ◽  
Yi Xia ◽  
Xiao-Ke Ku
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Friction Factor ◽  
Pipe Flow ◽  
Volume Concentration ◽  
Particle Diameter ◽  
Turbulent Pipe Flow ◽  
Particle Volume ◽  
Friction Factors

Numerical simulations of Al2O3/water nanofluid in turbulent pipe flow are performed with considering the particle convection, diffusion, coagulation, and breakage. The distributions of particle volume concentration, the friction factor, and heat transfer characteristics are obtained. The results show that the initial uniform distributions of particle volume concentration become nonuniform, and increase from the pipe wall to the center. The nonuniformity becomes significant along the flow direction from the entrance and attains a steady state gradually. Friction factors increase with the increase of particle volume concentrations and particle diameter, and with the decrease of Reynolds number. The friction factors increase remarkably at lower volume concentration, while slightly at higher volume concentration. The presence of nanoparticles provides higher heat transfer than pure water. The Nusselt number of nanofluids increases with increasing Reynolds number, particle volume concentration, and particle diameter. The rate increase in Nusselt number at lower particle volume concentration is more than that at higher concentration. For a fixed particle volume concentration, the friction factor is smaller while the Nusselt number is larger for the case with uniform distribution of particle volume concentration than that with nonuniform distribution. In order to effectively enhance the heat transfer using nanofluid and simultaneously save energy, it is necessary to make the particle distribution more uniform. Finally, the expressions of friction factor and Nusselt number as a function of particle volume concentration, particle diameter and Reynolds number are derived based on the numerical data.

Heat Transfer to Flat Strips Immersed in a Fluidized Bed

2011 ◽  
Vol 133 (7) ◽  
Author(s):  
Christopher Penny ◽  
Dennis Rosero ◽  
David Naylor ◽  
Jacob Friedman
Keyword(s):  
Heat Transfer ◽  
Power Generation ◽  
Nusselt Number ◽  
Fluidized Bed ◽  
Manufacturing Industry ◽  
Particle Diameter ◽  
Orientation Angle ◽  
Heat Treating ◽  
Maximum Heat ◽  
Maximum Heat Transfer

Heat transfer to objects immersed in a fluidized bed has been studied extensively across a relatively large range of geometries, though most work has looked at cylinders, a geometry important in power generation fluidized bed applications. As the power generation industry has been the primary stimulant to fluidized bed heat transfer research, very little information is available regarding geometries significant in heat treating applications. In this work, heat transfer to thin flat strips immersed in a fluidized bed is examined. This geometry is important in the steel strap manufacturing industry where many manufacturers use environmentally damaging molten lead baths to heat-treat their product. In order to determine the feasibility of a fluidized bed heat treating system as an alternative to the more hazardous lead-based process, an experimental investigation has been conducted in which Nusselt number data for flat strips with widths in the range of 6.35–25.4 mm are obtained using a laboratory-scale fluidized bed (310 mm diameter). Aluminum oxide sand particles in the range of dp=145–330 μm (50–90 grit) are used as the fluidized media within the fluidized operating range from 0.15Gmf to approximately 10Gmf. The strip orientation angle θo was also varied to establish the position from which maximum heat transfer is obtained. It was found that a decrease in particle diameter, an increase in fluidizing rate, and an increase in sample diameter resulted in an increase in Nusselt number. It was also observed that for the smaller samples tested, a maximum Nusselt number plateau was reached, at approximately G/Gmf=2.5. Finally, it was shown that an increase in θo (from 0 deg to 90 deg) resulted in an increase in Nusselt number. A correlation for the maximum Nusselt number was developed, providing excellent agreement within ±15%.

scholarly journals Numerical Study of Heat Transfer Enhancement of Internal Flow Using Double-Sided Delta-Winglet Tape Insert

Energies ◽  
2018 ◽  
Vol 11 (11) ◽  
pp. 3170 ◽  
Author(s):  
Agung Wijayanta ◽  
Muhammad Aziz ◽  
Keishi Kariya ◽  
Akio Miyara
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Friction Factor ◽  
Thermal Performance ◽  
Numerical Study ◽  
Performance Factor ◽  
Thermal Performance Factor ◽  
Enhanced Tube ◽  
Delta Winglet ◽  
Experimental Values

A numerical study was performed to investigate the thermal performance characteristics of an enhanced tube heat exchanger fitted with punched delta-winglet vortex generators. Computational fluid dynamics modeling was applied using the k–ε renormalized group turbulence model. Benchmarking was performed using the results of the experimental study for a similar geometry. Attack angles of 30°, 50°, and 70° were used to investigate the heat transfer and pressure drop characteristics of the enhanced tube. Flow conditions were considered in the turbulent region in the Reynolds number range of 9100 to 17,400. A smooth tube was employed for evaluating the increment in the Nusselt number and the friction factor characteristics of the enhanced tube. The results show that the Nusselt number, friction factor, and thermal performance factor have a similar tendency. The presence of this insert offers a higher thermal performance factor as compared to that obtained with a plain tube. Vortex development in the flow structure aids in generating a vortex flow, which increases convective heat transfer. In addition, as the angle is varied, it is observed that the largest attack angle provides the highest thermal performance factor. The greatest increase in the Nusselt number and friction factor, respectively, was found to be approximately 3.7 and 10 times greater than those of a smooth tube. Through numerical simulations with the present simulation condition, it is revealed that the thermal performance factor approaches the value of 1.1. Moreover, the numerical and experimental values agree well although they tend to be different at high Reynolds number conditions. The numerical and experimental values both show similar trends in the Nusselt number, friction factor, and thermal performance factor.

Theoretical Post-Dryout Heat Transfer Model

2018 ◽  
Vol 1 (1) ◽  
pp. 142-150
Author(s):  
Murat Tunc ◽  
Ayse Nur Esen ◽  
Doruk Sen ◽  
Ahmet Karakas
Keyword(s):  
Heat Transfer ◽  
Droplet Diameter ◽  
Heat Transfer Model ◽  
Transfer Model ◽  
Operating Pressure ◽  
Vertical Pipe ◽  
Two Phase ◽  
Experimental Values ◽  
Reactor Operating ◽  
Coolant System

A theoretical post-dryout heat transfer model is developed for two-phase dispersed flow, one-dimensional vertical pipe in a post-CHF regime. Because of the presence of average droplet diameter lower bound in a two-phase sparse flow. Droplet diameter is also calculated. Obtained results are compared with experimental values. Experimental data is used two-phase flow steam-water in VVER-1200, reactor coolant system, reactor operating pressure is 16.2 MPa. On heater rod surface, dryout was detected as a result of jumping increase of the heater rod surface temperature. Results obtained display lower droplet dimensions than the experimentally obtained values.

scholarly journals Uncertainties Analysis on the Prediction of Flow and Heat Transfer of Liquid Sodium with CFD Technology

2020 ◽  
Vol 2020 ◽  
pp. 1-13
Author(s):  
Zhanwei Liu ◽  
Xinyu Li ◽  
Tenglong Cong ◽  
Rui Zhang ◽  
Lingyun Zheng ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Friction Coefficient ◽  
Liquid Sodium ◽  
Heat Transfer Characteristics ◽  
Backward Facing Step ◽  
Heating Wall ◽  
Transfer Characteristics ◽  
Cfd Models ◽  
Flow And Heat Transfer

The prediction of flow and heat transfer characteristics of liquid sodium with CFD technology is of significant importance for the design and safety analysis of sodium-cooled fast reactor. The accuracies and uncertainties of the CFD models should be evaluated to improve the confidence of the numerical results. In this work, the uncertainties from the turbulent model, boundary conditions, and physical properties for the flow and heat transfer of liquid sodium were evaluated against the experimental data. The results of uncertainty quantization show that the maximum uncertainties of the Nusselt number and friction coefficient occurred in the transition zone from the inlet to the fully developed region in the circular tube, while they occurred near the reattachment point in the backward-facing step. Furthermore, in backward-facing step flow, the maximum uncertainty of temperature migrated from the heating wall to the geometric center of the channel, while the maximum uncertainty of velocity occurred near the vortex zone. The results of sensitivity analysis illustrate that the Nusselt number was negatively correlated with the thermal conductivity and turbulent Prandtl number, while the friction coefficient was positively correlated with the density and Von Karman constant. This work can be a reference to evaluate the accuracy of the standard k-ε model in predicting the flow and heat transfer characteristics of liquid sodium.

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