The Impact of Electrostatic Forces on the Dynamic and Heat Transfer Coefficient of Single Bubble Rising: Electrostatic Forces Effect on the Dynamic of Single Bubble Rising by CFD

The Impact of Electrostatic Forces on the Dynamic and Heat Transfer Coefficient of Single Bubble Rising: Electrostatic Forces Effect on the Dynamic of Single Bubble Rising by CFD

Mohammad Ali Salehi (University of Guilan, Guilan, Iran) and Samaneh Poursaman (University of Guilan, Guilan, Iran)
DOI: 10.4018/IJCCE.2016070103
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In this study, the effect of an applied electric field on the separation and rise of bubble was simulated by Computational Fluid dynamics and results were compared with experimental data. The numerical results showed proper agreement (10%) with experimental reports. The working fluids in the experiment were air, water, and oil. During the simulation, the effects of different voltages on the bubble, bubble ascent, Reynolds and Nusselt number were investigated. The results showed that the more polar air bubbles in the fluid changed and diverted its route. Applying an electric field, reduces separation time, resulting in the formation of bubbles and more bubbles generated at the same time that it increases the heat transfer.
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The process of the bubbles formation seems to be simple phenomenon, but actually contains very complex dynamic interactions. Bubble formation constitute an important part of many chemical and natural processes (Sarnobat et al., 2004). Bubbles production from a submerged orifice in the liquid, plays an important role in perception of phenomena involving heat and mass transfer, both in industrial scale, such as absorbers, chemical reactors, carbonated drinks, mineral processing, and natural such currents underwater and volcanoes (Di Marco et al., 2003).

Generally, the size of the bubble and its dynamic profile, measured with three factors: 1) the form of bubbles, 2) join to each other bubbles and 3) pop bubbles to smaller one. To modeling these processes is essential that the first stage of gas injection, growth and separation which is so important for bubble shape and its direction through the liquid, checked by using a numerical method with high accuracy (Ohta, Imura, Yoshida, & Sussman, 2005).

Over the past three decades, major advances in numerical and computational methods has been occurred, evaluating the behavior of complex gas-liquid interface in a viscous fluid has been possible by helping O'Leary and Lagrange methods. In both methods, problem can be solved in which two-phase fluid is assumed to be a mixture and by Navier Stokes equations on a fixed network, with specifications that are on the common surface. Two common methods of lattice constant are volume of fluid (VOF) and the level set (LS) method (Nichita, Zun, & Thome, 2010). On the other hand the use of electro hydrodynamic method to increase the heat transfer coefficient and control the process of formation bubble and the effective parameters, interest to many researchers in the world. EHD processing is a method of generating liquid droplets through the application of a large electrical potential difference. This method can be used in the chemical industry, energy and other related industries. (Enayati, Chang, Bragman, Edrisinghe, & Stride, 2011).

To evaluate the effect of electro hydrodynamic on the process of the formation of bubbles, first Cho et al. (1996) examined the effect of invariable electric field on rising process of air bubbles in the liquid cyclohexane and observed that by applying an electric field, air bubbles drawn in line of electric field and with increasing field intensity, gravity rate increases. Then Dong et al. (2005) evaluated the effect of electric field due to the direct current on the dynamics behaviors of bubble including growth, deformation and separation. They observed that with increasing field intensity, speed of deformation of bubbles increases as well as contact hermitage. The rate of heat transfer and producing bubbles in the beginning and in the presence of field is less than the mode with no electric field. Furthermore, the rate of bubbles production in the absence of field is more than in the presence of the field. With increasing electric field intensity, the max rising of bubble, decreases (Siedel, Cioulachtjian, Robinson, & Bonjour, 2011). Albadawi et al. (2013) used two models of VOF and S-CLSVOF (combination of VOF and LS model) to simulate bubble growth, separation and compared the result of these two techniques. The result of this comparison showed that the use of combined method, which is the force of surface tension is an effective force, has more accuracy compared with the fluid volume method.

As is evident from the researches, evaluation of the effect of EHD mechanism on the heat transfer in different processes, need to understand the details of the local flows around the gas-liquid interface for the growing bubble while the details of the process due to the limited measurement methods has not been determined by experimental methods. For this reason, the numerical simulation as an effective tool is efficient for a detailed analysis of flow, heat transfer and other related mechanisms. Therefore, the objective of this investigation was to study the impact of different electric field strength, different flow rates of gas and eventually different fluids, on the dynamics of rising single bubble by using Dynamics of Computational.

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