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首页> 外文期刊>International Journal of Heat and Mass Transfer >Heat/mass transfer from a drop translating in steady and time-periodic electric fields: External problem
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Heat/mass transfer from a drop translating in steady and time-periodic electric fields: External problem

机译：液滴在稳态和周期性电场中的热/质量传递：外部问题

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Enhancement of heat or mass transport from a spherical drop of a dielectric fluid translating in another dielectric fluid in the presence of steady and time periodic electric fields (both uniform and non-uniform) is investigated in this paper. The external problem or the limit of the majority of the transport resistance being in the continuous phase is considered. Using a finite volume formulation, the transient energy (species) conservation equation is solved for Peclet numbers (Pe) varying from 10 to 1000 and dimensionless electric field frequency (ω~*) from 10 to 50,000 using a fully implicit method. To map the infinite domain in the radial direction, an exponential transformation is employed that provides a fine grid spacing near the drop surface where sharp variations are expected and a coarser grid in the far field where low gradients prevail. The transient temperature distribution and the local and the average Nusselt numbers are obtained and the heat/mass transfer enhancement due to the application of electric field is determined. The effect of electric field is expressed in terms of L, the ratio of the maximum electric-field-induced surface velocity to the translation-induced surface velocity. For the steady and time-periodic electric fields, the heat transfer enhancement increases monotonically with Pe and with L. Also, the heat transport rate is higher when the continuous phase is more viscous compared to the dispersed phase. The steady uniform electric field gives the highest average Nusselt number for heat transfer from the drop surface to the continuous phase, followed by the non-uniform time periodic electric field and then the time periodic uniform electric field. The enhancement relative to pure translation exhibits a non-monotonic dependence on electric field frequency but the highest value is obtained at ω~*= 0. Earlier studies have shown that there is significant enhancement in the heat/mass transfer in the drop interior with a time periodic electric field compared to a steady uniform electric field when the majority of the transport resistance is in the drop. The results presented here show that an opposite behavior is obtained in the drop exterior, i.e. a steady electric field provides higher heat/mass transfer enhancement compared to a time periodic electric field, when the bulk of the transport resistance is in the continuous phase. Therefore whether the steady or the time periodic electric field provides the most enhancement of heat/mass transfer for a conjugate problem will depend on the relative transport resistance in the two phases.
机译：本文研究了在稳定和时间周期电场（均一和非均一）存在下，电介质的球形液滴在另一种电介质流体中平移时，热量或质量传递的增强作用。考虑了外部问题或处于连续相的大多数运输阻力的极限。使用有限体积公式，使用完全隐式方法求解了从10到1000变化的Peclet数（Pe）和从10到50,000的无量纲电场频率（ω〜*）的暂态能量（物种）守恒方程。为了在径向上映射无限域，采用了指数变换，该变换提供了在液滴表面附近的细网格间距（预期会出现急剧变化），而在较远的场域中则提供了较低梯度的较粗网格。获得瞬态温度分布以及局部和平均努塞尔数，并确定由于施加电场而引起的热/质传递增强。电场的影响用L表示，即最大电场感应表面速度与平移感应表面速度之比。对于稳态和周期性的电场，传热增强随Pe和L单调增加。而且，当连续相比分散相粘稠时，传热速率更高。稳定的均匀电场为从液滴表面到连续相的传热提供了最高的平均Nusselt数，其次是非均匀时间周期电场，然后是时间周期均匀电场。相对于纯平移的增强表现出对电场频率的非单调依赖性，但最大值在ω〜* = 0时获得。早期的研究表明，液滴内部的热/质传递显着增强。与大多数运输阻力处于下降状态时的稳定均匀电场相比，时间周期电场具有更高的稳定性。此处给出的结果表明，在液滴的外部处于连续相时，在液滴外部获得了相反的行为，即与时间周期电场相比，稳定电场提供了更高的热量/质量传递增强。因此，对于共轭问题，稳态电场或周期性电场是否能最大程度地提高热量/质量传递，将取决于两相中的相对输运阻力。

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