Convective effects on chemical waves. 3. Multicomponent convection in the iron(II)-nitric acid system
Convective effects on chemical waves. 3. Multicomponent convection in the iron(II)-nitric acid system
复制标题
化学波的对流效应。
DOI：
10.1021/j100156a050
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发表时间：
1991
期刊：
影响因子：
--
通讯作者：
I. Epstein
中科院分区：
文献类型：
--
作者：
J. Pojman;I. Nagy;I. Epstein
在以前的工作中，1我们分析了由移动锋引起的密度梯度的稳定性，以及自由对流的机制，这可能会极大地影响锋面速度。密度梯度是由释放或吸收的热量引起的，这是一种热效应。反应物和产物的偏摩尔体积的差异也会导致等温密度变化。我们确定，有两种不同的机制，对流可能会增加前速度，这取决于这两种效果的相对标志：简单对流和多组分（双扩散）对流。在前面的工作中，我们考虑了碘酸盐-亚砷酸体系中的简单对流。2在该系统中，简单对流增加了上升锋和水平锋的传播速度。下降的战线不受影响。这种类型的对流是烟雾上升的原因，也是燃烧的香烟过滤嘴朝上的速度增加的原因。3 Bazsa和Epstein 4在铁（II）-硝酸系统中观察到，在垂直管中，下降的锋面比上升的锋面传播得更快。最令人惊讶的是，不仅下降锋比上升锋传播得更快，而且必然是纯反应扩散锋，上升锋也比纯反应扩散锋传播得更快。简单的对流显然不是起作用的机制。一个模式的对流，增加前的速度上升和下降的锋是必要的，即使当密度梯度是静态稳定的。一种即使在表面上稳定的密度梯度下也会发生的对流称为
In a previous work, 1 we analyzed the stability of density gradients induced by traveling fronts, as well as the mechanisms of free convection, which may greatly affect the front velocity. Density gradients are caused by the heat released or absorbed, a thermal effect. The difference in thepartial molal volumes of the reactants and products can also result in an isothermal density change. We determinedthat there are two different mechanisms by which convection may increase the front velocity, depending on the relative signs of these two effects: simple convection and multicomponent (double-diffusive) convection. In the preceding work, we have considered simple convection in the iodate-arsenous acid system. 2 In that system, simple convection increased the propagation velocity for both ascending and horizontal fronts. Descending fronts were unaffected. This type of convection is the cause of smoke rising and the increase in the rate of a burning cigarette held filter side up. 3 Bazsa and Epstein4 observed in the iron (II)—nitric acid system that in a vertical tube descending fronts propagate more rapidly than ascending ones. What is most surprising is that not only do the descending fronts propagate more rapidly than the ascending ones, and necessarily the pure reaction-diffusion fronts, the as-cending fronts also propagate more rapidly than the pure reac-tion-diffusion fronts. Simple convection is clearly not the operative mechanism. A mode of convection that increases front velocity for both ascending and descending fronts is required, even when the density gradient is statically stable. A type of convection that can occur even with an apparently stable density gradient is called