Fundamental study of design of small size DMFC by using Marangoni convection

燃料电池被期望作为各种领域中的清洁能源。研制了一种PEMFC野外车。另一方面，DMFC适用于小型产品，如笔记本电脑和手机。然而，甲醇的供给方法是亟待解决的问题，因为与目前的情况相比，DMFC的尺寸需要1/10。目前，泵的尺寸都很小，为了使泵的尺寸大大缩小，必须开发新型的供水方式。为此目的，进行了基础性研究，以开发新型的甲醇供应，利用马兰哥尼对流。（A）气液两相流的影响：数值模拟了FC运行过程中化学反应产生的CO_2气泡对Marangoni对流的影响。模拟结果表明，气泡扰动界面，抑制了Marangoni对流。此外，还发现气泡抑制了催化剂上的化学反应并降低了电流密度。利用该仿真程序可以计算极限电流密度。(B)热力和溶质Marangoni对流共存效应：数值研究了热力和溶质Marangoni对流共存效应对流体流动的影响。结果表明，热Marangoni对流决定了液体中的流动结构。然而，它也被发现，溶质Marangoni对流是重要的局部结构流。特别是，溶质Marangoni对流引起的速度相对较慢，因为随着流动的发展，浓度梯度变得平缓。

A fuel cell is expected as a source of clean energy in the various fields. A PEMFC is developed in the field vehicle. On the other hand, a DMFC is suitable for small size product such as note PCs and cell phones. However, method of methanol supply is serious problem to be solved because 1/10 size of DMFC is required compare with the present situation. At present, small size of pump is used for it. In order to shrink the size very much, new type of supply method must be developed. For this purpose, fundamental study was carried out for development of new type of methanol supply by using Marangoni convection. The following results were obtained ;(A) Effect of gas-liquid two-phase flow:Numerical simulation was carried out for the effect of CO_2 bubbles which was induced by chemical reaction during FC running on the Marangoni convection. Simulation results showed the bubbles disturbed the interface and suppressed the Marangoni convection. Also, it was found that the bubbles suppressed the chemical reaction on the catalysis and decreased electrical current density. By using this simulation code, calculation of limit current density is available.(B) Co-existence effect of thermal and solutal Marangoni convection:Effect of co-existence effect of thermal and solutal Marangoni convection on fluid flow was numerically investigated. It was found that thermal Marangoni convection determine the flow structure in the liquid. However, it was also found that solutal Marangoni convection was important for local structure of flow. Especially, velocity induced by solutal Marangoni convection was relatively slow because the concentration gradient became gentle as flow developed.