Development of intelligent micro cooling system utilizing ER effects

我们试图开发一种新的利用液晶的冷却系统，它在外加电场的作用下表现出电流变效应，并通过温度控制来实现相变。在该项目的早期阶段，人们发现通过施加电场可以控制液晶的流动速度。但是，由于液晶具有较高的粘度和相似的换热特性，很难获得比水系统更高的冷却效率。因此，我们研究了近晶液晶作为功能流体的适用性，利用近晶液晶的屈服特性来控制电场强度和温度。在第二阶段，利用平行板式流变仪研究了近晶液晶相的电流变特性。从不同条件下屈服应力的变化，实验考察了近晶相取向结构的强度。当电场强度较低时，屈服应力与不加电场时的屈服应力基本相同。在直流电场阈值以上，屈服应力先增大后趋于恒定。此外，在屈服过程中拍摄了照片，发现在直流电场下产生的结构坍塌不是均匀的，而是类似斑点的。最后，用相同的近晶液晶测量了压力流中二维通道的屈服特性。流道入口处近晶组织的生长增强了系统的截止阀效应，由此可以认为，液晶流量控制有助于开发智能冷却系统。

We have tried to develop a new cooling system utilizing liquid crystal which shows ER (electro-rheological) effect under electric fields applied and phase change by the temperature control. In the early stage of this project, it was found that flow rate of liquid crystal was controllable with applying electric fields. But, it was also clarified that it was difficult to obtain higher cooling efficiency than the water system because of higher viscosity and similar heat transfer property of liquid crystal. Hence we have examined the applicability of smectic liquid crystal as a functional fluid to stop the flow utilizing its yield property controlled with the electric field strength and the temperature.In the second stage, ER characteristic in smectic phase of the liquid crystal have been investigated utilizing a parallel-plate type rheometer. The strength of the alignment structure in the Smectic phase is experimentally examined from the change in yield stress under various conditions. When the electric field strength was low, the yield stress was almost the same as that obtained under no electric field. Above a threshold of DC electric field, the yield stress increased and then became constant. Moreover, photographs were taken in yield process, and it is found that the collapse of the structure under the DC electric field is generated not uniformity but like spots.In the final stage, the yield properties with two dimensional channels in the pressure flow have been measured with the same smectic liquid crystal. The growth of smectic phase structure at the entrance of the channel increased the stop valve effect of the system.From these results, it is considered that the flow control with the liquid crystal is helpful to develop intelligent cooling systems.