Hydrodynamic transistor

Keywords Hydrogel Actuator Hydrodynamic transistor Pump Valve LSI... 

Tcontroi Control temperature of hydrodynamic transistor t Time... 

The hydrodynamic transistors shown in Table 2 can be classified in two types distinguished by the function of the gel actuator. The actuator of type B acts as servo drive actuating the valve seat. The actuator of type B is directly placed within the flow channel. Therefore, the stimulant, which is typically a component of the process medium, directly controls the sensor-actuator element. The hydrogel swells or shrinks by absorption or release of the process medium and regulates the channel cross-section. Figure 1 shows two examples of such hydrodynamic transistors. 

Fig. 1 Hydrodynamic transistors with direct acting hydrogel elements (a) with hydrogel particles according to (Arndt et al. 2000 Kuckling et al. 2003) and (b) with photopolymerised hydrogel posts according to (Beebe et al. 2000)...

Fig. 3 Antagonistic hydrodynamic transistor types. The fully swollen state is assumed as normal state of the hydrogel component (a) Normally closed hydrodynamic transistors, (b) Normally open hydrodynamic transistors. The hydrogel acts as servo drive...

The fixed regulation point, predefined by the type of the used hydrogel and by the valve design, is an essential problem of the hydrodynamic transistors. It is practically impossible to adapt the hydrogel element to each application. However, the adaption for applications is much easier if the device is designed adjustable (Richter et al. 2007b). 

Fig. 4 Mechanically adjustable hydrodynamic transistors, (a) Normally closed and (b) normally open hydrodynamic transistors according to (Richter et al. 2007b)...

In the meantime hydrodynamic transistors are ready for practical use. Their regulation precision (temperature 0.75 K, contents of alcohol 1 wt.-% (Richter et al. 2007b)) already has the required accuracy for many applications. The valve performance comprises an adjustable pressure resistance up to 18 MPa (Peters et al. 1997). The reported response time of the valves varies within the range of seconds or minutes which should be sufficient for most applications, because changes of liquid concentrations are typically processes with low dynamics. The possibility to adjust the hydrodynamic transistor control point is implemented which was a missing key feature required for the diversity of practical applications. 

Fig. 14 Electronically controllable hydrodynamic microtransistor, (a) Schematic set-up. (b) Volume phase transition temperature of microgel determined by DSC measurements (solid symbols) as well as operating point of the transistor device (open symbols) for different alcohol concentrations in water. Reproduced with permission from (Richter et al. 2007a) p. 1109-1110, copyright Wiley-VCH Verlag GmbH Co. KGaA.

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