Micro devices

The rapid advances made during the past decade in the field of production and use of high power micro-devices led to widespread interest in the problems of micro-fiuid mechanics and the need for both comprehensive and detailed treatment of the fundamental aspects of these phenomena. 

Reliable micro-scale measurement and control of the temperature are required in developing thermal micro-devices. Available measurement techniques can be largely classified into contact and non-contact groups. While the resistance thermometer, thermocouples, thermodiodes, and thermotransistors measure temperature at specific points in contact with them, infrared thermography, thermochromic liquid crystals (TLC), and temperature-sensitive fluorescent dyes cover the whole temperature field (Yoo 2006). 

Gad-el-Hak M (1999) The fluid mechanics of micro-devices. The Freemen Scholar Lecture. J Fluid Eng 121 5-33... 

Yoo JY (2006) Recent studies of fluid flow and heat transfer in thermal micro-devices. Nanoscale Microscale Thermophys Eng 10 67-81... 

Selected Properties of Liquids Used for Cooling Micro-Devices... 

When symmetry is given, there is no need to consider the flow in a micro device or even a micro channel as a whole, but favorably one can refer to only a small part of it and regard this as a true functional region. A first-approach description for slug flow, according to the above consideration, may therefore refer to the repeti-... 

The status of micro reactor and pTAS developments from the beginnings to 1998 is given in [64], Selected micro devices and applications are presented, and also key players, the foundations and the main drivers for undergoing such development. 

The most obvious, trivial consequence of micro-device miniaturization is a... 

The key attribute of flows in micro devices is their laminar character, which stands in contrast to the mostly turbulent flows in macroscopic process equipment. Owing to this feature, micro flows are a priori much more accessible to a model description than macro flows and can be described by first-principle approaches without any further assumptions. In contrast, for the simulation of turbulent flows usually a number of semi-heuristic models are applied, and in many situations it is not clear which description is most adequate for the problem under investigation. As a result, it stands to reason to assume that a rational design of micro reactors... 

Situation like microelectronics decades ago impetus by analytical chemistry lab-on-a-chip - biological applications microfabrication and micro devices scale out input-output board fast and hazardous reactions plug-and-play modules interconnects non-linear synthesis growth of scientific community industry s response selected key players and their activities [217]. 

The development of chemical micro processing was, among other influences, strongly promoted by continuing manufacturing and offering of micro devices, as... 

ISPP imits are not the only micro device imits of interest for space applications micro fuel cells, compact cleanup units for water treatment, portable heating and cooling units and devices for chemical processing and mining are considered [91]. 

Concrete applications of micro reactors for chemical analysis, albeit so far not a core application, have been described [5]. Among other uses in chemical analysis, micro devices for gas chromatography, infrared spectroscopy, and photoacoustic detection are mentioned. 

Schenk, R., Hessel, V., Hoemann, C., Kiss, )., Lowe, H., Schoneeld, F., Numbering-up of micro devices a first liquid-flow splitting unit, Chem. Eng. Technol. 26, 12 (2003) 1271-1280. 

Fabrication was done by photolithography and deep reactive ion etching (DRIB). The catalyst was inserted by sputtering. Such a prepared microstructure was sealed with a Pyrex cover. The bonded micro device was placed on a heating block containing four cartridge heaters. Five thermocouples monitored temperature on the back side. A stainless-steel clamp compressed the device with graphite sheets. 

Different from sole combinations of micro devices, this refers to a total system with many functional elements and flow-distribution and, recollecting zones, typically composed of 2-D plate-type architecture. Each of these plates usually has a separate fimction, comprising imit operations and reaction. Frequently, micro mixing and micro heat exchange fimctions and corresponding elements are employed. Often, the system can be composed of different elements resulting in different process flow combinations. Such an approach may be termed a construction kit. 

For both types of micro devices, a stainless steel frame was used as holder and Viton gaskets were applied for sealing ]72-74], A clear PMMA cover plate was also used and served for compression. This cover plate provided housing for a mini UV lamp used for irradiation. The detection imit was packaged in a similar fashion. Optical fibers were also integrated. 

Coupled with the latter investigations, it was shown that a diazo suspension can be fed through a micro device without leading to plugging [55]. This broadens the scope of micro processing applicability towards azo pigment formation. 

As micro devices, mixers from various suppliers (]R 19], [R 17]) were used [37]. These devices were each connected to a PTFE tube of length up to 150 cm. In addition, a tailor-made micro reaction system with parallel channels and integrated cooling was used (]R 26]). 

In turn, the interdigital micro mixer mixes much faster, provides more unique concentration profiles before reaction takes place and consequently changes the course of the reaction [125]. As a result, no high-molecular-weight polymer fraction is observed by GPC measurement and no fouling occurs, although the specific wall surfaces of the micro device are expected to promote deposition. 

The aim given above refers to the possibility of integration of multiple functions in a micro device here, this refers to the combination of flow processing and sensing [22]. 

These devices have gas and liquid streams which do not merge, i.e. are not fed into each other. Rather, by use of separate ports both phases are passed in their own encasing, e.g. their own micro channel. Thereby, dispersion of the phases is prevented and only one large specific interface is created for mass transfer (different from dispersive micro devices, see, e.g.. Section 5.1.2). The separate guidance of the phases allows to heat the phases separately, usually from the side most distant from the gas/liquid interface. 

As a further disadvantage, it is known concerning operation in many parallel micro channels that mixed flow patterns and even drying of the channels can occur [9, 10]. This comes from phase maldistribution to the channels. To overcome this problem, first solutions for phase equipartition have been proposed recently, but so far have not been applied for the mixers described here, but instead for mini-packed reactors, having feed sections similar to the mixers [11,12]. Nevertheless, numbering-up of dispersive-acting micro devices generally seems to be more complicated than for two-phase contactors (see Section 5.1.1). 

---