Phase micro

COMPUTER-AIDEDDESIGNANDMANUFACTURING(CAD/CAM)] (Vol7) Sokd-phase micro extraction... 

J.-L. Liao, C-M. Zeng, S. Hjeiten and J. Pawliszyn, Solid phase micro exti action of biopolymers, exemplified with adsorption of basic proteins onto a fiber coated with polyacrylic acid , ]. Microcolumn Sep. 8 1-4. (1996)... 

We attempt here to describe the fundamental equations of fluid mechanics and heat transfer. The main emphasis, however, is on understanding the physical principles and on application of the theory to realistic problems. The state of the art in high-heat flux management schemes, pressure and temperature measurement, pressure drop and heat transfer in single-phase and two-phase micro-channels, design and fabrication of micro-channel heat sinks are discussed. 

Poor flow distributions may result in localized dry hotspots which, absent control of the temperature fluctuations, may cause rapid overheating. Temperature and pressure fluctuations, and poor flow distribution, are the main problems that accompany the use of two-phase micro-channels. 

Experimental and numerical study of the pressure drop and heat transfer in a single-phase micro-channel heat sink by Qu and Mudawar (2002a,b) demonstrated that the conventional Navier-Stokes and energy equations can adequately predict the fluid flow and heat transfer characteristics. 

Qu W, Mudawar 1 (2002a) Experimental and numerical study of pressure drop and heat transfer in a single-phase micro-channel heat sink. Int J Heat Mass Transfer 45 2549-2565 Qu W, Mudawar 1 (2004) Measurement and correlation of critical heat flux in two-phase micro-channel heat sinks. Int J Heat Mass Transfer 47 2045-2059 Qu W, Mudawar 1 (2002b) Prediction and measurement of incipient boiUng heat flux in micro-channel heat sinks. Int J Heat Mass Transfer 45 3933-3945... 

In the study by Qu and Mudawar (2003a) experiments were performed to measure pressure drop in two-phase micro-channel heat sink containing 21 parallel 231 X 713 pm micro-channels. The pressure drop in the micro-channel two-phase region APtp was expressed as the sum of acceleration and friction components ... 

A new approach was developed by Lee and Mudawar (2005a) to improve the accuracy of pressure drop prediction in two-phase micro-channels. Since the bubbly and churn flow patterns are rarely detected in high-flux micro-channel flow, the separated flow model was deemed more appropriate than the homogeneous. 

Prodanovic V, Fraser D, Salcudean M (2002) On transition from partial to fuUy developed subcooled flow boiling. Int J Heat Mass Transfer 45 4727-4738 Qu W, Mudawar I (2003a) Measurement and prediction of pressure drop in two-phase micro-channel heat sinks. Int J Heat Mass Transfer 46 2737-2753 Qu W, Mudawar I (2003b) Flow boiling heat transfer in two-phase micro-channel heat sink. 1 Experimental investigation and assessment of correlation methods. Int J Heat Mass Transfer 46 2755-2771... 

For the study of flow stability in a heated capillary tube it is expedient to present the parameters P and q as a function of the Peclet number defined as Pe = (uLd) /ocl. We notice that the Peclet number in capillary flow, which results from liquid evaporation, is an unknown parameter, and is determined by solving the stationary problem (Yarin et al. 2002). Employing the Peclet number as a generalized parameter of the problem allows one to estimate the effect of physical properties of phases, micro-channel geometry, as well as wall heat flux, on the characteristics of the flow, in particular, its stability. 

Solid phase micro extraction (SPME) is a techniques in which a silica fiber coated with a thin film of polymer is brought into contact with an aqueous matrix where the organics in solution partition onto the fiber. The fiber is subsequently placed into the injector of a GC where the heat causes the release of analyte onto the column. This has been applied to endosulfan (a- and (3-) and endosulfan sulfate in water with limits of detection of less than 0.3 pg/L reported (Magdic and Pawliszyn 1996). 

Daumengrofes Labor aus Aluminium-Folie, Blick durch die Wirtschafi, June 1997 Heterogeneous gas-phase micro reactor micro-fabrication of this device anodic oxidation of aluminum to porous catalyst support vision of complete small laboratory numbering-up development of new silicon device [225]. 

Accordingly, serious commercially oriented attempts are currently being made to develop special gas-phase micro and mini reactors for reformer technology [91, 247-259], This is a complex task since the reaction step itself, hydrogen formation, covers several individual processes. Additionally, heat exchangers are required to optimize the energy balance and the use of liquid reactants demands micro evaporators [254, 260, 261], Moreover, further systems are required to reduce the CO content to a level that is no longer poisonous for a fuel cell. Overall, three to six micro-reactor components are typically needed to construct a complete, ready-to-use micro-reformer system. 

The design and fabrication of some gas-phase micro reactors are oriented on those developed for chip manufacture in the framework of microelectronics, relying deeply on silicon micromachining. There are obvious arguments in favor the infrastructure exists at many sites world-wide, the processes are reliable, have excellent standards (e.g. regarding precision) and have proven mass-manufacturing capability. In addition, sensing and control elements as well as the connections for the whole data transfer (e.g. electric buses) can be made in this way. 

Accordingly, chip micro reaction systems are frequently described in the literature. Most of them are made of silicon (see, e.g., [19, 56-62]) Glass can be manufactured by similar routes as for silicon and could hence constitute gas-phase micro reactors however, the glass chip micro reactors described so far were made for liquid-phase applications (see, e.g., [63-70]). 

The advantage of the two-phase micro flow contacting concept is easy phase separation, as the phases are never inter-mixed. However, in view of the normally facile separation of gases and liquids, this is not of major impact. A real large benefit stems from operating with gas and liquid layers of defined geometry with a knovm, defined interface, unlike most disperse systems having a size distribution of their bubbles in the continuous liquid. 

Applications Coupling of solid-phase micro-extraction and a micro-GC (separation times of 15 sec) is suitable for rapid field screening and potentially useful for process analysis. Odours at ppt level can be analysed by... 

E. E. Stashenko, J. R. Martinez, Sampling volatile compounds from natural products with headspace/solid phase micro extraction, J. Biochem. Biophys. Methods, 70, 235 242 (2007). 

F. De Angelis, A. Di Tullio, G. Mellerio, R. Quaresima, R. Volpe, Investigation by solid phase micro extraction and gas chromatography/mass spectrometry of organic films on stone monu ments, Rapid Commun. Mass Spectrom., 13, 895 900 (1999). 

M. van Bommel, B. van Elst, F. Broekens, Emission of organic acids from wooden construction materials in a small test chamber preliminary results of optimisation of the solid phase micro extraction technique, 4th Meeting of the Indoor Air Pollution Working Group, Copenhagen, 2001. 

S. Hamm, E. Lesellier, J. Bleton, A. Tchapla, Optimization of headspace solid phase micro extraction for gas chromatography/mass spectrometry analysis of widely different volatility and polarity terpenoids in olibanum, J. Chromatogr. A, 1018, 73 83 (2003). 

---