Micro evaporator

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. 

A micro-evaporator can also be attached to modem microwave digesters and are designed to reduce the acid solutions to a low or even a dry state. The principle is that samples are exposed to microwave energy under vacuum to accelerate volume reduction. An auto-detect feature of the CEM MAR 5 system is that a detector is installed to inform the operator when the evaporation is complete and automatically stops operation. Acid fumes are neutralised by an integrated vapour scmbber system. 

This condition can be applied for microcondensers and for micro-evaporators where an external two-phase flow sets as constant the wall temperature of the microchannels inside which a single-phase fluid flows. 

This boundary condition allows the analysis of micro-condensers and micro-evaporators with finite wall thermal resistance. It is evident that when Uy, tends to infinity, the T3 boundary condition reduces to the T boundary condition. 

Micro-condensers, micro-evaporators with negligible wall thermal resistance... 

Principles of a falling film microreactor have been applied to other falling film microdevices where enhanced mass transfer is needed, such as a falling film microabsorber and a falling film micro evaporator [43,50-52]. 

A Pyrex micro filter (Fig. XII, 2, 18) of 8 ml. capacity and furnished with a sintered glass disc is useful for the filtration of hot or boihng hquids. The long cylindrical tube reduces evaporation. The filter may be inserted into a test-tube with side arm (Fig. XII, 2, 13) and the filtrate collected in a centrifuge tube or semimicro test-tube receiver. 

Concentration of gel1, % Soil porosity, % Total Micro/total Mean pore diameter, pm Hydraulic conductivity, mday 1 Avialable moisture1, % Rate of evaporation 2, arb. units Transpiration ratio3, g g-1 Water use efficiency4, g kg-1... 

In Proceedings of 21st SemiTherm Symposium, San Jose, 15-17 March 2005, pp 1-7 Copeland D, Behnia M, Nakayama W (1997) Manifold micro-channel heat sinks isothermal analysis. IEEE Trans Comp Packag Manuf Technol A 20 96-102 Dupont V, Thome JR, Jacobi AM (2004) Heat transfer model for evaporation in microchannels. 

The uncertainty of calculating the Poiseuille number from the measurements must be taken into account. The viscosity-pressure relationship of certain liquids (e.g., isopropanol, carbon tetrachloride) must be kept in mind to obtain the revised theoretical flow rate. The effect of evaporation from the collection dish during the mass flow rate measurement must be taken into consideration. The effect of evaporation of collected water into the room air may not be negligible, and due to the extremely low mass flow rates through the micro-channel this effect can become significant. 

Two-phase heat transfer in micro-channel heat sink was associated with different mechanisms for low, medium, and high-quality flows. Bubble flow and nucleate boiling occur only at low qualities (Xe < 0.05) corresponding to very low heat fluxes. High fluxes produce medium-quality (Xe = 0.05—0.55) or high-quality (Xe = 0.55—1.0) flows depending on the flow rate, where heat transfer is dominated by annular film evaporation. Due to the large differences in heat transfer mechan-... 

Peles el al. (2000) elaborated on a quasi-one-dimensional model of two-phase laminar flow in a heated capillary slot due to liquid evaporation from the meniscus. Subsequently this model was used for analysis of steady and unsteady flow in heated micro-channels (Peles et al. 2001 Yarin et al. 2002), as well as the study of the onset of flow instability in heated capillary flow (Hetsroni et al. 2004). 

The idealized picture of the flow in a heated micro-channel is shown in Fig. 8.1a. Such flow possesses a number of specific properties due to its unique structure, which forms because of liquid evaporation and the interaction of pure vapor and liquid flows separated by the interface surface. The latter has an infinitely thin surface with a jump in pressure and velocity, while the temperature is equal. One can... 

The quasi-one-dimensional model of flow in a heated micro-channel makes it possible to describe the fundamental features of two-phase capillary flow due to the heating and evaporation of the liquid. The approach developed allows one to estimate the effects of capillary, inertia, frictional and gravity forces on the shape of the interface surface, as well as the on velocity and temperature distributions. The results of the numerical solution of the system of one-dimensional mass, momentum, and energy conservation equations, and a detailed analysis of the hydrodynamic and thermal characteristic of the flow in heated capillary with evaporative interface surface have been carried out. 

Carey VP (1992) Liquid-vapour phase-change phenomena. Hemisphere, Washington, DC Collier SP (1981) Convective boiling and condensation. McGraw-Hill, New York Ha JM, Peterson GP (1998) Capillary performance of evaporation flow in micro grooves an analytical approach for very small tilt angles. ASME J Heat Transfer 120 452 57 Hetsroni G, Yarin LP, Pogrebnyak E (2004) Onset of flow instability in a heated capillary tube. Int J Multiphase Flow 30 1424-1449... 

Smirnov VI (1964) A course of higher mathematics, vol II. Pergamon, London Stephan PS, Busse CA (1992) Analysis of the heat transfer coefiicient of grooved heat pipe evaporator walls. Int 1 Heat Mass Transfer 35 383-391 Tuckerman D (1984) Heat transfer micro stracture for integrated circuits. Dissertation, Stanford University, Stanford... 

Wallis GB (1969) One-dimensional two-phase flow. McGraw-HUl, New York Wayner PC, Kao YK, LaCroix LV (1976) The interline heat transfer coefiicient of an evaporating wetting film. Int 1 Heat Mass Transfer 19 487-492 Weisberg A, Bau HH, Zemel IN (1992) Analysis of micro-channels for integrated cooling. Int 1 Heat Mass Transfer 35 2465-2472... 

Weislogel MM, Lichter S (1998) Capillary flow in an interior corner. 1 Eluid Mech 373 349-378 Wu PY, Little WA (1984) Measurement of the heat transfer characteristics of gas flow a fine channels heat exchangers used for microminiature refrigerators. Cryogenics 24 415 20 Xu X, Carey VP (1990) Film evaporation from a micro-grooved surface an approximate heat transfer model and its comparison with experimental data. J Thermophys 4(4) 512-520 Yarin LP, Ekelchik LA, Hetsroni G (2002) Two-phase laminar flow in a heated micro-channels. Int J Multiphase Flow 28 1589-1616... 

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