Microstructured evaporators

Fig. 9 Microstructured evaporating surface for thin film evaporation (3D photo of surface using 3D laser scanning confocal microscopy, Olympus Corporation) [14]...

Whyatt et al. [516] presented early results generated with a combined system of independent and microstructured evaporators, heat-exchangers and reformers for isooctane steam reforming for a fuel cell of 13.7-kW electrical power output. Four... 

Barnes and co-workers have studied mixed-monolayer systems [278,281,283,284] and found some striking nonidealities. Mixed films of octadecanol and cholesterol, for example, show little evaporation resistance if only 10% cholesterol is present [278] apparently due to an uneven granular microstructure in films with cholesterol [284]. Another study of cellulose decanoate films showed no correlation between holes in the monolayer and permeation rate [285]. Polymerized surfactants make relatively poor water evaporation retarders when compared to octadecanol [286]. There are problems in obtaining reproducible values for r [287] due to impurities in the monolayer material or in the spreading solvent. 

Imbihl, Kiskinova, Janek and coworkers67 have also used XPS and spatially-resolved photoelectron emission microscopy (SPEM) to investigate oxygen backspillover between YSZ and evaporated microstructured Pt films prepared using microlithographic techniques (Figure 5.38). 

It has also been recently employed to investigate NEMCA by Imbihl and coworkers.28 Both porous Pt paste films and evaporated microstructured Pt electrodes prepared by microlithography were investigated. These microstructured electrodes were typically 500 A thick. 

Scheer, R. Diesner, K. Lewerenz, H. J. 1995. Experiments on the microstructure of evaporated CuInS2 thin films. Thin Solid Films 268 130-136. 

The next three chapters (Chapters 9-11) focus on the deposition of nano-structured or microstructured films and entities. Porous oxide thin films are, for example, of great interest due to potential application of these films as low-K dielectrics and in sensors, selective membranes, and photovoltaic applications. One of the key challenges in this area is the problem of controlling, ordering, and combining pore structure over different length scales. Chapter 9 provides an introduction and discussion of evaporation-induced self-assembly (EISA), a method that combines sol-gel synthesis with self-assembly and phase separation to produce films with a tailored pore structure. Chapter 10 describes how nanomaterials can be used as soluble precursors for the preparation of extended... 

Milnes and Mostaghaci [5.5] compared the consequences of different drying methods on the density, the sinter rate and micro structures of sublimated TiO-, suspensions. Evaporation of water in a micro-oven and by radiation heating leds to strongly bound agglomerates, while freeze drying resulted in softly bound secondary clusters. The freeze dried powder reached in 2 h of sintering 98 % of the theoretical density, while differently dried powders needed twice as much time and had a less fine microstructure. 

Fernandez, R., Ferreira-Aparicio, P, and Daza, L. PEMFC electrode preparation Influence of the solvent composition and evaporation rate on the catalytic layer microstructure. Journal of Power Sources 2005 151 18-24. 

This complex unit operation involves significant microstructural changes in fact, most of the desirable characteristics of fried foods are derived from the formation of a composite structure a dry, porous, crispy and oily outer layer or crust, and a moist cooked interior or core, whose microstructures form during the process (Bouchon et al., 2001). The high temperatures (around 160 and 180°C) cause water evaporation, which is transferred from the food towards the surrounding oil, whereas oil is absorbed by the food replacing part of the released water. This process results in products with a unique flavor-texture combination (Mellema, 2003). 

The RF thermal plasmas are suitable tools for making oxide ceramic microspheres, either dense or hollow. The microstructure of the product can principally be influenced by the structure of feedstock materials and to a less extent by the plasma operating conditions. Highly porous raw materials and/or the presence of blowing agents facilitate formation of hollow spheres. By varying the process conditions, one can primarily affect the thermal history of particles, hereby the degree of evaporation. 

Consequently such a microvaporizer uses a glass-silicon-glass stack with a microstructured silicon evaporator. This evaporator is heated up by a pulsed NIR-laser diode. Thus, the liquids which are in contact with the evaporator within a very short period of time are heated beyond their evaporation temperature. This arrangement not only requires a low energy to evaporate in comparison to the commonly used resistive heating, but the very rapid heating of the silicon vaporizer also allows for simultaneous evaporation of sample mixtures with components of different evaporation temperatures and partial pressures, respectively. Furthermore,... 

The dual-channel reactor is a silicon chip device and was manufactured by photolithography and potassium hydroxide etching [274]. Silicon oxide was thermally grown on silicon and thin films of nickel were evaporated for passivation because direct fluorination was carried out in this device. Pyrex was bonded anodically to the modified microstructured silicon wafer (see Figure 4.34, top). 

The microstructure of a sol, in terms of the nature and concentration of sol particles, significantly affect a membrane s properties such as average pore diameter and pore size distribution. Other critical parameters are the temperature and rate of evaporation used in the drying and calcination steps. Even though it is economical to obtain the final product form quickly, too rapid a drying rate forms cracks in the membrane. Crack formation is also dependent on thickness of the membrane. The work of Cini et al. [49], who prepared supported microporous y-A C membranes as catalyst supports, illustrates many of these effects. 

---