Welding diffusion

The characteristic positive features of diffusion-welded joints are as follows ... 

Typically, coatings most often in use as intermediate layers are silver, nickel, copper, and gold however, silver is used by far the most often. This is so because of the low dissociation temperature of silver oxide, making it relatively easy to obtain clean surfaces. Also, the typical thickness range of electroplates used, in practice, for diffusion welding is about 15 to 40/rm, but thicknesses as great as 130 )um must sometimes be used. A considerable variety of steel types as well as aluminum and a host of other difficult-to-join metals and even beryllium have been and continue to be diffusion bonded with the use of electroplated intermediate layers. 

Takeda T, Kunitomi K, Horie T, Iwata K. Feasibility of the applicability of a diffusion-welded compact intermediate heat exchanger to next-generation high-temperature gas-cooled reactors. Nucl Eng Design, 1997 168 11-21. 

Figure 8 Microetched foil of stainless steel for manufacturing micro heat exchangers by stacking and diffusion welding. (Source Ehrfeld Mikrotechnik, Atztechnik Herz.)... 

Takeda, T., Kunitomi, K., Horie, T., Iwata, K., Feasibility study on the applicability of a diffusion-welded compact intermediate heat exchanger to next-generation high temperature gas-cooled reactor, Nucl. Eng. Des. 1997, 168,11-21. Bier W., Keller W., Linder G., Seidel, D., Schubert, K., Martin, H., Gas-to-gas heat transfer in micro heat exchangers, Chem. Eng. Process. 1993, 32, 33-43. Schubert, K., Brandner J., Fichtner M., Linder G., Schygulla, U., Wenka, A., Microstructure devices for applications in thermal and chemical process engineering, Microscale Therm. Eng. 2001, 5,17-39. www.fzk.de, Forschungszentrum Karlsruhe, 17 July 2004. 

The band width in this study was limited to 150 mm but could exceed 1000 mm, thus opening a route to large-scale micro structured plate-like reactors comparable to the large-scale micro (or mini) structured heat exchangers from Heatric [96], These are manufactured by diffusion welding of stacked plates (Figure 4.114). 

The factor of the resulted heat emission of a hydride bed generally is proportional to effective heat conductivity of a bed and inversely proportional to thickness of a bed. The analysis of these equation shows, that factor of a heat transfer less than smaller factor of a heat emission and consequently it is of no used to increase strongly one of them, thus, not changing another. Results of experiments show, that for brazed and diffusion welded connections of the sorber case and heat-conducting insert R=(0.5-1.5) TO 5 (m2 K)/W. At contact of an insert and the case on tight fit R increases in 10-100 times and influence of contact resistance becomes comparable with influence of the resulted heat emission of a hydride bed. 

FIGURE 20 Scanning electron microscopy image of a diagonal cross-section of a diffusion-welded and subsequently anodically oxidized microstructured aluminum reactor [158]. (Adapted with permission from the Swiss Chemical Society.)... 

Channel tubes (88 mm o.d. and 4 mm thick) are of welded design and contain fuel assemblies which are cooled by boiling light water. The upper and lower parts of the channel are made of stainless steel and the central part, located in the active zone, is made from a zirconium/2% niobium alloy. The central part is joined to the upper and lower parts by vacuum diffusion-welded stainless steel/zirconium transition joints. The channel tube is attached to the upper duct by a welded joint, and to the lower one by a compensator unit, which is necessary to compensate for the difference in thermal expansion of the channels and ducts without destroying the leak-tightness of the reactor cavity. This type of joint makes it possible to replace a channel during reactor shutdown. 

DEVELOPMENT OF COMPACT HEAT EXCHANGER WITH DIFFUSION WELDING... 

In our study, a new CHX can be used over 900°C condition is designed and manufactured. The CHX consists of only plates welded with diffusion. The tensile and creep strengths in the diffusion welding are superior to those in the brazing especially in high temperature condition. 

Major features of the HCIHX in the HTTP and present CHX are described in Chapter 2 and 3, respectively. The design characteristics of the new CHX with diffusion welding and its test and results are described in Chapter 4. 

Development of Compact Heat Exchanger with diffusion welding 4.1 Development items and schedule... 

Effectiveness, pressure drop and differential pressure between two sides for the recuperator used in an existing gas-turbine plant are approximately 88%, 6% of GT plant total pressure drop and 1.4MPa, respectively, in addition, components with the brazing welding have never been used in primary components. The CHX with diffusion welding is one of the best candidates to solve above problems. 

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