Heat exchange integration

A totally enclosed air-to-water-cooled machine is a totally enclosed machine which is cooled by circulating air which, in turn, is cooled by circulating water. It is provided with a water-cooled heat exchanger, integral (IC7 W) or machine mounted (IC8 W), for cooling the internal air and a fan or fans, integral with the rotor shaft (IC 1W) or separate (IC 5W) for circulating the internal air. 

Heat transfer between gas and particle phases tend to be efficient due to the large volumetric concentration of interface surface. Hence this topic is rarely of significant concern and will not be dealt with in this chapter. Most of the chapter concerns heat transfer between the two-phase medium and submerged surfaces. This is the most pertinent engineering problem since heat addition or extraction from the fluidized or conveyed mixture is commonly achieved by use of heat exchangers integral to the vessel wall or submerged in the particle/gas medium. 

Costamagna P., Honegger K., 1998. Modeling of solid oxide heat exchanger integrated stacks and simulation at high fuel utilization. Journal of the Electrochemical Society 145,3995 4007. 

Since in most cases the task of the heat transfer cycle is to maintain the temperature in the fixed bed within a specific range, this concept is frequently described as an isothermal fixed-bed reactor . Since isothermal reaction control does not always provide optimum selectivity or yield, the concept of heat exchangers integrated in the fixed bed is also being increasingly used to achieve specific nonisothermal temperature profiles. The most common arrangement is the multitubular fixed-bed reactor, in which the catalyst is arranged in the tubes, and... 

The industrial scale reaction of synthesis gas to ammonia in pressure reactors takes place in a cyclic process in which the ammonia formed is removed from the reaction gas and the unreacted synthesis gas returned to the reactor. In addition to the ammonia formed, inert gases and the liberated reaction heat have to be continuously removed from the cyclic process. The excess heat of the product gas is used to heat the feed synthesis gas to the reaction temperature in a heat exchanger integrated into the reactor. Additional waste heat can be utilized for steam generation. The pressure loss in the synthesis gas due to its passage through the synthesis loop is compensated for and the fraction of synthesis gas converted replaced by fresh compressed synthesis gas ( fresh gas ). 

Fig. 6.13 Example of a heavy-pilot microstructured heat exchanger integrated 5 kW i reactor-heat exchanger system for selective oxidation to achieve gas purification of H2-rich reformer gas for fuel cells. (Source IMM.)...

A self-supporting SOFC-based power plant system, HEXIS (Heat Exchanger Integrated Stack), using circular planar elements has been developed by the Sulzer company in Switzerland for natural gas as a fuel and a power of up to 7 kW [26]. Field tests have started in summer 1997 commercialization is planned for the year 2002. The development goal is the construction of small-size systems in the power range of 1 - 200 kW. 

A different type of SOFC design is under development by Hexis [9]. The HEXIS (heat exchanger integrated stack) stack concept can be used for small co-generation plants. The metallic intercoimect in this case serves as a heat exchanger as well as a bipolar plate. 

Costamagna P., Honneger K., Modeling of Solid Oxide Heat Exchanger Integrated Stacks and Simulation at High Fuel Utilization, Journal of Electrochemical Society, Vol. 145, No.l 1, pp. 3995-4007, 1998. 

The present chapter provides an overview of several numerical techniques that can be used to solve model equations of ordinary and partial differential type, both of which are frequently encountered in multiphase catalytic reactor analysis and design. Brief theories of the ordinary differential equation solution methods are provided. The techniques and software involved in the numerical solution of partial differential equation sets, which allow accurate prediction of nonreactive and reactive transport phenomena in conventional and nonconventional geometries, are explained briefly. The chapter is concluded with two case studies that demonstrate the application of numerical solution techniques in modeling and simulation of hydrocar-bon-to-hydrogen conversions in catalytic packed-bed and heat-exchange integrated microchannel reactors. 

Figure 11.8 Frontal view of the heat exchange integrated microchannel reactor concept and the two dimensional unit cell (shown at the lower...

Recently, the Swiss company Sulzer Hexis AG has developed the concept of an SOFC for small-scale domestic application to provide heating on demand and to cover peak power requirements. This so-called Hexis (Heat Exchanger Integrated Stack) cell consists of circular zirconia electrolyte disks of about 12 cm diameter that carry the anode and cathode (Figure 7.38). The individual cells are... 

Figure 7.38 Solid oxide fuel cell Hexis (Heat Exchanger Integrated Stack) (Schuler, 2007) Reprinted with permission from Schweizerischer Verein des Cas- und Wasserfachs.

For the heat-exchangers integrated into the system design concepts, a minimum logarithmic driving force of 100 K was assumed. 

ISSUE TITLE ECCS heat exchanger integrity (SS 3) (WWER)... 

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