Tubular collectors

The structurally strongest shape is the tube this led to the development of a variety of evacuated tubular collectors (ETCs), as shown in Fig. 4. These can produce temperatures in excess of 200° C and can provide good efflciencies up to about 150°C. 

FIGURE 4 Three evacuated tubular collectors (ETCs). 

Solar systems can produce hot water at such temperatures, but either very good quality flat plate or evacuated tubular collectors (ETCs) must be employed thus the col-lectiou system will be expensive. Numerous installations of such systems have been completed, marty of which are technically successful, but very few (if arty) would be judged as economically viable. 

SOFC electrodes are commonly produced in two layers an anode or cathode functional layer (AFL or CFL), and a current collector layer that can also serve as a mechanical or structural support layer or gas diffusion layer. The support layer is often an anode composite plate for planar SOFCs and a cathode composite tube for tubular SOFCs. Typically the functional layers are produced with a higher surface area and finer microstructure to maximize the electrochemical activity of the layer nearest the electrolyte where the reaction takes place. A coarser structure is generally used near the electrode surface in contact with the current collector or interconnect to allow more rapid diffusion of reactant gases to, and product gases from, the reaction sites. A typical microstructure of an SOFC cross-section showing both an anode support layer and an AFL is shown in Figure 6.4 [24],... 

A variety of different types of collectors may be used, depending on circumstances. Dry collectors, for example, are widely used in different types of plants and are suitable for conditions where the dust is relatively free from moisture. They can be installed and operated at medium cost and high efficiency. They are normally located outside the plant and are made up of a box with an inverted conical base or hopper. Inside the box are hung a number of tubular or envelope-shaped filters through which the air is passed. The filters may be made of cotton, wool, paper, glass cloth, or synthetics. Dust is built up on the filters until the resistance to flow... 

The decreased contribution due to slow electron transfer kinetics for the microtubular electrode is also attributable to the higher underlying surface area of the tubular current collector. Because the surface area is higher, the effective current density for the microtubular TiS2 is less than for the thin film TiS2, which has a conventional planar current collector. The decreased contributions of film resistance and slow electron transfer kinetics also account for the higher peak current density of the microtubular electrodes (Fig. 27). 

The microtubular electrode concept described here also offers another possible advantage. In these concentric tubular electrodes, each particle of the Li intercalation material (the outer tube) has its own current collector (the inner metal microtubule). This could be an important advantage for Li+ intercalation materials with low electrical conductivity. This advantage was not demonstrated here because TiS2 has relatively high electronic conductivity. We have recently shown that electrochemical synthesis can be used to coat the gold microtubular current collector with outer mbes of a... 

Fig. 5.6 (a) Tubular plates for lead-acid cells, (b) Cross-section showing central lead current collector, active material and porous separators... 

SOFC can be manufactured in different geometrical configurations, i.e. planar, tubular or monolithic. Regardless of the geometrical configuration, a solid oxide fuel cell is always composed of two porous electrodes (anode and cathode), a dense electrolyte, an anodic and a cathodic gas channel and two current collectors. For the sake of simplicity the planar configuration is taken as reference, as shown in Figure 3.1. 

Bove R., Sammes N.M, 2005. The effect of current collectors configuration on the performance of a tubular SOFC. In Proceedings of the Ninth International Symposium on Solid Oxide Fuel Cells (SOFC IX), May 15-20, Quebec City, Canada, S.C. Singhal and J. Mizusaki (Eds.), Electrochemical Society, Vol. 1, pp. 780-781. 

The equations implemented are those defined in Sections 3.2-3.4, i.e. in a partial differential form, for each cell component. This approach is also referred to as Computational Fluid Dynamic (CFD). In order to illustrate the capabilities of the model, in terms of assessment of particular phenomena taking place within the fuel cell, one particular problem is analyzed for each geometry. In particular, for the disk-shaped cell, emphasis is put on the effect of the gas channel configuration on the gas distribution, and, ultimately, on the resulting performance. For the tubular geometry, three different options for the current collector layouts are analyzed. 

The choice of the tubular geometry, however, introduces a number of possibilities for the current collector layouts, and different cell performance is expected in each case. Three possibilities are here analyzed ... 

The authors applied this concept to both gas/liquid (see Figure 3.75) and liquid/ liquid systems (see Figure 3.76). This set-up consisted in the core of a tubular reactor with an interdigital micro mixer as dispersion unit (compare Figure 3.77). The peripheral equipment consisted of an automated pipetting robot, a fraction collector and a gas-chromatograph equipped with an automatic injector. 

Figure 1. The MHHP modular sorber diagram 1 - tubular case of the hydride module 2 -corrugated heat-conducting insert 3 - hydrogen ceramic collector-filter 4 - metal hydride 5 - tip of a metal hydride bed 6 - hydrogen manifold 7 - spacer plate 8 - heat exchanger shroud 9 - union 10 - flange-cover of a heat exchanger. Heat exchanger thermal insulation is not shown conditionally.

When comparing different solar collectors it is important to take into account the different quantities of radiation collected in each case. For a given receiver, the radiative power collected increases with aperture size (i.e., with concentration). However, this is not a linear effect and, for instance, a CPC with a two suns concentration ratio provides twice the aperture area of a nonconcentrating CPC. Nevertheless the power received by the tubular absorber is not doubled, because the former CPC misses around half of the diffuse radiation. Other important consideration is the fact that concentrating reactors are faster simply because they collect more radiation, which is associated with larger collector area. 

The anal3hical expression for the radiation flux distribution produced on the wall of a tubular receiver by a PTC (Figure 17) has been calculated by Jetter (1986,1987). Jetter s method is applied here to a particular PTC collector that has been used in our research group to study the degradation of several... 

EXAMPLE 13-10 Heat Transfer through a Tubular Solar Collector... 

Figure 20.3. Baghouse collectors, (a) Tubular shaker collector, (b) Baghouse collector with envelope filter bags. (Courtesy Scientific Dust Collectors 2002). (c) Bag wire retainers.

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