Cooling cross-flow

From a cross-flow point of view it may be of interest to mention the phosphoric acid fuel cell with the so-called DiGas system (Fig. 9), which is an air-cooled cross-flow configuration for use in utility-power stations [39]. The process air stream is diverted into two types of channels into individual cells with relatively small cross-sectional area, and into cooling plates (approximately one for every five cells) with a lai ge cross-section. Bipolar plates were molded from a mixture of graphite and phenolic resin, with a Pt-on-carbon cathode and a Pt anode combined with colloidal PTFE on a graphite-paper backing. 

Figure 9-105. Cross-flow Induced draft cooling tower. Used by permission of The Marley Cooling Tower, a United Dominion Co.

In July of 1997, a cooling tower at an ammonia and urea plant, originally constructed in 1968, caught fire and was destroyed. The plant produced 1,450 tons/day (1,315 tonnes/day) of ammonia and 240 tons/day (218 tonnes/day) of urea. The coolingtowerwasa 5-cell, induced draft, cross flow unit. It was constructed of redwood with steel supports and fiberglass fill. The capacity of the cooling tower was 50,000 gallons (190,000 liters). 

From the sample solution to be analyzed, small droplets are formed by the nebulization of the solution using an appropriate concentric or cross-flow pneumatic nebulizer/spray chamber system. Quite different solution introduction systems have been created for the appropriate generation of an aerosol from a liquid sample and for separation of large size droplets. Such an arrangement provides an efficiency of the analyte introduction in the plasma of 1-3 % only.6 The rest (97 % to 99%) goes down in the drain.7 Beside the conventional Meinhard nebulizer, together with cooled or non-cooled Scott spray chamber or conical spray chamber, several types of micronebulizers together with cyclonic spray chambers are employed for routine measurements in ICP-MS laboratories. The solvent evaporated from each droplet forms a particle which is vaporized into atoms and molecules... 

Successive Graphical Method of A Cross-Flow Cooling Tower... 

Design of Cross-Flow Cooling Towers and Ammonia Stripping Towers Wnek, Walter J. Snow, Richard H. 

A (Column) Internal for the Mist-Free Operation of Wet (Cross Flow) Cooling Towers... 

Method for the Calculation of Over-All Volumetric Enthalpy Transfer Coefficients in Cross-Flow Cooling Towers... 

Analysis of Multiunit Counter-Cross-Flow Cooling Tower Okubo, M. Hirai, E. Hayashi, Y. 

Cross Flow Cooling Tower Analysed Vouyoucalos, S. 

Opening in cooling towers through which air enters. Cross-flow towers tend to have a louvered air inlet face, while induced draft use a simple mesh screen or the leading face of polyvinyl chloride (PVC) fill-pack. 

Packing. The primary heat-transfer surface in a cooling tower usually slats in a cross-flow and cubes of corrugated polyvinyl chloride sheets in a counterflow. 

Typically, TSOFC use co- and counter-flow configurations whereas planar stacks sometimes favour cross flow simplifying manifolds attachment. The flow of air usually provides cooling to a stack in either design as does internal reforming (Sulzer Hexis). The flow regime strongly affects the distribution of gas composition, mechanical stress, stack temperature and ultimately current density. 

Further experiments were carried out by Janicke et al. [66] applying cooling oil. Surprisingly for a cross-flow heat exchanger, an exit temperature of 207 °C was determined for the heat carrier, whereas the product gas exited at 70 °C. This phenomenon was attributed to the fact, that most of the energy was transferred to the oil at the feed inlet. Subsequently the product was then cooled by the cold oil, which had heated up not yet. 

Taking into account typical numbers for a and D, this underlines that the channel width should be considerably smaller than 1 mm (1000 pm) in order to achieve short residence times. Actually, heat exchangers of such small dimensions are not completely new, because liquid cooled microchannel heat sinks for electronic applications allowing heat fluxes of 790 watts/cm2 were already known in 1981 [46]. About 9 years later a 1 cm3 cross flow heat exchanger with a high aspect ratio and channel widths between 80 and 100 pm was fabricated by KFK [10, 47]. The overall heat transport for this system was reported to be 20 kW. This concept of multiple, parallel channels of short length to obtain small pressure drops has also been realized by other workers, e.g. by PNNL and IMM. IMM has reported a counter-current flow heat exchanger with heat transfer coefficients of up to 2.4 kW/m2 K [45] (see Fig. 3). 

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