Shell-side exchanger pressure decrease

The shape of the coohng and warming curves in coiled-tube heat exchangers is affected by the pressure drop in both the tube and shell-sides of the heat exchanger. This is particularly important for two-phase flows of multicomponent systems. For example, an increase in pressure drop on the shellside causes boiling to occur at a higher temperature, while an increase in pressure drop on the tubeside will cause condensation to occur at a lower temperature. The net result is both a decrease in the effective temperature difference between the two streams and a requirement for additional heat transfer area to compensate for these losses. 

The experimental evaluation of other effects associated with the operative temperatures and stoichiometric ratio is performed in a range of pressure around 130 kPa, using the side channel air compressor whose characteristics are described in Table 7.1. The effect of the stack temperature on the voltage measured at the stack terminals is shown in Fig. 7.8. In this case, the temperamre is controlled by varying the water flow rate in the heat exchanger shell while the air flow rate and humidification conditions are the same as those of Fig. 7.7. It can be observed that a decrease in temperamre from 346 to 305 K determines a voltage reduction <10% up to 70% of load (200 A), while a satisfactory stack behavior at 313 K is detected in almost all load conditions (see Sect. 3.3). Then, the effect of the stoichiometric ratio is verified for three different loads at the stack and humidification temperature of 313 K. From Fig. 7.9, it can be noted that values of R higher than 2 are... 

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