Counter-current exchanger

For the sake of simplicity, without avoiding the rigor of the analysis, we describe only the combustion-driven architecture based on a counter-current exchanger layout (Figure 4.11). 

These two functions are plotted in Figure 4.12 it can be seen that the total efficiency increases with the exchanger performance whereas the specific power reaches a maximum at about 0.53 of e-NTU. The interesting result is that the efficiency of the counter-current exchanger exceeds the value of the intrinsic TE material efficiency tite (Equation 4.8, horizontal dotted line in Eigure 4.12) in the high e-NTU efficiency... 

Figure 4.12 Power (V/ ) and efficiency (Titot) characteristics of a counter-current exchanger TEG system. For comparison, the intrinsic TE efficiency (t te) without heat recirculation is reported.

The main function of the Loop at Henie (LoH) in the context of diuretics is further reabsorption and conservation of water and eiectroiytes from the remaining 30% of the fiitrate emerging from the PCT. This is achieved by a combination of counter-current muitipiier and counter-current exchange mechanisms in the LoH and the vasa recta respectiveiy which first concentrate and then diiute the filtrate during its passage. 

The Lurgi gas cleanup system, shown in Figures 2, 3, and 4, is a good example of the problems involved. Each of the five counter-current exchangers represents a series of complicated, simultaneous equilibrium and heat transfer calculations for a polar mixture, with a three- and possibly four-phase system. (If the solid fines are considered, the system is four, possibly five phases but the solid phase, which most likely stays with the tar, is generally neglected.) Neither the available enthalpy data, nor the available equilibrium correlations, are really adequate for such mixtures, and the problems would be worse if the pressures were higher, as they may be in the future. This is not to say that... 

In the counter-current exchanger, the efficiency e is given by he expression ... 

In the case of the counter-current exchanger for an efficiency close to unity, when we consider the irreversible portion of S at, we obtain by linearising ... 

Analysis Part (b) Counter Current Exchange We note that near the entrance to the reactor, the coolant temperature is above the reactant entrance temperature. However, as we move down the reactor the reacdon generates heat" and the reactor temperature rises above the coolant temperature. We note that reaches a minimum (corresponding to (he reactor temperature maximum) near the oitrance to the reactor and then increases as the reactor temperature decreases. A higher maximum temperature in the reactor, along with a hitter exit cont ersion. X. and equilibrium conversion. X, are achieved in the counter current heat exchange system than fw the co-current system. 

For counter current exchange we first multiply the rhs of the co-current heal exchanger energy balance by - I, leaving the rest of the Polymath program in Table 12-2.3 the same. 

Tabl El2-2.5 Polymath Program and Output for Counter Current Exchange... 

Analysis Part (c) For constant 7. the maximum reactor temperature. 870K. is less than either co-current or counter-current exchange while the. selectivity, = 2S2.9. is greater than either co-current or counter current exchange. Consequently. one should investigate how to achieve sufficiently high mass How of the coolant in order to maintain constant 7. ... 

Repeat part (a) for co-current heat and for counter current exchange and for adiabatic operation when the heat transfer coefficient is Ua = 30 J/s-kg cat-K with T = 50 C, with mc=0.25 kg/s and an entering coolant temperature of 50°C,... 

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