Exchangers, heat cocurrent

A schematic diagram of a parallel-flow (cocurrent) heat exchanger is shown in Fig. 9.4. 

Figure 15.6 Fluid temperatures can never cross in a cocurrent heat exchanger. 

One optimum requires a uniformly distributed entropy production rate in a heat exchanger, mixer, or separator. Consider the example of countercurrent and cocurrent heat exchangers shown in Figure 4.11. Temperature profiles... 

Example 4.11 Energy dissipation in countercurrent and cocurrent heat exchangers The two most commonly used heat exchangers are countercurrent and cocurrent at steady-state flow conditions as shown in Figure 4.17. Estimate the energy dissipated from these heat exchangers if the surroundings are at 290 K. Consider the data below ... 

Applying Eqs. (4.187) and (4.189) for cocurrent and countercurrent operations, we find Cocurrent heat exchanger I ... 

This ratio shows that the rate of energy dissipated in the cocurrent heat exchanger is almost twice the dissipation in the countercurrent heat exchanger. Although the heat exchanged between the hot and cold streams is the same, the countercurrent operation is thermodynamically more efficient. 

Table 1.4 Equations for the calculation of the normalised temperature variation Si, the dimensionless transfer capability Ni and the mean temperature difference in counter and cocurrent heat exchangers...

FIGURE 6.42 (a) Cocurrent flow pattern through a heat exchanger, (b) Typical temperature profiles through a cocurrent heat exchanger. 

A heat exchanger can be operated in co-, counter-, or cross-current mode. In practice the countercurrent mode is used almost exclusively since it is the most effective. Cocurrent heat exchangers are used only under special conditions (thermally labile... 

The double pipe, cocurrent heat exchanger is used to cool a distillate product using cold water circulating through the jacket as illustrated in Fig. 2.3. The overall heat transfer coefficient is taken to be U and the mass flow of distillate and water is and Wq, respectively. Under turbulent flow conditions, the fluid temperatures are taken to be uniform across individual flow cross sections. Find the relationship to predict how steady-state temperature changes with axial position, and from this, deduce an expression to compute the average AT... 

Figure 7.30 Flow arrangement and temperature profiles for cocurrent heat exchanger.

One optimum requires a uniformly distributed entropy production rate in a heat exchanger, mixer, or separator. Consider the example of countercurrent and cocurrent heat exchangers shown in Figure 4.4. Temperature profiles show that the driving force AP or 1/AP is more uniformly distributed in the counter-current than in the cocurrent flow operation. This is the basic thermodynamic reason why a countercurrent is better than a cocurrent operation. The duty of the exchangers depends on the flow rate and Met and outlet temperatures T and T2 of cold streams. The duty is the amount of heat transferred from the hot fluid to cold... 

Example 4.12 Energy dissipation in countercurrent and cocurrent heat exchangers... 

ATlm represents a true temperature difference for a perfect countercurrent as well as cocurrent heat exchange. For illustration purposes, the countercurrent flow (Figure 6.2a) is used to show how ATu xd is derived. 

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