Heat exchangers cocurrent flow

The direction of flow is important, as it has a pronounced effect on the efficiency of a heat exchanger. The flows may be in the same direction (parallel flow, cocurrent), in the opposite direction (counterflow), or at right angles to each other (cross-flow). The flow may be either single-pass or multipass the latter method reduces the length of the pass. 

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

In the first pass, both the hot and cold fluids flow in cocurrent flow through the heat exchanger, whereas in the second pass, the cold fluid now flows countercurrent to the hot shellside fluid. Half the heat exchange area is therefore in cocurrent flow and half in countercurrent flow. 

Figure 10 shows the differential heat exchange between a gas and a solids stream flowing countercurrently and cocurrently. The efficiency of the heat transfer equipment is to represented by the number of heat transfer stages... 

The practical heat-transfer coefficient is the sum of all the factors that contribute to reduce heat transfer, such as flow rate, cocurrent or countercurrent, type of metal, stagnant fluid film, and any fouling from scale, biofilm, or other deposits. The practical heat-transfer coefficient ((/practical) is, in reality, the thermal conductance of the heat exchanger. The higher the value, the more easily heat is transferred from the process fluid to the cooling water. Thermal conductance is the reciprocal of resistance (/ ), to heat flow ... 

In its simplest form, a heat exchanger may consist of two passages, with the cooling fluid in one passage and the warming fluid in the other. The flow direction of each of the fluids relative to one another may be countercurrent, cocurrent, or crossflow. 

Falling-film absorbers. These are usually vertical heat exchangers with the cooling medium in the shell and the absorption taking place in the tubes. The solvent flows downward, while the gas may enter either at the bottom (countercurrent flow) or at the top (cocurrent flow). 

Fig. 1.3. The effect of heat exchanger performance, NTU, and heat capacity ratio, h, on the normalized heat loss for heat-integrated processes in (a) countercurrent and (b) counter-cocurrent flow configuration.

The counter-cocurrent concept features a modular design it provides separate heat exchanger loops for heat recovery within the endothermic mixture and the combustion gas. Cocurrent flow of exothermic and endothermic process streams is principally favorable with respect to the controllability of heat release. 

Circulation systems with parallel and crossed cocurrent or countercurrent flow of the heat transfer medium (Fig. 16) arc commonly employed for liquid heat transfer media. The main part of the heat transfer medium is generally circulated with a high-capacity pump in order to achieve uniform heat exchange conditions. A partial stream is passed through a heat exchanger for supplying or removing the heat of reaction. The desired heat transfer medium temperature is at-... 

A hot fluid enters a heat exchanger at a temperature of 150°C and is to be cooled to 60°C by a cold fluid entering at a temperature of 28°C and heated to 37°C. Will they be directed in cocurrent flow or countercurrent flow Which flow can remove more heat ... 

Repeat this problem for a cocurrent (parallel) flow shell and tube heat exchanger. Here AT2 = temperature of hot fluid in cold fluid in. AT, = temperature of hot fluid out cold fluid out. 

Cross-flow monoliths have been explored by Degnan and Wei (11-12) as cocurrent and countercurrent reactor-heat exchangers. Four cross-flow monoliths in series were employed the individual blocks were analyzed by a one-dimensional approximation. They found good agreement between theory and experiment. 

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 ... 

The second issue for cooled tubular reactors is how to introduce the coolant. One option is to provide a large flowrate of nearly constant temperature, as in a recirculation loop for a jacketed CSTR. Another option is to use a moderate coolant flowrate in countercurrent operation as in a regular heat exchanger. A third choice is to introduce the coolant cocurrently with the reacting fluids (Borio et al., 1989). This option has some definite benefits for control as shown by Bucala et al. (1992). One of the reasons cocurrent flow is advantageous is that it does not introduce thermal feedback through the coolant. It is always good to avoid positive feedback since it creates nonmonotonic exit temperature responses and the possibility for open-loop unstable steady states. 

It was seen from the discussion of heat exchangers that the fluid streams are not strictly countercurrent. Baffles on the shell side induce crossflow, and in a two-tube-pass heat exchanger both countercurrent and cocurrent flow occur. To account for deviations from countercurrent flow, the logarithmic-mean teri5)erature difference is multiplied by a correction factor, F. Thus,... 

Saturated propane vapor at 2.00 x 10 psia is fed to a well-insulated heat exchanger at a rate of 3.00 X 10 SCFH (standard cubic feet per hour). The propane leaves the exchanger as a saturated liquid (i.e., a liquid at its boiling point) at the same pressure. Cooling water enters the exchanger at 70°F. flowing cocurrently in the same direction) with the propane. The temperature difference between the outlet streams (liquid propane and water) is 15°F. 

One of the simplest designs for a heat exchanger is the double pipe heat exchanger which is schematically illustrated in Fig. 1.19. It consists of two concentric tubes, where fluid 1 flows through the inner pipe and fluid 2 flows in the annular space between the two tubes. Two different flow regimes are possible, either counter-current where the two fluids flow in opposite directions, Fig. 1.19a, or cocurrent as in Fig. 1.19b. 

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