Plate heat exchangers flow arrangements

Figure 12.61. Plate heat-exchanger flow arrangements The number of transfer units is given by ...

Figure 12.61. Plate heat-exchanger flow arrangements...

A further advantage of the plate heat exchanger is that the effective mean temperature difference is usually higher than with the tubular unit. Since the tubular is always a mixture of cross and contra-flow in multi-pass arrangements, substantial correction factors have to be applied to the log mean temperature difference (LMTD). In the plate... 

The basic layout and flow arrangement for a gasketed plate heat exchanger is shown in Figure 12.60. Comer ports in the plates direct the flow from plate to plate. The plates are embossed with a pattern of ridges, which increase the rigidity of the plate and improve the heat transfer performance. 

For plate heat exchangers it is convenient to express the log mean temperature difference correction factor, F, as a function of the number of transfer units, NTU, and the flow arrangement (number of passes) see Figure 12.62. The correction will normally be higher for a plate heat exchanger than for a shell and tube exchanger operating with the same... 

The channels of most plate heat exchanger/reactors are switched in parallel, which reduces the pressure drop compared to alternative flow patterns such as serpentine flow fields. However, flow equipartition is crucial for parallel flow arrangements. It is achieved by perforated plates [89] when a whole stack of plates is fed in parallel from the plate front. Such pinhole plates create additional pressure drop. In case the feed gas is distributed to each plate first and then by a dedicated inlet section to each channel of the plate, a sophisticated geometry of this inlet section [90] helps to achieve flow equipartition. An alternative is the variation of the channel width over the reactor length axis [91]. 

Figure 14.11 Simulation of a cocurrently operated plate heat exchanger for diesel steam reforming coupled to a catalytic diesel burner. Left flow arrangement, second left fuel mass fraction in the reformer, third left fuel mass fraction in the burner, right temperature in the plate.

For the various reactions of fuel processing, different flow arrangements in plate heat exchangers have been proven to be the optimum, which is discussed below from a theoretical point of view and illustrated by practical applications. 

Besides microstructured heat exchanger/reactors constructed in the form of plates as shown in Figure 5.1, shell and tube micro heat exchangers are available. An example is shown in Figure 5.6. The heat transfer within the reactor tubes can be estimated with the asymptotic Nu or with Equation 5.12 for short channels. The outer heat transfer coefficient depends on the flow regime, the arrangement of the tubes, and the presence of baffles [8, 13]. For small-scale systems, capillaries submerged in constant temperature baths are commonly used. In this case, the main heat transfer resistance is mostly located at the outer side of the reactor. 

The equipment for reverse osmosis is quite similar to that for gas permeation membrane processes described in Section 13.3C. In the plate-and-frame type unit, thin plastic support plates with thin grooves are covered on both sides with membranes as in a filter press. Pressurized feed solution flows between the closely spaced membranes (LI). Solvent permeates through the membrane and flows in the grooves to an outlet. In the tubular-type unit, membranes in the form of tubes are inserted inside porous-tube casings, which serve as a pressure vessel. These tubes are then arranged in bundles like a heat exchanger. 

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