The pressure drop of condensing steam is a function of steam flow rate, pressure and temperature difference. This difference in pressure drop becomes lower for duties where the final approach temperature between the steam and process fluid becomes larger. In this case, most of the steam condenses in the top half of the plate, the mean vapor velocity is lower and a reduction in pressure drop of between 10-40% occurs. The reverse holds true for cocurrent flow. It can be shown that for equal duties and flow the temperature difference for countercurrent flow is lower at the steam inlet than at the outlet, with most of the steam condensation taking place in the lower half of the plate. It is interesting to note that for a set of steam flow rates and given duty the steam pressure drop is higher when the liquid and steam are in countercurrent rather than cocurrent flow.
Tranter plate and frame heat exchanger series#
The pressure drop of condensing steam in the passage of plate heat exchangers has been investigated experimentally for a series of different Paraflow plates. Since in many cases a plate unit can carry out the duty with one pass for both fluids, the reduction in the number of required passes means less pressure lost due to entrance and exit losses and therefore more effective use of the pressure. Bypassing in a plate type exchanger is less of a problem and more use is made of the flow separation which occurs over the plate troughs since the reattachment point on the plate gives rise to an area of very high heat transfer.įor most duties, the fluids have to make fewer passes across the piates than would be required through tubes or in passes across the shell. Additionally, large areas of tubes even in a well-designed tubular unit are partially bypassed by liquid and low heat transfer area are thus created. Considerable pressure drop is used without much benefit in heat transfer due to the turbulence in the separated region at the rear of the tube. Higher overall heat transfer coefficients are obtained with the plate heat exchanger compared with the tubular for a similar loss of pressure because the shell side of tubular exchanger is basically a poor design from a thermal point of view. Tests have been carried out which tend to confirm that fouling varies for different plates, with the more turbulent type of plate providing lower fouling resistances. The lower fouling characteristics of the plate heat exchanger compared to the tubular has been verified by HTRI's work. The effect of velocity and turbulence is plotted in Figure 3. Although flow velocities are low with the plate heat exchanger, friction factors are very high, and this results in lower fouling resistance. HTRI (Heat Trasfer Research Incorporated) has shown that for tubular heat exchangers, fouling is a function of low velocities and friction factor. The most important of these is turbulence. Materials used for pressing the plates have a very smooth surface. There are no zones of low velocity compared with certain areas on the shell side of tubular exchangers.Ĭorrosion is maintained at an absolute minimum by careful selection of use of corrosive resistant materials. The velocity profile across a plate is good. There is a high degree of turbulence, which increases the rate of foulant removal and results in a lower asymptotic value of fouling resistance. The plates are grouped into passes with each fluid being directed evenly between the paralleled passages in each pass.Īn important, exclusive feature of the plate heat exchanger is that by the use of special connector plates it is possible to provide connections for alternative fluids so that a number of duties can be done in the same frame. Recent developments have introduced the double wall plate. A double seal forms pockets open to atmosphere to prevent mixing of product and service liquids in the rare event of leakage past a gasket. The plates have corner ports and are sealed by gaskets around the ports and along the plate edges. The plate and frame heat exchanger (see Figure 1) consists of a frame in which closely spaced metal plates are clamped between a head and follower. The basic design remains unchanged, but continual refinements have boosted operating pressures from 1 to 25 atmospheres in current machines. The original idea for the plate heat exchangers was patented in the latter half of the nineteenth century, the first commercially successful design being introduced in 1923 by Dr.
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