On the issue of the direction of the gaps in the baffle plates for double-pass systems
Thread Content
This post was last edited by “Is this your business?” on January 16, 2018, at 10:22. GB151 contains a schematic diagram of a double-shell pass design; the direction of the baffle cutouts is indicated as being on the left and right sides. However, it does not explicitly state that cuts on the top and bottom sides are not allowed. In actual practice, there are indeed no double-shell heat exchangers with baffles on both the upper and lower sides. I asked the experienced worker, who said that it’s a deficiency on the left and right sides as well, but couldn’t explain why it’s not a deficiency on the top and bottom. After reviewing various sources, no clear explanation is provided for why the upper and lower sections cannot be used. The current hypotheses are as follows: 1. The double-pass partition plate needs to be welded to the baffle plates (some say spot welding, while others say double-sided welding); if the baffles have upper and lower sections, half of them will not be able to be connected to the partition plate. 2. Regarding the pressure drop, the article titled “Development of Engineering Drawings for Medium and Low Pressure Double-Shell Heat Exchanger Series” by Taoning mentions that the pressure drop in double-shell heat exchangers is 6 to 8 times higher than that in single-shell heat exchangers. Meanwhile, the use of double-arch baffle plates reduces the pressure drop by 15% to 60% compared to single-arch baffle plates. Although the effect of upper and lower baffle plates is not mentioned, it is speculated that the pressure drop caused by such baffle plates might be even greater, which is why they were not taken into consideration. Those who have other opinions or know the reason are kindly asked to share their insights.
The applicable ranges of the two types of openings, namely the upper and lower arches as well as the left and right arches, should provide some explanation; the upper and lower arches are not suitable for situations where the fluid in the shell side exists in a two-phase gas-liquid state, that is, the shell side must contain either pure liquid or pure gas. The left and right bows have a wider range of applications.
This post was last edited by wanlirn on 2018-1-16 at 13:29. 1) The flow area in the shell side is maximized when the areas between the tubes and at the gaps are approximately equal. I’ve forgotten how to calculate this exactly; you can find it in a book on heat exchangers. Take two heat exchangers of similar design, one with tubes arranged vertically and the other horizontally, and compare them. There’s nothing complicated about it – just design a few examples and you’ll understand. Many experienced engineers have already done the calculations; arranging the tubes vertically is better than arranging them horizontally in terms of heat exchanger performance and tube layout. That’s all. 2) Designing a double-shell heat exchanger in order to achieve pure counterflow or to increase the flow velocity in the shell side is not a good idea. Try to use double-shell heat exchangers as little as possible; they represent a last resort. If that’s unavoidable, a pure counterflow design with stacked double shells is still better than a double-shell heat exchanger. . . 3) Also, I’ve really never heard before why the baffle has to be welded to the split diaphragm
Not long ago, a colleague at my workplace built a double-shell, double-arch baffle heat exchanger with an inner diameter of 1400, featuring openings on the left and right sides. According to conventional design practices, the vertical partitions were not welded to the baffles.
The device I’m working on now has overlapping double shell circuits; this was suggested in the process design, presumably to increase the flow rate