On the heat transfer efficiency and heat transfer temperature difference of shell-and-tube heat exchangers
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I would like to seek guidance from experts and heat exchanger manufacturers. The heat exchanger manual specifies that for shell-and-tube heat exchangers, the temperature difference at the hot end should be no less than 20°C, and the temperature difference at the cold end should be no less than 5°C. Is this specification due to the relatively low heat exchange efficiency of shell-and-tube heat exchangers? Does that mean that if water at 65°C exchanges heat with crude oil at 40°C, the outlet temperature of the crude oil can only rise to 45°C? Is such a preliminary estimate correct? If it is incorrect, are there any limits on the intermediate temperature difference or the final temperature difference for heat transfer between the hot and cold streams in a shell-and-tube heat exchanger?
It means that if the temperature difference is too small, the required area will be very large, which is not cost-effective
There is already a post exactly the same, with a detailed discussion. Search for it.
There is already a post exactly the same, with a detailed discussion. Search for it.
There is already a post exactly the same, with a detailed discussion. Look for it.
Oh, it seems I’ve been misunderstanding things. Due to the dirty nature of the medium, the owner prefers to use shell-and-tube heat exchangers. If cost is not a factor, can shell-and-tube heat exchangers still help to bring the hot and cold media as close to each other as possible after heat exchange?
Well, I went through all the relevant posts, but there are still some doubts that remain unresolved. I saw a post to which you responded at http://bbs.hcbbs.cc/thread-952845-1-1.html, and I would like to ask further: if the process conditions are determined based on the requirement that the effective temperature difference after heat exchange be at least 5°C, can a suitable heat exchanger then be designed and manufactured? The current situation is that the final temperature of heat exchange is not specified in terms of process requirements; rather, it is required that the temperature after heat exchange at the hot end be as low as possible. After my initial calculations, the hot side can drop to 58 degrees, while the cold side rises to 57.5 degrees, resulting in a logarithmic mean temperature difference of 9.9°C. Is such a temperature selection appropriate? Is it possible to submit this to the manufacturer?
This post was last edited by wiseboy on 2017-6-25 19:33: “The logarithmic mean temperature difference is 9.9°C.” ” The effective temperature difference can be reduced to 5°C, but this is only possible for much larger areas; as a result, the cost of the equipment increases. You need to discuss this with the owner and make a trade-off. For manufacturers, the larger the equipment, the better ； For owners, large-scale equipment requires significant investment, but it offers a high heat utilization rate.
Yeah, I get it. Thank you! It turns out to be the relationship between equipment investment and heat utilization balance. I had been misunderstanding things; I thought it was the shell-and-tube heat exchanger’s low heat transfer efficiency that prevented the achievement of the temperature requirements specified in the process. In fact, as long as the heat exchange area is large enough, and a certain driving temperature difference is maintained, the temperature at the hot end can be reduced as much as possible.
Correct understanding. Therefore, under certain permissible operating conditions, the use of enhanced heat transfer elements can compensate for the loss of a larger heat exchange area, thereby allowing the required heat exchange area to be reduced to some extent while still meeting stringent process requirements.