How should the overall heat transfer coefficient K of a tube heat exchanger be determined more appropriately?
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How should the overall heat transfer coefficient K for a fixed-tube-sheet shell-and-tube heat exchanger be determined? In this case, cooling water and flue gas are used; the water flows through the shell side while the flue gas flows through the tube side. The main components of the flue gas, in terms of volume fraction, are nitrogen N2 (80%), carbon dioxide CO2 (10%), and oxygen O2 (10%), with no phase change occurring. It is known that the water temperature rises from 25 degrees to 29 degrees, while the flue gas temperature drops from 80 degrees to 35 degrees. What value is more appropriate for the overall heat transfer coefficient? I checked the empirical data; the K value for water–gas is around 16–279. I’d like to choose a K value that is more appropriate, so as to avoid having to reset this value if the subsequent calculations prove incorrect; after all, it’s not possible to use calculation software for that purpose. I hope a kind person can determine a K value that only needs to be calculated once, based on your experience. Thank you so much! This post was last edited by lx6418 on 2009-4-13 19:28]
I did the calculation a couple of days ago; K=25w/m2*k
The design conditions had better be more specific; otherwise, only approximate ranges are possible. Generally for shell-and-tube designs, the flow velocity of the gas in the shell side is necessarily low; it also depends on the composition of the flue gas, as well as factors such as whether there is any phase change ； If there is no phase change, it is advisable to use finned tubes to increase the heat exchange area; otherwise, the efficiency of the heat exchanger will be too low, resulting in higher costs and greater space requirements.
This can be looked up in chemical engineering design manuals; there is a range specified there. By choosing a small shop or liquor store, the margin for calculation will be larger.
The main components of flue gas and their volume fractions are nitrogen N2 (80%), carbon dioxide CO2 (10%), and oxygen O2 (10%), with no phase change.
Around 60 W/m2·K should be a suitable value
I chose several K values, but the calculations still weren’t correct; it’s frustrating~! ! ~~:Q :Q :Q :Q
Haha, me too. Let’s calculate it with software first
Provide a dirt thermal resistance; estimate it using HTRI’s design model and then carry out the rate calculation
Using K=60 gives a result that is closer to the correct value~~ Thank you all for your responses!