Center distance of heat exchange tubes
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GB151-1999, P22, 5.6.3.2: The center distance S between the heat exchange tubes should be no less than 1.25 times the outer diameter of the tubes; the minimum value is 1.25 times. What are the requirements for the maximum value?
In fact, under normal circumstances, the center distance between the heat exchange tubes is selected according to Table 12. This center distance S should be no less than 1.25 times the outer diameter of the tubes, as it is important that the distance between the edges of the tube openings is not too small. There is little significance to setting an upper limit. Typically, heat exchangers are designed to be compact and economical. If the heat transfer calculations are satisfactory, the values specified in GB151 are usually adopted.
Personal opinion: The center-to-center distance S of the heat exchange tubes should be no less than 1.25 times the outer diameter of these tubes. This is mainly due to considerations related to the welding of the heat exchange tubes to the tube sheet. Before the release of standard version 99, manual arc welding was commonly used for joining the heat exchange tubes to the tube sheet; when the distance between the tubes was too small, adjacent weld joints would merge together, thereby reducing the quality of those welds. The more advanced welding method of TIG automatic welding has now been widely adopted; the welds produced are neat and aesthetically pleasing, and reducing the pipe center distance appropriately does not interfere with adjacent welds. Regarding the upper limit, I agree with what was said on floor 2.